Configuration Warning near V1. Continue or stop?

[Empty Cruise]

RYR-738-JOCKEY,

Yes, I think we do need a discussion on weather it is safe to abort at V1... My question to start this off is: if you consider it unsafe to abort at V1, why then did you choose a V1 that you don't consider it safe to abort from?

Also, the definition of "safe" is up for debate. Is a 20 kts overrun into the approach lights at the other end unsafe? Is departing with retracted slats safe?

I think it is time these near-V1-reject-debates are put into perspective - if you're not comfy aborting from V1, you've got the wrong speed! If you feel it's safer to continue with a 0,1% chance that the aircraft is no longer in the take-off configuration, priorities might need be re-arranged. Damaging the undercarriage, gear doors and lower fuselage in an overrun - but having everyone walk away - is an option (albeit not on every runway - so the V1 should be set accordingly).

Empty.

[alf5071h]

Empty Cruise don’t try to double think the regulations and SOPs. Over many years of experience, the authorities and industry have debated the safety of RTOs. The accident data shows that the human making the decision is the weakest link.
See all of the text in FAR 25.109, note para (e) … determine the accelerate-stop distance if that means--
(1) Is safe and reliable;
(2) Is used so that consistent results can be expected under normal operating conditions; and
(3) Is such that exceptional skill is not required to control the airplane.
And also note para (h). If the accelerate-stop distance includes a stopway with surface characteristics substantially different from those of the runway, the takeoff data must include operational correction factors for the accelerate-stop distance. The correction factors must account for the particular surface characteristics of the stopway and the variations in these characteristics with seasonal weather conditions (such as temperature, rain, snow, and ice) within the established operational limits.

[john_tullamarine]

chornedsnorkack,


... the safety margins ... are not necessarily assured .. in case of any other failure condition

Depends on the A/L pertaining to the certification .. but that, together with variation in environmental conditions (esp runway surface), is the crux of the worries one should have ...


.. there is no "safe side" of V1 ... the certification assumption is that rejecting at any speed after V1 is unsafe ...

I suggest this misses the underlying point and principal real world risk concern.

The V1 concept (similar to much of the handling and performance aspects of certification) puts one of a set of lines in the sand. If the certification boundary conditions are replicated, then it is valid to presume a reasonable correlation between the certification data and the real world .. if not, then such a presumption will be tenuous to an extent reflecting the divergence.

If the particular runway condition is similar to the certification presumptions AND is distance limited for ASDR, then an accel-stop with a speed excursion likely will be fraught with an unpleasant lack of success .. the consequences are related to the particular environment only and have naught to do with the certification. If, on the other hand, the TODA/TORA is comfortably not limiting (ie not BFL limited), continuing with a delta below V1 (presuming Vmcg is not limiting) likely may be quite successful. In a similar manner, one can argue the complementary situation with limiting TODA/TORA, but non-limiting ASDR.

However, procedurally (ie from an SOP point of view), using the above argument is quite unacceptable as a general principle.


.. should then one make the assumption that ... warnings in critical flight phase should be assumed to be false warnings? That sounds a dangerous assumption.

Couldn't agree more. Two factors at work here ..

(a) procedurally, unless there is reliable evidence to indicate that a warning is false, it should (must ?) be considered valid

(b) historical reality is that many warnings are false and this needs to be considered in the captain's decision making process where there is time to reflect on multiple courses of action.

[Centaurus]

Further to the original post about going near V1and a configuration warning, the recent up-dated edition by Boeing for the FCTM B737-200, April 2005, makes an interesting distinction between low and high speed configuration warning. Quote in part: "Prior to 80 knots, the take off should be rejected for any of the following:
Activation of the master caution system.
System failure(s).
Unusual noise or vibration.
Tire failure.
Abnormally slow acceleration.
Unsafe configuration warning.
Fire or fire warning.
If the airplane is unsafe or unable to fly.

After 80 knots and prior to V1, the take off should be rejected for any of the following:
Fire or fire warning.
Engine failure.
If the airplane .is unsafe or unable to fly" Unquote.

I may be reading more into it than was intended by Boeing, but notice that there is no mention specifically after 80 knots of rejecting for an unsafe take off configuration warning. It is of course left to pilot judgement if he considers the aircraft is unsafe or unable to fly. This would perhaps tie in with a previous Pprune comment on this thread where Boeing suggested that a take off configuration warning nearing V1 was not necessarily a cause to reject the take off. Naturally Boeing cannot cover every conceivable eventuality and one presumes therefore it is odds on that a late configuration warning is a false warning.

[RYR-738-JOCKEY]

Centaurus wrote: "This would perhaps tie in with a previous Pprune comment on this thread where Boeing suggested that a take off configuration warning nearing V1 was not necessarily a cause to reject the take off. Naturally Boeing cannot cover every conceivable eventuality and one presumes therefore it is odds on that a late configuration warning is a false warning."

Frankly speaking, getting closer to V1 should not require more thought processing from the pilots. As an FO my job is to call out any failures. And I expect that my CP acts according to SOP. If close to V1 and the config warning sounds and it is "not neccesarily a cause to reject the take-off", who shall check the STAB/FLAPS/PARK BRAKE/SPEED BRAKE? My point being, I simply cannot see that there is enough time available to assess the situation.

[Empty Cruise]

alf5071h,

Sorry if I did not make myself clear enough - I advocate following yours and JTs advice and going with the numbers, and definitively not doing any second-guessing or double-thinking. In line with that, I take the liberty of questioning those who want to portrait a near-V1-reject as an unsafe manoeuvre which - although demanding - it clearly is not.

My protestations are against those who'd "take the chance, since said chance is so small" that the aircraft is still in the take-off configuration rather than aborting the take-off near V1. If your AFM says that high-speed T/O config warnings should be considered invalid, by all means, that is what we do. If your AFM hasn't got any such statements in it (and your SOP is not specific either), in my view there can be only one call - and that's "stop". You'd end up looking rather silly (and possibly looking slightly dead) having a config warning at V1-10 and then continuing only to find out that the aircraft is unflyable at Vr+10 and then trying to stop from that speed, right?

On the other hand - even if you bungle the reject and run over at 20 kts. - will you be better or worse off than if you continued with the slats retracted, or the stab out of trim? It might just be me, but I find the answer to this question fairly obvious. If you consider only "damage to aircraft", I recognise that the "continue"-crowd have statistics on their side. If you however consider "survivability", I know that the "stop"-mentality puts us in a much safer place. I have not done the maths, but it would be interesting to compare the numbers of fatalities on "mishandled rejects prior to V1" vs. "should not have attempted to leave the ground".

If people feel that a V1-reject is of questionable outcome, that alone is in my view and indication that these people are mentally aligned with the "call-V1-early-crowd" (debated at length elswhere). I suggest you might be better off not derating to the maximum but rather select a lower derate and/or V1 to keep the V1/Vr/V2 relationship intact. So to sum up my view: Fly the numbers, know your AFM, FCTM & SOP - and make your decisions accordingly. Don't make assumptions about the flyability of your aircraft.

Empty

[chornedsnorkack]

Originally Posted by Empty Cruise

On the other hand - even if you bungle the reject and run over at 20 kts.

With a bungled reject, is it actually very probable?

At 20 knots, an aircraft with good braking should be able to stop in less than 20 metres. With poorer circumstances like ice or hydroplaning, this could take longer, but still... an aircraft might come to full stop "five feet" or so before an obstacle, as in the (fictional!) Airport, but it is much more likely either to stop completely hundreds of metres before the end - or far after the end.

So, the consequences of overrun at high speed are not always trivial.

On the other hand, finding the craft unflyable is still worse.

Also, an aircraft at V1 in runway-limited load has spent around 60 % of runway and only 40 % is left for stopping. An aircraft which lands has about 100 %. But continuing a takeoff with flyable craft may be setting up the need to perform an overweight landing...

[Empty Cruise]

Chornedsnokack,

Agreed, 20 kts. might be unrealistic - so let's call it 60 or 80 kts. Even so, the vast majority of airports have RESAs that will damage the aircraft, but not beyond survivability. On those where that is not the case (KIL & FAE spring to mind), you go with the lowest safe V1.

However, at those very same airports - I really don't fancy my chances at FAE if I have to abort at Vr +5 because the aircraft did turn out to be unflyable... and the locals down at the foot of the hill prolly don't fancy a visit by an out-of-control-aircraft (God knows them people have seen some hairy tings happening to aircraft already).

Just my 2 kronurs worth

[AirRabbit]

Keep that attitude!

Originally Posted by Empty Cruise

GlueBall,
I take it your remark was rather tounge-in-cheek. If not, please expand on that philosophy - I'm eager to learn. I was just brought up with this wimpy "Train the way you fight - fight the way you train"-attitude that is obviously past its sell-by-date
Empty

Without even getting close to a tongue-in-cheek comment, there isn't anything "wimpy" about that attitude. Those of us who have been "in the business" for more than a few decades (at least those of us who really care - and Centaurus is certainly one!) have been trying unceasingly to instill that very attitude in all pilots; i.e., train the way you fly, and fly the way you train. Unfortunately, it wasn't until the advent of what I would call "modern simulation" (within the last 15 years or so) that really allowed this to be done in earnest. Training in an airplane doesn't really lend itself to proper or compete training and there are specific and documented reasons for this. In today's environment, the idea of having two sets of skills (relying on one in a simulator and the other in the airplane - which tends to get confusing in circumstances when split-second decision making is required) is an outmoded and a "detrimental-to-your-health" idea that should be expunged from every airplane training curriculum.
While I certainly don't mind having serious discussions punctuated every once-in-a-while with a little levity, sometimes "light-hearted" comments can be taken the wrong way. That is why I am glad that you had the temerity to ask the question you did - and it's why I jumped on your comment so quickly. Flying is one of the most rewarding and exciting and entertaining things humans can do (note, I did say "one" of the things...), but it is also tremendously challenging - especially when doing it as a professional - and as expansive as is the "wild blue yonder," it is no place for anything less than professional action all the time. And, speaking for those of us for whom the "art" of flying comes only with great practice and diligence (as opposed to those rare few who are "natural" pilots), let me encourage you that "practicing" anything with less than the attitude you've learned is certainly NOT wimpy. Ignoring that kind of attitude not only takes away valuable time from learning and practicing what is necessary and proper, it also more than likely reinforces incorrect decision making. There are a lot of folks who say, with varying degrees of tongue-in-cheek thought, "I'd rather be lucky than good." If you (not "you" specifically, but anyone), if you fly and you are depending on being "lucky," you're in the wrong business.
Keep that attitude, my friend, and don't let anyone talk you out of it!
______
AirRabbit

[Ignition Override]

Capt Claret: in 1979, following failure of an American Airlines DC-10 engine pylon, with separation of the engine and damage to the leading edge, one slat retracted.

But the crew had no indication of the change. They only thought that the engine had flamed-out, until the plane rolled out of control.

Maintenance technicians at the Tulsa facility used a very wrong procedure to change the engine under the wing.

[chornedsnorkack]

Originally Posted by Ignition Override

Capt Claret: in 1979, following failure of an American Airlines DC-10 engine pylon, with separation of the engine and damage to the leading edge, one slat retracted.
But the crew had no indication of the change. They only thought that the engine had flamed-out, until the plane rolled out of control.

Had the crew immediately realized that one slat was retracted, could they have done anything to keep roll control?

[Centaurus]

Chorned etc. Lower the nose and increase speed. Or reduce the thrust on the other engine at the same time lowering the nose for more speed. It may be a balancing act, but anything as long as the roll is stopped.