France’s air-crash investigation agency has released an updated report on what happened aboard Air France Flight 447, which crashed in the Atlantic two years ago.
As described here, the plane stalled at 38,000 feet–meaning that its speed slowed to the point where its wings no longer generated enough lift for the plane to remain in the air–and it then plummeted at 10,000 feet per minute into the Atlantic.
All the way down, the pilots tried to regain control of the aircraft, but failed. The plane remained in a stall despite having all its engines operating normally at full thrust.
(To visualise this, think of a plane with the nose up about 40-degrees– almost halfway to vertical–falling pretty much straight down, without much air moving over the wings. Planes can’t fly like that.).
The report makes it clear that at least one of the plane’s speed indicators failed when the plane was flying normally, and when it did, the auto-pilot cut out. The co-pilot then took over manual control of the plane. And, based on the report, it appears he then fatally screwed up. (UPDATE: Here’s an analysis from an actual jumbo jet captain. Link repeated below).
Specifically, the co-pilot pulled the plane’s nose up, causing it to climb and causing its speed to decrease.
Two stall warnings immediately sounded, indicating that the plane’s speed was becoming dangerously slow.
Eleven seconds later (not a rapid response), the co-pilot pushed the plane’s nose down a bit–but apparently not enough. The plane continued to gain altitude rapidly.
30-five seconds later, the stall-warning sounded again. The co-pilot continued to hold the plane’s nose up. Its “angle of attack” (position relative to the air flowing over the wings) continued to increase.
Shortly thereafter, having climbed rapidly from 35,000 feet to 38,000 feet, the plane appears to have stalled, with the co-pilot still holding the controls in a “nose-up” position. (Again, a stall is not an “engine stall”–it is a condition in which the angle of the air moving over the wings is too steep for the wings to provide enough lift to keep the plane in the air.)
[credit provider=”BEA” url=”http://www.scribd.com/doc/56453341/Point-enquete-af447-27mai2011-En”]
50 seconds later, with the plane back at 35,000 feet and now falling at 10,000 feet per minute, the pilot re-entered the cockpit. (He had been on break with the auto-pilot cut out). The plane’s engines remained near full thrust and were operating normally for the rest of the flight.About 35 seconds later, the co-pilot finally pushed the nose down–to no avail.
About 30 seconds after that, still falling at 10,000 feet per minute, the plane passed 10,000 feet.
About 1 minute later, the recordings stopped. The plane was falling at nearly 11,000 feet per minute (~130 miles per hour) when it hit the water. Its nose was still up.
Based on this preliminary report, and speaking as someone who has a pilot’s licence and used to fly small propeller planes, it appears the co-pilot screwed up. He was flying partially blind–one of the plane’s airspeed indicators blipped out–but he then moved the controls in a way that slowed the plane down and increased the “angle of attack” (angle of air flowing over the wings) and caused the plane to stall.
[credit provider=”BEA” url=”http://www.scribd.com/doc/56453341/Point-enquete-af447-27mai2011-En”]
Presumably, when flying an Airbus 330 at 35,000 feet at night in a storm, it is extraordinarily difficult to accurately gauge airspeed without the help of the airspeed indicators. But assuming the plane’s altitude and attitude instruments were still working, which they appear to have been, the pilot’s decision to pull the nose up seems to have been a fatal (and basic) error.Maintaining sufficient airspeed is the single most critical priority in any aeroplane. Planes cannot fly when they stall, and in many aeroplanes–most notably jets at high altitudes–it is extremely difficult to recover from a stall. So the pilot’s first and most important job is to maintain enough airspeed.
Now, this sounds simple, but at the time it probably was anything but. Immediately figuring out what is going on in an aeroplane in a storm at night when instruments cut out can be very difficult, especially if you don’t realise that the instruments have failed. The co-pilots may have misdiagnosed the problem and then tried to climb their way out of it. That said, pretty much the first thing you learn in flight school is that when there is any question about having enough airspeed, you push the nose down. Perhaps readers who have flown Airbuses in such conditions can explain how easy this error would have been to make and, once it was made, whether it would have been possible to recover if the pilots had done something different.
The text of France’s BEA report is below. The key section is in red:
History of Flight
On Sunday 31 May 2009, the Airbus A330-203 registered F-GZCP operated by Air France was
programmed to perform scheduled flight AF447 between Rio de Janeiro Galeão and Paris
Charles de Gaulle. Twelve crew members (3 flight crew, 9 cabin crew) and 216 passengers
were on board. Departure was planned for 22 h 00(1).
At around 22 h 10, the crew was cleared to start the engines and to leave the parking space.
Take-off took place at 22 h 29. The Captain was PNF, one of the co-pilots was PF.
The take-off weight was 232.8 t (for a MTOW of 233t), including 70.4 t of fuel.
At 1 h 35 min 15 , the crew informed the ATLANTICO controller that they had passed the
INTOL point then announced the following estimated times: SALPU at 1 h 48 then ORARO at
2 h 00. They also transmitted the SELCAL code and a test was undertaken successfully.
At 1 h 35 min 46, the controller asked the crew to maintain FL350 and to give their estimated
time at TASIL.
At 1 h 55, the Captain woke the second co-pilot and said “[…] he’s going to take my place”.
Between 1 h 59 min 32 and 2 h 01 min 46 , the Captain attended the briefing between the
two co-pilots, during which the PF said, in particular “the little bit of turbulence that you just saw
[…] we should find the same ahead […] we’re in the cloud layer unfortunately we can’t climb much
for the moment because the temperature is falling more slowly than forecast” and that “the logon
with Dakar failed”. The Captain left the cockpit.
The aeroplane approached the ORARO point. It was flying at flight level 350 [35,000 feet] and at Mach 0.82 [approx. 600mph] and the pitch attitude was about 2.5 degrees. The weight and balance of the aeroplane were around 205 tonnes and 29% respectively. Autopilot 2 and auto-thrust were engaged.
At 2 h 06 min 04, the PF called the cabin crew, telling them that “in two minutes we should enter an area where it’ll move about a bit more than at the moment, you should watch out” and he added “I’ll call you back as soon as we’re out of it”.
At 2 h 08 min 07 , the PNF said “you can maybe go a little to the left […]”. The aeroplane began a slight turn to the left, the change in relation to the initial route being about 12 degrees. The level
of turbulence increased slightly and the crew decided to reduce the speed to about Mach 0.8.
From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said “I have the controls”. The aeroplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row. The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS).
Note 1: Only the speeds displayed on the left PFD and the ISIS are recorded on the FDR; the speed displayed on the right side is not recorded.
Note 2: Autopilot and auto-thrust remained disengaged for the rest of the flight.
At 2 h 10 min 16, the PNF said “so, we’ve lost the speeds” then “alternate law […]”.
Note 1: The angle of attack is the angle between the airflow and longitudinal axis of the aeroplane. This information is not presented to pilots.
Note 2 : In alternate or direct law, the angle-of-attack protections are no longer available but a stall warning is triggered when the greatest of the valid angle-of-attack values exceeds a certain threshold.
The aeroplane’s angle of attack increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left. The speed displayed on the left side increased sharply to 215 kt (Mach 0.68). The aeroplane was then at an altitude of about 37,500 ft and the recorded angle of attack was around 4 degrees.
From 2 h 10 min 50, the PNF tried several times to call the Captain back.
At 2 h 10 min 51 , the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. The recorded angle of attack, of around 6 degrees at the triggering of the stall warning, continued to increase. The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight.
Around fifteen seconds later, the speed displayed on the ISIS increased sharply towards 185 kt; it was then consistent with the other recorded speed. The PF continued to make nose-up inputs. The aeroplane’s altitude reached its maximum of about 38,000 ft, its pitch attitude and angle of attack being 16 degrees.
Note: The inconsistency between the speeds displayed on the left side and on the ISIS lasted a little less than one minute.
At around 2 h 11 min 40 , the Captain re-entered the cockpit. During the following seconds, all of the recorded speeds became invalid and the stall warning stopped.
Note: When the measured speeds are below 60 kt, the measured angle of attack values are considered invalid and are not taken into account by the systems. When they are below 30 kt, the speed values themselves are considered invalid.
The altitude was then about 35,000 ft, the angle of attack exceeded 40 degrees and the vertical speed was about -10,000 ft/min. The aeroplane’s pitch attitude did not exceed 15 degrees and the engines’ N1’s were close to 100%. The aeroplane was subject to roll oscillations that sometimes reached 40 degrees. The PF made an input on the sidestick to the left and nose-up stops, which lasted about 30 seconds.
At 2 h 12 min 02, the PF said “I don’t have any more indications”, and the PNF said “we have no valid indications”. At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again.
At 2 h 13 min 32, the PF said “we’re going to arrive at level one hundred”. About fifteen seconds later, simultaneous inputs by both pilots on the sidesticks were recorded and the PF said “go ahead you have the controls”.
The angle of attack, when it was valid, always remained above 35 degrees.
The recordings stopped at 2 h 14 min 28. The last recorded values were a vertical speed of -10,912 ft/min, a ground speed of 107 kt, pitch attitude of 16.2 degrees nose-up, roll angle of 5.3 degrees left and a magnetic heading of 270 degrees.
At this stage of the investigation, as an addition to the BEA interim reports of 2 July and 17
December 2009, the following new facts have been established:
The composition of the crew was in accordance with the operator’s procedures.
At the time of the event, the weight and balance of the aeroplane were within the operatio-
At the time of the event, the two co-pilots were seated in the cockpit and the Captain was resting. The latter returned to the cockpit about 1 min 30 after the disengagement of the autopilot.
There was an inconsistency between the speeds displayed on the left side and the integrated standby instrument system (ISIS). This lasted for less than one minute.
After the autopilot disengagement:
the aeroplane climbed to 38,000 ft,
the stall warning was triggered and the aeroplane stalled,
the inputs made by the PF were mainly nose-up,
the descent lasted 3 min 30, during which the aeroplane remained stalled. The angle of
attack increased and remained above 35 degrees,
the engines were operating and always responded to crew commands.
The last recorded values were a pitch attitude of 16.2 degrees nose-up, a roll angle of
5.3 degrees left and a vertical speed of -10,912 ft/min.