A Skosh of Paranoia

cirrus-wreckage

A fellow pilot and I got into a conversation recently about an AOPA accident reconstruction. A Cirrus SR-22 pilot was instructed to enter the pattern downwind at Melbourne, Florida, and then was simply cleared to land without being informed about another aircraft on a straight-in final for the same runway. By the time the Cirrus was on base, the tower tried to fix the conflict by urging the pilot to cut a hard right turn toward the runway. The result was a fatal stall/spin accident.

My friend wrote:

I can all but guarantee that controller had forgotten about the Cirrus on the straight-in when he cleared the accident aircraft to land. I don’t know of any controllers that would clear someone to land from the downwind with the intention of them following an aircraft that was on a straight-in.

Recovery should’ve been simple, have the accident aircraft just continue northbound and make a 270 to join the final for 9R, once clear of the arriving Cessna for 9L and the Cirrus for 9R. Or, a go-around.

Yelling “Cut it in tight” is quite possibly the dumbest thing you can tell a landing aircraft to do unless you’re trying to get them killed.

I agreed with him: the controller probably forgot about the Cirrus and his urgent-sounding instruction to “cut it in tight” was a poor move. AOPA concluded that the issue was a communication breakdown, and while that might be a contributing factor, it’s not the controller who is responsible for the flight. It’s the pilot.

Despite the stall/spin character of the accident, this wasn’t necessarily a stick & rudder flying problem per se. It seems to me that his error was trying to please the controller, that commanding, disembodied voice on the other side of the frequency who seemingly knows best. A better idea might have been for the pilot to simply add power and climb straight out. Or make a (more gentle) turn. Or anything else, as long as he didn’t stall the aircraft.

It’s a shame we pilots feel the compulsive need to follow the flying directions of people who don’t know how to fly. If you step back and look at it from that perspective, the folly of abdicating even the slightest bit of our PIC authority and decision-making power to another becomes evident. But for some reason, this deferral seems to be baked into our DNA, and we ignore that tendency at our peril. Skepticism and a skosh of paranoia are not always a bad thing.

In this case, the smarter move would have been to simply say “unable, I’m going to climb out to the north and circle back onto the downwind” and let ATC deal with it. I actively watch for moments like these when I’m instructing, because they present a vital learning experience for the student that might save their hide somewhere down the line long after I’ve left the cockpit.

I bet if you played this clip for a dozen pilots and ask them to identify the fatal flaw, most would either blame the controller for the poor direction or the pilot for stalling the airplane. Both made errors, no doubt about it. But if you look at it from a larger point of view, I think the issue was simply trying to comply with a controller directive when the correct action would have been to realize it was patently unsafe to do so.

This is all after-the-fact Monday-morning quarterbacking, of course. I can’t claim to know what the pilot was thinking when he cranked into that tight left turn. Perhaps he thought the other aircraft was about to hit him and turned away for that reason. Sometimes immediate action is called for.

Speaking of which, I was being coached in the aerobatic box at Borrego Springs a few years ago and while in the middle of a figure — a 45 degree up-line, no less — the guy coaching me called over the radio and said, “Traffic, turn right NOW” and I simply did it. Good thing too, because a Bonanza went right through our waivered and NOTAMed airspace, totally oblivious to what was going on just feet from his aircraft. If I’d delayed by another second I’d probably be dead.

On the other side of the coin, I was taxiing out from the ramp at São Paulo/Congonhas Airport in Brazil a couple of months ago and the ground controller gave us a taxi route which required crossing a runway, but didn’t include the runway crossing instruction in the route. That was odd, but in foreign countries it’s not uncommon for them to use slightly different words or phraseology. I asked the other pilot to confirm with the controller that we were, indeed, cleared to cross that runway. ATC replied in the affirmative. Whew!

Still, something didn’t feel right. We looked at each other, I set the parking brake, and we agreed that we weren’t going to go anywhere until we were fully convinced that the controller knew exactly where we were. Long story short, our inclinations were correct and ATC was completely confused about our location despite our specifying the exact intersection numerous times. A skosh of paranoia already accompanies most international flying, but this really put us on our toes for the rest of the trip.

You’ll hear all sorts of advice on emergent situations. Some say never rush into anything, others will tell you immediate, decisive action is invaluable. It would be lovely if there was a single “best strategy” for every situation, but like many things in the world of aviation, there are times when one of those responses can save your bacon… and just as many when it might get you killed. The real trick is knowing which is which.

The Key to Good IFR: More VFR

asiana-214

The Asiana 214 investigation has proven to be every bit as interesting and disturbing as I’d predicted.

Most of the reporting and commentary has been focused on the pilot’s interaction with — and understanding of — the aircraft’s automation system. It seems clear they were having trouble getting the aircraft to do what they wanted during the approach into San Francisco.

You won’t hear pilots bragging about this at cocktail parties, but “what’s it doing now?” is uttered far too often on the flight deck. I myself have been puzzled about why the airplane didn’t do what I thought I asked it to do. Usually it’s a programming issue, but not always.

The most recent issue of NASA’s Callback publication, issue 407, details the story of four professional flight crews who had automation confusion issues similar to that experienced by the Asiana crew. So this isn’t exactly uncommon.

Either way, pressing the wrong button is not a criminal offense.

“Cleared for the Visual.” Gulp!

What is criminal is putting a captain on the flight deck of a passenger airliner when he’s unable to comfortably hand-fly it, because when the electrons aren’t flowing the way you want ‘em to, flying the airplane by hand is often the best course of action… not to mention the most fun, too.

Well, most of the time anyway.

The Asiana Airlines training captain who crashed a Boeing 777 at San Francisco International Airport in July was anxious about the visual approach, which he described as “very stressful,” according to investigators.

Capt. Lee Kang Kuk, an eight-year employee of Asiana on his first extended trip flying the 777, also told investigators he was confused about the operation of the airplane’s automation controls, according to a report released by the National Transportation Safety Board on Wednesday as the board held a hearing into the crash.

The 777’s speed dropped dangerously low on the approach, made with assistance of the PAPI lights but without vertical guidance from the ILS glideslope, which was out of service at the time. Both Asiana 214 pilots said they were unsure about the automation mode with respect to the autothrottles, which should have been engaged on the approach. Instead, the autothrottles were set to idle, according to investigators.

The training captain stated it was “very difficult to perform a visual approach with a heavy airplane,” according to the safety board summary of an interview with the pilot. Asked whether he was concerned about his ability to perform the visual approach, he said, “very concerned, yeah.”

An automation interaction problem — the so-called “FLCH trap” — I can understand. But inability to comfortably fly a visual approach? On the surface, that’s a major head-scratcher. When you dig a little deeper, however, it makes perfect sense.

The Key to Good IFR: More VFR

I don’t know how Asiana does it, but many foreign airlines hire their pilots “ab initio”, meaning they are trained by the airline as airline pilots from day one. They have no exposure to pleasure flying, aerobatics, or gliders because the concept of “general aviation” does not exist in most countries. Ab initio airline pilots receive only the minimum required VFR experience. As soon as they venture into instrument flying, the VFR world is left behind forever. They have no use for it! Or so they think.

I’d imagine many of them never fly under visual flight rules again for the rest of their lives. It’s sad. And it’s no wonder some of them are uncomfortable with the thought of flying a visual approach!

It’s not as if the weather was poor, the runway short, or the airfield surrounded by high terrain. There were no issues with density altitude, runway slope or width, or anything else. San Francisco International’s runway 28R is nearly 12,000 feet long. I’ve landed on it many times myself. The weather was clear, winds calm, and the airport is unmistakably large.

Sure, the controllers do tend to keep arriving aircraft quite high. But even from 10,000 feet on a tight downwind, it’s not rocket science to start slowing the airplane and adding drag. Unless you’re asleep at the wheel, you know what’s coming. And even if you don’t, you can ask. The controllers speak English, too. A visual approach in those conditions shouldn’t scare the pilot-in-command of any aircraft. In fact, if there’s an easier way to land an airplane, I’m not sure what it is.

Kids Can Do It — Why Can’t We?

To put this in perspective, consider a glider. It has no engine, and therefore cannot abort a landing attempt. Once you begin an approach to the runway, you are going to land, period. These aircraft have no instruments, no electronic guidance, and they fly in and out of airports without any visual landing aids whatsoever. The landing areas tend to be short, narrow, and rough. And here in the U.S., students as young as fourteen years old can fly them solo. Fourteen! They’re just kids, and apparently even with virtually no flight time, they have no trouble getting comfortable with something that a highly experienced major airline captain felt very uneasy attempting.

This begs the question of how Captain Kuk became so uncomfortable with a simple visual approach. I’d estimate that 75% of all approaches are visuals. I’d be shocked if Kuk hadn’t flown literally hundreds of them. As a scheduled airline pilot, he was required to undergo recurrent training every six months, and had been doing that for eight years.

So how did this level of discomfort with basic visual flying escape the schoolhouse? If Kuk’s training is anything like what we undergo in the Gulfstream, he may rarely have ever flown that kind of visual procedure in the simulator. Mostly what gets simulated are low-visibility conditions. The assumption that it’d almost be “cheating” to have visual references outside the aircraft might not have been correct. Visual approaches in the sim are typically combined with other anomalies: no-flap scenarios, windshear simulations, landing gear blow-downs, etc. But not the typical slam-dunk from a harried controller.

One wonders how many other airline pilots pale at the thought of flying a visual approach (or as the VFR pilots among us call it: landing). I know most airlines no longer allow circle-to-land procedures, but even the neophyte instrument pilot has to perform them to acceptable standards before being issued an instrument rating, and that’s infinitely more demanding than a visual approach. Instead of practicing an ILS PRM at San Francisco, perhaps we should be vectored in on one of those famously high downwinds and cleared for a visual approach from two miles up. Maybe we should train a little more like we fly.

And while we’re at it, taking a hint from that fourteen year old kid who just soloed a beat up Schweizer glider might not be so bad, either. Get out of the glass palace and into an actual airplane where there’s nothing to do except fly by looking out the window.

Gulfstream G650 Accident Report

The remains of the ill-fated G650

It’s been a year and a half since the tragic crash of Gulfstream Aerospace Corp’s G650 test aircraft at Roswell claimed four lives. Ironically, the aircraft recently received its FAA type certificate at almost the exact same time that the National Transportation Safety Board issued their final report on the accident.

I’ve been following the online NTSB docket for months — in fact, I’ve read the entire thing. It comprises thousands of pages of interviews, telemetry, analysis, company records, flight test cards, and transcripts. If you’ve got the time and are enough of an airplane nerd to stay awake while reading it, the accident docket provides a fascinating and detailed look into how a modern test flight program is conducted.

The NTSB’s ultimate conclusion is that Gulfstream (GAC) was to blame for the crash. They cited the company in three areas:

  1. technical deficiencies related to computing the critical angle-of-attack
  2. inadequate safety monitoring
  3. allowing scheduling pressures to affect decision making

In their own party submission to the NTSB, Gulfstream agreed that they were ultimately to blame and plainly accepted full responsibility for the accident. However, after reading the collected body of data the NTSB used to reach their decision, I can’t help but wonder if their expectations are realistic. Given the scope and severity of the required tests, it’s surprising that accidents aren’t more common. I’d like to look at a few of the mitigating factors in that regard.

First of all, by definition flight test is an inherently risky business. The accident occurred during “single engine continued takeoff” testing, definitely one of the most hazardous parts of the multi-year program. This phase of testing involved continuing a takeoff after an engine fails at the most critical moment. The airplane is aggressively flown to the very edge of its capability while operating with a dead engine. In fact, part of this is referred to as “abused takeoff” testing. They do this over and over again at different weights and CG locations.

If it flies half as good as it looks…

The crash occurred because the airplane stalled during one of these takeoffs. Gulfstream did not realize how much lower the critical angle-of-attack is in ground effect than it is in free air, and consequently the stall warning devices (stick shaker & pusher) were programmed to activate at too high an AOA. Estimating this “in ground effect (IGE) stall” phenomenon is not an exact science, and it’s easy to see why. New airplanes receive thorough stall testing, but it’s done well away from the ground. It’s impossible to test stall behavior while in ground effect without high risk of destroying the jet, so computer analysis is relied upon instead.

It’s also worth noting that while Gulfstream is one of the largest and most successful jet aircraft manufacturers, the G650 was a “clean sheet” design. GAC hadn’t really run a test program of this kind for more than half a century. In the late 1960’s, Grumman — best known for their tough-as-nails military aircraft — was riding high with the success of their business turboprop aircraft, which they called “Gulfstream”. The decision was made to develop a turbojet powered version called the Gulfstream II, and it was that aircraft which introduced swept wings, turbojet powerplants, all new systems, and more.

Everything since the G-II has been an incremental development. The G-III was a derivative of that airplane, and Gulfstream IV/450 was a follow on of the G-III. The same is true with the G-V/550. But the G650 was entirely new, and that came with increased risk. Fly-by-wire flight controls, near supersonic speeds, 33% more wing sweep, and so on. For example, Fokker Aerospace developed third-generation fully thermoplastic composite elevators and rudder which are 20% cheaper and 10% lighter than their predecessors.

Next, the NTSB took GAC to task for what they characterized as a lack of cooperation with their investigation. A hard drive containing telemetry data was inadvertently discarded, and Gulfstream requested that some information be redacted in the NTSB reports. Naturally, the Feds weren’t happy with any of that. But Gulfstream operates in a very competitive space. It costs billions of dollars to develop a new product, and their aircraft have some unique features that GAC wants to protect: the large signature windows, a wing free of leading edge devices, etc. The design data for their aircraft is closely guarded intellectual property and an important part of the company’s competitive edge. On the other hand, NTSB reports are public information. You can see why Gulfstream would be concerned about what gets published.

Gulfstream G650 production line in Savannah, GA

The most interesting finding in the NTSB docket is the revelation that the wing roll-off (stall) which caused this accident was not unique. On the G650, two previous roll-offs had been experienced, but when examined by Gulfstream’s flight test department, they were attributed to other causes (piloting technique, for example). Obviously this was a central part of the accident chain and represented the primary missed opportunity to prevent this tragedy. But flight test is a dynamic environment. A post-accident analysis from the safety of a Washington D.C. conference room is quite easy. Coming to the same conclusion from inside an active test program might be more challenging.

As part of the investigation, the NTSB interviewed current and former GAC employees and some fascinating information came to light. Here’s one passage from Lee Johnson, who was chief pilot and project pilot during the Gulfstream IV test program. He reveals that wing stalls occurred during IGE continued takeoff testing on that airplane, and — of particular interest to my fellow Gulfstream pilots — that it was solved by adding the those vortilons found on the G-IV/450 line:

Mr. Johnson was asked to describe an IGE wing stall that had occurred during the GIV flight test program. He said that, during the GIV program, he was performing abused takeoffs with a Federal Aviation Administration (FAA) certification test pilot in the right seat, a Gulfstream FTE in the jump seat, and, he thought, an FAA FTE aboard. They first discussed how to perform the maneuver, and then during the liftoff, the airplane pitched “very rapidly” and stalled. He had seen videos of that flight. The main landing gear wheels might have been a couple of feet off the ground, and the landing gear struts were extended. The airplane rolled right and hit the right wing tip. He applied flight controls to initiate a stall recovery, and the airplane rolled left, in part due to the impact with the ground. He then “jammed in” full rudder and was able to maintain the direction of flight over the runway. They then said “wow” and “we stalled.”

The on-board crew called the telemetry personnel who told them that the airplane wing tip had struck the ground, and Mr. Johnson responded by telling them that they were going to come back and land. The wingtip had scrapes on it but was otherwise undamaged. Gulfstream personnel from Savannah, including personnel from engineering, flight sciences, and structures, came out to look at the airplane. They did not fly for “a while” and it was concluded that the airplane had pitched up, similar to an accelerated stall, and had reached a stall AOA before the activation of the pusher. It later became known that engineering had not really looked at IGE when designing the GIV wing because they had assumed that the wing was the same as the GIII wing.

After the incident, they reviewed the data and determined that the AOA for stick pusher activation should be lowered so that it would activate before IGE stall occurred, in case an abused takeoff, such as applying full aft stick or by pulling too hard, was performed while the airplane was being flown operationally. They began testing with the new stick pusher activation setting after having “sort of” a review in Roswell, with a portion of it being done via conference call with personnel in Savannah. Everyone felt comfortable with the change to the stick pusher system and then they flew again.

The change seemed to work, but about a week later Mr. Johnson encountered another stall at a “little higher” altitude, with a wing drop but with no wing tip ground contact. The airplane floated down while it was still in ground effect and they were able to climb by adding power. Mr. Johnson concluded that the change in the pusher setting was not going to work. They then spent a month testing different leading edge stall configurations and became very familiar with the aerodynamics of the stall. They installed vortilons, which worked “real well,” and then performed natural stalls off the coast of Georgia, some as low as 2,500 feet above mean sea level to verify that they had enough margin beyond the stick pusher for anything that could happen IGE. They finished the program, and they did not have another IGE stall, and it worked well for 25 years. His impression was that nobody anticipated that the airplane’s stall characteristics would be that different in ground effect. Mr. Johnson said that, shortly before this interview, he had attended a Society of Experiential Test Pilots symposium where test pilots and engineers said they had not anticipated IGE stall to be a problem in test programs, and that is what happened in the GIV program.

The NTSB noted that scheduling pressure was a factor in the accident, but I’m not sure that’s quite accurate. While it’s true that the program was behind schedule, the real challenge for Gulfstream was ensuring the aircraft met the performance goals. Aircraft manufacturers start marketing and sales efforts long before the actual airplane is available to customers, and contracts contain guarantees that the jet will have specific range, airspeed, useful load, and runway performance. If the delivered product falls short, there are financial penalties for the manufacturer.

It can sink the whole program, in fact. Aircraft development is like opening a new restaurant: you’ve gotta spend ridiculous sums of money before you see the first dollar of revenue roll in. My friends in the restaurant business tell me it can cost millions. For a company like Gulfstream, development costs are measured in tens of billions. The stakes are high.

As it turns out, the G650 met or exceeded all the predicted performance metrics, in some cases by astonishing margins. For example, the airplane was originally designed with a 6,000 nautical mile range, but testing revealed that actual range is 7,000 nm. That makes the 650 competitive with Bombardier models that were predicted to outshine it. And Gulfstream’s model has come to market years ahead of what is predicted to be its primary competitor, the Global 7000, which won’t enter service until at least 2016.

The fastest business jet on the market.

From what I’ve been able to gather, the toughest part of the certification process was getting the airplane to meet the runway length requirements set out by Gulfstream. As with most aircraft, the Gulfstream G650 requires more runway to takeoff than it does to land. Oh, it can get off the ground pretty quickly, but runway requirements are not based on how much pavement you need to get into the air. Instead, it’s based on the distance required to accelerate to “decision speed” (the speed above which it is actually safer to continue the takeoff in the event of powerplant failure), and then bring the plane to a full stop.

The lower the takeoff speeds are, the less runway is required. The less runway required, the greater the number of airports that will be usable by that aircraft. Unlike your typical airliner, private jets go to some interesting places. High mountain resorts, tiny islands, and thousands of airports around the world which never see any airline service. Nobody wants to spend $65 million on a jet that can’t get in and out of the places they want to go.

The FAA requires an transport category jet like the G650 to be able to continue a takeoff with an engine out and still achieve specific climb performance. The test pilots on the 650 were required to use a very exacting technique to get the right airspeed, known as “V2″, when they reached 50′ above ground, pulling hard enough to reach altitude and airspeed simultaneously. The transcripts from the NTSB docket show them re-running tests when they were just one knot off the required number, an impressive level of resolution when the aircraft is accelerating so rapidly.

The remains of the ill-fated G650

The first wing stall the 650 encountered was attributed to pilot technique, and the second to an inoperative yaw damper. The software to electronically limit the AOA was not complete at the time of the test, and probably wouldn’t have helped anyway since everything was calibrated to what Gulfstream estimated the in-ground-effect critical AOA to be. Unfortunately that number was nearly two degrees off. When the airfoil stalls at just over 11˚, a two degree error is huge.

An analysis by Gulfstream after the ill-fated Flight 153 revealed an in-ground effect stall could be brought about by an angle of attack as low as 11.2˚ for the accident aircraft conditions, 3.25˚ below the out-of-ground effect stall angle of approximately 14.45˚. At the time of the accident however, the team was assuming a decrement of 1.5˚ for in-ground effect stall, leading to an angle of attack of 12.95˚. The stick shaker was also set to activate at 12.35˚, well above the actual 11.2˚ stall angle. The negative margin between stick shaker and stall meant the pilots received little or no warning of an impending or actual stall.

Hindsight is always 20/20, and perhaps Gulfstream really is where the finger should be pointed after this crash. It does seem like the IGE stall issue has been around at Gulftest for a long time. But as I said at the top, flight testing is by definition a hazardous activity. Pushing the envelope with new, high tech designs and building ever faster, larger airplanes in what is undoubtedly one of the most competitive industries will always entail risk. With all that goes into a modern test program, perhaps the biggest surprise is that accidents don’t happen more often.

Vmc Rollover

Remains of the Lycoming IGSO-540 powerplant

Last month a Beech Queen Air experienced a low-altitude failure of the left engine shortly after takeoff. The aircraft crashed into a densely populated area of Parañaque City in the Philippines and resulted in 14 fatalities.

The Queen Air was a precursor to the King Air 90 — essentially a large cabin-class twin with supercharged reciprocating engines. I’ve logged more than 2,000 hours of flight time in a military derivative of the King Air known as the U-21A, so the accident certainly piqued my interest.

During my years flying that aircraft, quite a bit of time was spent talking, thinking, training, and otherwise preparing for just the kind of scenario encountered by the pilots in this accident: a sudden engine failure while low on altitude and airspeed.

Catalina VOR/DME or GPS-B approach procedure

Even with our PT-6A-20 turbine powerplants, it was never going to be a cakewalk if it happened in real life. Thankfully it never did. But such a failure was one of the few things that absolutely had to be handled correctly and expeditiously if you wanted a fighting chance at keeping your aircraft aloft. That’s why we spent so much time training for it.

I recall more than a few dicey single-engine, partial-panel approaches to the Catalina Island Airport (KAVX) during recurrent training in simulated instrument conditions. Even with minimum drag and max power from the remaining engine, starting the exercise from a relatively low-energy state (though still well above Vmc) left the U-21A with little climb capability.

Add in the notorious downdrafts flowing off the cliff at the end of Catalina’s runway and the fact that the missed approach at Catalina takes you to a VOR which sits on a mountain 488 feet above airport elevation but only 1.8 nm from the field, and you can see the magnitude of the challenge.

At the time I was flying for that company, all training missions were done in the actual aircraft — no simulators. As such, we’d only perform low speed engine failures with plenty of altitude. Vmc rollover scenarios were approached, but for safety reasons never allowed to fully develop.

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Vmc is the “minimum controllable airspeed with the critical engine inoperative”.

When an engine suddenly quits, it starts creating drag instead of thrust. The “good” engine, however, is still producing thrust, causing airplane to yaw (and roll) toward the dead engine. Pilots counteract this using the rudder.

It works great — but the rudder only moves so far. The slower you fly, the less airflow the rudder gets and therefore the less effective it is at fighting the yaw. Once you’ve reached the rudder’s mechanical stop, you’ve also reached the limit of your ability to fight the yaw and the airplane will roll over.

The only way to maintain control at that point is to reduce or eliminate power from the good engine in order to restore control.

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I have often wondered exactly what it would look like if things went badly. Sure, the plane would yaw and roll toward the dead engine, just as it does during the Vmc demonstration that every pilot must perform on their multi-engine checkride.

But how quickly? Would idle thrust from the good engine allow recovery in time? Or would it break off into a spin? And if so, would that spin be recoverable given the fuel in the outboard tanks, the weight of the engines hanging out on the wing, and the size of the control surfaces?

These are questions that not even the manufacturer of the aircraft can answer. They don’t test a failure to maintain Vmc to it’s ultimate, stabilized condition. Nor do they typically perform full spin testing regimes on planes of that size and type.

It’s a big question mark, much like the “loss of all engines” scenario in a transport jet aircraft. No data is required from the manufacturer about best glide speed, engine-out range, etc., so none is provided to the pilot. The official line from the FAA is that if you follow procedure correctly it cannot happen, even though it has happened dozens of times in the past and will again in the future.

Actually, I can think of one exception to the lack of spin testing in multi-engine aircraft: the Beech B55 Baron. Raytheon spin tested it in 1998 using a Vmc rollover entry and concluded that the airplane was probably not recoverable.

In fact, among the nearly 100 spins they performed in the Baron, the only two which were unrecoverable without the use of a spin chute were the aggravated spins entered via the Vmc rollover method.

The spin tests performed to date included various flight configurations of the aircraft (e.g. power on, power off, asymmetric power right and left, gear up, gear down, flaps up and flaps down). In all but two of the spin maneuvers, the aircraft responded to the spin recovery technique described in the Baron flight manual — that is, immediately move the control column full forward, apply full rudder opposite the direction of spin, and reduce power on both engines to idle.

In two of the test spin maneuvers, deployment of a spin chute by the test pilot was necessary to effect recovery at a predetermined safe altitude. Both of these spins were performed with power to the left engine at idle, propeller windmilling, maximum continuous power on the right engine throughout the stall, the spin entry and one 360 degree turn.

The important fact demonstrated by these two spin tests is that any time asymmetric power is allowed to continue through spin entry and into a developed spin, a dangerous and possibly unrecoverable spin could be encountered. Raytheon believes this is true any time asymmetric power is allowed to continue into a developed spin to the right or to the left.

As far as the Vmc situation is concerned, at least some data is available on the Queen Air because the Parañaque accident was caught on tape.

Remains of the Lycoming IGSO-540 powerplant

I’ve watched this thing a dozen times, and it’s difficult to judge the aircraft’s airspeed or altitude except to say that both were fairly low, as one would expect shortly after takeoff. In other words, the energy state was low and there wasn’t much altitude to play with, so when that engine failed, the Vmc rollover began quickly and wasn’t going to allow the pilot much time to respond.

You can hear the sound of the Lycoming IGSO-540 engine backfiring before the camera even finds the aircraft. The backfiring was probably the reason the photographer was searching for the Queen Air in the first place. Then airplane begins to yaw and roll toward the dead (left) engine.

Within a few seconds the airplane reaches about 50 degrees of bank and breaks into a left-hand spin. I count about two seconds between the start of the spin and ground impact. It’s that fast.

How’s that for a wild ride? Hopefully it will remain on YouTube as a reminder for every multi-engine pilot: Vmc is not to be trifled with.

Air France Flight 447 Analysis

Recovery of Air France 447's vertical stabilizer

Popular Mechanics recently posted a relatively solid analysis of the 2009 Air France flight 447 accident. It has the rare virtue of being a good read for professional aviators and non-pilots alike.

The article indicates that the pilots — and there were what, three or four of them involved on the flight deck? — were seemingly unaware that the aircraft was aerodynamically stalled. It sounds impossible for a crew with ten thousand hours of flight experience to be so oblivious, but almost the exact same thing happened in the Colgan Air 3407 accident. The aircraft was stalled, the captain didn’t understand what was going on, and he physically held the plane in a deep stall all the way into the ground.

However, in this case, perhaps the problem isn’t that they weren’t aware of the stall warnings, the high pitch attitude or the descending flight path, but rather that they did not believe the airplane could be stalled at all.

That’s on par with believing in the tooth fairy.

The plane has climbed to 2512 feet above its initial altitude, and though it is still ascending at a dangerously high rate, it is flying within its acceptable envelope. But for reasons unknown, Bonin once again increases his back pressure on the stick, raising the nose of the plane and bleeding off speed. Again, the stall alarm begins to sound.

Still, the pilots continue to ignore it, and the reason may be that they believe it is impossible for them to stall the airplane. It’s not an entirely unreasonable idea: The Airbus is a fly-by-wire plane; the control inputs are not fed directly to the control surfaces, but to a computer, which then in turn commands actuators that move the ailerons, rudder, elevator, and flaps. The vast majority of the time, the computer operates within what’s known as normal law, which means that the computer will not enact any control movements that would cause the plane to leave its flight envelope. “You can’t stall the airplane in normal law,” says Godfrey Camilleri, a flight instructor who teaches Airbus 330 systems to US Airways pilots.

Ah, the myth of the un-stallable airplane! Is this what Airbus, airlines, and the FAA are allowing instructors to teach pilots? I certainly hope not. Electronics and fancy design features are no match for the basic laws of physics.

Let’s review. Any airfoil — propeller, main rotor, fan blade, stabilizer, wing — can be stalled. There is no such thing as a stall-proof airplane, just as there are no unsinkable ships (see: RMS Titanic). Anyone who teaches otherwise is a link in an accident chain.

Angle of attack

Now, stall resistant? Sure, under specific conditions, there are design elements ranging from canards to stick pushers to computerized flight control systems which may help prevent the airfoil from reaching the critical AOA. But to say that an airplane cannot be stalled is just foolish.

I’m not sure if it’s marketing hyperbole or human pride which causes such claims to be made. Even when an Airbus is flying under normal law, there are atmospheric factors (many of which happen to be found in the type of thunderstorm Air France 447 flew into) which can lead to a stall. Remember: a stall can occur at any airspeed. Mother Nature can dish out things no airliner can handle, even if it’s manufactured by Airbus.

But once the computer lost its airspeed data, it disconnected the autopilot and switched from normal law to “alternate law,” a regime with far fewer restrictions on what a pilot can do. “Once you’re in alternate law, you can stall the airplane,” Camilleri says.

It’s quite possible that Bonin had never flown an airplane in alternate law, or understood its lack of restrictions. According to Camilleri, not one of US Airway’s 17 Airbus 330s has ever been in alternate law. Therefore, Bonin may have assumed that the stall warning was spurious because he didn’t realize that the plane could remove its own restrictions against stalling and, indeed, had done so.

So because they haven’t seen it before, it can’t happen? Even on a clear blue day, computers can fail. Bugs can emerge in the very software they’re counting on to ensure a stall does not occur. The training these pilots receive sounds inadequate, to say the least. Sad to say, this is not a problem limited to US Airways or Air France or pilots flying the Airbus series. Stalls are poorly understood by a the majority of pilots in my experience.

Ironically, the weakest part of the Popular Mechanics piece also happens to be their description of a stall:

Almost as soon as Bonin pulls up into a climb, the plane’s computer reacts. A warning chime alerts the cockpit to the fact that they are leaving their programmed altitude. Then the stall warning sounds. This is a synthesized human voice that repeatedly calls out, “Stall!” in English, followed by a loud and intentionally annoying sound called a “cricket.” A stall is a potentially dangerous situation that can result from flying too slowly. At a critical speed, a wing suddenly becomes much less effective at generating lift, and a plane can plunge precipitously. All pilots are trained to push the controls forward when they’re at risk of a stall so the plane will dive and gain speed.

The author may have a perfectly valid understanding of aerodynamics. Perhaps he just wants to simplify the description for the magazine’s readership. Either way, the description is completely wrong. Stalls have nothing to do with airspeed and they don’t occur from flying too slowly. There is no critical speed at which the wing “becomes less efficient”. Stalls occur exclusively from exceeding the critical angle of attack, period.

Angle of attack and airspeed are not related. You can reach the critical AOA at cruise airspeed. At the opposite end of the spectrum, if you fly at zero G, an airplane will not stall even if the airspeed is zilch.

I don’t understand the reticence to explain AOA, even to a non-flying audience. The concept is stone simple. Everyone knows that any two non-parallel lines will eventually intersect to form an angle. Describing a chord line and the concept of relative wind shouldn’t take more than a paragraph or two. That understanding makes all the difference in the world. At least, it would have to the crew of flight 447.

Now it just so happens that the critical AOA will be reached at a specified speed under a specific center of gravity position IF the load factor is exactly 1g. But this Airbus was flying through a major thunderstorm in the middle of the Intertropical Convergence Zone. The would have been significant turbulence and the load factor on the airplane would have been all over the place. Assuming the load factor will always remain at 1g is simplistic at best.

Had the pilots considered that a stall would result from excessive angle of attack and not from a specific airspeed, they could have compared the high pitch attitude to the decreasing altitude and high vertical speed and figured things out. The problem was exacerbated by the A330’s design, which masked Bonin’s control inputs because there was no force feedback to the matching set of flight controls to let the other pilot know what the aircraft was being commanded to do.

It’s doubt the official accident report will see it this way, but it seems to be that the Air France 447 accident chain started many, many years ago when the Airbus was designed. It continued when the cruise pilots were in primary flight training and learned to associate stalls with airspeed rather than angle-of-attack. Thorough aerobatic training would have disabused them of that notion rather quickly.

It was only after those pieces were in place that a pitot system failure could have resulted in the loss of the airframe when the flight crew had seven miles of altitude with which to reach the conclusion that the airplane was stalled.