Thursday, September 22, 2016

What's Up with the Rollercoaster Takeoffs from Orange County?






If you've ever had the pleasure (or perhaps the terror) of taking off in a commercial plane from Orange County's John Wayne airport, you'll know that it is a takeoff unlike any other. Just seconds after liftoff, you will feel your stomach drop as the airplane does a very abrupt pushover. This pushover, similar to what you might feel on a rollercoaster or perhaps a hilly backcountry road, will make you light in your seat. You might even feel yourself being restrained by your seatbelt.

The next thing that you will notice is that the sounds in the cabin will change. Specifically, they will get much quieter. The roar of the engines that accompanies all takeoffs will diminish dramatically. You will sense that the nose of the aircraft has dropped significantly. The incline, or what pilots call the "deck angle" will have gone from the usually steep angle used for most takeoffs, to one that is barely distinguishable from level flight. And all this will seem to be happening much too close to the ground.

Finally, you may become aware of an annoying thumping that you feel in your chest. Don't worry, that's only your heart pounding.

You may think that this is it...game over...and wonder if there's enough time to squeeze a goodbye text to your loved ones before plunging into the Pacific ocean. But you should rest easy. You are not going to die (at least not today). What you have just experienced is known as a noise abatement takeoff. They occur hundreds of times weekly at John Wayne and are an FAA approved and in fact government mandated maneuver. That's right; pilots and airlines will be fined if they don't perform this type of takeoff.

So why, you may ask, are you being subjected to an experience that should probably be featured at the nearby Disney theme park? Well, as I mentioned above, noise. Noise and of course politics. For John Wayne airport is the only airport which mandates such a drastic noise reduction profile. And as legend has it, the Duke himself, the airport's namesake, had a hand in getting those restrictions put in place.

The departure path from John Wayne airport flies almost directly over Newport Beach. And as you may know, Newport Beach is a very well-heeled community. And while I'm not going to make judgements on wealth accumulation, one thing wealthy people are good at is getting things done. Starting with the arrival of the first turboprops and jets in the 1970s, community activism followed soon thereafter. Eventually lawsuits were filed and the restrictions were put in place.

Why Orange County?


John Wayne Airport dates back to 1923 when a landing strip was first opened by a man named Eddie Martin to host a flying school. Then known as Martin Field, Orange County assumed ownership in 1939 with the airport becoming to be known as Orange County Airport. The name was changed to John Wayne Airport in 1979 in honor of actor John Wayne, a nearby resident, upon his death.

Noise restrictions at the airport date back to 1985 when a local group representing residents who lived under the departure path sued the county. The resulting settlement implemented noise regulations and curfew requirements which remain in force today. Noise meters are deployed along the departure path to measure the sound footprint of each departing aircraft. Those restrictions are unique in being some of the first of their kind, and also just about the only of their kind.

In 1990, Congress, fearing that many localities could eventually hamstring the growth of aviation by implementing their own patchwork of noise restrictions, passed the Airport Noise and Capacity Act which outlawed curfews at airports. John Wayne was grandfathered in, however, due to the original lawsuit being filed in 1985.

Why the Rollercoaster?


So knowing why airplanes have to fly quietly, you may be wondering about the "how". And specifically, you might be wondering why airliners don't just use less thrust from the get-go instead of the roar followed by the pushover and silence. Without getting too technical about takeoff performance, much of it comes down to the runway length at John Wayne airport, or to be more specific, the lack of runway length.

The longest runway at John Wayne is less than 6000 feet long. At a scant 5701 feet to be precise, it is one of the shortest runways if not the shortest runway in the nation from which large commercial aircraft fly.

It is the nature of gaining flying airspeed in a very short distance which necessitates the full power takeoff. Once airborne, but before the flaps are retracted, the aircraft reaches a "cutback" altitude of about 800 ft. It is here where the engines are throttled back either manually or by the auto-throttles to a thrust which meets the minimum required climb gradient of about 2.5%. Less thrust also means a shallower climb angle, hence the pushover.

Once beyond the noise sensitive area, or about six miles after takeoff, the aircraft resumes its normal climb profile using full climb thrust.

Is It Dangerous?


I suppose that depends on your definition of the word dangerous. Any time you monkey around with large power changes on a turbine engine, you increase the odds of something going wrong. In fact, many engine failures occur not on initial thrust application such as takeoff, but rather on a large thrust reduction. That said, the odds of that ever happening are infinitesimal. Still, it isn't unknown for engines to fail as was dramatically illustrated by the uncontained engine failure on a Southwest Airlines 737 several weeks ago. Infinitesimal odds, but not zero.

So no, it isn't dangerous in the conventional sense of the word. Avoiding flights out of Orange County to avoid takeoffs using this procedure would be silly. And likely more dangerous as a longer commute up the freeway to LAX would definitely expose you to more absolute danger in your car. Of course, the safest course of action is to hide under the bed which still won't protect you from meteorites...or dust bunnies.

So when you do get on that airplane leaving the OC, be sure to get a window seat on the left side of the airplane which gives the best views of Catalina, relax and enjoy the ride. But don't put your arms in the air and scream as if on a real rollercoaster. People will stare.










Monday, September 19, 2016

Flying to Cuba on One Engine



Flying to Cuba on One Engine
Brian Hall (center) and his Bonanza in Havana


This past August saw an important landmark in aviation history with the first scheduled commercial flight between the US and Cuba taking place in nearly fifty years. On August 31st, a JetBlue Airbus flew from Ft Lauderdale to Santa Clara, Cuba with 150 passengers, journalists, and dignitaries. JetBlue is one of six US airlines which won approval to fly direct routes from the US to Cuba.

As historic as that occasion was, an equally historic flight took place earlier in 2015. Scooping the first scheduled commercial flight by over a year, was the first flight of a private civilian aircraft to Cuba from the US. On January 15 of last year former Air Force C-130 pilot and businessman Brian Hall flew his Beech Bonanza from Fort Myers, Florida to Havana. Flying under the rules of Part 91, Hall's flight was the first flight of this type in over fifty years.

Hall is hoping to start a new ferry service called CubaKat between Florida and Cuba. He flew to Havana to discuss business details with his Cuban employees and government officials. He might be considered a serial entrepreneur as he is currently the CEO of a marine engineering company and has had a hand in starting or running everything from ferry services to an airline to an energy services company and consultant services.

Flying to Cuba on One EngineWhile travel to Cuba for tourism is still not permitted under current rules, other reasons for travel such as cultural exchange are permitted. In addition to his proposed ferry service, Hall also spoke to Cuban officials during his visit about starting airline service between cities in Cuba itself. There is apparently a need for intra-island air transportation and Hall seems to be in the right place at the right time to capitalize on business opportunities in Cuba. He is proposing to start service using Cessna Caravans to deliver passengers and cargo.

Well as it turns out, Hall was a student pilot in my flight at the 98th Flying Training Squadron at Williams AFB in Phoenix, Az, nearly thirty years ago. The 98th trained students to fly the T-37 primary jet trainer while on their way to become Air Force pilots. After graduation from undergraduate pilot training, Hall went on to pilot C-130 Hurricane Hunter aircraft before leaving the service to start his career as a businessman.

The Road to Cuba


I was able to catch up with him about a week ago and ask him how his path led him to make history flying a single engine aircraft to Cuba.

He told me that his fascination with Cuba came from his grandparents who had often vacationed on the island. They would tell stories of their travels which captivated him. Many years later, he was able to arrange a retreat to Cuba for some family members and from that point on was hooked. He has since been back to Cuba many times on cultural exchange trips, though always having to travel by chartered aircraft.

In December of 2014, President Obama announced a restoration of full relations with Cuba thus ending decades of stalemate and embargo with the island nation. Hall knew that this was his opportunity to get in on the ground floor with the establishment of ferry service between Cuba and Florida. His CubaKat venture, which will use large catamaran ferries carrying up to 200 passengers, is still awaiting final government approval to begin operations.

In the meantime, Hall saw an opportunity to make a historical flight. He actually owns two aircraft, a single engine Bonanza and a twin engine Baron. And while the general rule for overwater flying is that more engines are better, Hall said he had insurance problems with taking the Baron to Cuba. As a result, he had to take his single engine 1953 Bonanza for the 217 mile journey to Havana.

While many pilots fly single engine aircraft to the Caribbean islands, Hall said that the one concession he made was to wear his life vest rather than to just have it available. The last thing a pilot wants to be doing if forced to ditch in a small aircraft, is to simultaneously fly the plane and make a distress call while figuring out how to don a life vest.

While planning for his flight, he did contact the US Immigration and Customs service who for some bureaucratic reason or another informed him that he couldn't make the flight as he had planned. It had something to do with Miami being the only approved airport for flights from Cuba. Being steeped in the culture of entrepreneurial risk taking, he found that it was in fact easier to beg forgiveness than to ask permission and had no trouble upon his return to the states.

Lacking the Basics


Hall told me that the actual mechanics of flying to Cuba were rather routine. The Cuban controllers were all perfectly gracious, spoke good English and his flight to Havana was uneventful. It was upon arrival that he realized that Cuba has a ways to go as far as aviation infrastructure is concerned. Routine expectations such as tie-downs and chocks, available at most US airports, were notably lacking. They also didn't have fuel, which might have been a problem had he not had the foresight to carry enough fuel for a round trip.

Since his first trip, Hall has been back to Cuba in his own plane three times. He says that the lack of overall infrastructure to handle the tsunami of Americans expecting to visit the island will be a brake on the tourism industry once the tourism ban is eventually lifted. Hall told me that one of his employees requested that he bring a toilet seat along on his next visit. It took two visits as the first one he brought was oval when a circular one was required.

Hall also mentioned that travellers to Cuba should not forget to bring enough cash to cover their expenses while visiting as there are almost no ATMs on the island. The Cubans, for their part, seem to be catching on that there is money coming along with their new island visitors. On one of his latest trips, a new $40 departure tax was levied which hadn't been mentioned or collected before. Of course you must pay if you wish to take off.

Cuba is His Passion


Even though the regulatory hurdles Hall faces to get his CubaKat venture going can be a real headache, he doesn't plan on quitting the island anytime soon. He's there to stay in one fashion or another. His motto is that if a businessman isn't earning, then he's learning. And Brian Hall, Air Force pilot turned entrepreneur turned Cuba evangelist seems to have enough passion and energy to do plenty of both.














Thursday, September 08, 2016

Is Aviation Automation Killing Us?



Is Aviation Automation killing us?



"When we design our systems, we need to assign appropriate roles to the human and technological components. It is best for humans to be the doers and technology to be the monitors, providing decision aids and safeguards."

 - Captain Sully Sullenberger

The past week has seen several high profile aviation incidents come to light. The first one was a preliminary accident report on the crash and fire which destroyed an Emirates Boeing 777 in Dubai last August. The second was the release of the final report by the Australian Transport Safety Bureau (ATSB) regarding an AirAsia Airbus A330-300 enroute from Sydney to Malaysia last year which suffered navigation and other system failures as the result of erroneous input by the pilots during preflight.

The Emirates crash tragically took the life of a responding fireman, while the AirAsia incident caused no injuries but did result in a diversion. Each incident had the potential for great loss of life, though. The improper use of automation can be implicated in both the Emirates and AirAsia events. Let's take a look at each of these and see if we can draw some parallels.

Emirates 521


The crash report on the Emirates flight, released by the General Civil Aviation Authority (GCAA) of the UAE details that the approach was flown by the captain. The autopilot was disconnected for the landing while the autothrottles remained engaged. The aircraft experienced a longitudinal wind component which changed from a headwind of 8 kts to a tailwind of 16 kts during the approach. As a result of the decreasing performance wind shift, the aircraft made a long touchdown.

An automatic system on the Boeing warned the crew about the long touchdown, and a decision was made to go around. So far so good. Going around rather than accepting a long landing due to shifting winds is the correct decision.

What happened next wasn't so good. The nose was raised, the flaps were reset and the gear were retracted, but go-around power was not added until three seconds before the aircraft impacted the runway with the gear partially retracted. The post crash fire destroyed the aircraft entirely.

Adding power during a go-around is...or should be, instinctual. It's considered aviation 101, or rather it used to be. Today's highly automated aircraft, however, all employ autothrottles which automatically advance themselves when the "Takeoff-go-around" or TOGA button is pushed. This is how go-arounds are performed on automated aircraft.

The 777, however, has a feature which disables the TOGA button after touchdown. This makes sense as you don't want the throttles to advance after landing in case of accidentally touching the TOGA button. After a normal landing, that is. There are times when a rejected landing, or go-around, occurs after touchdown. The reasons vary, but a landing can be rejected any time until the thrust reversers are deployed, even after the gear touch down.

This is what happened to the Emirates 777. It touched down, and then attempted a go-around without adding power. Questions remain as to whether or not the captain actually engaged the TOGA button but in any case, the captain should have manually pushed up the throttles for the go-around or ensured that the autothrottles automatically advanced.

Why would he not do that? Easy. It's called negative conditioning or negative training. Go-arounds are routinely practiced in all airline simulator training programs, but go-arounds after touchdown are practiced much less frequently. Over time, muscle memory will expect the autothrottles to advance themselves during a normal go-around as they always do.

Put a pilot in a highly dynamic situation such as a windshear landing, and then perhaps throw in a non-routine distraction such as the automatic runway length warning, and voila, muscle memory takes over and the throttles don't get pushed up. Automation, which is supposed to make flying easier and safer, might have helped make a crash such as this inevitable.

AirAsia X 223


On March 15 last year, an AirAsia A330 suffered multiple inflight malfunctions of  its navigational display systems rendering the aircraft incapable of either continuing to its destination in Malaysia, nor of returning to its origination point of Sydney due to low ceilings. The aircraft eventually landed uneventfully in Melbourne, which had clear weather.

Subsequent investigation revealed that the pilots made a data entry error during their pre-flight checks consisting of a single digit error in programming the aircraft's location.

Modern navigation systems on today's commercial aircraft are capable of guiding an airplane to a spot on the other side of the globe with accuracy down to several feet. But in order to know where to go, the computers on the airplane first have to know where they are. 

Part of the preflight process is to enter in the aircraft's current location in the form of a latitude and longitude. The pilot entering this data made some sort of fat finger error which resulted in the actually entered position being thousands of miles away from the Sydney airport. So after the aircraft departed, discrepancies between where it actually was and where it believed it was caused the computers to crash resulting in a nearly complete failure of the navigational system.

After identifying  and while attempting to fix the problems with the navigation systems, the crew compounded their problem by cycling two of their three flight computers to off and back on. This incorrect procedure resulted in the loss of other primary flight displays and rendered the aircraft incapable of flying even a simple approach back to Sydney necessitating the diversion to Melbourne.

Even after arrival at Melbourne, the aircraft had to make several attempts at a completely manual landing without the benefit of either the autopilot nor autothrottles. There is little doubt that flying a highly automated aircraft left the pilot's manual flying skills in a somewhat rusty state, which is completely expected.

Automation: Friend or Foe?


Automation of commercial airliners is with us to stay. It provides many benefits and economies but there are problems with its deployment which contributes to accidents and incidents such as these. The old aphorism which states that computers just allow humans to make mistakes faster and with more efficiency certainly applies here. 

Over reliance on automation is also well known to cause a deterioration in manual stick and rudder piloting skills, which go unmissed until they are needed. The crash of Asiana 214 in San Francisco several years ago was a perfect example of this.

But as Captain Sully warned in the quote above, automation is best deployed as an enhanced decision making tool, not something which a bored human being should be tasked to sit and watch, as it is today.




Wednesday, September 07, 2016

How I Raised Four Amazing Children as the Husband of an Airline Pilot



The Captain...with progeny



I, no we, my wife and I, have four amazing kids. No, seriously, they are. I couldn't possibly be biased, but I'll let you judge:

Marlon, the oldest, (not their real names) recently graduated as an officer from one of the service academies where he was a collegiate swimmer, and is now in training with a special forces unit. He was offered a pilot training slot but turned it down to go into special forces (a subject for a future post).

Bronwyn has recently returned from a two year dance school in Canada and is embarking upon her career as a professional modern/jazz dancer. Genevieve, my third, is also a cadet at a US service academy and in her sophomore year studying operations research, while Poppet, my youngest, is a high school senior sorting out her options. She is finding out that being a National Merit Scholar semifinalist means a mailbox full of Ivy League promotions on a daily basis.

So they're awesome kids, and what's more is they're really nice people, which in my book counts for more than their accomplishments.

But I am not going to be shy about taking at least some of the credit here because my wife, their mother, abandoned the family. At least weekly. Oh, she would always eventually come home only to fly out the door in a week or so leaving me alone with an infant and three toddlers for days on end.

She's not a bad person either, but she is an airline pilot. Part of her job description is to be gone. And she wasn't only gone for her three to four trips a month, but for many weeks of time every time her airline decided to send her to train on a new aircraft.

I've Got the T-Shirt


Short of actually giving birth to these children, there wasn't a single child rearing function that I was not required to master. They're 15,16 and 19 months apart so for a short while we had four in diapers. Did you know that a running clothes dryer can calm a crying baby in seconds? No, not in it, but rather on it where the changing table was. And I bet you didn't know that a bungee cord stretched from a bedroom door across the hall to the bathroom door is an excellent means to corral a toddler who won't stay in bed.

When giving baths, be sure to buy the cheapest conditioner available and then use about half the bottle per child per bath to ease the brushing of hair tangles. Learning how to apply drywall texture can also be a useful skill you will need to repair downstairs water damage from bath time. And doubling the recipe for hamburger helper, otherwise known as "Daddy goulash", leaves enough food to put in their thermos for a tasty and nutritious school lunch the next day!

Now I know that many of the stay at home dads and all of the moms reading this are thinking "So what? You're not doing anything that I haven't done." And you would be right. But to give credit where due, remember no one applauds the dancing bear for dancing well, but rather for being able to dance at all! The kids turned out OK, so I figure we must've done something right. What exactly that was, I have no idea, but there are a few clues. Here are my best guesses.

Full Disclosure


For full disclosure, I am also an airline pilot. My wife, Sandy, and I were both Air Force pilots which is where we met. Sandy flew transport aircraft in Desert Storm and left the military shortly afterward to start her airline career. She has flown numerous aircraft over a 20+ year career to include the 747 and is currently flying the 777 on international routes.

I have also been flying commercially for about 26 years, but after leaving active duty, I found a job in the Air Force Reserve. As a "weekend warrior", I flew the C-5 jumbo transport concurrently with my airline job until retiring from the military in 2002.

Can You Juggle?


The nature of being an airline pilot (or flight attendant) means that you can't bring work home. Once you park the jet and set the brake, you're free. This means that while you are home, you are one hundred percent home. There are no business calls to take, emails to answer or projects due on Monday.

Over the years, I've met quite a few "industry couples" trying to raise a family. The entry of women into the piloting ranks as well as men into the flight attendant ranks means that more "assortative mating" is occurring. This is a fancy way of saying that there are more pilot-pilot couples and flight attendant-flight attendant couples.

Each couple has to decide for themselves how they are going to structure their family life. Sometimes this involves one person giving up their career to be a full time parent while the other becomes the sole breadwinner. Where both parents keep working, as we did, an important decision has to be made. Will they both be gone at the same time or will they fly opposite schedules?

Both of these options have their advantages and disadvantages. We tried both and then settled on flying opposite schedules. We figure that after almost 30 years of marriage, we probably have maybe 10 years of time actually spent together. (We may have accidentally stumbled on another secret of a long and happy marriage!)

As far as the couples who choose to be away at the same time, both parents being away simultaneously can be made much easier with the help of a grandparent or other adult family member willing to help out. Many couples make these sorts of arrangements.

Who's This Person with Our Children?


For others who wish to fly the same schedule, but without the benefit nearby family, hiring a nanny is required. This is how we started. We found a lovely older woman through an agency and made arrangements for her to live in while we were both away. When Barb, our nanny, started, we had two children aged 7 and 22 months.

We quickly found out that we were profoundly uncomfortable with the arrangement. Barb was loving and warm, but we simply realized that we just didn't know her that well. I think we both came to this conclusion one night when talking on the phone while we were both on a trip. Sandy was in Medford, Oregon and I was in perhaps St Louis. We never had any reason to believe that Barb wouldn't take good care of our children, but we still wondered whether she would get up in the night to comfort a crying baby. And that was that.

We learned that we were expecting again soon afterwards. Two babies later and after Sandy returned to work, we started flying opposite schedules and haven't looked back. It's not quite as harsh as it sounds though. We'd typically fly perhaps three trips passing in the night and then enjoy a week off together. Airline schedules can be flexible and we had the ability to occasionally give away trips for some time off.

 Effectively Single Parent


So we ended up raising our kids as serial single parents. I can't be certain, but I think the kids learned some independence from this arrangement. Each of us had our own parenting style to which the kids had to adapt. But unlike real single parents, the parent who happened to be home at the time was, as I mentioned, completely available and involved. In a sense, the kids were the only full time residents in our house with Mom and Dad coming and going.

As the kids got older, they had to by necessity take more responsibility for their own activities. Telling Dad for instance that a form was due with a check for some activity did little good if when by the night before it was due, Dad was away and Mom was the parent on duty. I have little doubt as well that the kids used our part time status against us in ways we can only imagine.

As technology bridged the physical communications gap, keeping the travelling parent in touch with family life became much easier. In the days before cell phones we paid for our own personal "800" number which would ring at the house. Later on we used cell phones to call home, but now we mostly use video links such as Facetime or Skype. We would occasionally sit in on family meals and homework time as a disembodied head on the iPad, even from overseas.

We even took a stab at homeschooling for a few years after becoming disenchanted with our local schools. I could write pages on that experience alone, but I'll just say it was hectic, tiring and totally worth the effort. We eventually moved and put the kids back in public school.

High Expectations and Priorities


One thing we never lost sight of in the chaos of a dual airline career was the importance of family priorities. We always had sit down dinners at a set time and tightly controlled TV time. I think that children need guardrails and routines. Even though my wife and I would run the house somewhat differently, the kids knew that our priorities were the same.

Being kids of airline employees, our children have become adept at navigating air travel and have travelled extensively by themselves, even to overseas destinations. When it came time to look for colleges, we told our kids that we were in for half the cost and that we'd buy a car for whoever got a free ride through scholarships. I may end up buying three cars.

So that's it. When we started this journey, we had no contact with other parents who had done this and we more or less made it up as we went along. It worked out but I think our key to success was to keep focused on the important things.

 









Thursday, September 01, 2016

So How Do Jet Engines Work and Why Would One Blow Up?



Southwest Airlines engine failure


This past week a Southwest Airlines 737 suffered a very dramatic engine failure while on a flight from New Orleans to Orlando. It appeared as if the entire front of the engine came off judging from pictures taken from inside the cabin. The aircraft also suffered a rapid decompression which was most likely due to debris from the engine striking and puncturing a hole in the fuselage. Considering that the time of useful consciousness (TUC) at 31,000 feet is only one to two minutes, the crew did an outstanding job of prioritizing their emergency action responses and safely recovering the aircraft into Pensacola.

On September 8th last year a British Airways 777 aborted its takeoff from Las Vegas after its left engine failed and burst into flames. The entire left side of the aircraft was engulfed in flames by the time emergency responders were able to put the fire out. Again, thankfully, no one was injured. The aircraft was later repaired and returned to service.

So in these two high profile incidents, jet engine failures caused very dramatic and potentially life threatening damage to commercial airline flights. But how do jet engines work in the first place and what would make one blow up? Is there any way to make engines safer or are these types of mechanical failures just something with which we'll have to learn to live?

Suck Squeeze Bang Blow


Modern turbine aircraft engines are simultaneously simple in operation, yet highly complex precision machines. Their operation, which can be simplified into the title of this paragraph, consists of four elements. Air is first drawn into the front of the engine and is next compressed by a series of blades rotating on a center spool. 

This compressed air is then combined with fuel sprayed into the combustion chamber and ignited. The resulting flow of hot expanding gas flows over turbine blades also connected to the center spool and then exits at high speed providing thrust. The turbine blades provide power for the compressor blades and the process repeats.

The earliest jet engines were known as "pure turbine" engines where all the air from the inlet went through the hot section. Since then, large fans have been employed where only some of the air goes into the hot section but most of the thrust is created by the fan and bypassed around the core of the engine. High bypass engines are now the standard on airliners though pure turbines are still used on military aircraft.

And that's it. Conceptually quite simple and very few moving parts. 

What Could Go Wrong?


The truth is that because jet engines have so few moving parts in comparison to other types of engines, there is very little actually to go wrong. The problem is that when things on a jet engine do go south, they can make a big mess as seen in the two above mentioned incidents.

As far as the central operation of the compressor-turbine assembly is concerned, metal fatigue and subsequent failure are the primary culprits. Investigation of the BA 777 incident revealed that the spool in the high pressure section of the compressor had failed and parts of the compressor spool and blades were subsequently thrown through the engine case and cowling.

A similar metal failure was implicated in the crash of United 232 back in 1989 which claimed 111 lives. Thankfully, advanced metallurgy and inspection technologies make these types of problems quite rare.

The speculation of what caused the failure of the Southwest Airlines engine ranges from mechanical failure of the fasteners which keep the structure attached to possible failures of the engine anti-icing system which is located in that area. An NTSB investigation is ongoing,

Simple and Yet Complex


While the operating principles of jet engines are simple, many of the technologies used to make them work are quite complex. The metallurgy used in building the fan and compressor blades is state of the art. These structures are mostly made of titanium which while being extremely strong and flexible is notoriously difficult to cast. Titanium castings are required to be forged in a vacuum as any air can induce impurities resulting in cracks in the metal.

The tolerances required inside the fan and compressors of jet engines are extremely fine. Modern jet engines even have what is known as an ablative coating around the primary fan which is designed to wear away as the fan blades expand through heating. This keeps the gap between the fan and its housing as small as possible for efficiency.

As you might imagine, any solid object which is ingested by a jet engine can cause havoc. Any damage to the compressor section of a modern jet engine can cause what is known as a compressor stall which is a major disruption in airflow. When the airflow is disrupted, the fire can go out or be severely restricted. This is how Sully and his passengers ended up in the Hudson river courtesy of a flock of Canadian geese.

I should add a note about all the auxiliary components that, while not central to the operation of a jet engine, are attached to the engine in what is known as an accessory drive unit. It is located either beneath or on the side of the engine yet inside the cowling. Things like hydraulic pumps for the flight controls, generators, and fuel control units are driven through a drive shaft powered by the main turbine. Problems with these components may or may not result in engine failure depending on the affected component and the nature of the failure. 

In Conclusion


Modern turbine engines are models of efficiency and simplicity. They are highly reliable power plants and yet, like any machine, subject to occasional failure. That they fail so infrequently given the extreme conditions in which they operate is a testament to their design and upkeep.

Wednesday, May 25, 2016

Does Falling Asleep at the Controls Make You a Bad Pilot?



A Delta 767 gets intercepted by Greek F-16s after comm loss.
Delta 767 and Greek F-16s in formation.

Not necessarily, though it might very well make you a dead pilot if you were in a single pilot aircraft such as an F-16 or Cessna. But as far as airliners go, if the pilots take a snooze at altitude with the autopilot flying, the airplane stays on course and airspeed. Falling asleep is a physiological incident which can be due to many different reasons, but one thing it is not, is a moral failing. Let me explain.

In a recent event over Greek airspace, a Delta Airlines 767 flying a charter for the US military entered Greek airspace and did not check in with air traffic control. The Greeks then launched two F-16s which intercepted the airliner about 40 minutes after it entered into Greek airspace. Shortly after the intercept, the aircraft reestablished communications with air traffic control and proceded onto its destination of Kuwait.

There have been some unsubstantiated reports in Greek media that the fighter pilots saw the airline pilots unresponsive in their seats. The reports also claim that it was calls from the flight attendants who noticed the intercept which alerted the pilots to the situation.

Delta, for its part, reported that the aircraft couldn't make contact with Greek controllers after their handoff from a previous sector. That's plausible, though losing communications in an extremely busy part of the world for 40 minutes does seem unlikely. Maybe 5 or 10, but 40 is more difficult to swallow.

They Want You to Lose Communication


A little known fact is that many jurisdictions around the world actually love it when an airliner from a wealthy nation flies into their airspace without making contact. They then get to launch an intercept or search and rescue (SAR) forces and then send the bill to whoever has the deepest pockets. That would be Delta and the US government in this case.

Notice that it only took 18 minutes from the time the airliner entered Greek airspace to the launch of the fighters. There are rumors around that Greece itself is in some financial straits. They're smelling a payday. Sure there are legitimate reasons to intercept a comm-out airliner in today's crazy terrorist besotted world, but money also makes a good motivator as well. Win-win I suppose.

At any rate, any pilots worth their salt flying in this part of the world must know that going comm-out while crossing a flight identification region (FIR) boundary while bound for the Middle East will not be good.

So what other reason might there be?

They Were Snoozing (Maybe)


The nature of this job is many days and time zones away from home, back side of the clock flying, lousy diet, and hotel beds which only get the straw changed every other year. I jest about the straw beds, but I often feel like I've slept on one as my back will let me know when trying to roll out of bed. 

My point is that getting a reasonable amount of sleep on the road is a serious challenge, and that is if everything goes right. A noisy or inop air conditioner, maids knocking on the door early in the morning after a late night arrival or my personal favorite, hammer drills in a nearby room from construction crews can make a good night of sleep nearly impossible.

Even though most airlines have good fatigue policies which allow pilots to decline a flight with no sanction, there is no guarantee that halfway through a flight which you felt fine to start that you won't simply find it impossible to keep your eyes open. This can be in the middle of the day, perhaps right after lunch while sitting on the sunny side of the jet.

Do you do what you can to prevent this? Sure. Get up and stretch, get a cup of coffee, or take a restroom break. Even after all that you might still be droopy. So it is by far from implausible that this happened to both of the guys or gals up front.

Are They in Trouble?


No, they are not. As I mentioned above, falling asleep is a physiological incident and not a moral failing. There will be no scene from 12 O'clock High with Gregory Peck chewing out a guard who has fallen asleep at his post. What will happen is the crew will fill out various safety and fatigue reports (if that indeed is what happened) and life will go on. And if it was merely a case of lost comm, mostly the same thing will happen.

Their reports will go into a safety database where de-identified safety data will hopefully guide any policy changes which need to be made. Yea, that may be somewhat idealistic, but the point is the crew will live to fly another day.

And as I always brief to my copilots, I never want to wake up and find them sleeping! (Just kidding!)

Sunday, May 22, 2016

Egyptair 804



Egyptair 804 was lost over the Mediterranean Sea
Egyptair A320


Egyptair 804 disappeared over the Mediterranean Sea last week. The aircraft, an Airbus A320, was carrying 56 passengers and 10 crew when it vanished from radar screens at about 2:30 am local time (00:30Z). There were no survivors.

While recovery of the wreckage is underway, the only other notable factor concerning the accident was a flurry of automated maintenance messages received from the aircraft shortly before its disappearance.

The system, known as Aircraft Communications Addressing and Reporting System (ACARS), is used to send data messages about the operational and mechanical status of an airliner to the company for various uses. For instance, when you bring up the arrival status of your flight on your phone, that exact arrival time is derived from data sent over ACARS. The system also sends maintenance status reports to help track the mechanical status of the aircraft and also to alert ground maintenance personnel of impending problems.

This system sent the following messages:

00:26Z 3044 ANTI ICE R WINDOW
00:26Z 561200 R SLIDING WINDOW SENSOR
00:26Z 2600 SMOKE LAVATORY SMOKE
00:27Z 2600 AVIONICS SMOKE
00:28Z 561100 R FIXED WINDOW SENSOR
00:29Z 2200 AUTO FLT FCU 2 FAULT
00:29Z 2700 F/CTL SEC 3 FAULT
no further ACARS messages were received.


These messages indicate that smoke was detected by the lavatory and avionics smoke detectors and that the window heat computer detected an overheat condition. The avionics bay is an area below the cockpit where most of the aircraft's computers and radios are located. What these messages mean when taken together is anyone's guess. They could possibly indicate the presence of an onboard fire or might only indicate multiple erroneous inputs from a failure of the reporting system.

At this point no determination can be made about the nature of the malfunctions or their origins. This will no doubt have to wait until the data and voice recorders are recovered. This recovery effort is underway.

Saturday, May 14, 2016

How to Dodge a Thunderstorm and Not Spill Your Coffee



Very few aircraft will survive an encounter with one of these big guys
They have big teeth too!

Well it's spring. It is a time when, according to Tennyson, a young man's fancy lightly turns to thoughts of love. Being an old grizzled coot firmly in the grip of matrimony for more than a score of years now, my fancy begrudgingly turns instead to the spring return of every pilot's nemesis, the thunderstorm.

I fondly recall a time years ago while sitting in Air Force ground school in Lubbock, Texas. The instructor drew a shape on the board and asked us students to identify the shape. It looked like the state of Texas which some brave soul ventured to point out. The instructor corrected him with a shouted "NO". "That," he exclaimed, "is an airborne emergency!"

His meaning was that flying in the state of Texas in the spring meant doing battle with, or rather attempting to avoid doing battle with the towering giants which would daily sweep across the panhandle. Because even today, with all of our technology and shiny fast moving flying machines, there is still virtually no airplane that can survive a thunderstorm penetration. And I'm including everything from fighters to helicopters to especially airliners in this category.

But wait, you cry! How about those hurricane hunter planes? Aren't hurricanes worse than thunderstorms? Actually no, they're not. At least not in an airplane. A hurricane can certainly muss your hair while airborne, but they are mostly lower altitude phenomena and have limited vertical development. There may be thunderstorms embedded in a hurricane which the hunter aircraft are careful to avoid, but overall, nothing on earth can match the fury of a well developed hammer-headed storm reaching to over 50,000 ft.

Ok, but can't we just fly over them? No, again. Most airliners can only climb up to the low 40s whereas I mentioned above, a large storm can easily reach to 50k. Even should the storm be a "smaller" one and top out in the 30s, the area above the storm can be quite turbulent as the storm grows and should hail get ejected out of the top of one of these babies, that's exactly where you'll find it. So no, going over a developing cumulonimbus is never a good idea. It is always best to avoid a storm laterally.

Wandering into one of these bad boys will easily make the top of your list of worst things to happen in an airplane. The gusts from violent up and down drafts will produce severe turbulence and the volume of rain your engines will swallow can easily put the fire out. An encounter with hail will scratch your shiny paint job just microseconds before it permanently bashes your radome and the leading edges of your wings into a very non aerodynamic shape. And that is if your windshield doesn't shatter.

Thunderstorms are to be avoided at all cost.

Houston to Chicago


Our trip had us returning from an international destination to be followed by the last leg to Chicago. Then we were done. My F/O lived in base so he was just going home while due to the late arrival time, I was going to the crash pad to be followed by an early morning flight home. We parked the jet at the international terminal, cleared customs and went to look for some dinner before meeting another jet in the domestic terminal. My F/O was diverted away from the automated kiosk into the longer line to an agent for some reason so I'd catch up with him later.

My big decision now became where to eat. The oriental place is good but expensive, while the Mexican place had a long line. I opted for Subway. Nothing like living on airport food. The other option is to carry a food bag, which many crew members do, but an international flight means no fresh food can pass. Little wonder that so many airline pilots are fat. (That's my story, and I'm sticking to it!)

I made a quick trip by the pilot lounge and then went to the gate to meet the incoming aircraft. We were supposed to push at 8:00 pm but the board said the flight was expected out at 8:25. It pulled into the gate dutifully at 7:50 meaning that this was planned for a 35 minute turn. We used to do these in as little as 15 or 20 minutes, but the planes are bigger and people are slower and carry more stuff to stow, hence the 35 minute turn.

Weather Reroute


The reason I stopped by the pilot lounge was to get a wifi signal to update the weather app on my iPad. The company spent a ton of money to give us all iPads with a comprehensive weather app. The only problem is that it's useless without a wifi connection, and we're not allowed to use the onboard wifi. This makes the whole thing quite useless for weather. Rumor has it that this will change soon but I'm not holding my breath.

What I did see during my brief lounge visit was that a large system of thunderstorms was camped out just east of the Mississippi river valley, stretching from perhaps eastern Arkansas up to southern Michigan. I guessed that this meant that we were not going to be flying the most direct route. It turns out I was correct.

When I got the flight plan, it showed that we were going to take a very circuitous route to Chicago. We were routed north over Oklahoma City and then to Omaha followed by Fort Dodge, IA at which point we'd make a turn to the east. I don't know if our dispatcher came up with this route by himself or whether it was given to him by air traffic control, but it was what we were given.

What we were also given was a ton of fuel. The normal route should take about two hours, but this roundabout route was going to be 2+45. The 737 burns about five thousand pounds an hour, plus we have to have our required reserves of 45 minutes of extra gas. On top of that we had gas for two alternates listed as Detroit and Columbus, and also extra fuel in case we had to hold. All of that fuel added up to about 27 thousand pounds.

Now it has been said that the only time you've got too much fuel on board is if you are on fire. While true, having too much fuel when you're trying to land on a short runway in bad weather can be a problem as well. More gas means a heavier airplane. And the Chicago weather was forecast to be ok for our arrival, but thunderstorms were threatening. Another limitation is our structural landing weight limit. There is an upper weight limit for landing that must be met. Carrying too much fuel might put us above that limit in which case we'd have to burn it off or divert. 737s cannot dump fuel like many other aircraft.

The dispatcher put a note on the release to pump us up to 29 thousand pounds if other limits were met, but come push time, the extra fuel never showed up. I was fine going without it as we were planned to land with 12 thousand pounds, about double what we normally have on landing.

Off We Go!


After a last minute runway change requiring new takeoff data, we blasted off at about 8:45. The sun had set and there was a beautiful blue orange glow to the west. Also visible was a rather large storm several hundred miles distant. It turned out to be over central Texas but we could see it perfectly from Houston. Air traffic control stopped our climb at 37,000 feet, 2000 feet shy of our planned 39,000 ft. I assumed that this was due to other traffic conflicts.

My hat is off to the controllers who must not only keep all the airplanes separate, but who must also thread all their traffic through a constantly shifting map of storms. As an additional challenge, their radar systems do not show weather very well. They rely upon pilots to tell them where they can and cannot go. It's crazy, but I have apps on my phone that have better weather readouts than that.

We watched the lights of the Dallas Metroplex go by followed by Ok City and Kansas City off to our right. Prior to getting to Omaha we were cleared to cut the corner to Fort Dodge. It was at this point that things started getting funky. We were first cleared one arrival over Joliet, and then quickly by another arrival farther to the north. Finally, the controller just gave us a northeasterly heading and a descent.

Storms were approaching Chicago from the west and were closing the normal arrival routes. Controllers have to get very creative when this happens. We were lucky that our arrival was so late as the traffic flows were diminished. Had this happened during peak arrival times, we would likely have held or diverted. The new plan was to take us in north of the city, over the lake and south to Midway. The controller's challenge was to get us across the arrival traffic going into O'Hare. For this he had us expedite our descent to below their arrivals.

I was also thinking about my possible options should Midway get hit by a storm. One of our alternates, Columbus, was already being hit by a storm but Detroit was still good. Since we were only a few miles south of Milwaukee by this point, I checked the weather there. Their visibility was only 1/8th of a mile which made that not a great choice. Behind us, though, was Minnie which had good weather.

Like a quarterback, you're always keeping an eye on your open receivers while you avoid the linebackers.

Smooth as Butter!


We got fussed at several times to expedite our descent below the O'Hare arrival corridor. The problem is that to increase descent, one must increase airspeed by pointing the nose lower. We were also getting the poop knocked out of us by turbulence, and our turbulence airspeed is only 280 kts. So we do the best we can to get down without beating ourselves or our passengers up too much.

Once we were below the bumps and over the lake we broke out of the weather and everything smoothed out. We were given a turn to the south and enjoyed a beautiful view of downtown Chicago from the north which we almost never see. After passing downtown we were given a vector to the downwind to runway 4R at Midway. 

Abeam the airport the controller cut us loose and cleared us for the visual. This rarely happens any more and I used the opportunity to hand fly the approach just like we always did in years gone by. Off went the autopilot and autothrottles. My flying skills may get a little rusty when using all the magic day after day, but the rust knocks right off and I rolled out on glidepath right at a thousand feet fully configured.

The aviation gods smiled upon me because I had one of the best touchdowns at Midway that I've had in a long time. The runways are short, so you normally just try to not land long and accept whatever kind of touchdown you can manage.

Well, we taxied clear, contacted ground and the company to let them know we were there, and of course, as day follows night, after a long day and delays, we have to hold out for our gate. Then we get assigned another gate, then back to yet a third gate, and then we wait for marshallers to guide us in. The important point here to remember is that if you shut down an engine, you will then likely be required to turn into your running engine. Think of trying to turn left on ice when only your left rear tire is turning. It doesn't want to go.

Anyway, we get it shut down, I even get a compliment about the landing, and then it's off to the crash pad for about four hours of shuteye before my flight home. Well as they say, it's hard work, but it still beats working for a living.


Dodging thunderstorms for fun and profit















Sunday, May 01, 2016

How to Fly with a Jerk





Yea, they're out there. The perfectionists, the disgruntled, the narcissists and especially the ones who are going to teach you the "proper" way to fly. Spend enough time in the front of an airliner and sooner or later you will be paired to fly with a jerk. Short of calling in sick, you will have to spend the next several days locked in a closet sized space for hours on end with the south side of a northbound horse.

So how will you cope? Remember that you have an important job to do and to do it well, you have to work with the other pilot. There was a time when the standard method of dealing with a jerk was to simply not deal with him or her. This could've meant each pilot scanning the 10 or 2 o'clock positions permanently while never interacting save for required checklist callouts.

That strategy clearly has drawbacks and can seriously degrade safety. There's a reason that airliners still have two pilots (for now). You're a professional even if the other guy or gal is less so, and the folks in back are counting on both pilots up front to conduct themselves as such. With all that in mind, here's the Captain's guide to surviving a pairing with a jerk! (Me included.)

Don't Keep It to Yourself


I think that most people are generally conflict averse. I know I am. Most of us don't go around looking for a fight or trying to cause trouble, especially on the job. We want to get through our day, finish with zero airspeed at the correct gate and go to the hotel. So when a situation crops up that causes us some consternation, a first reaction may be to just keep it to ourselves. After all we place a high value on good cockpit relations and rationalize that some internal discomfort is not too high a price to maintain a cordial cockpit atmosphere.

Don't fall for this rationalization. It is built on a fallacy. For starters, if the other guy is doing something that bothers you, he may not even realize it. Secondly, your discomfort won't go away. It will only fester and get worse. Trust me on this. And if you keep your feelings to yourself for any length of time, it can get really awkward when you finally do speak up. It is always best to get things off of your chest as early as possible.

Don't Ever Accept Non-Standard Operation


Again, there may have been a time in the distant past where the Captain was omnipotent and not to be questioned no matter what he did, even if it fell outside of standard operating procedures (SOP). Those times are absolutely long gone. You have a legal and moral duty to make sure that the aircraft is always operated by the book. Does this mean that you must become a pecksniff and point out every deviation no matter how minor? No it does not; there is a middle ground between being a bag of sand in the seat and what we sometimes refer to as a "check F/O".

Getting back to the professionalism part, when the aircraft is operated in a non-standard fashion and something bad happens, claiming that the other guy was flying is of course no defense. My advice is to predetermine your own personal boundaries and then stick to them. You'll sleep better at night. If push comes to shove, which it hopefully never will, take the airplane if you must, and after landing grab your gear and get off the airplane. This will of course involve scheduling and chief pilots but your career is worth it.

And I want to add a note here about bringing in third parties to a dispute. I believe in handling conflict personally whenever possible. The outside resources available to you are your union's professional standards people and your chief pilot. The first thing either of these people will ask is whether you discussed the matter with the other person. If you reply in the negative, your credibility drops. Nobody will care about your issue more than you, so start there. 

The pro standards folks and (most) chiefs are great, but my thoughts are that if the guy you're flying with is that big of a jerk, the pro standards folks are probably already well acquainted with him. Taking an issue to a chief pilot should be an absolute last resort. You don't want to be known as the guy who runs to management with a personality conflict. Gross or continued non-standard flying? Maybe. Just be ready to defend your actions.

Sometimes You Have to Just Suck it Up


I personally like to let my F/Os fly the airplane any way they'd like as long as it is within SOP, but that's just me. Some cappies like to dictate how the plane should be flown or how a system should be operated. According to most airlines' procedures and FARs, they are within their rights to have it done the way they want it done, again as long as it is within SOP.

As an F/O, you learn to become a chameleon and do it the way the boss likes it to be done. For instance, in the age old argument of whether or not to run the packs on high on a hot day in a 737, everyone has an opinion. But if the guy in the left seat has a preference, his vote is the one that counts. Hopefully he will be willing to listen to your reasons. If not, there's not much that can be done until you upgrade yourself.

My airline has a "bid avoidance" feature that can be used by F/Os to avoid people with whom they really don't want to fly, but it comes with the price of subrogating their own seniority. This feature didn't exist when I was in the right seat so the "suck it up" or "talk it out" methods were all that were available. It did, though, in some measure force people to get along to some degree.

Take a Look in the Mirror


If you find that you seem to end up having more than a few tiffs in the cockpit, then perhaps the problem doesn't lie with the other guy. If it seems to you that everyone you fly with is a pig-headed jerk, then that may become a clue for you. I think this advice is especially useful for captains. F/Os are naturally inclined to become chameleons, so if you find that your cockpit has a tense atmosphere or you spend a lot of time eating alone in the hotel, perhaps some introspection is merited.

Captains, on the other hand, really get very little feedback. Some are conscientious enough to ask how they're doing, but many are not. Most people with a blind spot are unaware that they have one, which is why my above advice to not keep things to yourself may be more useful than first thought.

Do I have war stories about conflict in the cockpit? Yes I do. I think conflict of some sort with another pilot is inevitable given enough time. My personal technique is to try to not bring up topics which might be touchy such as union issues or politics. I'll talk about that stuff all day long if it comes up, but it is much easier to "kick someone's anthill over" when discussing those things as opposed to Da Bears. And I'm not a huge sports fan, but being at least somewhat conversant in sports can be helpful.

In Conclusion


Unlike many other workplace environments, a cockpit is an especially bad place for conflict. Both pilots must make an effort to recognize and to quarantine conflict. Getting things on the table early and using techniques such as humor can go a long way to defuse the bad feels. Pilots aren't necessarily known for being great "people people" but getting along up front should be considered as essential a skill as maintaining airspeed on final.

 Of course, I always get to fly with my favorite jerk.





Thursday, April 21, 2016

A Troubling Report from Rostov



An interim report on the crash of FZ981 has been released
Reconstruction of the FlyDubai 737-800 wreckage



The Russian Interstate Aviation Committee has published an interim report on their investigation into the crash of FlyDubai FZ981. The report is quite troubling as it suggests that the aircraft did not suffer a low speed event or stall, but rather hit the ground with flying airspeed in an extreme nose down attitude. The report is here.

The report starts with the facts that are already known: the aircraft attempted one approach which was aborted followed by an extended time in a holding pattern. Nearly two hours later, a second approach was attempted and a second go around was initiated at 721 ft above ground level (AGL).

The report states that a possible reason the second go around was initiated was due to a sudden increase in indicated airspeed of 20 knots to 176 knots. This is entirely plausible as a gust of this velocity would cause the flaps to automatically retract to avoid an overspeed. Should this happen while on final approach under 1000 ft AGL, the correct decision would be to go around.

Windshear


There has been some speculation that windshear might have been the primary cause of the crash. I think it is important to differentiate between the windshear which might be generated due to convective activity (a thunderstorm) as opposed to gusts found in frontal activity. The weather was consistently poor for many hours preceding the crash with gusty winds but no reported thunderstorms.

The winds were reported as 20 degrees off of runway heading at 27 knots gusting to 42 knots. These winds would certainly make for a difficult approach and landing as the plane would be bucking like a bronco, but they would not be a challenge to staying airborne. Windshear found in thunderstorms can threaten an aircraft on approach but there is no indication such conditions existed here.

Anomalies on the Go Around


It was on the second go around that trouble started. The crew set the flaps to 15 and retracted the gear which is normal procedure. At a height of 1900 ft, the pilot flying pushed on the control column which decreased pitch and caused airspeed to increase. It is at this time that the flaps would normally be retracted so as to not overspeed them. The report states that the flaps automatically retracted to position 10 while the speed increased to over 200 knots.

The flaps blow-up protection on the 737-800 is designed to prevent damage to the flaps due to unintentional overspeeds. Called the Flap Load Relief system, it will retract the flaps from 15 to 10 when the airspeed indicates 201 knots. The flaps will automatically re-extend to the selected position of 15 when the airspeed falls below 196 knots.

It was at this time that the thrust was reduced slightly and the flaps auto-extended themselves back to 15. The thrust was then increased back to full power while pitch and airspeed increased. The flaps once again auto-retracted to 10 where they remained until impact.

The aircraft continued on a rather steep climb of 3150 feet/minute until reaching an altitude of nearly 3000 feet. A vertical velocity of 3000 feet/minute on a go around is steep but not necessarily a problem. The aircraft is by now light having burned its holding fuel, and is not carrying a full load. Pilots can choose to use somewhat less than full thrust in these types of situations but using full thrust is not procedurally wrong. It just means you might have a greater likelihood of overshooting an altitude or causing a flap overspeed which is what happened.

Pitch Over


It was at this time that the aircraft pitched over and began its fatal dive. The report states that the FDR recorded a simultaneous push on the control column accompanied by 12 seconds of forward stabilizer movement. Let's take these one at a time.

Pitching over to stop a steep climb is completely normal. Pitching over which results in a -1g acceleration is not. Normal gravity is 1g. Anytime you feel light in your seat, you're at something less than 1g. A zero g pushover would mean everything in the cabin would float. You'd come off your seat slightly. It would be uncomfortable and rarely happens. A negative 1g acceleration is effectively the same as if your seat was upside down and you were hanging from the seat belt. It would be extremely uncomfortable and short of extreme turbulence just doesn't happen. And it appears to have been caused by a combination of flight control and trim input.

Stabilizer trim is designed to compensate for airspeed changes affecting how the airplane flies. As an airplane increases speed, the nose naturally wants to come up to attempt to maintain the same airspeed as before. Pilots would have to keep pushing on the control column when accelerating to maintain level flight. Trim repositions the horizontal stabilizer to relieve this force. It is controlled by a thumb switch on the yoke which activates an electric motor to actually move the entire horizontal stabilizer and align it with the slipstream. 

On the 737 there is a large wheel next to the throttles which also is connected to the trim motor. This wheel allows manual positioning of the trim if the motor fails and also provides visual feedback to the pilots when the trim motor is running. Normal trim technique is to trim in bursts of one or two seconds. The trim motor on the 737 has two speeds for use depending on whether the flaps are extended or not. The high speed setting is active when the flaps are down. 

A 12 second run of the trim motor, especially in high speed mode, would never be needed during normal operations. This might lead to some speculation that the aircraft suffered what's known as "runaway trim" where the switch might stick and run the trim uncommanded. Boeing has provided several safeguards to prevent this from happening. There is an electric stab trim cutout switch located on the center control stand which removes electric power from the system. 

In addition, power is removed from the system any time pitch inputs don't match the control column inputs. This means the motor cannot trim forward when a pilot is pulling aft and vice versa. Lastly, the trim wheel is designed to be grasped and held when running if all else fails. With these safeguards, a runaway trim problem seems unlikely.

Final Dive


The report states that after the forward control column and trim inputs, the aircraft entered a dive after reaching a peak altitude of just under 3300 ft and subsequently hit the ground in a 50 degree nose low attitude at a speed of over 320 knots. Normally an airliner doesn't see a descending pitch attitude of more than 5 or 10 degrees nose low.

I honestly don't know what to make of this report. The crew flew a somewhat sloppy go around allowing the speed to increase where the flaps blew up, but that by itself wasn't gross or necessarily dangerous. The flap load relief system functioned as designed.

The question to be answered is why the pilots initiated the pushover and simultaneous forward trim? The airplane essentially dove into the ground. I am sure various mechanical or structural failure and other possible scenarios are being considered. The investigators have their work cut out for them.

This is just a preliminary report and the CVR tapes, while referenced in the report, have not been released to the public and may provide more context.