Understanding Air France 447 (18 page)

02:13:10 As a result of constant aft stick input, the elevator returned to full nose up. The airplane pitched up toward 15° and the angle of attack returned to greater than 45°, reaching even as high as 60°.
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02:13:18 Bonin remarked, “We’re there, we’re there, we’re passing level one hundred” (10,000 feet). “What is, how come we’re continuing to go down now?”

Robert instructed the captain to see if a reset of the flight control computers could help. The captain remarked that it “won’t do anything,” but he apparently reset PRIM 1 and SEC 1 anyway.

02:13:36 Bonin called out, “Nine thousand feet.” The sidestick was still about half way back, the elevator and stab were at full nose up (trying to comply with Bonin’s pitch-up order), and the thrust levers were in TOGA.

Robert said, “Climb climb climb climb!”

To which Bonin replied, “But I’ve been at max nose up for a while.”

Realizing that Bonin had been doing the wrong thing for some time, the captain said, “No no no, don’t climb!”

Robert said, “So, go down,” and pushed his own stick forward for five seconds while the thrust levers were reduced to climb. Bonin continued to pull back.

02:13:40 A synthetic voice announced, “DUAL INPUT” five times, indicating that both sidesticks were displaced from neutral. Robert had failed to announce that he had taken control of the airplane, or to use the takeover push-button to cut out Bonin’s sidestick commands. Bonin’s nose-up and Robert’s nose-down pitch commands cancelled each other out. Robert commanded, “So give me the controls, the controls, the controls to me.”

Bonin released the stick and said, “go ahead, you have the controls, we are still in TOGA, eh?”

At 02:13:49, with the sidestick held forward by Robert, the pitch attitude decreased to about 5° nose down. The indicated airspeed rose to about 90 knots and the stall warning sounded again. Robert eased up on the forward stick input and, despite having said he had the controls, Bonin pulled back on his sidestick for a few seconds.

02:14:00 The nose began to rise again

02:14:05 The captain said, “Watch out, you’re pitching up there, you’re pitching up.”

02:14:07 Robert began pulling full back on his sidestick, saying, “I’m pitching up, I’m pitching up.” The thrust levers were retarded to idle for two seconds and the nose pitched up reaching 16°.

Bonin added, “Well, we need to, we are at four thousand feet!”

02:14:10 The captain warned again, “You’re pitching up.”

02:14:16 At 2,500 feet above the water, and within the operating range of the radar altimeters, the ground proximity warning system (GPWS) activated, warning of the high vertical speed close to the surface. The synthetic voice said, “SINK RATE, PULL UP!, PULL UP!”

The captain gave permission, “Go on, pull.”

“Let’s go, pull up, pull up, pull up!” said Bonin.

The thrust levers were moved to TOGA both pilots pulled their sidesticks aft as the airplane pitched up toward 16°.

Bonin pushed the takeover push-button on his sidestick cutting out Robert’s commands. “PRIORITY RIGHT” was announced by the synthetic voice. A red arrow in front of Robert illuminated and pointed to the right where Bonin was pulling full back on the stick.

Bonin, still not having understood what happened said, “[expletive] we’re going to crash”

The GPWS commanded, “PULL UP!”

“This can’t be true” Bonin said.

“PULL UP!” repeated the GPWS.

Bonin pled, “But what’s happening?”

The captain commanded, “Ten degrees pitch.” The GPWS continued to alert “PULL UP!”

Robert pushed his sidestick forward but Bonin still held the takeover push-button so Robert’s inputs were blocked. Both engines were operating at near maximum thrust and the angle of attack was in excess of 45°. The airplane impacted the water 16° nose up, in a 5° left bank with a forward ground speed and vertical speed both at 107 knots (10,900 ft/min).

Were there more indications lost than just airspeed?

It is clear that for about 90 seconds, the crew of AF447 had a hard time determining if they were climbing or descending, as the airplane fell from 32,000 to 10,000 feet. Vertical speed indications were erratic. Most probably due to the effect of the high angle of attack on the static ports.

The following exchanges beg the question if the crew had lost more instrument indications than just airspeed.

PF: Pilot Flying

PNF: Pilot Not Flying

CA: Captain

The crew, or at least the pilot flying, had an obvious difficult time determining if the airplane was ‘going up’ or ‘going down.’ It is unlikely that he suddenly forgot how to read an altimeter. There is no mention in the report indicating the loss of indications other than airspeed. During this entire exchange, while there was confusion on whether they were going up or down, they were in fact going down in the range of 15,000 feet per minute. That is over 170 miles per hour - in the vertical axis!

I have spoken with some of the world’s leading experts on this airplane, both test pilots and experts on its recording systems. They are not relying on the English translation of the transcript. There was no reason for the altitude display to have been lost. They stated that if it had been, there would have been other faults registered with the air data and display management computers, but there were none.

As they were descending through 30,000 feet, First Officer Bonin declared, “I have a problem, it’s that I don’t have vertical speed indication.” In the prior seconds, the angle of attack exceeded 45°, and the recorded vertical speed had become erratic. In simulator recreations I have seen the vertical speed indication go blank when the vertical speed reached 20,000 feet per minute (shown below). I take him at his word that he did not have a vertical speed indication. However, all indications show that the altimeter continued to operate.

The crew saw an airplane with operating engines, pitched up, erratic airspeed, an altimeter moving many times faster than they have ever seen one move, and a vertical speed indicator that was blank, erratic, or pegged beyond the limit of its normal display range. It most likely presented a picture that did not make any sense. The captain remarked, “It’s impossible.” This was a situation where they could not imagine that all of these indications were true, but what to believe? Alternate sources for the data were selected, but it made no difference.

There are also hints that the attitude displays on the two primary flight displays may also have been lost for an unknown period of time. However, Airbus and the accident investigators state that they do not believe that happened.

Both first officers declared that they had “no more valid displays.” This is not a statement that would be expected with the loss of just airspeed and vertical speed. Then the source for the left side instruments, both air data and heading/attitude were switched to the ADR 3 backup, having been previously selected to the right side.

The captain said, “The wings to flat horizon, the standby horizon.” Why he would refer to the standby horizon if the two primary attitude displays were operating is a mystery. The most logical explanation is that they were not working. No other similar incident had reported a loss of attitude display. That is until a Mihin Lanka A321 (Mihin Lanka is the budget airline of the Democratic Socialist Republic of Sri Lanka) in March, 2013. The airplane was en route from Jakarta, Indonesia to Colombo, Sri Lanka.

My sources revealed that the flight was cruising at FL 340, 500 miles southeast of Colombo Sri Lanka (a position approximately 4° North latitude), and encountered turbulence at which time the autopilot disconnected with multiple ECAM alerts. The crew lost airspeed indications as the airspeed values fell below 30 knots. Altitude indications jumped 580 feet due to the loss of a reliable Mach value to correct the static pressures. The flight control law downgraded to Alternate Law and the autothrust was lost. The crew also reported the loss of both attitude displays on their Primary Flight Displays (PFDs) for up to 20 seconds. The loss of an attitude display in this type of scenario is certainly unexpected, and seems inconsistent with the condition.

A preliminary evaluation was said to have revealed that at least two of the three AOA probes, the total air temperature probe, and pitot tubes, and engine ram air pressure sensors had suffered an icing incident. But there was no evidence of any loss of attitude display as reported by the pilots since all the inertial reference data remained valid.

Perhaps the crew of AF447’s apparent confusion was due to inoperative attitude displays on their PFDs, an erratic or inoperative vertical speed indication, and a rapidly declining altitude indication. We will never know for sure.

The BEA recommended that aircraft undertaking public transport flights with passengers be equipped with an image recorder that makes it possible to observe the entire instrument panel. This equipment would have clarified the “no more usable displays” statement and resolve questions such as the pilots reporting loss of attitude displays when the feeding data remained valid.

Could it Have Happened in a Boeing?

There were many voices that were quick to say that had this been a Boeing, with a conventional yoke control column and not the Airbus sidesticks, that the accident would not have happened. The theory being that the other pilot would see that the pilot flying was pulling back for long periods of time and corrected it.

We can never know for sure, but support of that theory comes from a segment of the cockpit voice recording when the airplane was passing through about 9,000 feet:

02:13:36 Bonin called out “Nine thousand feet”. At this time the sidestick was about half way back, as it had been for the previous 40 seconds, though no one else could see this.

Robert remarked, “Climb climb climb climb!”