Airbus crash/training flight

[HarryMann]

Ignoring the hypothesis that load limitation (and whatever they are chosen as) comes into the abnormal or 'lost it' laws... or came into the equation sometime after the onset of the event -

We have 3 accidents currently under discussion where 'H Trim' and it's management are not only constantly being mentioned, but probably crucial to either a) onset b) recovery of these 'control losss' situations.

[DC-ATE]

PJ2 -

Of course, you're correct. I didn't mean just "any" pilot. And I understand the laws in place regarding the disposition of CVR data. I'm just a sceptic, as you might've been able to tell!

[PJ2]

DC-ATE - Re trained guys, yeah, thought so. Re "skeptic", yep, I'm a skeptic too...of a process that contemplates releasing such data to a wide group under the assumption that they will come up with as good or better a report than the specialists who've done the work in some cases, for decades.

I know of no cases where the reports had the scent of "compromise" due to political, legal or corporate influence.

I do know of several final reports in which dissenting opinions by interested parties and even designated investigators are included.

What I have seen far more of, is, once the confirmed truths regarding an accident are in print for all to see, it is special interest groups, and that includes airlines, pilots' associations and the regulator, that embrace, dismiss, deny or "correct" conclusions according to their own interests.

[DC-ATE]

Having been "close" to a couple of investigations, I could argue the "compromise" bit, but I won't get into it. Suffice it to say, even accident investigators make mistakes.

[TyroPicard]

Tree

Are we reading the same report?

Yes, but I was responding to your complaint about the A320 manuals

My factory AI manuals do not make any mention of the fact that a HS trimmed full stop cannot be controlled by elevator. Neither was that covered during my training.

specifically with reference to the selection of TOGA thrust following the stall warning, and the subsequent control law change to Direct.

[NigelOnDraft]

TP... I might be going over things again, but summarising what seem to be a few "crucial" parts in the timeline.

specifically with reference to the selection of TOGA thrust following the stall warning, and the subsequent control law change to Direct.

At/from 15:45:11 TOGA EPR was being achieved. THS was in the position it remained until the accident (almost full Nose Up), Elevators going to Full Nose Down. IAS ~110K, Pitch ~17nu (?), gently descending.

Over the next 9s, the nose goes down further (to ~5nu?), the aircraft goes to Direct Law (FACs fail), and the elevator "blends" to the stick (over ~5s). IAS increases quickly to ~130K.

What then happens? All seems to go wrong at 15:45:21. From this point Pitch starts a steady rise to ~60nu, IAS starts to decrease as per pitch/climb. The only thing that happens at that point is the Sidestick being neutralised for 1-2s, and the Elevators following. Assuming that leads to and through an accelerated stall, beyond the stall life gets pretty undefined

So I would say Full Nose Up THS and Full Down Elevator, even with TOGA Power, does seem to control the aircraft, so long as you are not stalled.

The only time the THS should be in autotrim, I reckon is 15:45:52 to 15:45:57. However, Flight Control Laws "blend" from one to the other (see Normal => Direct above), so an "instant reaction" might not be expected. And in the latter part of that period the Elevators are going to Full Nose Down (limiting 'g'?) so in fact the THS being frozen is only assisting the recovery.

I might agree with those who say it hit the sea limited it to 2.5g. I am not sure that removing this limit would have saved them... Flaps were up in the recovery, so clean Vstall ~137K? 2.5g then on stall at 217K. 217K was only reached at 15:46:03, 3s before impact. At impact they might have achieved a little more 'g', but nowhere near enough to save them... (263K = 3.7g)

NoD

[bsieker]

Originally Posted by CONF iture

So, Bernd, these lines have been automatically drawn (?) and have not been manually erased (?), or have been manually drawn (?)

My bet is that they have been automatically drawn, and not been erased. This looks like some common plotting software used all over the world; the plots from the Sao-Paulo runway overrun look the same.

I have long taken an issue with the straight lines that are drawn even between data points 4 seconds apart. In some cases this has lead people to believe that a parameter had started to change immediately after one data sample, because the line to the next point was rising from there on, when in fact other parameters (sampled more often) made it clear that this was not the case.


Bernd

[HarryMann]

bsieker

Almost certainly. A scatter chart without linear interpolation would be much more appropriate, but to an experienced engineer, they would 'by inspection' see this obvious truth anyway and ignore the lines a silly auto-plotter drew. Especially with 4 seconds between them!

[CONF iture]

Thanks Bernd.

Also, how would you explain the third AOA, the G load, the flaps, the landing gear, ... parameters are absent from the report ?

[TyroPicard]

I think NoD's summary seems accurate.

Re that last para and G capability

I might agree with those who say it hit the sea limited it to 2.5g. I am not sure that removing this limit would have saved them... Flaps were up in the recovery, so clean Vstall ~137K? 2.5g then on stall at 217K. 217K was only reached at 15:46:03, 3s before impact. At impact they might have achieved a little more 'g', but nowhere near enough to save them... (263K = 3.7g)

I have done some analysis and maths.... figures are approximate but I'm fairly confident that the big picture is correct.... but it all comes with the caveat that I am completely unqualified to do this!

At 45:58, near the end of the final stall warning:
ALT 2400'
PITCH 35° ND
BANK 85° RT → 95°RT
CAS 135 kt
V/S > 6,000 '/min - from the gradient of the altitude slope
SLAT/FLAP unknown but greater than CONF 1 - therefore 2.0 G limit applies in pitch until Slat Zero.

Because of the AOB the nose is still dropping - at 46:00
ALT 2,000'
PITCH 50° ND
BANK 60° RT
CAS 170 kt
V/S > 15,000 '/min

Assuming pitch of 10° NU required to miss the sea, and starting from wings level, I calculate the average G required as:
from 45:58 average CAS 150kt, 1.83 G
from 46:00 average CAS 180 kt, 2.65 G.
I reckon that's just about possible from :58 with some flap, but impossible from :00 with Flap zero selected. (why???) - so the difference between success and failure is down to the bank angle. So why 95° of bank?

BOAC mentioned (post 984) the reversal of aileron effect on a stalled wing, and there seems to be fairly compelling evidence of that at 45:12 to 45:15 followed by left rudder picking up the dropped wing. Then again during the low-speed parabola at 45:55 left sidestick leads to right roll, the roll that led to 95° bank and the excessive ND pitch. It may be that stick neutral in roll and rudder to control the bank would have worked to keep the wings level while they sorted out some effective pitch control.

There are still plenty of unanswered questions, and I wish to make clear that I am not directing any criticism at the crew. We have had days to analyse what they had to fix in seconds. This could have happened on a line flight - no airtest required following a C check, and it's not at all difficult to imagine a scenario in which a stall warning occurs by accident/omission at 3,000 ft.

Assuming my analysis is correct, what would I like to see from Airbus?
Guidance in FCTM on upset recovery, particularly flight below Vs
Upset training
I'm sure you can think of some more - I'm off for a beer.
TP

[BEagle]

One other point.

Inertial effects on the sidestick - or rather, the pilot's arm operating it, at high +Gz and extremes of bank angle? A state with which he would be unlikely to be familiar...

...and which no simulator 'upset training' can replicate.

When I flew one of HM's jet bombers, we were taught NEVER to exceed a RoD greater than your height in thousands of feet. So, at 10000 ft, 10000 ft/min was OK, but at 2000 ft, 2000 ft/min would be the limit. And so on.

The crew got themselves into uncharted territory as soon as they exceeded the AoA value at which the test should have been abandoned. Very shortly afterwards, sadly they were totally out of their depth.

[Dani]

Rudder input?

I agree with most specialists what happened during the last seconds of the XL flight. Thanks, TyroPicard, Lemurian and others for their in-depth information and interpretation of the published data.

One thing that hasn't been discussed here is the rudder. Why is it used during the deadly maneuver? Why on earth do you ever touch the rudder during stall or near-stall exercises? Maybe it didn't add to the bad state of what they were in, but it surely didn't help. Of course this captain was in a terrible situation, but I hate it when I see that experiences airlines pilots don't get the basics of flight.

Reminds me of some very useless rudder inputs on American Airlines flight 587 in Sept 2001.

Dani

[Lemurian]

TyroPicard

what would I like to see from Airbus?
Guidance in FCTM on upset recovery, particularly flight below Vs
Upset training

Actually, it's not that easy as there are a few obstacles - mainly because of mixed fleets and some resistance from the training departments ;
This is from one A.I bulletin :
..."for us, an aircraft that is
out-of-trim, for whatever reason, should
be re-trimmed. Whereas the airline instructors
were against the use of trim
because of concerns over the possibility
of a pilot overtrimming and of trim runaways
which are particularly likely on
some older aircraft types which are still
in their fleets.
We spent a lot of time discussing the
use of elevator trim and we never
reached agreement. All the major US
airlines were adamant on their policy to
recover first using “primary controls”
which excluded any reference to trimming..."

About Stall Recovery
..."To recover from a stall, the angle of attack
must be reduced below the stalling
angle. Apply nose down pitch control and
maintain it until stall recovery. Under
certain conditions with under-wing
mounted engines, it may be necessary to
reduce thrust to prevent the angle of
attack from continuing to increase...
Remember, in an upset situation,
if the airplane is stalled, it is first necessary to
recover from the stall before
initiating upset recovery techniques.
This is something that we are
well aware of in testing, but it
was either being totally ignored
or misunderstood..."

About Use Of Rudder (That's for Dani, too !)
..."We also spent a lot of time discussing
the use of rudder. The existing
training courses all emphasised
using rudder for roll control at low
speeds. It is true that the rudder remains
effective down to very low
speeds, and fighter pilots are
accustomed to using it
for “scissor”evasive manoeuvres
when flying not far fromthe stall. But large airliners,
with all the inertias that they possess,
are not like fighter aircraft. Based
on our experience as test pilots we are
very wary of using rudder close to the
stall. It is the best way to provoke a loss
of control if not used very carefully,
particularly with flaps out...


The whole article is an eye-opener...
As for the accident itself, so far I've remained the only one to mention the likely possibility of a major spatial disorientation which exacerbates the overall loss of SA...
Your thoughts ?

[DC-ATE]

Lemurian -

This is from one A.I bulletin :

Do you happen to have the date of that Bulletin?

[HarryMann]

News of a training/check flight Loss of Control just announced (on BBC)
Believe to have been some time ago

EasyJet 737 Checkflight
Nr Norwich, UK
Hyd switched off (manual reversion check?)
A/c became uncontrollable and lost 10,000'
Recovered at 6,000'

Suspected Trim, or C.of G. problem

[jimjim1]

Trim vs primary controls

My few and sparse posts seem to be vanishing

I have read all the posts in this thread and I think I am raising an issue that has not been voiced explicitly even though I am not 'qualified' to do so.

From Lemurian

A.I bulletin
...
All the major US
airlines were adamant on their policy to
recover first using “primary controls”
which excluded any reference to trimming..."
...

Thing appears to be that on the aircraft type in question; the elevator trim *is* a "primary" control in that it is required to be varied for normal manoeuvering.

Of course, mostly the pilots don't see the behaviour as "triming" (and it surely is not trimming in the traditional sense) since it gets taken care of by the computer. Except this time.

Can anyone see a reason that the seperate trim control lever/wheel/switch exists on this type? Since the stick commands "g" (or load factor) surely the seperate trim control is anachronistic? Does it belong in the same bin as the mixture levers?

[BOAC]

Originally Posted by Dani

Why is it used during the deadly maneuver?

- I think, if you look at the FDR, we are seeing an 'instinctive' reaction to a predominantly right wing down attitude that is not being controlled as expected by aileron - my reckoning is that the wing was either classically or g-stalled a lot of the time. My reading of the reaction is - nothing else is working, so I need rudder, and apart from the danger of inducing a spin, there is some evidence it may have helped limit the roll?

[NigelOnDraft]

HarryMan's heads-up to the AAIB Bulletin Link on the EJ 737 Norwich incident is well worth reading for it's relevance to this thread:

1. Not clearly defined or understood Test Schedules
2. 1 "small" (in normal operation terms) Maintenance error/misunderstanding - surely to be expected and partly why the test flight is being carried out in the first place
3. Misunderstanding / mishandling / unexpected events leading to a loss of control (again, a Flight Test Profile will be intolerant of such factors)
4. Loss of control, which invariably in a swept wing high performance aircraft will lead to a significant loss of height
5. Recovery actions do (eventually) work

Of course, one had a happy outcome, one did not... and being very broad brush... why? 1 crew actually performed their check at the specified altitude (~FL150), allowing time and space to recover... 1 did not.

Even a straight wing Jet Provost demands a minimum entry altitude of 15,000' for a 2-3 turn Spin.

So for all the ***** about FBW, we see a very similar sequence of events leading to a similar loss of significant altitude, in an aircraft about as far removed from FBW as we see flying today.

Lemurian - your use of Rudder post is potentially very relevant to the A320 accident. Large amounts of rudder were used, and are hardly going to help with low speed / "stalled" (Hi Alpha) aerodynamics. 15:45:15 sees Full Left Rudder (& Pedal, opposed by the Yaw Damper) at an IAS of ~100K or less... AoB might be 45R, but as your post again indicates, ignore AoB or whatever, you must recover from the "stall" before trying to recover from the attitude problems.

Overview - re-reading the Test Schedules in the Interim Report, it is clear that the "full back stick Min Speed on Alpha Max" should have seen a stable speed of 107K +/-3K. How did this crew, prepared (?) to do this test, and understanding (?) the principles behind it, and hazards associated with it (?), slow the aircraft to 92.5K without asking "what's going on here"

AoA probes - interesting that in Airbus' Test Schedule, before doing any of this low speed stuff, their profile demands a clean low speed check of all 3 AoA values... which seems rather relevant in this case with 2 AoA values seemingly "frozen" - which would have been revealed.

For the non Jet pilots here, just realise what seems to have been done. The crew, @3000', with Gear and Full Flap down, deliberately slowed the aircraft to 15K below the (equivalent) Minimum / Stall speed, and then applied Full Rudder (NB swept wing aircraft do not necessarily "stall" in a conventional sense, they just lose lift, develop a high RoD then "depart" which is a polite way of describing a flick into a potentially unrecoverable spin). Would you do that in a C150?

NoD

[Dani]

By BOAC:
My reading of the reaction is - nothing else is working, so I need rudder, and apart from the danger of inducing a spin, there is some evidence it may have helped limit the roll?

Might be true but in any case: You never touch the rudder (in any aircraft) to avoid spin, you use the rudder to recover from spin.

I hope you have also some aerobatic license and/or experience in small, light and fast aerobatics-capable planes. Then you remember that you only use the rudder to put an aircraft into spin. The correct procedure to avoid stall is to push the aircraft and later to increase thrust/power. I'm also experienced in military aviation and I have never heard of rudders helping there (but military aviation is a wide field), so I really don't know why these guys always play around with the pedals all the time, might look fancy (when all works out).

Rudders are basically just there for a crosswind landing and OEI handling (engine failure). Nothing else. Leave them - period.

Dani

[BOAC]

Dani - you have misread my post. Yes, I have a fair bit of experience in aeros and use of rudder in military a/c to promote/control roll, but I was merely answering your query, not advocating a technique

It is fairly clear to me that the crew had little idea they were stalled.

Originally Posted by NoD

and then applied Full Rudder

- I think it may be pertinent to point out that according to the FDR, it appears that the crew applied SIGNIFICANT aileron in a stalled condition BEFORE applying lots of rudder, my assumpton being that the aileron aggravated the wing drop as discussed?