Concorde's Take Off Performance Falsified?

[Agaricus bisporus]

December’s edition of Scientific American magazine contains the following letter from one Jon Modrey, an MD11 FO with Gemini Air Cargo from Orlando, FLA.

“…masks the inherent reduced safety permitted by the Concorde’s government certifiers. Any other four engined transport aircraft could have sustained the Concorde’s damages and made it back for a safe landing. In order to permit the Concorde to operate on existing runways, it’s certifiers redefined it’s take off safety speed, or V2, to a speed so low that the loss of two engines would not permit the aircraft to climb without first diving a few thousand feet to build up speed. Other four engined transports have not been afforded this convenient definition of V2 and can in fact lose two engines on takeoff and still climb and maneuver to a safe landing.”

Contentious stuff that! If we can ignore the drivel about diving thousands (!) of feet and any other aircraft flying with all that damage I am curious about his main thread, the assertion that Concorde’s V2 figures are unrealistically low. This seems to be a most serious charge, and I am keen to see if there is any factual evidence whatever to back up Mr Modrey’s accusation.


1) Can Concorde genuinely climb with the loss of two critical engines at the published V2?

2) If so, is the climb performance acceptable, or marginal, or only possible under ideal test conditions, as opposed to normal operating parameters?

3) Is there any evidence, anecdotal or otherwise of collusion amongst the certifying authority(s) in the matter of Concorde’s V2?

Concorde pilots, technical or performance experts, or anyone else with a view, can you clear the waters?

[Flap40]

I always thought performance was based on only loosing ONE engine.

You might get away with loosing two in some types at light enough weights, but I'm sure that there are no guarantees.

[Budgie69]

No commercial 4-engined transport can survive the loss of 2 engines on takeoff at normal operational weights. 3 engine ferries (which assume the loss of one of the remaining engines at V1) require special techniques and very low takeoff weights.

[mutt]

V2 on 4 engine aircraft is based on losing one engine at a critical point in the takeoff, this point is defined as V1 or VEF. I do not know of any commercial airliner that operates on the premise of 2 engines failing at that critical point.

Jim Modey should look closely at the VMCA2 of a 4 engine airliner and then read the accident report of the EL-AL B747 flight from AMS.

I would be extremely surprised if the CAA allowed for a re-definition of V2 to satisfy Concorde!

Mutt

[ 01 January 2002: Message edited by: mutt ]</p>

[twistedenginestarter]

To the uninitiated - which is what this guy looks like - Concorde can look dodgy. However it is a different type of plane so its ability to retain control and its sensitivity to stall allow narrower margins whilst being as safe as an ordinary jet.

All the evidence I've ever seen shows certification to have been as rigorous as for anything else.

Concorde would have survived on two engines I think. The problem was loss of control which was not caused by lack of power but rather lack of physical parts of the wing.

[BEagle]

Point of order, Mr Chairman! In the mighty Vickers VC10 Funbus, we regularly lose one at V1 and another stops producing thrust at V2...at MTOW!! In the simulator, fairly obviously!! It flies perfectly well so long as sound flying skills, well practised drills and good CRM are applied. But try it above RTOW, without having recomputed the speeds, with a FE shutting down an engine still producing thrust before V2 is achieved..........

[P22]

Point of order denied BEagle. Both Budgie and Mutt said 4-engine COMMERCIAL jet aircraft.

[BEagle]

No-one's told the ac that, when it's full of pax and at MTOW, it is no longer the civil airliner it once was!! I undersand that it had to prove that it had this excess performance in its early days due to the suspicion (unfounded) that a single engine failure would invariably become a double engine failure due to the pairing of the engines?

[747FOCAL]

It's going to depend how close to Vlof and where you lose the second engine. And what obstacles you have in front of you. If you have no obstacles you will probably be okay as long as you can get to Vlof with two engines.

By the way, the Concorde that crashed was one of the few certified to take off with two engines. It wasn't the lack of thrust that got them, the fire cooked the hydraulics and he lost control. What, you think he steered into that hotel with a nice field right next to it?

[basil fawlty]

Here we go again....... <img src="rolleyes.gif" border="0">
BEagle, please give the "RAF obviously have higher standards and are better aviators than everyone else" implication a rest. Its becoming a bit tiresome, old boy.
Please go and fly your "VC10 takeoff on two engines" fantasy sortie in the sim.....Maybe with Blair and Co. commiting many millions of pounds of taxpayers money to making Britain look "big and important" around the world (Afghanistan, Bosnia, Sierra Leone etc) you may well have the chance to get some real hours in...
:)

[mutt]

BEgle you are right in saying that that the VC10 is a commercial airliner, I guess that I should have quantified a 4 engine wing mounted airliner!!!!!! <img src="wink.gif" border="0">

747FOCAL I sincerely wish that you try that profile in the sim, you might be surprised!

MUTT

[P22]

BEagle

The CAA removed the VC10 from my licence because they said that it was no longer in 'commercial' service. One of our (BOAC) VC10s suffered a double failure at RTOW on departure from Calcutta in 1970.
I think that the VC10 is one of the few large four-engine aircraft that could survive a double failure (as well as Concorde????). Certainly the 747-400 wouldn't stand a chance at anywhere near RTOW.

P22

[jbc2001]

Not sure if available thrust would be the critical factor. What about the loss of the vortex lift component from the wing? If memory serves, the aircraft rolled (stalled?) onto the burning wing. Wonder if any training sim would include a sufficiently accurate wing model to show the effects.

[BEagle]

basil - please reserve your vitriol for Manuel! I wasn't implying that the RAF's standards are necessarily 'higher', merely that to fly out of the DEFATO scenario safely and competently, you do need regular sim practice, etc - and you do NOT need a FE shutting down an engine which is producing thrust before you know that you can survive without that thrust. In any case, Nigel taught the RAF how to do it properly in the first place...

I certainly agree that a 2-e fail on a wing-mounted 4-jet at high AUW and at V2 would be far less likely to be survivable. The rear-mounted 4-jet design of the VC10 was economically less advantageous in the short term, but the design was probably inherently 'safer' until the advent of highly reliable ETOPS twinjets rendered commercial 4-jets somewhat unnecessary.

[ 01 January 2002: Message edited by: BEagle ]</p>

[Hand Solo]

I'm sure the fact that they had no hydraulics, the gear stuck down and only half a wing were rather more significant factors than the loss of thrust in two engines. Perhaps Jon Modrey would like to consider the Sioux City DC10 which only lost thrust in one engine but still didn't fly too well without any hydraulics. Of course, if Concorde was made and certified in America this subject wouldn't even have been raised!

[Agaricus bisporus]

HEY HEY HEY GUYS!

PLEASE!

This is important!

I am trying to ascertain if an unwarranted slur has been cast against one of the finest flying machines ever, and against the inherent integrity of our CAA, and people are bitching about whether an aircraft is one type or another beacuse of the colour of it's paint.

Someone said Concorde is one of the few certificated to fly on two engines. Is this in the take off case? Can you please substantiate that statement?

Secondly, the statement that a B747 cannot survive a double engine failure at limiting TOW, again, can I have a substantiation of this please.

I am not at all happy to see a thoroughly inaccurate seeming report rubbishing our government, our authority and the superlative product of the European aviation industry and all I ask you for is fact to back up a stiff letter to SA to put this matter to rest, and to put this MD FO back in his box if appropriate.

Accurate info requested, please.

(;

[Dick Deadeye]

Agaricus bisporus, a while back JF posted something that is worth reading (as always) about Concorde.
[quote]So far as Vzrc goes, the perhaps the following data may be of interest. It is for the aircraft at MTOW (185,070 kg) at LHR, on an ISA day with zero wind:

V1: 164 kts
Vzrc-3e-Gear Down: c190 kts (so not routinely calculated)
VR: 193 kts
V2: 215 kts
Vzrc-2e-Gear Up: 260 kts (Calculated for every departure)
Vzrc-2e-Gear Down: 316 kts (Above the sea level Vmo of 300 kts!)

My final comment: Just look at the jump in Vzrc when you go from three engines to two engines. About 70 kts. If the gear is stuck down that becomes an awesome 126 kts.<hr></blockquote>

My mate Nigel says that they fly the climb out at 250 kts, not V2, so not too far away from a two engined climb out capability, so long as the gear is up, but if the gear is down, then no chance!

If that **** Modrey really thinks that a B747-400 will climb away at MTOW after losing TWO engines and with the gear still down, then I hope I never fly on any airline he has anything to do with.

IT WILL NOT.

How he knows exactly what damage the Concorde sustained, and when, is also open to debate, along with his crassly stupid statement that any other four engined type would have survived to a safe landing.

Sounds like a new hire who knows the square root of f$ck all about large jet operations!

[carbheatcold]

I seem to recollect a number of years ago a Continental 747 (-100 or -200) suffering a double eng failure whilst departing LGW 26L and only just clearing the hills and the village of Rusper to the west dumping fuel in the process. He had been able to get the gear up I believe so reducing the drag but I am sure the whole thing was more about luck than judgement.

[BEagle]

atiuta - the certification of the VC10 was certainly to the exacting standards of the CAA at the time. The fact that it is still flown by non-civil users is nihil ad rem. But it was clearly not certificated to lose 2 engines simultaneously - and hence 50% of its thrust - in the same manner that, say, a 777 losing a single engine would be required to be today.

However, it was required to have sufficient excess thrust to survive the statistically assumed DEFATO likelihood placed upon it by virtue of the close-paired engine design. The difference between military and civil operation is merely that every military captain must practise a heavyweight double engine failure and 2-e approach in the simulator at least every 6 months - we have the luxury of sufficient simulator time available to be able to do so. Training captains also practise 2-engine work in the aircraft, but we only do so with the engines retarded to idle thrust once the landing gear is up, never simultaneously and never at a critical stage of flight; our student captains are required to cope with the simulated failure of an engine above V1 followed by a second failure once the aircraft is safely airborne, the landing gear is up and visual committal height has been achieved. Unlike the near simultaneous smacking closed of 2 HP cocks which Nigels used to have to cope with, so an old 8000+ hour BA VC10 man tells me!

The only 'beyond civil operation' which was once considered was the so-called Military Operating Standard which increased MTOW from 323000 to 340000 lbs if and when operationally essential. It came with various risk assessments; however, I don't think that it was ever used in anger and I don't think that it would ever be considered today.

Lastly may I ask that this pointless 'civil v. miltary' rhetoric is curtailed? It helps no-one, is unwarranted and utterly counter productive.

[ 02 January 2002: Message edited by: BEagle ]</p>

[Flap 5]

It is curious to know why Scientific American has used information from a First Officer with a minor carrier, are we missing something here? Does this chap have knowledge and experience beyond his rank? Could they not find someone more experienced and knowledgeable?

I fear that the answer goes back to the days when Concorde first flew and the American authorities made every effort to keep it out, because it had not been made by an American company. This article seems to be another crude attempt to discredit Concorde and it is all the more surprising in such a reputable magazine.

[buck-rogers]

I'm sure that loosing half your payload of fuel out of only one side of the aircraft would have contributed further regardless of the thrust issue. The imbalance would have had to be corrected with the elevons as tons of fuel poured out with increased drag screwing things up further. There comes a point I'm sure that you can't do any more no matter how much thrust you've got.

I think it should be applauded that the pilot and Concorde stayed up as long as they did rather than some sceptic bleating on and waving a slide-rule about. <img src="mad.gif" border="0">

[Budgie69]

I was never qualified for 3-engine ferries on the 747-400. If one of the select group of aviators who are is on the forum could they please put up some details of weights speeds, and technique.

[Speedbird48]

OK Guys, lets get away from the slanging match and the fact the the RAF may get more simulator time than civilians and look at a few facts.
The MD11 "expert" would perhaps like to try his airplane at MTOW with the gear stuck down, one engine out and T/O flap extended, with out losing a second engine. Losing hydraulics for the controls would add another factor that would not help. Although the three engines against four issue will be a factor.
Also as Gemini has only had MD11's for about two years and has only been in existance for three and he is an F/O must show something but then I am doing the slanging now!!
As one of the few Americans that was qualified on the VC10, it will indeed fly away on two at MTOW, BUT, only IF "everything" is in your favor. By thatI mean wind/temp./density alt/obstructions/pilot technique etc. PLUS of course that the Flying Pilot asks for the gear to be raised and/or the Non Flying Pilot does indeed raise the gear. So leave the Engineer screwing up part out of it, Beagle, pilots are not the almighty even if you are RAF! Actually if the two pilots forget I daresay, even in the RAF, the F/E would remind you to do it,if you would listen!
I also note the the publication that printed the letter is one of the "great" aviation magazines??
The A/F Concorde guys did their very best with what they were given and do not need to be outguessed by Monday Morning Quarterbacks.
If the airplane had rearview mirrors they might have been a bit better off but that is not reality.

[BEagle]

To be pedantic, if the VC10 has suffered a double engine failure with the landing gear down, the drill is not to raise it! So if the FP asks for the gear to be selected up, that call would certainly be challenged by the other pilot and by the FE! It's because the doors opening into the airflow will cause even more drag than if the gear is stuck down.....just when the last thing you want is any more drag. Also, the subsequent loss of hydraulics could well cause some of the landing gear to adopt a 'Grand Old Duke of York' position - neither up nor down!!

Sorry, FEs, I am most certainly not having a 'generic' dig at you guys as I really value your part in our crews. A dig, however, at any company whose CRM seemingly allows uncommanded engine shut downs. And finally, yes, pilots are indeed not almighty

[Genghis the Engineer]

A fascinating debate, although I'm sorry to say that I know little about the VC10 and less about the Concorde, from a professional level.

However, I would comment that suggestion that certain radical manoeuvres are flown in the sim, may be meaningless. Sims are designed to accurately simulate middle-of-the-envelope handling, they will extrapolate happily to all sorts of corners of the handling envelope, but this is rarely on the basis of actual flight test data.

Far too often something happens, and you later read "30 pilots all tried to achieve this in the sim, but couldn't, so the pilot in the actual case was superhuman", which is complete sphericals. The sim was probably not accurately representing what happened - because to do so somebody would have to go and obtain meaningful FT data. And, quite honestly, very few test pilots are that daft.

G

[polzin]

EASY! Hand Solo. This is not a American vs. British thread. Fact is that the Americans and the British figure performance differently. It has been ten years since I did a comparison of the two and Im sorry I cant say more, but I do remember that each system had its good points. In fact , after being taught the differences, I wondered why someone didnt combine the two and come out with a superior product.

I am now Y2 compliant !

[Sven Sixtoo]

To provide an example of Ghengis' point.

Some years ago I was involved in exploring the options in a Sea King post tail rotor failure. We found, in the sim, that it was perfectly possible starting from a 40' hover to pull pitch, climb vertically while ignoring the violently spinning visuals to 2000', then shut down the engines and execute a successful EOL. Curiously, we never wrote this technique up as advice to crews. <img src="eek.gif" border="0"> <img src="wink.gif" border="0">

[bblank]

It is a diversion from the main topic but Flap 5 raised some questions that, because they were so pointed, should receive answers.

It is curious to know why Scientific American has used information from a First Officer with a minor carrier

They didn't.

are we missing something here?

It seems.

Does this chap have knowledge and experience beyond his rank?

I'll let you pilots hash that out. The quoted item does not indicate knowledge of material factors in the accident but it may have been edited.

Could they not find someone more experienced and knowledgeable?

They could have but they weren't looking for anybody.

I fear that the answer goes back to the days when Concorde first flew and the American authorities made every effort to keep it out, because it had not been made by an American company.

Fear not.

This article seems to be another crude attempt to discredit Concorde

Nope - it was not an article.

and it is all the more surprising in such a reputable magazine.

Nope. Scientific American has a section called "News Scans" in which they report on items in the news that pertain to technology or science. In that section a few months ago they ran a positive news item on the return of the Concorde.

What was quoted here, essentially in its entirety, was a brief letter to the editor. The letter was critical of Scientific American's article. That would have been clear had the first few words of the letter been included but they were probably snipped because there would have been no context in PPRuNe. The editors of Scientific American perhaps felt that it was only fair play to air an opposing viewpoint. As usual, editors do not endorse the opinions of their readers even though they publish them.

In Scientific American the authors of major articles get a chance to rebut any readers' letters that are published. I do not think the authors of News Scans items get that opportunity and, Agaricus bisporus, it doesn't seem likely that you will either. Since the journal does not vouch for the opinions of its readers they have no reason to correct them.

[john_tullamarine]

An interesting thread, indeed. A couple of points, if I may ..

(a) I am not aware of any 3/4 engined aircraft which has been certificated on the basis of a dual failure during the early takeoff phase. In general, the weight penalty to permit this would be commercially non-viable.

However, there is an en-route requirement which looks at the situation of a second failure and perhaps this has caused some confusion. I suspect that the great majority of us who have flown 3/4-motored birds have done numerous local training exercises with the second failure occuring sometime typically in the third or fourth segment... energetically dumping, descending, re-configuring etc., with a sigh of relief when a shallow climb results ....

(b) There is a problem when people look at the published rules and then generalise. Two points are relevant...

(i) by agreement between the design organisation and the regulatory authority, the certification basis is frozen during the early design work up of a new Type. To do otherwise would be intolerable .. the certification goalposts would change position with each subsequent rulebook amendment.

(ii) it is not at all unusual for specific rules to be reworked for a specific certification exercise.

This usually arises where the aircraft has a problem meeting a particular requirement but the designer is able to negotiate some sensible horse trading with the authority on the basis of equivalent safety determinations to achieve a workable outcome. There are numerous examples of this.

One must refer to the SPECIFIC rules, at the particular issue, for a specific Type and, if you can get access to the variations, such determinations. Then you make any assessment of what was required and whether the design did or did not achieve that which was required.

In respect of the Concorde (and I have no specific knowledge of that design's certification) it would have been quite incredible if the performance rules had not been varied to accommodate the quite different aerodynamic characteristics of a delta when compared to the more conventional civil planforms for which the existing rules were developed.


The various airworthiness authorities may not get it right invariably. Mistakes can occur and not be picked up until later .. hence the various processes of certification reviews which have been imposed on some Types post introduction to commercial service. This appears to have been done in respect of the Concorde's tyre design and/or tank protection requirements following the accident.

Ladies and gentlemen, I do think that we have to rely on the airworthiness people having a reasonable degree of professional integrity ...

[ 02 January 2002: Message edited by: john_tullamarine ]</p>

[go with the flow]

Pruners

A very detailed explanation of Vzrc and other peculiarities of delta winged craft is to be found in the thread called vortex bursting, tech log.

[willbav8r]

I'm certainly no expert, but with all the hypothesising and analysing in this interesting thread, something made me think of the following;

If the *wing* is on fire then surely the "basic" aerodynamics of the airfoil have been compromised? Regardless of the fact that structurally there were problems, and a loss of thrust from the engine (s) caused a stall or loss of control, Mr Bernouli's principle must rely on there being air creating differences in pressure and thus - lift. But if air cannot flow over a wing, because it is engulfed in flames, don't we have a major factor missing from the equation?

Then a changing c of g, weight loss as the fuel burns/escapes and structural damage are also factors, not to mention loss of thrust, gear down, tailwind, AF 744 with dignitaries in view, wheel spacers missing, AD's not complied with, overweight (have I missed anything?)

Just a thought. Interested if this would be something taken into account?

[WOK]

Gentlemen: (and very probably ladies):

I understand the group dynamic that drives all this theorising, but it is becoming a rerun of the endless speculation immediately post-accident.

The report is out. It has been exhaustively written by experts who have all the available facts to hand. Regardless of one's personal prejudices (and I am no Francophile) it is a fact that the BEA is a well-respected and very experienced organisation.

'SC crashed because there was not enough thrust to overcome the tremendous drag in the flight regime it was in. It departed controlled flight in exactly the manner expected of a slender delta in such circumstances.
These are unarguable facts, governed by well-used laws of physics.

There really is no point in theorising alternative modes of departure.

I grant that it is possible to come up lots of 'what if's and 'if only's relating to how the aircraft came to be in that situation, and I know many will continue to do so.

Can I just ask that if you feel the need to contribute to that kind of discussion you base your contributions on known facts rather than what popular rumour/your mate's theory says happened. (In short - read the report before you claim it is wrong/ a whitewash/whatever).

As for the claim that TSS stds were written around Conc's performance - I suggest whoever wrote this researches when the elements of TSS were written relative to the flight test programme.

Of course they are different to conventional requirements - could you apply conventional defns of Vs and Vb, for example, to a wing which can see an alpha increase of 16 or so degrees from cruise conditions without stalling?

Finally: Double engine failures. I haven't flown a VC10. I have flown 747s and Concorde and I can tell you that the Conc is markedly more capable of dealing with a dbl failure at V1 at RTOW than a 747 *BUT* in both cases the chances of a successful outcome are very very slim indeed. The conc has a very good likelihood of flying through a dual failure at 500' successfully, more so than a 747, but so what? That didn't happen at CDG.

Anyone care to contribute something new?

[WOK]

It would be too long and boring to go into depth here, but:

Dealing with DP Davies' quote: it is true that AT TIMES certification and development were going on side by side. Read no more into the comment than that - don't forget that this is still true for any type which operates outside the current norms. As an example, take the 777: ETOPS on service entry - the certification requirements for ETOPS on entry were being developed at the same time as the aircraft and while it was being certificated. Also, don't forget what happened when the GE90 proved incapable of passing the 'blade off' test.

The 747 didn't have manual reversion on the flt controls and the certification requirements would have been changed to reflect this.

This type of refining of the requirements while types are under development is common to the point of normality - concorde was no exception.

The quotes are largely paraphrased in order to make the book accessible to a wider audience and a certain amount of reading between the lines is required.

In terms of performance margins, TSS reqs exceed equivalent BCARs or whatever, and manoeuvre margins hugely so.I believe this is also noted in the same book. There are many areas where TSS is more restrictive, which should demonstrate that there was no conspiracy to fudge the requirements.

The numbers emphatically are not fudged, and the fact remains that SSC has larger performance margins than subsonic long-haul aircraft.

If only the man himself was still here to give us the whole chapter and verse.

PS TSS is not a secret document - it is available in the public domain for perusal. Unfortunately the only hard copy I know of is owned by BA and is NOT available to the public!

[Dan Winterland]

In any aircraft with paired engines, it has to be an assumption that the catestrophic failure of one engine would be likely to lead to the failure of the adjescant one. Of the two types I have flown with paired engines, we used that assumption and trained for it regularly - it was a tricky situation but one that was surviveable if the correct techniques were applied.

One of these was the VC10, which was originally certified for this situation. It happened to BOAC twice to my knowledge, both times the aircraft landed safely.

The DEFATO (Double Engine Failure After Take Off) drill in the VC10 sim was one of the most demanding things I have ever done, but regular practice was necessary IMHO.

[4dogs]

Folks,

Jon Modrey, an MD11 FO with Gemini Air Cargo from Orlando, FLA has done most of us a favour.

He has demonstrated that assertions of aviation "fact" will be tracked down and debated at length on these fora.

I was a little surprised that no one brought up the fact that the FAA varied the performance requirements of the B767-300 due to Vs1g testing rather tyhan Vs testing and the fact that it would be commercially unfortunate if the "new" aeroplane looked like having worse/different numbers to the -200. Furthermore, the changes made to accommodate the B777 were not a reflection of aerodynamic differences such as faced by DGAC/CAAUK with slender delta and supersonics - perhaps that may have been a more fruitful question for Jon to pursue.

Most importantly, as a consequence of his writings, I now know the name of TSS, the existence of which I was aware. I am also happy to know that WOK's assertion: "In terms of performance margins, TSS reqs exceed equivalent BCARs or whatever, and manoeuvre margins hugely so...The numbers emphatically are not fudged, and the fact remains that SSC has larger performance margins than subsonic long-haul aircraft." is relatively easily verified and, I think, very unlikely to be found untrue.

For all of that, I must thank Jon and his letter to the editor.

PS Perhaps after Jon has read FAR 25 and its amendment history, plus the squillions of ADs and other supporting documents about compliance with that FAR, he might get the most politically controlled and manipulated regulator outside the old Communist blocs to test real knowledge of the certification requirements of the aircraft in which he apparently occupies an important seat.

[john_tullamarine]

R4D .... great to see you are still in the land of the living ... have you been on holidays ? ... and I trust that the day at the Bend went well.

Without checking my archives I cannot be certain as to just when it came in, but I suspect that the alternative stall demonstration requirement quite predated the 763 ?

Your main point .. that the pprune board promotes debate remains very valid .. I suspect that we all learn quite a lot from these pages.

[Bullethead]

The B747-400 can, at MTOW and up to about 30C, suffer an engine failure after V1 and then a further engine failure, on the same side, shortly after Vr and successfully climb away if the first thing you do is select flaps to 10 regardless of the speed. You will be below F10 manoeuver speed but you have to get rid of some drag and accelerate. If you persist with trying to fly with F20 still selected you probably make a very large black hole somewhere. Not a recommended procedure of course but if saves your ar$e one dark and dirty night who cares? <img src="eek.gif" border="0"> <img src="eek.gif" border="0">

[4dogs]

JT,

As you know, consultants don't have holidays, they just have interludes in the work programme! Unfortunately, I missed the Bend as one of ny VSCs (very significant client) required my presence elsewhere.

Yes, the change permitting Vs1g did predate the B763 but postdated the amendment applicable to the original TC. The problem may have been triggered by CAAUK certification requirements, I am not sure. In any case, those students of FAR 25 and its clones will find that the numbers do not add up - Boeing negotiated a slightly different set of ratios and margins with the good ole FAA.

As for the comments about what B744s will do - I think the main thrust of the topic was certification requirements, of which none that I am aware require guaranteed performance in the event of suffering a second engine failure during the take-off sequence if the risk assessment indicates that secondary damage is highly improbable.