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New (2010) Stall Recovery's @ high altitudes

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New (2010) Stall Recovery's @ high altitudes

Old 5th Aug 2010, 07:03
  #121 (permalink)  
 
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I guess experimental lift slope curve data is the only way to go; although I did ASSume at least part of the leftward alpha shift of those curves with increasing M would have been due to that relation, and of course in this case Mach and Reynold's numbers intertwine inseparably ...it must be a true supercritical design...I don't suppose you could provide the NACA designation for the airfoil..would a Cm change also affect the Alpha effective?

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Old 5th Aug 2010, 15:30
  #122 (permalink)  
 
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For the out of trim situation.

The ATR I flew had a very valuable feature. Every time the trim was actuated more than a couple seconds the trim whooler would give an aural warning. Very useful with A/P on when slowing down. Always triggered looking at the trim and energy state of the aircraft. You knew immediately that something was changing more rapidly than it should.
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Old 5th Aug 2010, 17:02
  #123 (permalink)  
 
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And about how pilots (for instance me) sense stall:

At the bottom I have listed two references. The FAR reference shows something about the discussion which might be of interest. In fact the statement is that there has to be a warning whatsoever to indicate a possible high AoA situation before C/L MAX. It also states that a stall warning shall be given 7 percent over the determined stall speed.

The whole certification never goes over the absolute limit. No one wants to crash a multimillion testbed. Interesting to learn from the certification documentation that the aircraft hast to be controllable by use of the normal devices up to certificated stall.

IMHO this means we're safe to recover as long as we react with the first warning and do not take it over to fully stalled wing.

It also states IMO the two possibilities to fulfill the requirements for stall testing whereas when fitted with a stall identification system there is no need to take the plane over C/L MAX.

The aircraft I flew and actually fly did and do not show aerodynamic buffet at high AoA. Both were fitted with STICK SHAKER and STICK PUSHER for that particular reason. Previous type gave no aerodynamic indication. Actual type does have an aerodynamic buffet inducer on leading edge - still for some reason it has been fitted with both warning devices as well and FCOM does not rely on buffet.

To the discussion about the speeds: When flying IMHO I give a sh... if the warning is IAS/CAS/EAS/M dependent, corrected or not. If one of the clues triggers be it aerodynamic or artificial there is normally no time to wonder if it may have another margin of 4 kts indicated to reach C/L MAX or not because we are at 30'000 feet. The manufacturer had to show that these devices would alert before it got out of hands. Anyways I may be in a speed range where my hairs at the back of my neck stand already up or should.

INDICATION
The only way as indication of impending approach to stall on current type I have is the red and black band coming up from the bottom of my PFD to "indicate" AoA C/L MAX. FCOM states that this is slightly before reaching aerodynamic C/L MAX.

PERCEPTION
To perception comes attitude vs. power vs. change in altitude = experience. If on A/P no direct clues are given. Need to assemble information from 3 different locations PFD/ENG DISPLAY/TRIM BAND. Additional clues could be airspeed noise as it get's silent or missing engine noise.
Handflown it may become mushy and soft.

AS FOR THE SPEED DISCUSSION
The only thing I have on the front end is airspeed - indicated airspeed IMO. I say indicated airspeed because this is what I have. An indication on my PFD of actual measured and corrected for whatever the ADC does speed of the air mass I'm in. And I have a booklet based on mass which tells me what speed is still save (1.3 Vs) and I don't know if it is Stall1g or the older certification and to be honest - I don't care because I have no influence on that whatsoever. Still AoA and the margin above C/L MAX when STICK SHAKER or STICK PUSHER triggers may account for any deviation with altitude M, R number etc. (at least I hope the manufacturer did so)

The aerodynamic buffeting from the leading edge vortex generator may as well be already covered by the STICK SHAKER or STICK PUSHER.

RECOVERY
It looks as I've been one of the lucky guys to train o.k. from the beginning. Lower the nose apply power as far as practicable control roll with ailerons was what we were taught from the beginning. From own experience in stalling a Piper Warrior to recovery from spins I have learned: Piper stalled nicely power off. Was fluttering down like a leaf in one after another secondary stalls and only application of rudder put it wings over. Ailerons were still working fine.
I wanted to go a bit further after CPL/IR training and used an EXTRA and VOTEC aerobatic plane on several occasions to train stall and spin recovery from fully stalled conditions. Obviously a treat in these A/C but the lesson learned was again - NO RUDDER on "impending stall". Any excessive rudder application had me upside down before I could think and made things much worse. Still the ailerons neutral nose down worked to NOT FULLY stall the A/C.

MY POINT
It makes quite a difference if recovering from an approach to stall or a fully developed stall with it's unknowns.

Funny that all manufacturers tell about the same story about stall recovery.
Funny that all aircraft I know disconnect A/P when stall warning is given.
Finally RTFM!

MY QUESTION ABOUT TRAINING
Maybe the trouble with use of rudder is that basic training started to mix up stall recovery with spin recovery at some point?

MY ADVICE
Know your pitch and power for the most important configurations. Know your trim.

MY CONCLUSION
The whole discussion is about stall recovery. But there is no such thing in training. It ends at impending stall except if you take aerobatics or manufacturer defined stall speed!

Simulators are NOT ABLE to represent a fully stalled condition.

Altitude helps - a lot.

It depends if you are approaching a stall and start recovery in time and you are still within the envelope that was tested and agreed upon as: "Shows a behavior which can be handled with normal piloting skills...". If your aircraft whatever type goes wing over and dives at 45 deg nose down you're on your own as a test pilot. I guess that in large transport aircraft the only thing that counts then is good luck and enough energy say altitude below. The day I may have some extra money to spend I'd like to go to the 3D SIM and train that.

To clarify I would put the recommendations into three different sections.
  • Approach to stall where there IS margin and the first warnings kick in timely. Still the aircraft is flyable and ailerons efficient. You don't know what the margin is so better be quick. Loss of altitude included. You were on the lucky side.
  • Stalled to the point where we are over the apex of C/L MAX. The relatively sudden drop in lift may cause a lot of trouble such as nose down or it wings over for whatever disturbance which made stalling asymmetrical. Here you are outside the envelope and it will get very interesting. Good luck!
  • After the primary stall where you find yourself in whatever position possible depending on attitude, energy state, aircraft type and you're out of any tested envelope on the type such as a spin. Good luck!

Some information worth considering:
AERO : Upset Recovery
FAR AC 25-7A page 189 ff

And some information from NTSB reports on what happens in a full stall. Better be high up.

DCA08FA075

CHI06IA127

DCA97MA049

DCA97MA016

DCA03IA005

EXECUTIVE SUMMARY

Still I think the training given in the original #1 post is sensible.

Keep the blue up and safe landings.

Last edited by error_401; 7th Aug 2010 at 07:57. Reason: additional reference added / removed irrelevant notion
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Old 6th Aug 2010, 00:06
  #124 (permalink)  
 
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(p-pinfinity)/(1/2rhoV^2)/Cpi=1/[1-M^2]^.5+ [M^2/1+{1-M^2}^.5]*(cpi/2)

or maybe just 1/[1-M^2]^.5

With the greatest of respect we are talking about stall recovery procedures for jet engined aircraft flying at high levels. Those of us who dare to ventue up there use a formulae that better suits our purpose, and one that is understood by those with less than level 2 English.

We know we have to sacrifice something for the screw up that just happened, irrespective of whether the fault was ours or not. If the screw up was a stall at high level....the penalty is altitude.

If we stall at high level, we are going down! Any recovery action should recognise this fact.
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Old 6th Aug 2010, 07:57
  #125 (permalink)  
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Nice post from error_401.

It occurs to me that no one (including me) has yet cited the certification requirements, although I have referred to them. The definition of "stall" is in CS 25 201 (d). See also the accompanying comments in AMJ 25 201. The current document is downloadable from The EASA Certification Specifications WWW page. I should point out that most transports in use today were certified to forerunners of this document, not this precise document, and that engineers are very particular as to precisely which version of the document a given aircraft was certified to.

Notice that none of the characteristics in CS 25 201 (d) refer to C_L_Max.

Notice that stall characteristics are only required to be demonstrated from (a) level flight, at low speed (so, Vs1g stall), with engine power appropriate for a slow deceleration rate; and (b) a moderate level banked turn under similar conditions.

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Old 6th Aug 2010, 08:08
  #126 (permalink)  
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Originally Posted by error
MY QUESTION ABOUT TRAINING
Maybe the trouble with use of rudder is that basic training started to mix up stall recovery with spin recovery at some point?
- possible, but what is not properly understood is that there is no other roll control available on a fully stalled wing. If 'use of rudder' put you 'on your back' you used it incorrectly. Not quite sure why you were using it "on impending stall"?

As you say, we should never get to the point of 'fully stalled', so aileron usage remains quite practical, but sadly some of our colleagues are managing too. Hopefully the initiatives coming out of the Toronto conference will go a long way to address this.
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Old 6th Aug 2010, 09:39
  #127 (permalink)  
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BOAC,

the Toronto session at the 2010 AIAA Guidance, Navigation and Control annual meeting was just one waypoint in a long history of targeted research on LOC.

Any "initiative" started long before, with targeted research programs. For example, here an article on Loss of Control from the AAIA organ in March 2003. NASA Langley's work was well represented at the 2010 AAIA GNC meeting, it seems, as one would expect from such a research program.

I can't find the papers yet on the Langley server, but there appear to have been two contributions from NASA Langley on safety research to the AAIA GNC annual meeting last year (Chicago, 2009). Here is one: Aircraft Accident Prevention: Loss of Control Analysis, and here is the other: Methodologies for Adaptive Flight Envelope Estimation and Protection. Neither appears to be directly related to your concerns about unremarked longitudinal trim changes.

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Last edited by PBL; 6th Aug 2010 at 10:04.
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Old 6th Aug 2010, 11:13
  #128 (permalink)  
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A helpful contact has provided some useful content from Toronto.
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Old 6th Aug 2010, 13:06
  #129 (permalink)  
 
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The presentations in Toronto were certainly not the first on loss of control. But the landscape has changed in the last year; not only is loss of control clearly identified as the leading cause of accidents in transport category aircraft worldwide, but the lobby efforts brought to bear by the Colgan families have generated a great deal of pressure for change in training.

The former has brought us the original point of this thread, namely, changes to stall recovery procedures from the major manufacturers. The latter has brought us the 1500 hour requirement with the associated training requirements.

As to error 401's post...the whooler on the ATR was definitely a wise idea. Trim motion is a cue that has become seriously deficient in modern designs...I still miss the trim wheel in the 727!

That said, we have to be careful about generalizations:

"Lower the nose apply power as far as practicable control roll with ailerons was what we were taught from the beginning. From own experience in stalling a Piper Warrior to recovery from spins I have learned: Piper stalled nicely power off. Was fluttering down like a leaf in one after another secondary stalls and only application of rudder put it wings over. Ailerons were still working fine." But the ailerons on a swept wing jet may not be working fine. That was a major point made by the manufacturers last week at Toronto. A fully stalled jet transport is laterally unstable and roll control will not correct the problem.

Rather than stomp the rudder, the manufacturers emphasize unloading the wing and "unstalling" it, getting flow reattachment and hence regaining aileron control.

"Go to the gym and get arms strong enough to pitch down even when trimmed pitch up. You should not be flying a turboprop if you are not able to hold ailerons with engine failure at V1. One should really be able to hold against the pitch up moment when applying power on a jet or at least be aware of it."

Again, Airbus pointed out that in the event that the pitch trim has been run up to the stall, so that the airplane is fully trimmed to the speed at which the stall takes place, the elevators may not have adequate authority to overcome the pitch up generated by the application of full thrust on underslung engines. Going the the gym has nothing to do with it...

You really can't mix apples and oranges in many areas, even if you can in others. Single engine trainers are not the best at teaching large jet characteristics...and high wing turboprops do not necessarily behave the same way as jets with underslung engines and swept wings do. This is what gets us in so much trouble...
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Old 6th Aug 2010, 18:03
  #130 (permalink)  
 
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The trim-in-motion cues are useful; the requirement originated from certification in the days when trims could runaway – they shouldn’t in modern aircraft.
However, the more valuable cue is the trimmed condition of the aircraft. In conventional aircraft this is indicated by the residual control force at constant attitude. If there is an unwanted force then trim can be changed – another cue for trim-in-motion. Most modern autopilot / auto trim systems have low / high airspeed cut-outs; beware those that don’t.

I have seen some very bad trim practices, e.g. trimming during the flare, which if used by habit in other situations can result in unexpected loss of speed – pilots are reluctant to hold a force. IMHO, there are pilots who appear not to understand the principles of ‘trim’, nor have they been taught how to trim.
Trim is often used as a datum about which the aircraft can be manoeuvred. In roll there is no requirement to trim with manoeuvre, but in pitch, if the intent is to change speed, this requires that the trim datum must also change.

Try the following as a LOC sim exercise; with hands-off (autopilot engaged) mistrim in roll up to the max fuel asymmetry limit, as the crew take over disengage the autopilot. A real event – 737, mis handled fuel cross transfer – 120 deg roll!
Repeat with a pitch offset – more difficult to engineer, and the crew’s response should be considerably different – why; compare levels of surprise, expectation, normality.

I put aside modern (unconventional) aircraft which may have different trim philosophies and thus potentially unique problems and solutions.
Anyone recall the Hunter trim follow-up system (aah Hawker), how similar is this concept to the Airbus?
What happened if the follow-up was switched off during a tight turn, use actions for a conventional aircraft, but in an Airbus – look at the ECAM, manual trim?

Mansfield check PMs
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Old 6th Aug 2010, 19:27
  #131 (permalink)  
 
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Error 401, #125, re “ The whole certification never goes over the limit.
See #103. Stall certification is one of the most extensive series of tests during aircraft development. Aircraft have to be recoverable in situations up-to, during, and post stall; you should be able to affect a safe recovery at any time (altitude permitting) providing the situation is not mis handled; and therein is a problem.

Re “ wing leading edge device” This may have been a ‘stall breaker’ to deliberately induce a loss of lift on the wing inboard section. For a swept wing, this provides the necessary nose down pitch at the stall – for recovery; it’s not intended as a warning or indication, e.g. Avro RJ.

The EFIS low speed symbols may only be an indication of the airspeed at which stall warning / stall may occur; the level-flight accuracy is generally good, but in manoeuvres errors can increase.
The display is for airspeed, and unless your aircraft has novel weight-CL computation, the stall airspeed may only be an approximation (albeit quite accurate) based on trim curves and alpha, e.g. Avro RJ.

‘If on autopilot’; a modern autoflight system should disconnect the autopilot and autotrim system at stick shake, providing additional warning (AP disc) of the low speed (but not stalled) situation.

‘Recovery’; fly the aircraft (use the controls) as recommended by the manufacturer. If the nose is lowered – AOA reduced, and airspeed is increasing, the wing is producing lift (not much) and the controls should work (not well), the aircraft will not spin. The wing may have stalled, but the fin / rudder will not have, nor the tailplane
Somehow basic training has generated a great fear or phobia about spinning. First the aircraft has to be stalled, and the condition maintained; second there has to be yaw / roll, etc, etc.
There is an incipient phase where recovery may be self evident; in large aircraft, mass / inertia effects may provide additional time, or more likely spin resistance.
Recovery – yes, basically all aircraft are the same.

Have knowledge, use this knowledge, negate bias or false knowledge, control surprise, and follow the manufacturer’s recommendations.
And as you state: -
Funny that all manufacturers tell about the same story about stall recovery.
Funny that all aircraft I know disconnect A/P when stall warning is given.
Finally RTFM!


“Attitude helps”; yes, in defining situations which have progressed beyond normal operations – the period of identification and avoidance. As above, pilots require more 'thinking attitude'.

… whatever type goes wing over and dives at 45 deg nose down you're on your own…”, no not so; follow the standard recovery procedures.
Don’t focus on CL MAX, that’s for the classroom, unless the aircraft has a CL gauge.

The aspects of stalling which might not have been tested are generally combinations of control mishandling; also, system failure or extreme weather encounter (including wake turb).
Training stalls can be approached with confidence; an actual stall can be avoided or recovered with similar confidence. Just don’t stall near the ground.
At altitude, don’t rush; the aircraft is still ‘flying’ albeit below the stall speed, so fly the aircraft.
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Old 6th Aug 2010, 20:21
  #132 (permalink)  
 
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of course those are the nice perfect stalls...don't forget the wing-snapper types...FAR 25.343 has a huge loophole
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Old 6th Aug 2010, 21:28
  #133 (permalink)  
 
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or as mentioned before...the secondary stall, caused by incomplete recovery I think adrenaline, if you know to pitch down' will take care of any positive pitchning moments induced by thrust application... I mean If a 100 lb woman can lift a car,...and a stewardess can survive a 35000' fall....you'll overcome it because a seconday stall is guaranteed to be more much more fun than the initial upset

or as Langwiesche puts it -to paraphrase- AoA is the difference between where an airplane looks like it's going and where it actually is going...there's plenty of horrible math to back that
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Old 7th Aug 2010, 07:35
  #134 (permalink)  
 
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Thanks for all comments and valuable insights

@BOAC - I fully agree. Fully stalled you are left with rudder only. Now in that situation I would give it a try. We tried both ways into bank = spin out of bank depended on situation and pitch up = nose went up nearly vertical or rolled over. But then again this was in an aerobatic single.
BTW. To have it flip was part of the fun with an EXTRA 300 at 5'000 AGL. We also managed some recoveries.

@ Mansfield - Agree the notion was merely about the forces involved if pitch trim was at the very back. This will be type dependent. Sadly true that maybe elevator has not enough authority. I'll modify it later as it has more to do with asymmetrical flight and applies only to aircraft with conventional controls.

@ PEI 3721 - I should have added: "Never ever give up"
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Old 7th Aug 2010, 08:39
  #135 (permalink)  
 
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A real event – 737, mis handled fuel cross transfer – 120 deg roll!
Repeat with a pitch offset –
Now that surprises me. During type rating training using the 737-300 Cat D simulator, the instructor briefs there will be a 1500 kg difference between wing tanks and asks the pilot to conduct a final approach and land. This is to give the crew the experience at fuel imbalance if it should occur due to lack of attention when cross-feeding.

In our simulator there is a slight roll but easily controlled. Aileron trim is not needed. This backs up the FCTM statement that lateral control is not significantly affected when operating with fuel beyond normal balance limit and that the primary purpose of fuel balance limitations on Boeing aircraft is for structural life of the airframe and landing gear and not for controllability.
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Old 7th Aug 2010, 09:03
  #136 (permalink)  
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Now that surprises me.
- real event, very close to hull loss.
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Old 8th Aug 2010, 16:20
  #137 (permalink)  
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While looking through the WWW for papers related to the 2010 AIAA GNC conference papers on LOC, I came across a RAeS FOG report from 2008 or later (there is no date on it) on upset recovery that I thought might interest some: Airplane Upset Recovery Training; History, Core Concepts, and Mitigation

In Section 2.2.8 is a statement highlighted in boldface, about swept-wing aircraft, expressing what many have said here:
Originally Posted by RAeS FOG
in upset recoveries, USE OF RUDDER IS generally NOT RECOMMENDED and in some cases expressly forbidden
The working paper was put on the WWW by the company for which J. M. Cox works.

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Old 8th Aug 2010, 17:00
  #138 (permalink)  
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I quite agree with that. Unfortunately you have mis or selectively quoted, because 2.2.8 concerns upset recoveries and not specifically stall recoveries, which were covered in previous sections and 2.2.8. commences with 'High speed high altitude flight'

If you read on a little, paras 3.3 1a and 3.3 3 b specifically discuss the way rudder should be used in LOC recoveries. Rudder is also taught as a means of inducing roll at extreme pitch angles durng upset training and from the same document from which you quote

If control provided by the ailerons and spoilers is ineffective, rudder input may be required to induce a rolling manoeuvre for recovery. A small amount of rudder input is sufficient. Excessive rudder applied too quickly, or held too long, can result in loss of lateral and directional control.

The simple message, however, is if you do not know what to do with the rudder AND how to do it, it is best to leave it alone. Applying incorrect rudder is a sure path to a further disaster than the one you are in.
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Old 8th Aug 2010, 20:48
  #139 (permalink)  
 
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The Rudder is probably only useful in a spin; a spin entered by having applied the rudder and side slipped in the first place

The only other thing I can think of is some 'uncertified' mechanical failure that would require as much rolling moment as possible---unfortunately the one example we've seen was that MD-80 jack-screw malfunction on the Stab and was a completely unsurvivable event
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Old 9th Aug 2010, 07:41
  #140 (permalink)  
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BOAC,

I am not sure what you are quibbling about. Of course I have selectively quoted - all quoting is selective.

The FOG in 2.2.8 is addressing loss of lateral stability (wing drop) and says rudder use to arrest it is not recommended and may be expressly forbidden. As far as I know, wing drop is most likely to occur during progress into a stall, so, apparently unlike you, I read this comment as being highly relevant to stall.

In Section 3 they talk generally about unusual attitude recovery, and the advice is intended to be clear: destall the wing before anything else.

When talking in Section 3 of unusual attitudes with decreasing AS at high angles of bank in the case in which ailerons and spoilers are ineffective, they do suggest to try a little rudder to induce a roll, and guard this advice quite specifically. Well, of course they say that - what other option do you have if all other roll control is demonstrably ineffective and you need to roll?

I read them as saying: priority number one, destall the wing; if a wing drops, don't use rudder to arrest it, unless you get into high angles of bank while still stalled, and need to roll to drop the nose, in which case a little rudder, briefly, may be required to induce a roll.

Given the propensity of some on this forum to read a quote or an interpretation as the opinion of the writer, rather than of those quoted, let me emphasise that in the case of discrepant readings it is up to the FOG to clarify what they mean, not me. I am just reading what they wrote. But if one wants to be sure what they meant, I do know a couple of people in the group so can ask directly if it's something major.

I do note that in the three places in which they mention rudder use, in only one of them do they mention the possibility of structural damage in injudicious use of rudder. I guess this is because they are primarily talking about very low airspeed situations.

I also note that this is not the only document concerning upset recovery. A U.S. working group also prepared the upset recovery aid, a fairly large document, between 2004 and 2008. It may be found on the FAA WWW site: the Upset Recovery Training Aid, as well as by the FSF.

PBL

Last edited by PBL; 9th Aug 2010 at 07:51.
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