Concorde crash: Continental Airlines cleared by France court

[Nick Thomas]

SLFinAz I still stand by comment that the UA 232 flight is a Red Herring. I do agree with you when you say the engine should have not been shut down below 400ft, but because something shouldn't be done doesn't automatically mean that it must be the primary cause of the accident. For you to convince me that you view is worthy of consideration you will have to refute the findings of the BEA.
There are many theories being put forward in this thread and for them to have any credence they must be backed up by verifiable facts. Quoting Heritage Concorde, newspapers or other forums do not pass that test. You can belive what you want but that does not entitle you to overlook the vast body of evidence that has been tested by a far more rigorous body than this forum. Nor does trying to claim that the accident investigation is trying to hid the truth. In fact to be blunt this thread reads very like all others where people claim that there is a conspiracy in place.

[Lyman]

Nick Thomas

Would you consider viewing the runway photography of the skid marks and making a comment?

I see evidence of oscillatory movement about the bogie's horizontal plane.

For me, with some experience in vehicular investigation, the marks show a distinct wobble, such that a rate and distance of displacement can be readily discerned. Given the expected ground speed of the bogie, a cycles per second can be ascertained.

There is also evidence of tread crush, the siping width varies in concert with this cyclical action. This is indicative of side loading, or "scrub".


Will you please comment? Thanks.

I know the pic is from other than BEA, but it is intriguing, and I believe it is genuine.

[Nick Thomas]

Hi Lyman
I am not an accident investigator so am unable to draw conclusions from those photographs. From reading this thread I know you think they are important and that is your right so to do. My view is that there are two opposing views represented on this thread. One in it many guises doesn't accept the BAE report and will spare no effort in promoting their theories. The other (of which am a member) take the view that out of the available information present, the BAE report is the most useful in understanding what happened.

Where I do agree with those who don't accept the report or parts of it, is that the many other failures brought to the fore after this sad crash should be addressed but that doesn't mean that they actually caused the crash. In other words am of the view that even if all these points had been addressed before the incident the crash would have still occurred with the same awful outcome.

From previous conversations with you on this forum(when you were know as Bearfoil) I respect that you are trying to establish the truth. My path towards getting a better understanding of this tragic event is a different one to yours and therefore for me looking at the photographs you mention, will be of little value, as I am not expert enough to draw conclusions from them. The other reason am disinclined to view them is that it would mean that in order to be fair I should carefully study all the other evidence presented here that questions the report.

In science when something new is postulated it normally undergoes a peer review and if that is favourable it is then included in the body of scientific knowledge. Of course over time this theory will again be tested and if then found wanting the body of scientific knowledge will be revised to accept this new development. Why do I mention this. Well for my understanding of this incident to be increased or changed, then the BAE report will have to be challenged by another body of similar standing. As I have said earlier I am not an expert in this field and I therefore have to trust those who are considered to be so. I presume that other people posting here will not agree with my last point but may I suggest that in questioning the report you must have considerable confidence in your ability to understand third hand a very complex accident

[AlphaZuluRomeo]

Originally Posted by Lyman

I know the pic is from other than BEA, but it is intriguing, and I believe it is genuine.

No Lyman, I'm sorry but this pic is from page 64 of the final report; there are other pics from the runway in pages before and after that.
All those pics show places where Concorde was after the destruction of the tyre from wheel #2. Hence I fail to see where you're heading to?

As previously quoted:

Originally Posted by AlphaZuluRomeo

Quote from B. Sieker (op. cit. in my #160): The report makes a point of recording that there was no sign of abnormality in the taxying and takeoff run up to the point of tyre destruction. There was no shimmy, no deviation from track, the brake temperatures were equal RHS and LHS, and the longitudinal acceleration was consistent with the TO mass and ambient conditions. Let us accept that ensemble as evidence that any bogie misalignment due to the missing spacer became a potential problem only after the destruction of the tyre.

I would also take this opportunity to say that I fully agree with Nick Thomas' excellent last two posts #222 & #224 just above.
Well said, Sir, and tip of the hat to you.

[Lyman]

Nick Thomas, AZR...

Thanks to you both. Your input is most helpful.

Briefly, I conclude the bogie is rotating about its horizontal plane as a result of a missing stand-off spacer. I do so because the tires are tracking irregularly in a plane which would ordinarily not be active.

Yes the marks were deposited after the rupture. The artifact that describes the shape of the tread cut suggests the tire was still reasonably intact at the site of the strip's insult.

If this contravenes BEA material, I think it worthy of mention..

So there we are.

A very enlightening discussion, and again, thank you.

Cheers

[AlphaZuluRomeo]

Hi Lyman,

Originally Posted by Lyman

The artifact that describes the shape of the tread cut suggests the tire was still reasonably intact at the site of the strip's insult.

I'm sorry, I don't understand this

Originally Posted by Lyman

If this contravenes BEA material, I think it worthy of mention..

Sure! If, it would
But I don't think this contravenes BEA conclusions. As for the material (=the picture ??), as previously stated it is from BEA.

[philip2412]

Hello AZR,

pls allowe me one question,would the concorde have hit the strip if the spacer had been in place ?

Thank you

[DozyWannabe]

Originally Posted by philip2412

pls allowe me one question,would the concorde have hit the strip if the spacer had been in place ?

All other things being the same, yes it would have.

From what I've read regarding accident investigation, if physical evidence and eyewitness evidence diverge, then it is standard procedure to consider the physical evidence as more reliable, as eyewitness evidence has been proven to be one of the less reliable sources - dependent as it is on human perception and psychology.

The missing spacer is unlikely to have altered trajectory prior to contact with the metal strip, it would simply have had a very marginal effect on acceleration (and possibly a barely-perceptible level of vibration) given the sheer amount of thrust-to-weight involved.

At the risk of re-stating the obvious, no amount of errors on AF's part (of which there were undoubtedly several) would be sufficient to negate the errors made by CO. Mistakes made by both organisations must be combined and considered as a whole (and indeed the BEA report always reflected this).

[CliveL]

Lyman

Briefly, I conclude the bogie is rotating about its horizontal plane as a result of a missing stand-off spacer.

As you requested, I looked at that picture very carefully, and yes, there is evidence of a shimmy-like oscillation in that part of the track. However, I also looked at the other pictures in the BEA report (which is the source of the Heritage picture) and I could not see any evidence of similar oscillations when the aircraft was on the tarmac.

So I have some questions for you ..

I am no expert on shimmy, but I do know that it depends on a critical relationship of feedback between tyre forces and gear structure. The tyre force/slip characteristics would change substantially when the gear moved from tarmac to grass, so why are you sure that shimmy was present throughout all the TO? The BEA certainly didn't think so. Could shimmy be present only in the grass-bound part of the roll?

By the time the FE called the #2 engine failure and fire warning and then shut down #2 the aircraft had been airborne for several seconds. There would have been no shimmy once airborne, so why do you think it such an important factor in his decision to shut down #2? Why would it trump the engine failure and fire warnings? [The debate as to whether he should have shut down at that time is another matter]

At the time when the aircraft passed over that region (97611.5 on the BEA datum) it was at about 203 kts and had an AoA of 9 deg. One second later it lifted off, still at 203 kts but with an AoA of 11 deg. At the time we are discussing then about 80% of the weight was being carried by the wing so only 10% was on the LH gear. Since any forces transmitted to the airframe must depend on ground reaction and slip why do you think that the gear had a important effect at this point?

Shimmy, as I understand it, is a cyclical rotation of the wheels about the main leg. Again at the time we are talking about, the aircraft sideslip was 3 deg. Allowing for +/- 3 deg oscillation because of the missing spacer that would mean the wheels oscillating between zero and 6 deg would it not? Why would the time they were at less than 3 deg not offset the time they were at more? Or in other words, why should shimmy change the average force?

I notice that in your argument you do not mention the sideforce generated by the tyres. Have you any reason to neglect that contribution? I would think it a bigger effect than the drag and what is more it would have been acting behind the CG and giving a moment to restore the aircraft towards the centreline.

[Lyman]

CliveL

I am most grateful for your response. To start...

"I notice that in your argument you do not mention the sideforce generated by the tyres. Have you any reason to neglect that contribution? I would think it a bigger effect than the drag and what is more it would have been acting behind the CG and giving a moment to restore the aircraft towards the centreline."

Let us begin with brake release. First off, a skidding tyre has less authority to affect direction. If skidding from the start, the left bogie is having less effect on direction than the right. That means the a/c will tend right, and may explain the Captain's initial left ruddering. (with four healthy engines))

For the record, I would suggest that as a whole, asymmetrical thrust had far more to do with track than tyres. If the left bogie had one tyre out of line, the bogie as an entirety would have less authority for directional control than the right bogie. Notice the tire marks on the picture showing roll prior to kero stain?
Only the left side?

This is suggestive of misalignment of left bogie. Notice also the straight track. This suggests that the misalignment is well managed. After the tank rupture, and fire, the bogie has less to do with track than thrust inequalities, imo.

You make a good point re: weight on wheels at the runway light image. The skid marks are light, narrow, and show the wing carries the a/c here. They also show more emphatically the stresses on the tyres from the outset. Free of most weight, they shimmy and wobble more readily.

I am interested in discussing the rest of your post. I'll leave at this point for you to respond if you wish.

Again, thank you

[DozyWannabe]

Another very important factor to bear in mind is that unlike with most powered ground transportation, where the motive power of the engine is transmitted to the ground *through* the wheels and tyres, an aircraft's thrust is independent of the wheels, which serve only to maintain heading and not to transmit propulsion mechanically (at least in a direct sense). An unbalanced wheel on a drive axle will therefore have a considerably greater effect on ability to control direction than a similar imbalance on a non-driven axle.

The lateral trajectory of the aircraft shows no abnormal signs of instability prior to contact with the metal strip, so it can therefore be concluded that the guidance of the correctly-fitted wheels along with the force of the forward thrust were more than capable of overriding any instability that the wheel with the missing spacer might have caused.

It is also therefore reasonable to conclude that the veer to the left coinciding with the strip contact was at least largely caused by a combination of the forces involved in loss of the tyre, loss of thrust from the port engines due to hot gases and the loss of grip caused subsequent to the tyre's destruction.

Another thing to bear in mind with the eyewitness testimony is the simple difference in perception that can be caused by the difference in speed of light vs. speed of sound. In general eyewitness testimony will tend to report perception of fire or visible evidence of explosion before any audible abnormality, and this is generally regarded to be because of the speed of light vs. sound perception. The firemen in this case may well have seen the fire before they heard anything abnormal with the takeoff (such as unusual engine noise or even the sound of a tyre failure) for this very reason.

[Lord Bracken]

Let us begin with brake release. First off, a skidding tyre has less authority to affect direction. If skidding from the start, the left bogie is having less effect on direction than the right. That means the a/c will tend right, and may explain the Captain's initial left ruddering. (with four healthy engines))

Concorde engines didn't all spool up at the same speed (3 + 1 iirc) so this was normal.

[CliveL]

Let us begin with brake release. First off, a skidding tyre has less authority to affect direction. If skidding from the start, the left bogie is having less effect on direction than the right. That means the a/c will tend right, and may explain the Captain's initial left ruddering. (with four healthy engines))

I guess I should have specified that I meant conditions after the tyre was demolished. The BEA report (18.2.3.3) deals with the situation before that and all the evidence presented there says that the missing spacer and consequent freedom of bogie to yaw had no effect on the trajectory in that phase. I know no better.

For the record, I would suggest that as a whole, asymmetrical thrust had far more to do with track than tyres.

I'm wholly with you there

[Chris Scott]

Quote from CliveL:
"By the time the FE called the #2 engine failure and fire warning and then shut down #2 the aircraft had been airborne for several seconds. There would have been no shimmy once airborne, so why do you think it such an important factor in his decision to shut down #2?"

I think Lyman is arguing that violent vibration caused by main-wheel shimmy may have influenced the F/E's decision to shut down engine #2, even though the a/c was still getting airborne. While the root cause of any shimmy would be removed once the wheels left the ground, my experience suggests significant vibration might continue until the auto-brakes have stopped wheel rotation. I don't know what criterion is required on Concorde for autobrake, but it's likely to be near the start of an active gear-retraction sequence. In this case, as we all know, gear-door damage led to the selection of gear UP being refused or aborted by the retraction system at some stage in the sequence. Perhaps you or others can comment.

Having said that, I'm not aware of any evidence to support Bearfoil's intuition.

[DozyWannabe]

Originally Posted by Lord Bracken

Concorde engines didn't all spool up at the same speed (3 + 1 iirc) so this was normal.

Indeed - this was discussed in detail on the old thread here:

Originally Posted by Bellerophon

You call 3-2-1 Now, start your stopwatch, pre-set to countdown from 58 seconds, and slam the throttles fully forward till they hit the stops. Four RR Olympus engines start to spool up to full power and four reheats kick in, together producing 156,000 lbs of thrust, but at a total fuel flow of 27,000 US gallons per hour. A touch of left rudder initially to keep straight, as the #4 engine limiter is limiting the engine to 88% until 60 kts when it will release it to full power.

And some further detail on startup at pushback here:

Originally Posted by M2dude

The trick was to get as many hydraulic systems online ASAP during engine start/pushback, and that's where the sequence was defined. Now my tired/worn out/time-expired brain recollects that number TWO engine was started first, this gave us GREEN and YELLOW systems, followed by number THREE engine, which now gave us BLUE system. Once these engines were successfully started the 2 air start trucks (oh for that darned APU) could be disconnected and preliminary system checks, including full and free flying controls, could be carried out. After push-back the outboard engines were started by using adjacent engine cross-bleed (as BRIT312 quite correctly stated years ago, there was no 'cross the ship' cross-bleed duct), the remaining system checks would be carried out.

Something I recall from the time I was reading these discussions was that during critical phases the FE would have been watching the engine instrumentation like a hawk, and given that the takeoff run was proceeding relatively normally prior to strip contact it would be far more likely that abnormalities in that instrumentation would have been the trigger for engine shutdown rather than a split-second increase in vibration. All evidence suggests that the crew thought they were dealing with an engine fire and had little time (or inclination) to determine its cause in the short time between strip contact and impact.

[CliveL]

Dozy

the wheel with the missing spacer

That's a trap I fell into also - it wasn't a wheel with a missing spacer it was the bogie pivot, so all four wheels on that bogie were affected.

But let me draw your attention to the comment in the BEA report (18.2.3.3 again)

A displacement in the horizontal plane is, on the other hand, abnormal. It requires predominance of horizontal loads over vertical loads, which is not the case during the takeoff phase.

This is (presumably) the reason why the pre-burst trajectory was not affected.
Easy to see that if vertical loads on the bearing predominate the 'slack' will be taken up by the axle moving to the top of the female part not to the rear which would produce a yaw.

[CliveL]

Concorde engines didn't all spool up at the same speed (3 + 1 iirc) so this was normal.

That was indeed so, but #4 was spooled up with the others at 60 kts and the left rudder input from the FDR trace was at 100 kts - no obvious reason for it either.

[CliveL]

Hi Chris,

Nice to see you back again

While the root cause of any shimmy would be removed once the wheels left the ground, my experience suggests significant vibration might continue until the auto-brakes have stopped wheel rotation.

I'll buy that! (at least as a contributory cause). I don't know of course, but I wouldn't bet against auto-brake being NBG along with a lot of other functions.

[DozyWannabe]

Cheers for that Clive - interesting stuff!

Originally Posted by CliveL

That was indeed so, but #4 was spooled up with the others at 60 kts and the left rudder input from the FDR trace was at 100 kts - no obvious reason for it either.

Us engineers are pre-disposed to be concerned with "why" in that situation, however is it not likely to be the case that a line pilot would simply correct as necessary and worry about the "why" once airborne? After all, the possibility exists that it may simply be an unexpected lateral gust...

Regarding Chris's very salient point, I have to ponder just how significant such vibration would be compared to that which might be expected from a damaged engine as suggested by the warning systems. To my mind this is reinforced considerably by the fact that a trained Concorde flight crew would be acutely aware of just how critical engine problems are during that phase of flight and prioritised that problem almost instantly.

[CliveL]

After all, the possibility exists that it may simply be an unexpected lateral gust...

There was damn all wind in any direction ....

I have to ponder just how significant such vibration would be compared to that which might be expected from a damaged engine as suggested by the warning systems.

But engine 2 had no real internal damage - in fact the BEA report says specifically that the internal state was not such as would cause surge. Equally there is no mention of any engine failures that might give rise to a genuine fire warning from flames inside the nacelle.