Understanding Air France 447 (23 page)

For some time they were battling control of the roll, trying to get the wings level, often with little success, despite full control inputs.

There were also the apparent contradictory indications from the stall warning. Once the angle of attack reached 45° as they descended through 34,000 feet, each time the nose pitched down and the angle of attack reduced, even slightly, it allowed the pitot-static system to measure more airspeed, bringing the stall warning back on.

Could it possibly have seemed better to them when the nose was higher and the airspeed indication low or blanked out, because the stall warning was silent? Did they somehow believe that the stall warning was erroneous? Other pilots who encountered loss of airspeed indications, and had transient stall warnings, reported that they thought the warnings were false, because they had not strayed too radically from level flight. For them, the stall warning was incongruous with the stable pitch attitude and power settings they had flown. The stall warning margin is narrow at that speed and altitude and is not difficult to trigger due to turbulence or minor pitch inputs.

They may have been so overwhelmed by trying to keep the airplane upright, by the other alarms, by trying to communicate with each other, with calls from the cabin, and calls for the captain, that the stall warning was tuned out altogether.

In the AF447 transcript, no explicit mention of the stall warning was ever made by the crew. However, the selection of TOGA thrust followed the stall warning by five seconds and remained there while the stall warning continued for another 49 seconds. Two seconds after the stall warning stopped the thrust levers were retarded to idle. During that time Robert exclaimed, “But we’ve still got the engines, what’s happening?” The thrust levers were returned to TOGA 46 seconds later after a subsequent series of intermittent stall warnings, and Bonin remarked “Okay, we’re in TOGA.”

To me it paints a picture of an initial loss of situational awareness that they were not able to recover from until a very low altitude. Their loss of awareness of how they drained the airplane of energy in a 3,000 foot climb, and the apparent contradiction of a 15,000 ft/min descent with the nose pointed up with full power, made the indications of that descent incomprehensible until it was too late to do anything about.

Their actions indicate that they thought that all that was required for stall recovery was the application of full power, and when that alone was not working, they did not know what else to do.

At the heart of the matter seems to be the crews inability to comprehend the situation. Could fatigue have been a factor in the crew’s inability to analyze and correct the situation?

Even though Bonin deferred to comments and suggestions Robert had made (the presence of ozone, St.Elmo’s fire, the slight diversion for weather), Bonin was the pilot in command. Robert would have had to reach a given threshold of intolerance before simply offering tips and observations to the pilot flying would turn into taking command of the airplane. By the time the captain arrived back in the cockpit Robert seemed to be a confused as anyone when he said “But we’ve got the engines, what’s happening? Do you understand what’s happening or not?” Only when Bonin stated “I don’t have control of the airplane anymore now, I don’t have control of the airplane at all,” did Robert respond with “Controls to the left.” This could have meant that he was taking over, but at the time the airplane was rolling past 30° to the right. Bonin had already had is sidestick full left, and Robert made left roll inputs himself for a few seconds. Bonin did not relax his full back and left inputs at all, and the airplane’s bank increased towards 40° to the right.

It is possible they were too tired to be performing well.

The captain had allegedly stated at 01:04, "I didn’t sleep enough last night. One hour – it’s not enough."

About an hour before the loss of airspeed event, the captain offered First Officer Bonin an opportunity to take a nap. One must assume that he had some reason to offer this, such as him looking or behaving tired. The captain said, “Try maybe to sleep twenty minutes when he comes back or before if you want.” Bonin turned down the offer, “Oh … that’s kind” he said, “For the moment I don’t feel like it, but if I do feel like it, yeah.”

One might tend to conclude that Bonin clearly said he was not tired. After all they had only pushed back three hours earlier. But the captain followed up with “It’ll be a lot for you.” Thus apparently knowing and trying to convince Bonin that he had already had a long day and he was probably not well rested.

When Robert returned from his break and described his ability to sleep on his break as “so-so,” he asked Bonin if he was OK. He probably had a reason to ask.

It has been postulated that once the A/P disconnected the issue of fatigue would have been overridden by the adrenaline of the moment. Maybe it did to a degree, to make them awake, and to give more strength to pull back on the sidestick, perhaps without even knowing it. This is the source of strength that allows mothers to inexplicably lift cars off of their children. But I do not think it is the source for better mental performance.

It is during these high stress events that we read of soldiers, fire fighters, police, and other situations of high stress where they perform under this stress not by working out the proper solution with clear thought, but that their training ‘kicked in.’

As mammals, our hard-wired reactions to stressful situations are to freeze, run away, or fight back. Thinking of a brilliant solution to the problem at hand is usually not in that mix. The pilot flying needed to know to push forward on the stick, not more strength to pull back.

The two first officers may have been affected by a degree of combat stress. Combat stress has been defined as “The perception of an imminent threat of serious personal injury or death, or the stress of being tasked with the responsibility to protect another party from imminent serious injury or death, under conditions where response time is minimal.
³⁵
” I think it is clear that much or all of those conditions applied in this case.

Tunnel vision, auditory exclusion, the loss of fine and complex motor control, irrational behavior, and the inability to think clearly have all been observed as byproducts of combat stress. Consider the multiple alarms sounding (autopilot disconnect cavalry charge, stall warning, chimes, and the constant sounding of the C-chord). It is possible or likely that these were tuned out (i.e., auditory exclusion)? Bonin’s overcontrolling the roll and pitch inputs despite admonitions from Robert to the contrary, build a case for the loss of fine motor control.

In 1950, S.L.A. Marshall's
The Soldier's Load and the Mobility of a Nation
was one of the first studies to identify how combat performance deteriorates when soldiers are exposed to combat stress. Marshall concluded that we must reject the superstition that under danger men can be expected to have more than their normal powers, and that they will outdo their best efforts simply because their lives are in danger. In many ways the reality was found to be just the opposite, and individuals under stress are far less capable of doing anything other than blindly running from or charging toward a threat. Humans have three primary survival systems: vision, cognitive processing, and motor skill performance. Under stress, all three break down.

When Bonin’s training ‘kicked in,’ it seems likely that the only training he had to deal with the stall warning was the application of TOGA power. When that failed, they were out of ideas and there was no mental capacity to reason out a new one. The next level down of instinctual reactions from him may have been to simply pull back on the stick.

Studies show that 17 hours awake is equivalent to .05 alcohol level. The combination of the startle effect with a diminished mental capacity due to fatigue and stress, during a time when there was a need to think quickly and accurately, and/or call upon past training that may not have been adequate for this situation, may have led to the failure to maintain level flight initially, and then to the apparent confusion which inhibited their ability to comprehend and recover the airplane.

Training

Many comments have been made on various forums concerning the training aspect.

One of the factors missing in training and pointed out in the final report’s recommendations
³⁶
, related to the lack of “specific and regular exercises dedicated to manual aircraft handling of approach to stall and stall recovery at high altitude.”

All three pilots had their A330 and A340 training in the context of an additional rating, taking into account their previous A320 experience, and based only on the differences between the types. As a result none had done any stall training in a A330 or A340 simulator, because the protections, indications, and warnings between these three aircraft are virtually identical.

Stall training, not only at Air France but industry wide prior to the accident, concentrated on stall recognition and recovery at low altitude, where those incidents were considered most likely to occur. Even though there had been stall accidents originating at high altitude (as previously noted).

While the principles of stall recovery are similar in both altitude regimes. Significant differences between low and high altitude do exist:

• Significantly less excess power is available at high altitude, requiring recovery primarily with pitch for angle of attack reduction.
  
• A lower stall angle of attack at the Mach numbers experienced with high altitude flight, and consequently a narrower stall margin than at low altitude.
  

Stall training, however, focuses on prevention and recovery
before
the actual stall is encountered, or “incipient” stall recovery.

In stall training exercises, students recover at the first indication of a stall, that is the stall warning or perceived buffet. The simulator training is not carried into the full stall scenario, nor is the simulator designed to do so.

Prior to the accident most stall recovery training also focused on minimal loss of altitude in the recovery. Rapid application of full power was the initial action, and at low altitude the application of full power often solved the angle of attack problem by itself. Very little pitch down was required to make the recovery and altitude loss was minimized. But again this was recovery from an incipient stall, not a full stall. Pilots were taught to take action as soon as the stall warning or other signs of stall presented themselves. Also keep in mind that stall training in the simulator begins with “OK, we are going to do some stall training now,” and it is not presented in the environment encountered by this crew.

Pilots are also taught that in Alternate and Direct laws the flight envelope protections are lost (as stated on the ECAM when the control law degrades), and that one must be more careful in handling the airplane. However, in the case of AF447, the stall warning first sounded momentarily at 02:10:10, almost immediately after First Officer Bonin inexplicably more than tripled the pitch attitude to 11°. It was silent for 38 seconds then sounded at least four times before TOGA was selected at 02:10:55. While some nose-down inputs were made, the pitch attitude continued to increase and sufficient stick input to establish a nose-down recovery attitude was not made.

The ECAM presented: “Alternate Law, protections lost.” First Officer Robert only got as far in the ECAM procedure to say “Alternate Law protections, lo…”. The transcript reads “Alternate Law protections (law/low/lo),” indicating that the transcriber did not understand what Robert was trying to say. This message is one that would need to be relayed clearly to the pilot flying, and there would need to be assurance that he understood it, as it affects the way he flies the airplane. At the same time that Robert was reading that step, Bonin was asking him about the previous one, “engine lever?” That is because Robert’s reading of that step was also unclear. So, it is not clear that Bonin, the pilot flying ever really understood that the airplane was in Alternate Law and that the flight envelope protections were lost.

During certification flight tests, the real airplane was not fully stalled at high altitude, and therefore data on aircraft behavior and performance beyond that was non-existent. It is impossible to create a realistic simulator model from data that does not exist. I have performed a high altitude full stall scenario in A330 simulators by two different manufacturers and each one behaved somewhat differently. In those simulators it took about 10,000 feet to recover from the fully stalled situation at high altitude. I have no idea of the accuracy of this in relation to the actual airplane’s ability to recover from an extreme fully stalled situation at high altitude.

In later tests by Airbus, angles of attack up to 14° were reached with significant buffeting, and that was proved to be recoverable. The point at which it might not be recoverable is an unknown. It would come as no surprise to many if the airplane was not recoverable at all from angles of attack in excess of 40°. But during the flight, even though extremely high angles of attack were reached (up to 60°) whenever the sidestick was positioned forward, the nose pitched down and the angle of attack reduced. How much altitude it would take to complete a recovery is anyone’s guess, but it would be many thousands of feet.

There is no training in spin recovery of airliners either. A spin is a result of an asymmetrical stall. The entire focus of training is to prevent those scenarios. In my opinion, AF447 may very likely have ended up in a spin had it not been for an active automatic yaw damper working furiously throughout the remainder of the flight to counteract yawing motion. A spin would have resulted in an even greater descent rate and a much lower likelihood of recovery on instruments alone.

There is an old saying that says, “A good pilot uses his superior knowledge to avoid situations that require his superior skill.” Acquiring that superior knowledge is the trick. Memorizing the facts and answering the test questions does not always develop insight. In fact, it rarely does.