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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 12th Jun 2014, 18:41
  #81 (permalink)  
 
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Bonin pulled the A330 into a fully developed stall

DozyWB - you make some good points and I agree both Airbus and Boeing have gone some way to educate the flying public on correct AoA reduction techniques. Flight testing FAR/JAR25 demands AoA reduction then 20% above stall speed before adding power.

Low alt, approach to stall min height loss recovery was stressed by FAA and CAA examiners for PPL and Commercial pilots - it instilled the wrong message at the foundational stage of flight training. In aircraft with underslung engines or tractor propellors adding thrust adds to the pitch up moment (not so much at high altitude grant you). Slowing down also activates aft pitch trim (AF447 A330 had maximum aft tailplane trim) which makes recovery even more difficult as the Thomsonfly Bournemouth stall episode revealed: Air Accidents Investigation: 3/2009 G-THOF

The Airbus get out of jail free option (Windshear, Terrain, Woop Woop pull up, etc) was regularly emphasized for LST/Initial Type Rating training - essentially (in normal/non degraded mode) it allows you to get to the light buffet (Cl max) with maximum thrust and no stall. It requires Full Aft stick and TOGA. What did Bonin consistently do in the confusion? The BEA have a video of the flight recorders that has not been on general release - it shows the side stick positions on both sides - the FO also applied aft inputs (his seat was found wound aft at the sea bed).

Bonin was spooked long before the fatal events - read his reaction to the smell of ozone. But his techniques and both pilot's ignoring a stall warner speak of poor training and poor understanding of the situation their reactions had created.

Have you discovered how much gliding Bonin had done and how long it had been since he stalled a glider? The BEA AF447 investigator at a recent RAeS Upset recovery lecture did not consider his glider training to have been very frequent or recent to events.

Apparently the junior crew had practiced unreliable airspeed some time before AF447 and the SIM route was from Rio with drifting ADIRUs.
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Old 12th Jun 2014, 19:03
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Originally Posted by angelorange View Post
DozyWB - you make some good points and I agree both Airbus and Boeing have gone some way to educate the flying public on correct AoA reduction techniques.
Cheers!

The Airbus get out of jail free option (Windshear, Terrain, Woop Woop pull up, etc) was regularly emphasized for LST/Initial Type Rating training - essentially (in normal/non degraded mode) it allows you to get to the light buffet (Cl max) with maximum thrust and no stall. It requires Full Aft stick and TOGA. What did Bonin consistently do in the confusion?
OK, but was this "option" ever trained at high altitude? It not only looks inappropriate for high-altitude ops, but also seems to be at odds with what the manual states in that situation (i.e. 5 degrees nose up, thrust lock)...

It also doesn't explain Bonin's apparent (and inappropriate) concern about overspeed which followed shortly after, causing him to attempt to deploy speedbrakes. I agree that his reverting to the procedure you describe is a possibility, but the rest of it looks to me like he was throwing almost random elements into the mix (likely due to panic). Nor does it explain why he pulled up so soon after AP disconnect.

Bonin was spooked long before the fatal events - read his reaction to the smell of ozone. But his techniques and both pilot's ignoring a stall warner speak of poor training and poor understanding of the situation their reactions had created.
True, but as I said, 5 other pilots (most of them captains and some of them military veterans) have in the past become similarly spooked and made exactly the same mistake. I refer back to the tests done by the BEA in which 80% of the pilots they studied immediately pulled up in response to an unexpected stall warning.

Have you discovered how much gliding Bonin had done and how long it had been since he stalled a glider?
I think I have something with the qualifications and when he did them kicking around somewhere, but the point I was trying to make was that while training was certainly deficient - it doesn't necessarily follow that Bonin "didn't know how to fly", as the media seem to have suggested.
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Old 13th Jun 2014, 02:11
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it doesn't necessarily follow that Bonin "didn't know how to fly", as the media seem to have suggested.
Caricature or the future ???
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Old 13th Jun 2014, 03:02
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Seems like perhaps only 0.0001% of airline pilots have ever experienced any form of PIO and most do not understand the implications of the AF447 roll PIO encounter right after the autopilot dropped out.

All that wing rocking that Bonin did had the effect of destroying his trust in the reliability of his aircraft's control system so that later when the pitch control system did not behave as he expected (upon stall encounter), he assumed that that had failed too.

Folks have been minimizing the roll oscillation. Statements such as,"it wasn't that bad", "the roll rates were not that high", "he recovered roll control within 30 seconds" seem to predominate. I maintain that those with that view simply do not understand the nature of the PIO beast.

From my very limited exposure to a roll PIO in an older simulator, two PIO oscillation cycles is sufficient to grab your complete attention, and 30 seconds of fighting a PIO oscillation is a lifetime. The rest of you are going to have to take this on faith unless you also have had some sort of a PIO encounter. (And if you do have such experience, lets hear from you.)

Bonin's roll PIO was started by his initial excessively large roll input. The roll PIO was continued by an incorrect control strategy (Trying to get ahead of the roll oscillation). The reason he fell into this trap starts with lack of training in a simulator in roll direct at altitude (ALT2B mode). The other ~ 35 aircraft that successfully survived loss of airspeeds apparently did not encounter a roll PIO.

That Bonin used to fly gliders has very little bearing on the AF447 outcome. When the chips were down, he could not transition smoothly to manual control under night instrument conditions. If he had been gentle with the controls and had just kept on truckin, this would have been a non-event.

As Gums would say, "That's my story and I'm sticking to it."
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Old 13th Jun 2014, 07:25
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Machinbird
As Gums would say, "That's my story and I'm sticking to it."
I'm with both of you on that one.

PIO is a very surprising event, and the problem lies in recognising it from the beginning. If not recognized the trained corrective action (to counter the unintended roll) agrevates the problem.

The same applies for the stall situation. Without recognizing an imminent stall situation prior stall warning by analyzing the energy situation of the aircraft (climb- gaining altitude - loosing speed) the stall warning might have been judged as invalid and caused by the failing speed indication. We all had faulty warning lights before, and first thing we do when one shows up or "Betty Bitch" is shouting is validating most of those warnings before acting. Excluding the stall from the equation it comes down to the basic trained behaviour: The aircraft goes down, therefore increase pitch to make it go up again.
That's what they did, and what others with stick shakers did.

Last edited by RetiredF4; 13th Jun 2014 at 11:20.
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Old 13th Jun 2014, 15:08
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@Machinbird, RetiredF4:

You're right - however if I recall correctly from the mega-thread and the report's DFDR graphs, the PIO was on its way to being stabilised, and was almost there at the point the aircraft stalled (apex of the zoom climb) - suggesting that the PF was at least getting a feel for the roll aspect. Unfortunately the consistent backpressure (intentional or not) while doing so meant that stabilising the roll became something of a moot point as the aircraft went into a full stall.
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Old 13th Jun 2014, 16:45
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Originally Posted by DozyWannabe View Post
I didn't forget, sir - and I don't want to argue with you. Maybe it was my bad for misunderstanding, but the previous post to which you replied referred to "the stupid stall recovery [being] taught", which you actually underlined in your quote. Therefore it appeared to me that you were saying that "teach[ing] process" was a *bad* thing. Apologies if I got it wrong.
No, my point was to agree with him about teaching the correct process. His point on "min alt loss stall teaching" can have some unintended outcomes in terms of what the pilot has as his objective and actions during stall recovery. The key is to teach the correct stall recovery technique, which will take care of losing altitude (minimize it) by unstalling the aircraft and returning (and maintaining) a flying AoA. IT is in how you teach stall prevention and recovery that the lesson is correctly or incorrectly learned. Teach the correct process.

As to "lower the nose" there's a more technically correct idea behind that regarding "reducing the AoA' though in most stalls reducing pitch attitude will help with the AoA problem one is dealing with.

Sorry to bite at you there, I could have been less terse.

@ Machinbird:
From my very limited exposure to a roll PIO in an older simulator, two PIO oscillation cycles is sufficient to grab your complete attention, and 30 seconds of fighting a PIO oscillation is a lifetime.
Amen, Deacon.
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Old 13th Jun 2014, 23:15
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PIO's

Be careful taking advantage of an old dinosaur that can't take any of you up and demonstrate some rather severe aerodynamic conditions, and then how to avoid them or recover.

BTW, Roulli had a great discussion on the USAF tanker crash due to "dutch roll". It seems to have a fair amount of PIO present once the yaw and roll got out of phase.

Retired has one great point about being aware of your energy state, and then your response to an abnormal event. Being low and slow requires a different technique than when you have a warning or loss of a flight parameter ( think airspeed) being high and fast. I can guarantee all that on approach with all the drag devices out and the plane not handling as crisply as when at 400 knots and clean, that my initial reaction for a stall indication was relax back pressure or even push forward a bit. For roll excursions I would relax pressure on the stick and watch for a second or two.

'bird had a great video on the other thread about PIO, and that sucker lost it in about 2 seconds due to his very high "q".

In all fairness to Doze, his idea of the "startle factor" seems to have a basis. But sheesh. We were trained to not get hyper-startled and do things until we figured out what was going wrong.

later from the peanut gallery...

Last edited by gums; 13th Jun 2014 at 23:16. Reason: typo
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Old 14th Jun 2014, 03:08
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Originally Posted by gums View Post
BTW, Roulli had a great discussion on the USAF tanker crash due to "dutch roll". It seems to have a fair amount of PIO present once the yaw and roll got out of phase.
Aye, but let's not forget that the A330 is a much more modern design and its more advanced aerofoil and yaw damper designs make it much more forgiving.

In all fairness to Doze, his idea of the "startle factor" seems to have a basis. But sheesh. We were trained to not get hyper-startled and do things until we figured out what was going wrong.
Of course, but what I've been trying to get at is that the training as it stands might not be enough. Specifically I'm concerned about the "inexperience" or "magenta line" narrative overshadowing the fact that we've had several accidents now where even very experienced pilots have been spooked by a sudden abnormality and proceeded to respond in such a way that their aircraft was lost. Startle effect isn't a new phenomenon, but it is nevertheless somewhat poorly-understood on the line. To be frank, I'd be inclined to consider it a type of incapacitation that needs to not only be trained against on an individual level, but also trained in terms of recognition in one's colleagues and consequent assumption of control until the colleague calms down.
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Old 14th Jun 2014, 08:03
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Devil

Originally Posted by DozyWanabee
Aye, but let's not forget that the A330 is a much more modern design and its more advanced aerofoil and yaw damper designs make it much more forgiving.
Reading the KC-135 mishap report shows that nothing happened in that Dutch Roll PIO that can't be done with a new A330, any modern or new plane. Dutch roll is the most basic PIO (Pilot induced oscillation). The loss of rudder in flight followed by the total destruction of the plane in three parts and explosion in flight followed by CFIT and fire shows the potentiel danger of any oscillation. The modern data recorder and conversation showed exactly that any modern and new plane cannot resist better to resonance developing very quickly threw the pilot's pedals and feet out of the flight envelop.
(Figure 6 page 11/54, figure 9 page 14/54 , Conclusion of Brigadier General Steven J. Arquiette page 48/54 of the 1534 pages report)

Last edited by roulishollandais; 14th Jun 2014 at 08:32. Reason: add report refs
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Old 14th Jun 2014, 16:26
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Interesting development, but that journo wants a quiet word had, because this bit:

The autopilot, unaware of the error, lowered the nose of the airplane in an attempt to increase airspeed. Unable to maintain altitude, the autopilot disengaged, at which point three human pilots were unable to correct for the error.
is unsubstantiated nonsense. The autopilot disconnected because of the discrepancy in airspeed, that much is true, but I don't think it lowered the nose. As I recall the aircraft ended up slightly nose-down at disconnect because of a bump of turbulence.
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Old 14th Jun 2014, 17:56
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Rubbish is rubbish

Yeah, Doze, et al, whoever wrote the article doesn't seem to understand aero, flight control systems, autopilot implementation, and the beat goes on.

Sheesh. After so many years, one would have a better idea of how the plane worked and basic aero, ya think?

- All of us here have a decent understanding of the basic and reversion control laws for the jet. However, I can't find details on the AP implementation.

I raise this issue due to my Viper experience( early years) when we lost a troop who was on AP and slowly descended into the Salt Lake. Unknown to us at the time, the AP had an AOA limit that was basically half the "normal" limit - think 13 degrees versus 27 degrees. So with a mission abort at heavy weight, the troop turned back and was BZ changing channels, IFF and such while slowly descending in a gray sky with low ceiling and over a lake that was smooth as glass that day. We single seat folks used everything we could, contrary to popular depictions of us.

- With an AP disconnect and a reversion to the next lower law, the "startle factor" is in play, as some here have opined. And then maybe not realizing the system was in a reversion law with less "protection", hence the "pull back" syndrome. After all, "you can't stall this jet, huh?"

- Maybe the AP control laws depended more upon airspeed than AoA? But my understanding is Otto disconnected immediately.

Good grief, this accident will be the poster child of system design, human factors and sensor faults.
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Old 15th Jun 2014, 19:03
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Originally Posted by Machinbird
Folks have been minimizing the roll oscillation. Statements such as,"it wasn't that bad", "the roll rates were not that high", "he recovered roll control within 30 seconds" seem to predominate. I maintain that those with that view simply do not understand the nature of the PIO beast.
Originally Posted by Dozy
You're right - however if I recall correctly from the mega-thread and the report's DFDR graphs, the PIO was on its way to being stabilised, and was almost there at the point the aircraft stalled (apex of the zoom climb) - suggesting that the PF was at least getting a feel for the roll aspect. Unfortunately the consistent backpressure (intentional or not) while doing so meant that stabilising the roll became something of a moot point as the aircraft went into a full stall.
Dozy, have you considered that the one size fits all roll direct control gain became more appropriate as the aircraft decelerated?

As for startlement effects, the initial strong control input that started the roll PIO could have been from startlement, or possibly from annoyance at having to take control. In any case, it was an unfortunate response to a situation that merely required minimal control inputs.
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Old 15th Jun 2014, 22:29
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I can't find the use of "standby gains" in the pubs I have recieved from you guys. Only the "direct" mode resembles what we used to fly with pure mechanical connections ( no hydraulics).

Seems the "alt" laws still use rate commands, and I can see this if the rate sensors are still active, and no reason to think they would be influenced by pitot-static problems, ya think. We had a Viper fly for about 10 minutes or so after a large pelican smashed the radome and the AoA sensors - no airspeed and no AoA, only inertial inputs, absolute pressure and "standby gains". The damage apparently got to the flight control computers, which eventually failed. The pilot was flying on instruments the whole time, as the blood covered the forward part of the canopy.

So I go with Doze that the roll PIO was pretty much dealt with by the time the jet ran outta energy and defeated the AoA protections ( same as Viper deep stall entry).

I also go with 'bird that the "startle factor" should not have been the primary cause of later control inputs. There was even a call about "alternate" law early on, wasn't there?

Finally, seems to me that the jet's control surfaces would have been trimmed pretty well when the pitots froze and AP disconnected. In short, let the jet go where it is trimmed before doing anything rash and getting into the roll PIO we are theorizing. BTW, I can't seem to find when the pitot system came back on line. If it did, did the input to the FLCS have to be enabled by the crew?
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Old 16th Jun 2014, 01:28
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One of the things I have often wondered about was the sidestick control, left hand verses right hand. I would think normally the Captain or the pilot in control would be seated in the left seat and using his left hand on the sidestick. However, in this instance, the pilot in control was seated in the right seat and would be using his right hand on the sidestick. Considering the abrupt A/P disconnect and reversion to alternate law, plus the startle factor, might this seating arrangement have played a part in first the roll control situation and then the subsequent continual pitch up problem, e.g., lack of sidestick control sensitivity because of not using the usual (dominate) control hand and sidestick? Would it have an influence or make a difference? Just asking…
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Old 16th Jun 2014, 01:38
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Dinosaur sir,
You will need to re-read how Alt 1 and Alt 2 differ.
Your forgetter is working too well.

Hi Turbine D, Assuming Bonin was right-handed, then he would have been using his stronger arm to fly the aircraft. This made it easier for him to jerk the aircraft around initially.
A number of Airbus pilots have remarked in the past that it would have taken a lot of work to make the lateral control inputs that were made due to the viscous damper in the lateral channel. I suspect that his arm was burning with fatigue after the first 30 seconds and that his ability to make small corrections was then compromised as a result.

Last edited by Machinbird; 16th Jun 2014 at 01:51. Reason: Add response to Turbine D
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Old 16th Jun 2014, 01:53
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However, in this instance, the pilot in control was seated in the right seat and would be using his right hand on the sidestick. Considering the abrupt A/P disconnect and reversion to alternate law, plus the startle factor, might this seating arrangement have played a part in first the roll control situation and then the subsequent continual pitch up problem, e.g., lack of sidestick control sensitivity because of not using the usual (dominate) control hand and sidestick? Would it have an influence or make a difference? Just asking…
As Bonin was copilot .. he was used to control the plane from the right seat (so right hand) .. his usal place
Robert had taken the seat (left) of Dubois (captain) ....
So .. no influence there .... AFAIK
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Old 16th Jun 2014, 12:39
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Originally Posted by Machinbird View Post
Dozy, have you considered that the one size fits all roll direct control gain became more appropriate as the aircraft decelerated?
It's possible, but given the situation I'm inclined to give the PF the benefit of the doubt and think that he was indeed bringing the roll under control.

As for startlement effects, the initial strong control input that started the roll PIO could have been from startlement ... it was an unfortunate response to a situation that merely required minimal control inputs.
Or no control inputs at all! The A330 is a very stable platform - and whatever one may think of Learmount, I'm inclined to agree with his opinion that with no further inputs the aircraft would have simply ridden out the turbulence as best it could, and after 30 or 40 seconds the ice would have melted from the pitot tubes and the speed indicators come back online.

I'm basing my "startle effect" call on previous similar incidents where pilots made an erroneous initial call on the problem (in some cases because the warning systems were giving misleading signals). Those incidents are Birgenair 301, ColganAir, NWA6231 and West Caribbean 708. In the Birgenair case, the Captain as PF seemed to fixate on the first warning he received, which was an erroneous overspeed. In the case of West Caribbean, the Captain thought he was dealing with a dual engine flameout. In both of those cases, the F/Os correctly diagnosed a stall and inappropriate attitude, but the Captain did not respond.

The other reason I suspect the AF447 pitch input to have been inadvertent is because the two F/Os had been discussing not being able to exceed their present altitude for safety reasons only a few minutes before. At AP disconnect they had well over 30,000ft to play with and they knew that to climb would increase risk. To initiate a climb would therefore be completely illogical, and I suspect this is (at least in part) why the PNF was initially so incredulous as to what seemed to be happening.

Originally Posted by gums View Post
I also go with 'bird that the "startle factor" should not have been the primary cause of later control inputs. There was even a call about "alternate" law early on, wasn't there?
There was an "Alternate Law" call from the PNF to which the PF did not respond - we therefore don't even know if he heard it (which - if he didn't - to my mind supports the "startle" theory)

BTW, I can't seem to find when the pitot system came back on line. If it did, did the input to the FLCS have to be enabled by the crew?
You can see the speeds coming back online in the DFDR traces at about 02:10:35 - at that point the aircraft is established in the climb at around 37,000ft.

No, there was no need for the crew to perform an action to bring them back online.

Originally Posted by Machinbird View Post
A number of Airbus pilots have remarked in the past that it would have taken a lot of work to make the lateral control inputs that were made due to the viscous damper in the lateral channel.
Did they? Must confess I don't remember so well. As far as I know the primary damping mechanism in the sidestick is actually spring-driven, and the simulator version I had a chance to get to grips with was actually very responsive and not too difficult to deflect once you had it going. The springs do centre the SS, and there is a small degree of 'breakout' force, but once deflected it offers enough resistance to let you know it's deflected, but not enough to cause physical issues.

Last edited by DozyWannabe; 16th Jun 2014 at 13:54.
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Old 16th Jun 2014, 18:13
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Snoop UAS

Origin of that text ???

Originally Posted by Winnerhofer 16th Jun 2014, 17:53 * #113
URA
Unreliable Airspeed

Historical and recent accidents and incidents have highlighted the risk associated with unreliable airspeed (URA) events. These events are normally transient in nature and can cause multiple, seemingly unrelated warnings and failures. The following philosophy and guidelines are provided to assist in reducing the risks associated with URA events.

URA Philosophy
The keys to successfully dealing with a URA event are recognition, procedures, and training
The aircrew’s recognition of and initial reaction to a URA event are critical
Manufacturers should attempt to ensure unreliable airspeed events are clearly identifiable to aircrews
The most important function of the aircrew during an in-flight URA event is to maintain control over the aircraft’s flight trajectory and energy situation by selection of attitude and power settings so that the aircrafts flight parameters remain within normal limits
Crews should be aware of the instruments and critical systems that are not affected by a URA event (e.g. Attitude displays, engines)
Procedures and training for URA events should include the effect of a URA event on other aircraft systems, and potential alerts/warnings and indication system inaccuracies that could be expected
Crew coordination and communication are important elements in successfully addressing a URA event
URA Guidelines
URA procedures should provide information on attitude and power settings that enable crews to maintain the aircrafts flight parameters within normal limits during in-flight unreliable airspeed events for all phases of flight
URA procedures should address the availability and use of independent alternate sources of airspeed information (e.g. GPS, inertial, angle of attack, etc.)
URA procedures should include memory items for critical immediate action steps
Training programs addressing URA should exist at beginning (ab initio/MPL), initial, and recurrent levels
URA training should include both simulator and academic phases
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Old 16th Jun 2014, 18:43
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I suspect it's a Winnerhofer "original". The usual contraction for unreliable airspeed is UAS as far as I know!

That said, the points are fair...
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