The ensuing controversy on the Airbus continues.
Two years ago an Airbus A330 fell to her death in the Atlantic Ocean. We’d heard rumors she’d fallen apart in the sky. That she’d lost all her flight instruments due to a known pitot static problem, that Airbus would immediately fix. We’d heard that we would never know the truth.
But the truth has surfaced from the watery grave. The press is leaking snippets. But with each sound bite, and piece of data they presented, we can make an analysis as to what really happened to AF flight 447.
To our non-aviation readers:
PF: Pilot Flying
PNF: Pilot Not Flying.
I am writing not to discredit the pilots, the company, or the airplane, but so we as pilots can learn from this incident so it won’t happen to anyone us, or anyone else.
AF 447 flew into the heart of a storm. But they knew what was ahead. They had discussed the pending turbulence as a crew. They briefed the flight attendants. They were in a cloud layer, but their awareness of the turbulence, the precipitation, and the need to navigate to the left indicated they were utilizing the radar.
2:08:07: PNF states, “You can maybe go a little to the left…”
2:10:05: The autopilot and then auto-thrust disengaged. The PF said, “I have the controls.” Then the plane rolled right, and the PF made a left nose-up input leading to the first stall.
We have to ask, why the nose up input? Why the roll to the right?
Was the PF’s attention drawn away from what he was doing, by looking at the instruments? I suspect he inadvertently looked right and the stick came with him.
The first time I flew the A330 took a bit of getting use to. I banked left, returned the stick to neutral and the plane continued in the left bank. I had to move the stick to the right to roll the wings level and then put the stick in neutral again. How proficient were these pilots at hand flying their aircraft? Combine that with the turbulence …
Why did he pitch up? Not sure… but there was obviously a lot of confusion with both pilots.
We also know that the autopilot and auto-thrust remained disengaged. Could they have got them back? Perhaps. Did they try? The report didn’t indicate that they attempted, but the ensuing instability of their aircraft would have prevented the re-engagement of the autopilot, even if it had been available.
2:10:16: The PNF said, “so, we’ve lost the speeds” then “alternate law”
What in the heck is alternate law?
Alternate law is a downgraded flight control law caused by a combination of failures. In this case, the AF moved from normal law, to alternate law, because of the loss of airspeed due to the pitot static system. In this mode the automation, protections, and handling characteristics are reduced. Depending upon the degree of failure, the autopilot may have been available . In Alternate law the pitch control is similar to normal law with maneuver protection, plus automatic pitch trim is normally available.
I suspect that the PF would have known that he was inadvertently pitching up if trim wasn’t available because of the ensuing backpressure .
A big difference in alternate law, verses normal, is that alternate law replaces pitch attitude protection, alpha protection, and high-speed protection with low and high-speed stabilities.
Low Speed Stability
Low Speed Stability replaces alpha protection and is activated by speed instead of angle of attack. At 5-10 knots above stall speed a nose down command is produced to avoid further decrease in airspeed. This nose down command can be overridden by pilot with aft side-stick, and the aircraft can be stalled. The instruments were guiding them to pitch down, and yet they did the opposite. Why?
A level below Alternate Law is Direct law, which provides direct side-stick to flight control surface relationship; similar to the non-fly-by-wire aircraft I’m use to flying. There are no protections. There is also no pitch trim and the autopilots are not available.
The Trouble with Alternate Law
Alternate law provides some protections and guidance. But none of that will help the pilot if they don’t know “how to” fly the plane without the autopilot. When was the last time these pilots hand flew their plane? If they weren’t proficient they could easily mismanage the banking, and pitch. Combined with the distraction of airspeed problems, a storm, and a stick shaker… this could be confusing especially if they’d never done it except for initial training.
2:10:16 the flight continues…
Their angle of attack increased to 10 degrees and the plane climbed. The PF pushed the nose forward while he continued to move the sidestick left and right. The rate of climb came down to 700 ft per minute but the roll rate between 12 degrees right, and 10 degrees left…. Indicated he still fought the roll, but it appeared he was getting the pitch under control. Momentarily.
2:10:50: PNF called for the Captain to return to the flight deck. Calling for the Captain while fighting to maintain control clearly indicates the PNF didn’t know how to manage the plane either. First rule of thumb in an emergency: Fly the airplane. Talk later.
2:10:51: Stall warning, again! They pushed the thrust levers to TOGA, but the PF maintained nose up inputs, and continued to increase the horizontal stabilizer to trim a nose up condition, from 3 to 13 degrees in one minute. The separation of airflow over the wings became too great and the wing stopped producing lift. Added power at the critical angle of attack did nothing but exacerbate the problem.
They needed to pull the power off. Push the nose forward. Get the wings flying. Then add power. Why didn’t they do that? When was the last time they performed stall training ?
Then 15 seconds later the speed on the ISIS (Integrated Sstandby Instrument System) increased to 185, it was then consistent with the other recorded speed. Yes… there speed had come back. And then the angle of attack continued up to 16 degrees. Why were they continually pulling back?
2:11:40: The captain returned. “During the following seconds, all of the recorded speeds became invalid and the stall warning stopped.” Why?
Note: With speeds below 60kts the angle of attack is considered invalid, and below 30kts the airspeed is invalid. At this time… 35,000 feet, an angle of attack exceeding 40 degrees and vertical speed -10,000 ft/min. Roll oscillations up to 40 degrees. The PF made inputs on the sidestick to the left and nose-up stops, lasting about 30 seconds.
2:12:02: PF said, “I don’t have any more indications” and the PNF said, “We have no valid indications.” At which time the thrust levers went to IDLE and the engines’ N1 was at 55 %. 15 seconds later we can see pitch-down inputs. The angle of attack decreased, the speeds became valid and stall warning sounded again.
This report didn’t share what the captain said, but we can only imagine. Under his guidance the brought the power back, and pitched the plane down. They just didn’t have altitude.
Unusual attitude training at one time was prevalent. We closed our eyes and the other pilot would bank, roll and pitch up or down. Then we would open our eyes and fly the plane to level. In my 747, we still do this type of training. But with the automated aircraft, they don’t feel it necessary. Imagine opening your eyes and seeing a pitch of 15 degrees, with a vertical speed of -10,000 feet per minute, and no airspeed indication.
2:13:32: PF said, “We’re going to arrive at level on hundred” 15 second later the PNF started helping him the PF fly the plane. Unfortunately when two sidesticks are used at the same time while flying without automation, in the same direction their demands are summed by the computers up to a full deflection of a single sidestick. If they were operated simultaneously in the opposite direction, they cancel each other out. Helping the other pilot fly is never a good thing to do in this plane.
The PF said, “Go ahead, you have the controls.” He either gave up, or knew that two pilots couldn’t fly at the same time. Either way, the angle of attack stayed above 35 degrees.
Recordings stopped at 2:14:28.
Last recorded values: -10,912 ft/min, ground speed 107 knots, pitch of 16.2 degrees nose up, roll angle of 5.3 degrees left, and magnetic heading 270 degrees.
228 People Died
We only know what BEA was willing to tell us in their release, which wasn’t much. Despite the known airbus problems, was that enough to take out this plane? Could another crew have survived the same incident?
When had these pilots last experienced stall training? When a stall occurs the pilot must pitch forward. Not pull the stick aft. Despite what they saw, that should have been an ingrained reaction. Why didn’t they?
For anyone who flies the Airbus and your flight instruments die, loss of autopilots, loss of auto-thrust and leaving no altitude, airspeed, or pitch indications, worst case scenario, do this:
- Select Flight Path Angle (TRK/FPA) on the Flight Control Unit. This selection will provide guidance for level flight. Selecting the TRK/FPA displays the Flight Path Vector indicating the Flight Path Angle relative to the horizon, independent of aircraft attitude. When this symbol is centered on the horizon, the aircraft is in level flight. The Flight Path Vector uses ADIRS inertial data.
- Don’t mess with the thrust levers. If a malfunction occurs, they default to thrust lock and will maintain the setting at the time of the failure.
- Select Data on the MCDU to read the GPS ground speed and GPS altitude.
I recommend that you hand fly the plane without the automation . One day you might have to, and won’t remember how. With the information presented in this report… it’s evident that’s exactly what happened in this scenario. Was there more to it? Of course, but we can only know what they’re willing to tell.
Suggestion to airlines:
- Include hand flying at altitude in your recurrent training programs.
- Enable pilots to maintain proficiency beyond legality. Allow them to visit the simulator if they feel they’re not proficient.
Automation is wonderful, but it can destroy a pilot’s skills.
- Pilots kick off the autopilot and fly your plane occasionally. You never know when your life will depend upon it.
Suggestion to Airbus:
- Input a switch on the overhead panel that the pilots can immediately put the plane in direct law, when everything falls apart, enabling them to have the feel of a real airplane. Not that the bus isn’t real, but it’s not what we’re used to flying.
From the cockpit of Darby Bradshaw, fly safe.
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