Configuration Warning near V1. Continue or stop?
And then one day your non-standard '15 kts' becomes what? 20...., 30...?
Probably the most potentially dangerous, non-SOP attitude I've read on this thread.
NigelOnDraft and qwertyuiop have the correct answer!
Probably the most potentially dangerous, non-SOP attitude I've read on this thread.
NigelOnDraft and qwertyuiop have the correct answer!
ECON cruise, LR cruise...
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Bafanguy,
Have had uncommanded flap retraction in a small TP - on a 1300 m runway. Thank God, it occured at V1 -15 kt. and we stopped quite easily - but I sure as hell didn't have time to look around and see what had caused the horn to start blaring. It turned out that flap maintenance had been carried out during the night, and some of the microswitches had been locked out. I took this incident to prove that two things can and do go wrong at the same time
.
Ever since then, I subscribe to the same school of thought as qwertyuiop
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Have had uncommanded flap retraction in a small TP - on a 1300 m runway. Thank God, it occured at V1 -15 kt. and we stopped quite easily - but I sure as hell didn't have time to look around and see what had caused the horn to start blaring. It turned out that flap maintenance had been carried out during the night, and some of the microswitches had been locked out. I took this incident to prove that two things can and do go wrong at the same time
.Ever since then, I subscribe to the same school of thought as qwertyuiop
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Ten plus years ago, the company I worked for suffered a series of high speed aborts on the 767 fleet due to config warnings arising late in the takeoff roll. The eventual cause was traced to moisture in certain "cards" in the E&E compartment.
The official word from Boeing was: If the config warning hasn't sounded in the low speed regime, DON'T STOP if it sounds later in the takeoff.
The official word from Boeing was: If the config warning hasn't sounded in the low speed regime, DON'T STOP if it sounds later in the takeoff.
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Definition of V1
Originally Posted by qwertyuiop
Surely the answer is;
If you get a Config warning before V1 the aircraft CAN stop, but may not fly. Unless you brief otherwise you STOP.
If you get a Config warning before V1 the aircraft CAN stop, but may not fly. Unless you brief otherwise you STOP.
On a runway, there is a speed above which a plane that aborts will overrun. V1 should not be more than this.
There also is a speed under which the plane cannot fly with a very well defined single-point failure - namely 1 critical engine out, all other systems intact. The cause of being not allowed to fly might be inability to accelerate with the good engine/s to climb above the screen height by the end of runway, or clear obstacles further on flightpath. Or else the inability at slow airspeeds to keep the aircraft on runway against asymmetric thrust plus crosswind.
"Balanced field length" seems to be the length of runway where there are no margins of safety over and above the accelerate-stop distance. An aircraft could take off from a shorter runway, but is not allowed to, because there is a stretch of takeoff where one engine out would cause a certain crash.
Whereas if the craft takes off from a longer runway, there would be a stretch where both aborting and continuing would be safe... there would be leeway for pilot judgment what to prefer, no?
But BFL and V1 are defined by reference to a specific one-point failure - one engine inoperative. Configuration warning is a quite different error condition.
Examples to wrong configuration causing crashes include the Chinese Bae 146, as well as the first 747 to crash in Nairobi. In Nairobi, the slats did not deploy - the aircraft got airborne, but stalled past the end of runway and crashed with many deaths.
Did the pilots at Nairobi have (and miss) any chance to realize what happened and abort?
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"Balanced field length" seems to be the length of runway where there are no margins of safety over and above the accelerate-stop distance ...
I think that you are trying to make BFL into something more complex than it is .. viz., just a convenient procedure which makes the result of the AFM calculation, however performed ...
ASDR = TODR (TODR being whichever TOD case is most limiting)
no more, no less.
Its only real value is that it gives the quickest calculation and/or the simplest derivation of the speed schedule.
I think that you are trying to make BFL into something more complex than it is .. viz., just a convenient procedure which makes the result of the AFM calculation, however performed ...
ASDR = TODR (TODR being whichever TOD case is most limiting)
no more, no less.
Its only real value is that it gives the quickest calculation and/or the simplest derivation of the speed schedule.
Thread Starter
Essential Buzz. Your reply quoting a Boeing advice on the matter certainly has got my attention. I suppose you wouldn't have that advice on paper would you? It opens up the subject more than I thought. Please PM me with the info or where I could lay my hands on it. Where there is runway length well in excess of the balanced field length content especially allowing for reduced braking on wet or slippery runways then the abort decision may not be critical, although it may frighten the passengers. I sometimes wonder if pilots are fully aware of how much runway is to spare and keep it up their sleeve for a nasty event.
Simulator instructors occasionally see things that horrify them when it comes to rejected take off actions and I have no doubt in my mind that in the real event the chances are delays will occur due indecision and dare I say momentary shock and incompetency and an over-run occurs. Depending on the over-run area characteristics (road, ditch, cliff edge and you name it), someone is going to get hurt. There is no shortage of documentary evidence on this subject going back fifty years in old ICAO Accident Reports.
A high speed rejected take off on minimum runway length is something of a gamble that all actions are faultlessly executed. A decision to continue in the case of a late config warning is also a gamble. Historically the former has resulted in more fatalities than the latter. Or so I believe personally, anyway.
Simulator instructors occasionally see things that horrify them when it comes to rejected take off actions and I have no doubt in my mind that in the real event the chances are delays will occur due indecision and dare I say momentary shock and incompetency and an over-run occurs. Depending on the over-run area characteristics (road, ditch, cliff edge and you name it), someone is going to get hurt. There is no shortage of documentary evidence on this subject going back fifty years in old ICAO Accident Reports.
A high speed rejected take off on minimum runway length is something of a gamble that all actions are faultlessly executed. A decision to continue in the case of a late config warning is also a gamble. Historically the former has resulted in more fatalities than the latter. Or so I believe personally, anyway.
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Originally Posted by Centaurus
Essential Buzz. Your reply quoting a Boeing advice on the matter certainly has got my attention. I suppose you wouldn't have that advice on paper would you? It opens up the subject more than I thought. Please PM me with the info or where I could lay my hands on it. Where there is runway length well in excess of the balanced field length content especially allowing for reduced braking on wet or slippery runways then the abort decision may not be critical, although it may frighten the passengers. I sometimes wonder if pilots are fully aware of how much runway is to spare and keep it up their sleeve for a nasty event.
Originally Posted by Centaurus
Simulator instructors occasionally see things that horrify them when it comes to rejected take off actions and I have no doubt in my mind that in the real event the chances are delays will occur due indecision and dare I say momentary shock and incompetency and an over-run occurs.
Originally Posted by Centaurus
Depending on the over-run area characteristics (road, ditch, cliff edge and you name it), someone is going to get hurt.
Originally Posted by Centaurus
There is no shortage of documentary evidence on this subject going back fifty years in old ICAO Accident Reports.
A high speed rejected take off on minimum runway length is something of a gamble that all actions are faultlessly executed. A decision to continue in the case of a late config warning is also a gamble.
A high speed rejected take off on minimum runway length is something of a gamble that all actions are faultlessly executed. A decision to continue in the case of a late config warning is also a gamble.
Whereas continuing is a much bigger gamble. The plane might take off and climb with no problems if the warning was false alarm. Or the plane might barely pass the screen or obstacles, yet make no contact and suffer no damage, and eventually land unhurt. Or alternatively, the plane might hit something at a great speed, trying desperately to gain speed and climbing capability above V2, or enter stall or spin.
Originally Posted by Centaurus
Historically the former has resulted in more fatalities than the latter. Or so I believe personally, anyway.
chornedsnorkack I suggest that you revisit your performance course notes, or review the Airbus advice: Getting to grips with aircraft performance (pdf 7.88mb)
Also see the FAA Take off training safety aid.
And Certification rules for large aircraft, (pdf 4.1mb) CS25.101 page 10 onwards deals with performance.
If anyone wishes to do their own ‘in service’ flight testing then see: Flight test guide for certification of transport category airplanes, (pdf 3.3mb) page 71 onwards.
Also see the FAA Take off training safety aid.
And Certification rules for large aircraft, (pdf 4.1mb) CS25.101 page 10 onwards deals with performance.
If anyone wishes to do their own ‘in service’ flight testing then see: Flight test guide for certification of transport category airplanes, (pdf 3.3mb) page 71 onwards.
Moderator
chornedsnorkack,
(a) may I echo alf5071h's observations ...
(b) Logically speaking, using a single V1, or a single other speed decision point, whether V1-15, V1-20, V1-30... means neglecting to take account of how much or how little there is excess runway length to spare
Having selected a V1, the AFM data provides a certification distance for a set of cases - ASDR, TODR (AEO, OEI), TORR (AEO,OEI) etc. It is then a matter of the ops eng (or pilot) repeating the calculation a few times to match the AFM data to the particular runway environment. This can be done conservatively (ie all the cases fit but RTOW is not optimised) or to the optimally limiting case (in which the case the RTOW is maximised).
(c) I think official V1 and BFL numbers are supposed to incorporate pilot reaction time somewhere, setting it as 2 seconds. If you think it is going to be more, like 3 or 4 seconds or whatever, you might try and estimate the results - with accompanying changes to V1, BFL, MTOW
The reaction times vary with the Design Standard version relevant to the particular Type's certification. The specifics are in the individual distance data items (eg ASDR). Particularly with older Standards, the fat is less and the pilot's flexibility (near V1) reduced. If one desires any given time delay during the accel-stop transition, that is fairly straightforward .. but not for estimating ... calculating.
(d) Whereas continuing is a much bigger gamble
Probably we are more interested in risk outcomes than the gamble per se. Regardless, the historicals suggest that your postulate is false in that, for near V1 failures on limiting runways, the probability of an acceptable outcome appears to be weighted towards the GO option. One should also qualify comments by considering whether the case in question is a limiting runway and, if so, which case is limiting. In the conservative case of a grossly non-limiting runway, the arguments can become academic/legal procedural.
(a) may I echo alf5071h's observations ...
(b) Logically speaking, using a single V1, or a single other speed decision point, whether V1-15, V1-20, V1-30... means neglecting to take account of how much or how little there is excess runway length to spare
Having selected a V1, the AFM data provides a certification distance for a set of cases - ASDR, TODR (AEO, OEI), TORR (AEO,OEI) etc. It is then a matter of the ops eng (or pilot) repeating the calculation a few times to match the AFM data to the particular runway environment. This can be done conservatively (ie all the cases fit but RTOW is not optimised) or to the optimally limiting case (in which the case the RTOW is maximised).
(c) I think official V1 and BFL numbers are supposed to incorporate pilot reaction time somewhere, setting it as 2 seconds. If you think it is going to be more, like 3 or 4 seconds or whatever, you might try and estimate the results - with accompanying changes to V1, BFL, MTOW
The reaction times vary with the Design Standard version relevant to the particular Type's certification. The specifics are in the individual distance data items (eg ASDR). Particularly with older Standards, the fat is less and the pilot's flexibility (near V1) reduced. If one desires any given time delay during the accel-stop transition, that is fairly straightforward .. but not for estimating ... calculating.
(d) Whereas continuing is a much bigger gamble
Probably we are more interested in risk outcomes than the gamble per se. Regardless, the historicals suggest that your postulate is false in that, for near V1 failures on limiting runways, the probability of an acceptable outcome appears to be weighted towards the GO option. One should also qualify comments by considering whether the case in question is a limiting runway and, if so, which case is limiting. In the conservative case of a grossly non-limiting runway, the arguments can become academic/legal procedural.
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I'm with qwertyuiop,
Surely you should react as briefed, that's the point of V1, if a config sounding horn is an abort then you abort. If it happens at V1 or above then you take off. The whole point of V1 is to remove the processing time for the pilot during a critical phase of flight. You mention all things that are a stop and stop if ANY of them happen.
Just be very clear in your take off brief what your intentions are.
Surely you should react as briefed, that's the point of V1, if a config sounding horn is an abort then you abort. If it happens at V1 or above then you take off. The whole point of V1 is to remove the processing time for the pilot during a critical phase of flight. You mention all things that are a stop and stop if ANY of them happen.
Just be very clear in your take off brief what your intentions are.
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Originally Posted by alf5071h
the Airbus advice: Getting to grips with aircraft performance (pdf 7.88mb)
Also see the FAA Take off training safety aid.
Also see the FAA Take off training safety aid.
The FAA takeoff safety aid seems to complain (in 1993) that data to estimate actual speed where the takeoff could be safely aborted from a non-runway-limiting-weight case are often not available. Is it still the case?
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Aircraft at hight gross weights on limiting runways will do better in the air than trying to stop on the runway remaining.
Mutt
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Like all generalisations, the hurt is in the detail. Not such a simple matter, I fear ... consider turbulence, for instance, and whatever get up and go you may have thought you had has just got up and gone ....
The main protection is that we don't have very many critical flight phase failures .. it is always most important to keep in mind very firmly the fact that the book data is based on reasonably good conditions .. turbulence, shear, inversions, speed control etc., for OEI climb are the killers ...
The main protection is that we don't have very many critical flight phase failures .. it is always most important to keep in mind very firmly the fact that the book data is based on reasonably good conditions .. turbulence, shear, inversions, speed control etc., for OEI climb are the killers ...
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Centaurus - Sadly I have no documentary evidence to support my reference to Boeing's feedback. At the time discussions were definitely held between the Fleet Manager's Office and the manufacturer, but this was only summarised by way of a Notice to Crew, or similar.
Ironically, I was (unsuccessfully) seeking a copy of that very notice some years later as the same company had a different policy on their 737 fleet! (Anecdotally, I understand the 737 has had similar false config warnings - also due to corruption of circuit boards buried somewhere in the E&E compartment.)
As an aside, I wonder about the possibility/likelihood of a slat retracting during the takeoff roll. Even if it is possible, I would have thought a "slat-generated" warning would be much more likely to be caused by a problem with a micro-switch/proximity sensor instead of something that should be hydraulically locked in place.
In the end, it all gets down to "balance of risk", which is invariably assessed with the wisdom of hindsight!
Ironically, I was (unsuccessfully) seeking a copy of that very notice some years later as the same company had a different policy on their 737 fleet! (Anecdotally, I understand the 737 has had similar false config warnings - also due to corruption of circuit boards buried somewhere in the E&E compartment.)
As an aside, I wonder about the possibility/likelihood of a slat retracting during the takeoff roll. Even if it is possible, I would have thought a "slat-generated" warning would be much more likely to be caused by a problem with a micro-switch/proximity sensor instead of something that should be hydraulically locked in place.
In the end, it all gets down to "balance of risk", which is invariably assessed with the wisdom of hindsight!
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Originally Posted by john_tullamarine
Like all generalisations, the hurt is in the detail. Not such a simple matter, I fear ... consider turbulence, for instance, and whatever get up and go you may have thought you had has just got up and gone ....
The main protection is that we don't have very many critical flight phase failures .. it is always most important to keep in mind very firmly the fact that the book data is based on reasonably good conditions .. turbulence, shear, inversions, speed control etc., for OEI climb are the killers ...
The main protection is that we don't have very many critical flight phase failures .. it is always most important to keep in mind very firmly the fact that the book data is based on reasonably good conditions .. turbulence, shear, inversions, speed control etc., for OEI climb are the killers ...
a) the book data are based on a rather specific failure condition - OEI and all other systems intact? And that therefore, the safety margins certified in case of OEI are not necessarily assured to be available in case of any other failure condition, like wrong configuration?
b) that there is no "safe side" of V1 in the case of balanced field/runway limited takeoff weight, because the certification assumption is that rejecting at any speed after V1 is unsafe (overrun) and continuing at any speed below V1 also is unsafe (whether through inability to climb to screen height with OEI, or through veering off the side of runway due to asymmetric thrust of the good engine/s)?
The main protection is that we don't have very many critical flight phase failures ..
[QUOTE=Centaurus]In most take off safety briefs the mention is made of the various events that warrant a rejected take off. A Take off configuration warning is one of those events.
If rejecting the take-off for the TOC warning is part of your companies SOPs, and the Pilot briefed that (s)he would reject the take-off for a TOC warning then they should rejected the take-off.
Rejecting before V1, all the data shows that you will stop safely.
It is also dangerous to try and take comfort from the fact that you got away with it the simulator, the aeroplane may perform somewhat differently. The Lufthansa crash off RW 24 Nairobi in the '70s was attributed to the lack of deployment of leading edge devices, a stark reminder as to just how critical LE devices are to low speed lift.
If rejecting the take-off for the TOC warning is part of your companies SOPs, and the Pilot briefed that (s)he would reject the take-off for a TOC warning then they should rejected the take-off.
Rejecting before V1, all the data shows that you will stop safely.
It is also dangerous to try and take comfort from the fact that you got away with it the simulator, the aeroplane may perform somewhat differently. The Lufthansa crash off RW 24 Nairobi in the '70s was attributed to the lack of deployment of leading edge devices, a stark reminder as to just how critical LE devices are to low speed lift.
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Back to the topic. I see that different pilots apply different interpretations of a situation which ideally should be treated exactly in the same manner. The T/O config warning in my craft sounds if:
-trailing edge flaps are not in the flaps 1 through 25 T/O range, or
-leading edge devices not configured for T/O, or
-speed brake lever not in the down position, or
-spoilers not down with the speedbrake lever in the down position, or
-parking brake is set, or
-stab trim not set in the T/O range
So FLAPS, STAB TRIM, PARK BRAKE, SPEEDBRAKE not in T/O config. I would say that all warnings should be treated without any assumption that it may be a nuisance warning. And furthermore if you get THIS warning the aircraft IS unsafe to fly, hence the trigger-sources.
So, below V1: Abort. One can dispute weither an abort at V1 is safe or not, but one should not treat abort cases as if they can be independently evaluated from case to case. That is what causes trouble...when pilots have different ways of assessing a particular situation. Stick to your SOP.
-trailing edge flaps are not in the flaps 1 through 25 T/O range, or
-leading edge devices not configured for T/O, or
-speed brake lever not in the down position, or
-spoilers not down with the speedbrake lever in the down position, or
-parking brake is set, or
-stab trim not set in the T/O range
So FLAPS, STAB TRIM, PARK BRAKE, SPEEDBRAKE not in T/O config. I would say that all warnings should be treated without any assumption that it may be a nuisance warning. And furthermore if you get THIS warning the aircraft IS unsafe to fly, hence the trigger-sources.
So, below V1: Abort. One can dispute weither an abort at V1 is safe or not, but one should not treat abort cases as if they can be independently evaluated from case to case. That is what causes trouble...when pilots have different ways of assessing a particular situation. Stick to your SOP.