Orval Fairbairnnot long after the crash:
I just got this email from a retired airline pilot:
From a retired NWA buddy of mine
This from Brent Stratton, a friend and NWA pilot I flew the B-757 with
out of our Tokyo base.........Now obviously on the A-330
Well, I'm sure you have all heard of the Air France accident. I fly the
same plane, the A330.
Yesterday while coming up from Hong Kong to Tokyo, a 1700nm 4hr.
flight, we experienced the same problems Air France had while flying
thru bad weather.
I have a link to the failures that occurred on AF 447. My list is almost
the same.
http://www.eurocockpit.com/images/acars447.php
The problem I suspect is the pitot tubes ice over and you loose
your airspeed indication along with the auto pilot, auto throttles and
rudder limit protection. The rudder limit protection keeps you from over
stressing the rudder at high speed.
Synopsis;
Tuesday 23, 2009 10am enroute HKG to NRT. Entering Nara Japan airspace.
FL390 mostly clear with occasional isolated areas of rain, clouds
tops about FL410.
Outside air temperature was -50C TAT -21C (your not supposed to get
liquid water at these temps). We did.
As we were following other aircraft along our route. We approached
a large area of rain below us. Tilting the weather radar down we could
see the heavy rain below, displayed in red. At our altitude the radar
indicated green or light precipitation, most likely ice crystals we
thought.
Entering the cloud tops we experienced just light to moderate
turbulence. (The winds were around 30kts at altitude.) After about 15
sec. we encountered moderate rain. We thought it odd to have rain
streaming up the windshield at this altitude and the sound of the plane
getting pelted like an aluminum garage door. It got very warm and humid
in the cockpit all of a sudden.
Five seconds later the Captains, First Officers, and standby airspeed
indicators rolled back to 60kts. The auto pilot and auto throttles
disengaged. The Master Warning and Master Caution flashed, and the
sounds of chirps and clicks letting us know these things were happening.
Jerry Staab, the Capt. hand flew the plane on the shortest vector
out of the rain. The airspeed indicators briefly came back but failed
again. The failure lasted for THREE minutes. We flew the recommended
83%N1 power setting. When the airspeed indicators came back. we were
within 5 knots of our desired speed. Everything returned to normal
except for the computer logic controlling the plane. (We were in
alternate law for the rest of the flight.)
We had good conditions for the failure; daylight, we were rested,
relatively small area, and light turbulence. I think it could have been
much worse. Jerry did a great job fly and staying cool. We did our
procedures called dispatch and maintenance on the SAT COM and landed in
Narita. That's it.
However, the report shows they flew pitch and power and things worked out; within 5Kts of desired speed. The only thing that remained amiss was the alternate law condition for the remainder of the flight. The bottom line is they didn't crash.
Reading the details contained in today's BEA report (past the summary) one gleans that the stall warning only sounded twice during the ill-fated descent; first immediately after disconnection of the A/P and again 2 minutes later. Two stall warning amongst all whistles and bells going off, whereas in fact they were stalled the entire time.
Perhaps the PF was pitching up because he was losing altitude and was applying full power to regain it, not knowing he was stalled. It appears that below a certain threshold the data become NCD, i.e., NON COMPUTED DATA so it isnt even considered valid by the system, and that might be a cause for the stall warning to disappear completely. That has been observed in an incident investigated 2 months ago...
This actually is really surprising. It seems as though it's possible that the relative airflow at a pitot in a severe stall might be oblique enough to cause the sensed airspeed to drop below a threshold which means that the way the stall warning system is designed, if the stall progresses far enough, the computer will stop reporting the condition. This just seems horrible... Given that a stall has an entry point, and one hopes an exit as well, it seems as though it would make much more sense for the flight computers to set a flag when the stall is detected, and then clear that flag only when reliable air data indicates the plane is flying again. Until the flag is cleared, the stall warning continues.
SO, if you're nose-up, descending through FL100, w/100% N1, how is it possible to not know you're in a stall? Spatial Disorientation. It's dark, you can't see the horizon, the instruments are telling you things that don't make sense...
Since the PF progressively and slowly over 2-3 mins pitched the plane up, with high power, the speed bleed was in real life slow and small, and thus the trade off between AOA and pitch attitude happened slowly and discreetly, the further away the AOA grew from the actual pitch of the airplane, the more the THS trimmed up to keep the pilot input. This is one of those tricky areas in Airbus; trim being automatic. The pilot doesn't look at the trim wheel per say nor do they trim on the stick because there isn't a function like that. Since the aircraft was heavy, the actual pitch attitude didn't get to 40o, but rather the aircraft was decending pitched up slightly and the angle between the direction descent and the wings was 40o. The aircraft probably looked like it was in a slight climb attitude...it is a very very tricky situation in an airliner, and since they weren't in a sim - they were in it for real - add in the confusion, the panic, the high heartbeat, the callouts that they were getting near 10,000 feet and im sure the weather outside was lightning and turbulent...it became a soup of a situation.
British CAA recently released a document concerning stall recovery technique
Applicability: RETRE, TRIE, TRE, SFE, TRI, SFIAirbus subsequently released the following
Effective: Immediate
STALL RECOVERY TECHNIQUEflightcrewstandards@caa.co.uk.
- Recent observations by CAA Training Inspectors have raised concerns that some instructors (both SFIs and TRIs) have been teaching inappropriate stall recovery techniques. It would appear that these instructors have been encouraging their trainees to maintain altitude during recovery from an approach to a stall. The technique that has been advised is to apply maximum power and allow the aircraft to accelerate out of this high alpha stall-warning regime. There is no mention of any requirement to reduce the angle of attack – indeed one trainee was briefed that “he may need to increase back pressure in order to maintain altitude”.
- It could be argued that with all stall warning devices working correctly on an uncontaminated wing, such a recovery technique may well allow the aircraft to accelerate out of danger with no height loss at the lower to medium altitudes. The concern is that should a crew be faced with anything other than this idealised set of circumstances, they may apply this technique indiscriminately with potentially disastrous consequences.
- The standard stall recovery technique should therefore always emphasise the requirement to reduce the angle of attack so as to ensure the prompt return of the wing to full controllability. The reduction in angle of attack (and consequential height loss) will be minimal when the approach to the stall is recognised early, and the correct recovery action is initiated without delay.
NOTE: Any manufacturer’s recommended stall recovery techniques must always be followed, and will take precedence over the technique described above should there be any conflicting advice.
- Any queries as a result of this FCTN should be addressed to Head of Flight Crew Standards at the following e-mail address:
Captain David McCorquodale
Head of Flight Crew Standards
21 April 2010
For the A320 fleet:That notwithstanding, it seems to me that the BEA has put all the facts out there...they just aren't saying outright what the cause of the accident is. From where I'm sitting, this is pretty cut and dried:As soon as any stall indication (could be aural warning, buffet...) is recognized, apply the immediate actions :
- NOSE DOWN PITCH CONTROL . . . . . . . . . . . . . . . . . . . . APPLY
This will reduce angle of attack
Note: In case of lack of pitch down authority, reducing thrust may be necessary
- BANK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . WINGS LEVEL• When out of stall (no longer stall indications) :
- THRUST . . . . . . . . . . . INCREASE SMOOTHLY AS NEEDED
Note: In case of one engine inoperative, progressively compensate the thrust asymmetry with rudder
- SPEEDBRAKES . . . . . . . . . . . . . . . . . . . CHECK RETRACTED
- FLIGHT PATH . . . . . . . . . . . . . . . . . . . RECOVER SMOOTHLY
• If in clean configuration and below 20 000 feet : - FLAP 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SELECT
Note: If a risk of ground contact exists, once clearly out of stall (no longer stall indications), establish smoothly a positive climb gradient.
I believe if one reads the report carefully, it is pretty clear what the problem was. The event that started everything were the crappy Pitot tubes failing/icing, but as a hobbyist with plenty of theoretical knowledge of commercial flight and the procedures and physics involved, I think it's pretty clear that the crew made some grave errors in this accident. We can debate whether other crews would have performed differently, better, worse, or the same, but I personally think that since this is the first outcome of its kind despite pitots having frozen/failed plenty of times before, it puts this event in a particular light.
I believe that there is certainly no design issue with the A330 that caused this issue. The faulty pitots have been replaced, but now it's time to teach pilots how to fly a plane so they can execute when feces hits the fan.