A330 Apparently Stalled, Impacted The Ocean Descending More
Than 10,000 FPM
The French accident investigating agency BEA has released a
document culled from the initial findings from the Air France
Flight 447 accident which occurred nearly two year ago. The report
indicates the Airbus entered a deep stall from which the cockpit
crew was unable to recover. While icing on the speed sensors is
not specifically mentioned, the pilots do indicate that
"we've lost the speeds."
File Photo
All times are expressed in UTC.
At 0155, the Captain woke the second co-pilot and said
"[...]He's going to take my place". The Captain attended the
briefing between the two co-pilots, during which the PF (Pilot
Flying) 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 airplane approached the ORARO point. It was flying at flight
level 350 and at Mach 0.82 and the pitch attitude was about 2.5
degrees. The weight and balance of the airplane were around 205
tonnes and 29% respectively. Autopilot 2 and auto-thrust were
engaged.
At 0206:04 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 0208:07 the PNF (Pilot Not Flying) said "you can maybe go a
little to the left ". The airplane 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 0210:05, the autopilot then auto-thrust disengaged and the
PF said "I have the controls". The airplane 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). BEA
notes that 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, and that autopilot and auto-thrust remained
disengaged for the rest of the flight.
At 0210:16 the PNF said "so, we've lost the speeds" then
"alternate law". (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. This information is not presented to
pilots.) The airplane'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 airplane was then at an altitude
of about 37,500 ft and the recorded angle of attack was around 4
degrees.
From 0210:50, the PNF tried several times to call the Captain
back. At 0210:51, 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.
BEA Graphic Showing Route Of 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
airplane's altitude reached its maximum of about 38,000 ft, its
pitch attitude and angle of attack being 16 degrees. BEA notes that
the inconsistency between the speeds displayed on the left side and
on the ISIS lasted a little less than one minute.
At around 0211:40, the Captain re-entered the cockpit. During
the following seconds, all of the recorded speeds became invalid
and the stall warning stopped. 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
airplane's pitch attitude did not exceed 15 degrees and the
engines' N1's were close to 100%. The airplane 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 0212:02, 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 0213:32, 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 0214:28. 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
airplane were within the operational limits.
- 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 airplane climbed to 38,000 ft.
- The stall warning was triggered and the airplane stalled.
- The inputs made by the PF were mainly nose-up.
- The descent lasted 3 min 30, during which the airplane 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.
In publishing this initial report, the BEA says "This note
describes in a factual manner the chain of events that led to the
accident and presents newly established facts. The initial analyses
will be developed in a further interim report that is scheduled to
be published towards the end of July."