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High altitude stall recovery B737

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High altitude stall recovery B737

Old 21st Feb 2018, 17:48
  #81 (permalink)  
 
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Cent #85, flap 40-15.
This illustrates one of the problems of procedural teaching; the accident crew were in a GA mindset, whereas due to the RA/AT malfunction recovery from an approach to the stall was required.

With the continuing focus on procedures, situations may be considered the same without checking for differences or need to adapt.
Thus expecting a stall recovery procedure to be the same at high altitude and low altitude might not be correct. Unstalling the wing by reducing the AoA would be consistent, but the subsequent recovery might vary with altitude, weight, configuration, etc. Crews have to be prepared to reassess stressful situations and modify procedures accordingly.

I suspect that the absence of detail in the Boeing procedure for high level stall refects the above, where the answer is ‘it all depends’. Unfortunately there is less understanding or ability to judge what ‘it’ is.

Re my #82, lest anyone thinks that they can recover from a stall at low altitude within 800ft, then reconsider terrain profiles and obstacle clearance.
The safety lesson is to focus training on how to avoid an approach to the stall particularly in the descent and approach phases of flight, and not low altitude stall recovery. This training would provide greater consistency and avoid the need for surprising situation assessment and emergency procedure recall.
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Old 21st Feb 2018, 23:39
  #82 (permalink)  
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Clean at altitude, the B737 has a gentle stall behaviour, easily within FAR25.203 criteria. Adding power is as noted almost irrelevant at high altitude. The most notable characteristic is a low frequency moderate vertical acceleration at the flight station, from aerodynamic buffet on the tail.

At low to mid altitudes, the effect of thrust is more significant, and will reduce nose down elevator authority for a fixed trim condition. At the low to mid altitudes, if conducted dirty, the stall buffet is pronounced, with moderate to heavy vertical acceleration felt at the flight deck. The aircraft meets 25.203 again, but you can expect reasonably sharp rolloff if the stall is accelerated. Any mis rigging of the slats will result in a rolloff with autoslat extension as well.

The stalls at low to high altitude, clean through to landing configuration are obvious with good control response available, with the caveat that thrust couple can compromise the fixed trim pitch authority. While the B737 has a speed trim system, with it working, the stick force per g remains positive through the flight regime.

Any test or flight resulting in aerodynamic stall requires an inspection per the AMM, which is heavy on the empennage, for good reasons. The buffet is pronounced. Having investigated other types that have had deep buffet boundary excursions, resulting in flow conditions that have literally torn carbon fibre outer elevators in half, buffet events should be taken seriously with post flight inspections.

Mach buffet on the B737 is different to the stall buffet, but is probably not going to be recognised as such without cross check of the instruments. The onset on a B737 at 1.0G is very gentle, and increases amplitude as speed increases. The frequency of Mach buffet is higher than the stall buffet. In both cases, any unloading of the aircraft will reduce the buffet amplitude.

The most recent changes to the FCOM for all Boeing and Airbus aircraft are rational, and reflect the necessity to ensuring the AOA is reduced. The discussion on roll, rudder etc continues to approach areas of structural integrity concerns. The use of bank might well be applicable when you are flying a Folland Gnat with a jammed full aircraft nose up stabilator, but otherwise, it doesn't take much bank to get the nose coming down in the real world. Sim training ends up with examples of extreme flight angles being exhibited which will be pretty interesting in a dark night, when the reason for the upset is possibly due to instrument failure or vertigo etc. Goldilocks rule.

Unless you have ripped off tail feathers, then every aircraft known to man (other than the F101) will look after itself if the damn pilot stops mussin' with it. The aircraft will recover unless the pilot prohibits that by his actions, which we as a group have routinely done. AF429 had full back stick on for almost the entirety of its descent, there is no Cessna, Pitts, Cub, Boeing or Airbus that will survive that level of mishandling. Other than the aforementioned 101, even T tails will recover; post the magic B727 zoom climb in the eastern US from having pitot heat turned off, Boeing conducted a vigorous deep stall series and could not get the plane to "dig in", or "pitch up" (again, not so for the F101), and unless mishandled further, the plane recovered when left to its own devices.

For Airbus drivers, the control laws which are pretty neat when they are working proper like (as all computers dooooooooo.....) you are inherently set up for a pitch issue on reversion, like Perpignan, the stab trim is outside of your immediate experience of use, until the moment when you absolutely need it to control thrust pitch couple, and get the nose down so that you can collect your thoughts. The addition of the note on the ECAM of use THS trim is nice, but probably not within the cognitive capture of a dynamic upset event, where you are guaranteed to have lots of stimuli happening promptly. If THS is used, the plane is a happy camper, alternatively, if the thrust coupling is not disturbed, the plane will exhibit normal speed stability (unless you have uncommanded flight control inputs through bad sensors etc.... which is not detected as a sensor failure, almost hardly ever happens... :| ).

P.S. If you try hard enough, a B737 will autorotate... data showing that had been found in the smoking hole in the ground before today. >180 degrees a second is not impressive for a Pitts but it is pretty impressive for Ma and Pa in 35EF. AOA management will make for happier endings.

The B737 is not a bad aircraft, it wants to fly if the pilots don't mess with it too much.

In respect to AMS, going into the hover, OGE in any jet aircraft, with insufficient altitude to recover is going to end badly. The failure of the LH LRRA ws insidious, as the immediate result was not apparent to the PF and certainly the PM and the other people not looking at the energy state of the aircraft. The more emphasis management has on the flight crew acting as observers and monitors of the system, the more frequent the failure mode of out of the loop control will occur. Humans are poor at monitoring systems, that is the thing that computers do well. Humans are capable of identifying patterns that are otherwise unprogrammed, but not always. The slam dunk approach that was flown at AMS places the aircraft and crew in a position that care is needed to ensure that the performance of the aircraft as a system is monitored effectively, the systems need to act correctly and in a timely manner to achieve the outcome. In the end, the failure of the ATS to maintain a target airspeed as it had already gone to idle for the landing was not identified, and the energy loss on pitching to the glideslope and the associated speed bleed was not recognised. It was a high workload event, and the crew were unable to deal with the cognitive demand on the day, and stuff happened. Expectancy of the system behaviour being nominal becomes a reinforced trait of our flight crew due to the overall success that occurs on almost all occasions, except when it doesn't. Healthy skepticism is hard to maintain for a complete career.

Last edited by fdr; 21st Feb 2018 at 23:57.
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Old 22nd Feb 2018, 01:39
  #83 (permalink)  
 
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FDR.I thought you died long ago.Anyhow, thats a superb post, excellent, love it.
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Old 22nd Feb 2018, 01:51
  #84 (permalink)  
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still alive, out of the test world and back having some fun at low level in a jet. Birds get big quick down there.
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Old 22nd Feb 2018, 06:18
  #85 (permalink)  
 
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The safety lesson is to focus training on how to avoid an approach to the stall particularly in the descent and approach phases of flight, and not low altitude stall recovery
PEI. That is certainly one point of view, although it has one small problem.
It is akin to saying I will not teach you how to swim because that is too dangerous. Instead I will teach you how not to go near the water.

Or put another way. I will not teach you how to defend yourself against a bad guy but will teach you which pubs to avoid.. Get the drift?
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Old 22nd Feb 2018, 08:37
  #86 (permalink)  
 
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A37575, all adrift in a choppy sea.
Life and flying are uncertain; there are no absolutes, but the more the industry seeks absolutes ( SOPs, or inappropriately focussed training), then the greater the need for understanding and judgement of ‘it’ - the unexpected, surprise; - more management thought, planning, and refocussed training.

As much as pilots need to know which parts of town to stay out of (and how to judge that), so too the mechanics of stalling, because no situation (or town) will be identical. ;

FDR #87,
101 experience at PAX, or real experience north of the border ? There is lot more common sense up there.
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Old 22nd Feb 2018, 17:08
  #87 (permalink)  
 
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misd-agin

This is the first time I see this montage/video of the stall/accident although I have read the reports in the past and coming away with my head shaking on how the pilots managed to crash an aircraft that was basically functional.

This video reinforces what I thought and I have to agree with you that their training was definitely sub-par but it also points to that their basic flying skills were non existent.
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Old 24th Feb 2018, 00:24
  #88 (permalink)  
 
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Ponder

IF power is the way out of a stall ..... how the hell then do gliders ever recover from a stall ... ?
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Old 24th Feb 2018, 00:53
  #89 (permalink)  
 
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G-THOF Bournemouth. They had dropped speed on approach but not stalled, decided to GA and TOGA stalled the aircraft had problem lowering the nose.
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Old 24th Feb 2018, 05:08
  #90 (permalink)  
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TOGA didn't stall that aircraft. Poor airmanship by the PF did. He had a problem lowering the nose as you say. That was only because he was too slow to respond to the normal expected pitch up when thrust was applied and then exacerbated the problem by failing to apply sufficient forward stab trim quickly enough to gain more elevator effectiveness; thus permitting the aircraft to pitch up beyond a reasonable climb attitude.
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Old 24th Feb 2018, 07:31
  #91 (permalink)  
 
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Speed below VLS on approach especially at lower altitude is poor airmanship anyway. But here it worked in reverse. He didn't power out of stall but selected TOGA for GA but the effect was same. Even in unstalled condition at lower speed if pitch up cannot be controlled how can anyone power out of stall?
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Old 24th Feb 2018, 10:10
  #92 (permalink)  
 
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IMHO full TOGA for a all engine GA is asking for trouble. I wonder what the teaching is at various operators. There are some who advocate the use of similar thrust, 85-90%-ish, that auto single TOGA gives. In manual flight, if not trained, or if SOP stipulates, PF firewalls thrust and all hell breaks lose. Controllable into nearly uncontrollable PDQ. It happened at Narita in an Airbus, but that included a mode & trim issue as well, if I remember. See my video of the Tarom airbus at Paris. In the documentary, I'll add that link, it said that the a/c responded as designed. I'm not sure if this was an inadvertent selection of GA with odd thrust & trim settings; I'm not an AB man. But it is scary of that & the Narita incidents had some startling but correct a/c reactions.
BOH was pure pilot induced.

And we still wait the report of the Russian? B737 stall crash on GA in Poland? It was their 2nd approach and they made a GA from above MDA and seemed to have pilot induced trim issues combined with thrust couple etc.


My previous #76 showed a digital reconstruction, but this clip was part of a more complete documentary into a/c confusing pilots; as you hear in the narrative. I do not know the build up to the incident, but damned glad these pilots knew how to stop digging and climb out of the hole.

Last edited by RAT 5; 24th Feb 2018 at 19:11.
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Old 24th Feb 2018, 10:20
  #93 (permalink)  
 
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Ok probably dumb question from SLF, supposing you do get into high altitude stall due to no idea what airspeed you have, so you revert to attitude (ie put nose down) and appropriate power. Now what is the likelyhood that you overspeed and aerodynamic breakup from that position?, how would you know without airspeed info.... just asking, seems like diving from high altitude might be both necessary and fraught.
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Old 24th Feb 2018, 17:53
  #94 (permalink)  
 
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If the airspeed information is lost, we'd fly an appropriate pitch and power combination that will keep the plane safe until we can recover reliable airspeed information.
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Old 24th Feb 2018, 20:07
  #95 (permalink)  
 
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Thank you check airman, I have managed to absorb "fly attitude and power" but that was not my question what if the craft is already in high altitude stall? in diving out of that stall how significant is the risk of overspeed and without ASI how to manage that risk?
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Old 24th Feb 2018, 22:26
  #96 (permalink)  
 
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The aircraft is tested to well beyond the published maximum speed. Faced with the choice of a potential overspeed or underspeed, I'll take my chances with the overspeed.
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Old 25th Feb 2018, 02:18
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what if the craft is already in high altitude stall? in diving out of that stall how significant is the risk of overspeed and without ASI how to manage that risk?

I would have thought common sense airmanship would apply. You don't have to do a Stuka type dive to un-stall the wings. See: https://en.wikipedia.org/wiki/Junkers_Ju_87


if there is a problem with all three ASI's and you have stalled it as well, then it is not your day
In that event, keep the nose slightly below the horizon for 30 seconds and keep out of buffet then very gently level out. Not forgetting to set cruise power as part of the un-stalling procedure. Count on losing at least 3000 ft in the recovery procedure. There is probably no QRH procedure for that combination of events so you simply have to `wing it`.
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Old 25th Feb 2018, 03:21
  #98 (permalink)  
 
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Originally Posted by Judd View Post
. You don't have to do a Stuka type dive to un-stall the wings.
Well... sometimes you do, though. AF447 was at about 40 deg. AOA for much of its ride down. So to unstall it they'd have had to put the nose down in that vicinity. Let's say 30deg. That might as well be vertical with respect to how it would feel to a pilot only used to conventional attitudes.
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Old 25th Feb 2018, 04:01
  #99 (permalink)  
 
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Yes, reducing the AOA is imperative and it is the only way out.
I'm still amazed that AOA indicator is not mandatory, as it should be the no. 1 instrument for the recovery of the flying wing.
The incident of Tarom at Orly is a textbook example of recovery from a hairy stall situation.
Here is the video with the actual CVR:
(click watch video on youtube, will work)
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Old 25th Feb 2018, 04:41
  #100 (permalink)  
 
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Originally Posted by Vessbot View Post
Well... sometimes you do, though. AF447 was at about 40 deg. AOA for much of its ride down. So to unstall it they'd have had to put the nose down in that vicinity. Let's say 30deg. That might as well be vertical with respect to how it would feel to a pilot only used to conventional attitudes.
yes AF447 was on my mind when i asked the question, that was a deep stall and I believe a "stuka" dive was the only option that could have saved them from that situation, as to how it would feel? well on a black night and considering falling like a stone and no ASI .... how would it feel? probably like standing still. hence my question how would you know when to pull up, perhaps "count to thirty" is the right answer after all
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