Is V1 called 'Decision Speed' or 'Action Initiation Speed'?
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Is V1 called 'Decision Speed' or 'Action Initiation Speed'?
I always thought V1 was called the 'Decision Speed' but according to an airline (Boeing) pilot, the correct name for V1 is 'Action Initiation Speed'.
Every book/online resource I have refered to says that V1= Decision Speed. I have never come across this 'Action Initiation Speed' term. Now I know that the action should have been initiated before V1 is reached but you can also say that the decision needs to be taken before V1 is reached.
Can somebody please tell me what the correct term for V1 is?
I'm asking because there was a question in a recent airline exam I had taken asking for the correct term for V1. I marked 'Decision Speed'.
Every book/online resource I have refered to says that V1= Decision Speed. I have never come across this 'Action Initiation Speed' term. Now I know that the action should have been initiated before V1 is reached but you can also say that the decision needs to be taken before V1 is reached.
Can somebody please tell me what the correct term for V1 is?
I'm asking because there was a question in a recent airline exam I had taken asking for the correct term for V1. I marked 'Decision Speed'.
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hawtin
I have not herd the term action initiated speed but it is correct to say V1 is the maximum speed at which first action to reject take off is taken. You do not decide at V1. Decision speed is the older definition of V1.
I have not herd the term action initiated speed but it is correct to say V1 is the maximum speed at which first action to reject take off is taken. You do not decide at V1. Decision speed is the older definition of V1.
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It is still termed as decision speed. Below is reproduced from Airbus document.
V1: Decision Speed
V1 is the maximum speed at which a rejected takeoff can be initiated, in the event of an
emergency. Additional information on this “Go/No-Go” decision can be found in the
Flight Operations Briefing Note entitled
V1: Decision Speed
V1 is the maximum speed at which a rejected takeoff can be initiated, in the event of an
emergency. Additional information on this “Go/No-Go” decision can be found in the
Flight Operations Briefing Note entitled
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From FAR Part 1, Sec.1.2, Abbreviations and symbols:
V 1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V 1 also means the minimum speed in the takeoff, following a failure of the critical engine at V EF , at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.
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So what IS the correct term for V1? Airbus says 'Decision Speed', Boeing Pilot says 'Action Initiation Speed'. FAA says something else. Transport Canada has another definition, Indian DGCA says..er..well..nevermind..
Last edited by hawtin; 24th Jul 2013 at 17:12.
I reckoned V1 was the "Go" or "No Go" speed, ie. at V1 one has enough runway left to safely take off with a power failure, or can safely brake in the distance remaining and not run off the end.
I'd made my "decision" before I reached V1 !!
But then I'm an Old Fart.
I'd made my "decision" before I reached V1 !!
But then I'm an Old Fart.
Last edited by ExSp33db1rd; 24th Jul 2013 at 18:33.
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To my knowledge there is no universally accepted "correct term for V1". The Boeing term describes its role in the accelerate-stop, but in the continued takeoff there is no action at V1 (except for the PF taking his hand off the TL's).
Historically, V1 started out as the "critical engine failure speed". When the recognition time delay was accounted for it became the "engine failure recognition speed". Still later the regulation was amended to take account of takeoff rejection for reasons other than engine failure and V1 was termed "takeoff decision speed". That term was abandoned because the abort decision should not be taken at V1, and the definition in FAR Part 1 was adopted instead.
Historically, V1 started out as the "critical engine failure speed". When the recognition time delay was accounted for it became the "engine failure recognition speed". Still later the regulation was amended to take account of takeoff rejection for reasons other than engine failure and V1 was termed "takeoff decision speed". That term was abandoned because the abort decision should not be taken at V1, and the definition in FAR Part 1 was adopted instead.
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Is V1 called 'Decision Speed' or 'Action Initiation Speed'?
It's also important to remember that these days for a modern airliner V1 is an almost arbitrary speed based around minimising engine wear.
Obviously it is a speed that can by stopped from and also a speed from which the take off may be continued, however it would frequently be possible to stop from a faster speed, or indeed continue from a slower speed.
Unfortunately the pilot will not usually have this information and will be unable to tell on a daily basis where in the stop/go bracket V1 has been located.
Obviously it is a speed that can by stopped from and also a speed from which the take off may be continued, however it would frequently be possible to stop from a faster speed, or indeed continue from a slower speed.
Unfortunately the pilot will not usually have this information and will be unable to tell on a daily basis where in the stop/go bracket V1 has been located.
‘V1’ depends on the context being considered; design, certification, operation.
Definition: V1 is defined as the takeoff decision speed (via ICAO)
Certification: V1, in terms of calibrated airspeed, is selected by the applicant (manufacturer); however, V1 may not be less than VEF plus the speed gained with the critical engine inoperative during the time interval between the instant at which the critical engine is failed, and the instant at which the pilot recognises and reacts to the engine failure, as indicated by the pilot’s initiation of the first action (e.g. applying brakes, reducing thrust, deploying speed brakes) to stop the aeroplane during accelerate-stop tests. (EASA CS 25 certification – FAR similar)
Operations: V1 means the maximum speed in the take-off at which the pilot must take the first action (e.g. apply brakes, reduce thrust, deploy speed brakes) to stop the aeroplane within the accelerate-stop distance. V1 also means the minimum speed in the take-off, following a failure of the critical engine at VEF, at which the pilot can continue the take-off and achieve the required height above the take-off surface within the takeoff distance. (EASA operations)
Thus V1 is variable, it not uniquely VEF, it relates to decisions and action, and as a pilot it is very important to understand the operational implications of V1.
Definition: V1 is defined as the takeoff decision speed (via ICAO)
Certification: V1, in terms of calibrated airspeed, is selected by the applicant (manufacturer); however, V1 may not be less than VEF plus the speed gained with the critical engine inoperative during the time interval between the instant at which the critical engine is failed, and the instant at which the pilot recognises and reacts to the engine failure, as indicated by the pilot’s initiation of the first action (e.g. applying brakes, reducing thrust, deploying speed brakes) to stop the aeroplane during accelerate-stop tests. (EASA CS 25 certification – FAR similar)
Operations: V1 means the maximum speed in the take-off at which the pilot must take the first action (e.g. apply brakes, reduce thrust, deploy speed brakes) to stop the aeroplane within the accelerate-stop distance. V1 also means the minimum speed in the take-off, following a failure of the critical engine at VEF, at which the pilot can continue the take-off and achieve the required height above the take-off surface within the takeoff distance. (EASA operations)
Thus V1 is variable, it not uniquely VEF, it relates to decisions and action, and as a pilot it is very important to understand the operational implications of V1.
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I have a recollection that falls in line with the Boeing guy. V1 is the latest speed by which stopping actions must commence. I believe that in certification, a time of 1 second is allowed for the decision to stop. The actions must commence by V1 itself at the latest, and 2 further seconds from V1 speed are allowed for the stopping configuration (ie. applying brakes, selection reverse and spoilers as installed).
So, decision must be made 1 second before V1, which is where many operators state in OM-A that the "V1" call must be completed by V1. One second to decide, two seconds commencing at V1 to configure the stopping actions.
So, decision must be made 1 second before V1, which is where many operators state in OM-A that the "V1" call must be completed by V1. One second to decide, two seconds commencing at V1 to configure the stopping actions.
Jazz, the quotes @#11 are from the relevant certification and operations requirements.
You might clarify your recollection and ‘false’ beliefs about certification by referring to CS 25, the info is around para 25.107 and associated AMC.
bleeke, you might benefit from reading the Takeoff Safety Training Aid and CS 25 as above.
As far as you should be concerned (certification assumptions about probability, exposure, effect, etc) the trim will not run away in the time scale being considered, nor would there be a control block providing you complete before takeoff control check correctly. Certification assumes that checks are done, but accidents indicate that the human is still the weakest link in safety.
You might clarify your recollection and ‘false’ beliefs about certification by referring to CS 25, the info is around para 25.107 and associated AMC.
bleeke, you might benefit from reading the Takeoff Safety Training Aid and CS 25 as above.
As far as you should be concerned (certification assumptions about probability, exposure, effect, etc) the trim will not run away in the time scale being considered, nor would there be a control block providing you complete before takeoff control check correctly. Certification assumes that checks are done, but accidents indicate that the human is still the weakest link in safety.
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As HN39 and PEI 3721 have observed, the meaning for V1, and its sensible operational implementation, has varied over the years. One needs to look at individual TCDS and then the cited frozen design standards to match one with the other.
General approach for quite some time now -
(a) by V1 the first stopping action has already been initiated
(b) if not, the the aircraft is launching with the problem.
based on the observation that the risk involved in stopping is much greater than that associated with continuing.
(.. acknowledging that such is an idealised construct and sensible based on statistical history .. there will exist circumstances, on occasion, where the commander's outcome will be better doing things differently)
As to what one might call it, doesn't really matter .. decision speed, Friday night at the movies, etc., so long as the embodied strategies are understood both for the particular certification and sensible operational risk management.
As always the underlying rule is "don't crash".
General approach for quite some time now -
(a) by V1 the first stopping action has already been initiated
(b) if not, the the aircraft is launching with the problem.
based on the observation that the risk involved in stopping is much greater than that associated with continuing.
(.. acknowledging that such is an idealised construct and sensible based on statistical history .. there will exist circumstances, on occasion, where the commander's outcome will be better doing things differently)
As to what one might call it, doesn't really matter .. decision speed, Friday night at the movies, etc., so long as the embodied strategies are understood both for the particular certification and sensible operational risk management.
As always the underlying rule is "don't crash".
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PEI,
Still though,
Dual Engine failure (on some airplanes you'll have no choice anyway).
Reverser operating.
Control malfunction (ie rudder hard over).
Multiple main gear tire failures.
Collision with foreign object (ie truck on the runway).
A few more that I can't think of at 2 am...
While extremely remote I know of at least two of these occurring recently. Timely action by the flight crews (in one case after Vr) saved their lives.
Still though,
Dual Engine failure (on some airplanes you'll have no choice anyway).
Reverser operating.
Control malfunction (ie rudder hard over).
Multiple main gear tire failures.
Collision with foreign object (ie truck on the runway).
A few more that I can't think of at 2 am...
While extremely remote I know of at least two of these occurring recently. Timely action by the flight crews (in one case after Vr) saved their lives.
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As to what one might call it, doesn't really matter .. decision speed, Friday night at the movies, etc., so long as the embodied strategies are understood both for the particular certification and sensible operational risk management.
Going by the above posts, would it ok to say that there isn't any?
ps: thanks everyone for replying.
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unfortunately it does matter
Like so many questions in so many exams .. a bit silly.
Presuming that one of the other two alternatives was "none of the above" and that the fourth was irrelevant, I would go for "none of the above".
However, presumably the relevant course provided the "approved" answer somewheres along the way, as is the normal way of doing things ?
As we all understand, in the exam it is a matter of providing whatever canned answer is appropriate to the particular examiner's foibles regardless of its degree of sillyness. No benefit in falling on one's sword to make an unwinnable point.
Unless, of course, we are talking about a specific Type. Then, one would refer to the relevant TCDS, the relevant frozen Design Standards and ACs .. the answers you have cited may, then, well be the correct (if outdated) items. They would, however, remain pertinent to the particular certification.
Like so many questions in so many exams .. a bit silly.
Presuming that one of the other two alternatives was "none of the above" and that the fourth was irrelevant, I would go for "none of the above".
However, presumably the relevant course provided the "approved" answer somewheres along the way, as is the normal way of doing things ?
As we all understand, in the exam it is a matter of providing whatever canned answer is appropriate to the particular examiner's foibles regardless of its degree of sillyness. No benefit in falling on one's sword to make an unwinnable point.
Unless, of course, we are talking about a specific Type. Then, one would refer to the relevant TCDS, the relevant frozen Design Standards and ACs .. the answers you have cited may, then, well be the correct (if outdated) items. They would, however, remain pertinent to the particular certification.
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Thanks vilas, HazelNuts39, PEI_3721 for the definitions. This question was recently asked in Jet Airways' written exam and has already invited a lot of healthy discussion.
One thing everybody seems to agree on is the significance and applicability of this speed i.e. V1 is the maximum speed at which a rejected takeoff can be initiated, in the event of an emergency.
There are a lot of conflicting definitions.
Airbus, in its Flight Operations Briefing Notes-Understanding Takeoff Speeds and Revisiting the “Stop or Go” Decision clearly states that V1 is the Decision Speed.
Then there is FAA's Pilot Guide to TakeOff Safety. This is a training document published on FAA's website and not an actual regulation. Quoting from it:
Originally Posted by Pilot Guide to TakeOff Safety
One common and misleading way to think of V1 is to say “V1 is the decision speed.” This is misleading because V1 is not the point to begin making the operational Go/No Go decision. The decision must have been made by the time the airplane reaches V1 or the pilot will not have initiated the RTO procedure at V1. Therefore, by definition, the airplane will be traveling at a speed higher than V1 when stopping action is initiated, and if the airplane is at a Field Length Limit Weight, an overrun is virtually assured.
Last edited by aditya104; 25th Jul 2013 at 13:03.