The official report into the DC9 reads:IMMEDIATE CAUSE: "The Commission Aircraft Accident Investigation of the Eastern Republic of Uruguay, determined that the probable cause of the accident immediately, that a pressure altitude of 30,000 ft., copilot, who was in charge of controls of the aircraft, flight raised such a condition, which led him to extend the slats. This was done at a rate well above the limit of the structural design of the slat system, developing, asymmetries by extension andlor damage to themselves, with the consequent loss of control and inability to recover. The interpretation of the co-pilot on the need to extend the slats would have been a result of the incorrect low-speed (IAS), caused by blockage of the pitot tubes RESULT atmospheric icing. Unable to determine whether such obstruction was a result of the crew did not activate the heating system through the selector switch, after the launch, or failure of that system.ENDEMIC AUSES: a) Lack of indication of Mach No. speedometers installed on the accident aircraft within its flight envelope, with air speeds below 250 KIAS. :( Lack of training of pilots' flight instrument failure "and" upset recovery. " c) Lack of training of pilots in the recovery approach to the loss of the DC-9 aircraft in "clean configuration"in accordance with the procedures in the FCOM, Section 5, 10-0-0, code 30. d) Lack of education and training of pilots in the management of resources in the cockpit (CRM). e) No warning light PITOT / STALL HEATER OFF "in the annunciator panel of failures of the aircraft. f) Impairment of operational procedures for flight clearance.It was nothing to do with a high-speed/shock stall.

The accident report sequence of events is backwards:Proper, logical (as in Occam's Razor) sequence of events:

1. Aircraft unwittingly entered a thunderstorm while crossing a cold front,
2. Pitot freezes-up.
3. IAS indication decreases.
4. Seeing IAS decrease in midst of a thunderstorm is really, really frightening!
5. Pitot-Heat warning light is inoperative, therefore
6. Pilot adds thrust to maintain IAS.
7. But in reality accelerates beyond Mmo.
8. High-speed stall causes nosedive.
9. Regardless of IAS, due to extreme nose-down attitude pilot knows aircraft is accelerating wildly,
10. Pilot cuts thrust and dirties-up aircraft (extend flaps, slats and gear, sticks hands out of window).
11. But aircraft is already beyond recovery (see previous post, "High-Speed Stall Detour" section).
12. Slat assymmetry due to lost slat simply adds rolling moment to an aircraft already at an unrecoverable attitude

I don't think that the DC-9 crash was due to flow separation at high mach number.If one looses a complete slat assembly at very high speed it's most probably the resulting rolling moment that will lead to the extreme nose down dive.

See #12 above (previous post).

In a DC-9 / MD80 it's not possible above approx M0.95 to achieve any intentional rolling motion even with full aileron deflection, so in this case it would not have been possible to roll the plane upright again.

Indeed, shockwave-induced airflow detachment over ailerons renders them ineffective. Even so, slat assymetry would have exceeded aileron authority anyway, and even if it didn't due to Mmo overspeed the center of lift was too far behind the CG to raise exceeding elevator authority to raise the nose. Insufficient elevator authority + insufficient aileron authority = loss of control.

The highspeed stall you mention doesn't occur at Mmo. At that speed you might get a slightly turbulent boundary layer aft of the just forming shockwave.Mmo is not the speed at which a high-speed stall will occur, rather, as the name implies, the maxumum Mach number allowed (for the aircraft to still be safe.)

See above, and recall the combined effect of uneven spanwise distribution of wing generation of lift (more lift at the root), thus uneven spanwise distribution of shockwave (larger shochwave at the root), thus uneven spanwise distribution of loss of lift (more loss at the root), resulting in the average center of lift moving rearwards. Add the fact that at transonic speeds the center of lift moves rearward anyway, even if the wing is unswept and without flow detachment, and yu see why you will not be able to raise the nose (and why military super-sonic fighters have stabilators (moving tailplanes).Mmo is not the speed at which a high-speed stall will occur, rather, as the name implies, the maximum Mach number allowed (for the aircraft to still be safe.)

At Mmo you need a higher than normal AoA / G load to achive flow separation, that's why I mentioned the 'missing' AoA and hence 'accelerated' stall.

This is correct. In-thunderstorm turbulence could well have provided the G's needed to trigger an accelerated stall at Mmo. This is why flying in the coffin-corner is so dangerous (but of course flying fast is an industry requirement due to passenger expectations, etc. etc.). In this case an "accelerated stall" is just a case of a high-speed stall at G > 1. Same as in the case of accelerated stall at lower speeds, "accelerated stall" is a misnomer because you can stall at any low speed for (low-speed stalls) and similarly you can stall at any high speed (in the vicinity of Mmo) for high-speed stalls, though to a lesser extent.

Mdf is the lowest speed where serious flow separation occurs but that's almost impossible to reach at level flight for subsonic planes due to the extreme drag rise.

See above. But in a commercial airliner in an uncontrolled dive you will have flow separation, followed by wing separation and fuselage separation.

'Highspeed stall' sounds IMHO a bit misleading as the flow separation at straight and level flight doesn't occur as rapidly and complete as during a 'normal' stall.

Onset migh not be as sudden, but the result can be even more lethal. Consider highly swept delta wings don't really ever "stall": drag starts to increase at a faster rate while lift levels off and smoothly begins to decrease. All smooth and controllable. The AoA can go to 120º (i.e. past vertical) and back to normal, ergo the Cobra Maneouver (vectored thrust required).Cheers,- jahman.

The extracts are not reporting the sequence of events. They are presenting, as it says, the IMMEDIATE CAUSEand ENDEMIC (secondary) CAUSE. That's how accident reports are written. The sequence of events will be given elsewhere in the reportI don't have a link to the full report - do you?

Can you provide a link to support your sequence of events - such as the full accident report?

See below. (Had to wait for another post because the board was conjoining two posts I wanted to keep saparate to avoid exceeding a board limit on max quotes.)

The official report into the DC9 reads:IMMEDIATE CAUSE: "The Commission Aircraft Accident Investigation of the Eastern Republic of Uruguay, determined that the probable cause of the accident immediately, that a pressure altitude of 30,000 ft., copilot, who was in charge of controls of the aircraft, flight raised such a condition, which led him to extend the slats. This was done at a rate well above the limit of the structural design of the slat system, developing, asymmetries by extension andlor damage to themselves, with the consequent loss of control and inability to recover.

See re-ordered list of events at the beginning of this post.

The interpretation of the co-pilot on the need to extend the slats would have been a result of the incorrect low-speed (IAS), caused by blockage of the pitot tubes RESULT atmospheric icing.

This is incorrect: As icing reduces IAS gradually and slowly, pilots respond by increasing thrust. Slat/flap deployment at 30,000 ft would be as a result of a IAS excursion incorrectly perceived as sudden due to pilot inattention, an unlikely event considering the aircraft was in the midst of a thunderstorm, thus pilot attention to primary flight instruments was likely at it's maximum.

Unable to determine whether such obstruction was a result of the crew did not activate the heating system through the selector switch, after the launch, or failure of that system.

I recall the heater warning light was a known inop. This was pretty well covered in the film Air Force, Incorporated.

ENDEMIC CAUSES: a) Lack of indication of Mach No. speedometers installed on the accident aircraft within its flight envelope, with air speeds below 250 KIAS. :( Lack of training of pilots' flight instrument failure "and" upset recovery." c) Lack of training of pilots in the recovery approach to the loss of the DC-9 aircraft in "clean configuration" in accordance with the procedures in the FCOM, Section 5, 10-0-0, code 30. d) Lack of education and training of pilots in the management of resources in the cockpit (CRM). e) No warning light PITOT / STALL HEATER OFF "in the annunciator panel of failures of the aircraft. f) Impairment of operational procedures for flight clearance.

Assuming, of course, recovery in the midst of a thunderstorm with iced pitots is possible.

It was nothing to do with a high-speed/shock stall.

I'm sure the pilots of Austral Flight 2553 are comparing notes with same of Air France Flight 447.Remember, never base your conclusions solely on accident investigators subject to industry pressures!Cheers,- jahman.

1.Indeed, shockwave-induced airflow detachment over ailerons renders them ineffective. 2. Add the fact that at transonic speeds the center of lift moves rearward anyway, even if the wing is unswept and without flow detachment, and yu see why you will not be able to raise the nose (and why military super-sonic fighters have stabilators (moving tailplanes).3. The AoA can go to 120º (i.e. past vertical) and back to normal, ergo the Cobra Maneouver (vectored thrust required).

1. On the DC-9 the engineers predicted and the test pilots confirmed it that the loss of effectiveness is not due to flow detachment but due to the opposite wing bending moment at very high mach number.2. The DC-9 and many other airliner have a fully automatic mach trim to counter the nose down moment. Concering trim, a stabilator on a fighter works in the same way as the stabilizer of the DC-9 3. For a Cobra maneuver there's NO thrust vectoring necessary.As you most probably know, the DC-8 (and other airliners) have been flown at speeds greater than Mach 1. So it's highly improbable that the DC-9 went out of control due to flow separation. (see Mach trim and Mach capability)

See below.

Where's the link?I never base any conclusions on the unsuppported evidence of anonymous posters in on-line forums.

1. On the DC-9 the engineers predicted and the test pilots confirmed it that the loss of effectiveness is not due to flow detachment but due to the opposite wing bending moment at very high mach number.

I see, so that would be partial aileron reversal due to aeroelasticity (partial in that reversal was down to aileron ineffectiveness, but not all the way to reversal). Interesting. This of course up to the M number tested, which might be either side of the M number excursion of the accident aircraft triggered by the inoperative IAS reading, perhaps also including a safety restriction limiting the CG to a specific range for safe trans-sonic flight (that the accident aircraft might also have exceeded).

2. The DC-9 and many other airliner have a fully automatic mach trim to counter the nose down moment.

Interesting. Can I assume effectiveness would be limited up to a certain M number beyond Mmo?

Concering trim, a stabilator on a fighter works in the same way as the stabilizer of the DC-9

Indeed. My reference to stabilators is the greater control authority of a moving surface (vs. a fixed surface plus trailing control surface) required for supersonic flight (and combat.)

3. For a Cobra maneuver there's NO thrust vectoring necessary.

Interesting. So longitudinal static stability is enough to right the aircraft then?

As you most probably know, the DC-8 (and other airliners) have been flown at speeds greater than Mach 1. So it's highly improbable that the DC-9 went out of control due to flow separation. (see Mach trim and Mach capability)

We don't really know what M number the aircraft reached, as well as as any G-loading due to severe turbulence that could have been present in the thunderstorm core during the TAS excursion, that in combination could have triggered a high-speed stall.But a central issue remains: You are in the midst of a severe thunderstorm at FL300, eyes glued to the PFD, quite concerned as you see IAS gradually decreasing, possibly aware of conflicting IAS readings, plus "in the know" the DC-9 can go trans-sonic (as you now mention) without loss of control: What are the chances as a pilot you will add thrust vs. extend slats/flaps? Seems adding thrust was the likely course of action, then an uncontrolled nosedive, then a panicked extension of slats/flaps/gear. A wild G-loading excursion when transiting from the downdraft to the immediately adjacent updraft of a thunderstorm could very well have stalled the aircraft right then and there (either slow or high-speed stall, or even a combination of both) from the G-loading alone. Could even have ripped the wings off.And if IAS kept decreasing in spite of adding thrust (or even if they didn't add thrust), again perhaps in the core of a thunderstorm (they were crossing a front), would they not rather have departed their assigned FL to increase IAS than risk extending flaps and slats, a dangerous manouver in the face of uncertain IAS readings?So the accident report's claim that incorrect slat deployment caused the accident, well, I have my doubts. In the face of unknowns (I seem to recall the CVR and FDR disintegrated on impact at significantly more than M1, like M1.2 or M1.5, but it's been many years since I saw the movie), accident boards do tend to fill-in the blanks with the pilot's names in the manner most suitable to anyone and everyone else.

Where's the link?

"See below", meaning as in the rest of the post below.

I never base any conclusions on the unsuppported evidence of anonymous posters in on-line forums.

You shouldn't, and neither do I. Watch the film.Cheers,jahman.

"See below", meaning as in the rest of the post below.

So you don't have a lin to the report and the rest of your post is pure conjecture.Thanks for reminding me not to pay any attention to anonymous posters with no facts to support their ludicrous assertions.

So you don't have a lin to the report and the rest of your post is pure conjecture.Thanks for reminding me not to pay any attention to anonymous posters with no facts to support their ludicrous assertions.

You can disagree without being incredibly rude (unwarranted too).You also need to sharpen your reading skills because the link is provided (won't go out of the way to reproduce it again for unmannered folk like you), neither will I reply to any of your posts on this thread.Have a good day.Cheers,- jahman.

You can disagree without being incredibly rude (unwarranted too).You also need to sharpen your reading skills because the link is provided (won't go out of the way to reproduce it again for unmannered folk like you), neither will I reply to any of your posts on this thread.Have a good day.Cheers,- jahman.

The only link you gave was to that infallible source wikipedia. My comments were warranted. You said "But in reality accelerates beyond Mmo. High-speed stall causes nosedive" Even wikipedia doesn't say that. What's your source, or did you just invent it?

HeyI was planning on flying from KEDW to KBAB at FL260. Is this a realistic U-2 cruising altitude, or do they only rarely hang around the lower flight levels?

1.Interesting. Can I assume effectiveness would be limited up to a certain M number beyond Mmo?2.Interesting. So longitudinal static stability is enough to right the aircraft then?

1. Yes, approx Mdf2. Apparently, as neither the Su-27 nor the Mig-29 have thrust vectoring

HeyI was planning on flying from KEDW to KBAB at FL260. Is this a realistic U-2 cruising altitude, or do they only rarely hang around the lower flight levels?

As the IAS limit on the U-2 is rather low (around 240 AFAIR) FL260 seems to be way too low. Also the fuel flow at such a low FL would be rather high.

The only link you gave was to that infallible source wikipedia. My comments were warranted. You said "But in reality accelerates beyond Mmo. High-speed stall causes nosedive" Even wikipedia doesn't say that. What's your source, or did you just invent it?

Everything you said so far can be said in a completely different tone. I would recommend you try it for effect.I see I need to be explicit: Go to this link here. Before you say "Oh! But that's just a movie!", the producer is a LAPA pilot that resigned from that airline in disgust after the LAPA Flight 3142 accident, became an investigative documentarist, made a very successful film on that accident, and then went on to make the cited film about the accident subject of this thread (now totally hijacked). In his opinion, essentially everything the official report says is rubbish.Regarding the high-speed stall causing a nosedive, you might want to brush-up on Mach Tuck, as you have not yet grasped what I tried to explain (perhaps I failed there) about spanwise distribution of lift, spanwise progression of a stall and how stall progression moves the wing's center of lift rearward. So it's not that "even Wikipedia doesn't say that"; perhaps you're just not familiar with Mach Tuck.As far as Wikipedia, well, if you disagree feel free to dive-in and correct, but note there are folks aplenty there with a deep and wide knowledge of aerodynamics that just might stomp on your edits if they are incorrect or even imprecise. Just in case, make sure to read up on Mach Tuck in p. 43, Chapter 4 "Aerodynamics of Flight", Pilot's Handbook of Aeronautical Knowledge, Flight Standards Office, Federal Aviation Administration, U.S. Department of Transportation, United Staes Governmet, Publication FAA-H-8083-25A (sorry fellow posters, I want to get my references correct or mgh-folk might stomp on me!) so you won't introduce any mistakes with your Wiki edits. mgh, go buy the book, all others check here.I have other sources too that I would recommend reading, especially Aerodynamics for Naval Aviators, another easy-to-read book fully dedicated to, um, the subject of Aerodynamics. Finally, if you're interested in the topic of things that go really, really fast, as in M > 5, there's also Hypersonic Flow Theory (of the Applied Mathematics and Mechanics Series), by Wallace D. Hayes (Co-discoverer of the Area Rule). The math in it will really ah, shock you so to speak, as it did me (must have missed a math class here and there! Seriously, it's mostly gibberish to me although some concepts percolate at the qualitative level). A nice book to display on a shelf (right next to that Revell model of the X-15) and impress your friends with!Seriously, mgh, it's been fun bashing you around, but let's try and keep it civil so we can all get along and have some fun, shall we? Thanks!Cheers,- jahman.

Let's forget the bluster and deal with the point.You still cannot produce any evidence to support your assertion that that Austral 2553 exceeded M_mo , its altitude that it entered a nose dive beflore the slats were deployed. A link to a link to a film in Spanish isn't evidence.

Let's forget the bluster and deal with the point.

You mean the "bluster" part where you quote me and say:

But in reality accelerates beyond Mmo. High-speed stall causes nosedive"Even wikipedia doesn't say that. What's your source, or did you just invent it?

because you're unfamiliar with Mach Tuck? Being rude and wrong at the same time, and then not conceding when called, my, you're some sort of fella!

You still cannot produce any evidence to support your assertion that that Austral 2553 exceeded M_mo , its altitude that it entered a nose dive beflore the slats were deployed. A link to a link to a film in Spanish isn't evidence.

Go get the film, get someone to translate it for you. Not my fault if you don't have the film and don't speak spanish, and I don't have to prove anything to you. You didn't see an analyisis of how far the torn slat was found from the crater, and whether that distance supported the early deployment vs. mach tuck scenarios, now did you? Well, I did. You think an "official" accident report from a third-world country deserves the same credibility as one from the NTSB? Are you that naive? Further, your previous mumblings about anonymous posters are rubbish, because you don't know whether the names of posters are real. But I'm sure you already knew that, like you knew about mach tuck.Now go away.Cheers,- jahman.