Call V1 3 to 5kts prior
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Boeing Flight Crew Training manual as issued to our Airline.
As the airspeed approaches V1 during a balanced eld length takeoff,
the effort required to stop can approach the airplane maximum stopping
capability. Therefore, the decision to stop must be made before V1.
the effort required to stop can approach the airplane maximum stopping
capability. Therefore, the decision to stop must be made before V1.
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Gentlemen....
The issue of V1 is a touchy one. Many operators have different policies, based on their individual experiences.
One thing to note, depending on when the aircraft was certified, the V1 issue is different. As stated above, we're supposed to have something like two seconds reaction time...and still be able to get it stopped. But, this is based ont the new certification standards (both JAA and FAA).
I'm not sure about the NG737, but the older ones were certified under the old system...whereas, you really need to be transitioning to the 'stopping mode' at (or before) V1. Under the old certification standards, any speed above V1 (in an abort scenario) is not good (e.g. two seconds after reaching V1).
The Bus, on the other hand, even though it was produced under the old set of standards, meets the new criteria. That is, you can actually 'initiate' the abort at V1...and still have runway to get it stopped. "Initiate" means, you recognize the need to reject the takeoff (at V1), and promptly do the drill. Again, under the old certification standards, you don't have this.....under the old standards, you really need to have the stopping process going for you as you reach V1.
I can't remember exactly when this certification change occurred, but I'm thinking it was around the early nineties. Again, not sure about the 737NG, as it may still be certified under the original 737 certification rules.
From a practical standpoint, we're talking about only a couple of knots. Sure, as stated above, screen height is affected to some degree, but not significantly...i.e. not nearly the difference of 35 feet vs. 15 feet (dry vs. wet).
Of course, this is all based upon a 'balanced field length'. Some might define 'balanced field length' as "You're dead if you stop; you're dead if you go!" Again, in practice, if bad things happen near V1, you need to be "go minded" as Boeing and Airbus (both) recommend. Who defines 'near V1' is why we have stripes on our shoulders.
Fly safe,
Pantload
One thing to note, depending on when the aircraft was certified, the V1 issue is different. As stated above, we're supposed to have something like two seconds reaction time...and still be able to get it stopped. But, this is based ont the new certification standards (both JAA and FAA).
I'm not sure about the NG737, but the older ones were certified under the old system...whereas, you really need to be transitioning to the 'stopping mode' at (or before) V1. Under the old certification standards, any speed above V1 (in an abort scenario) is not good (e.g. two seconds after reaching V1).
The Bus, on the other hand, even though it was produced under the old set of standards, meets the new criteria. That is, you can actually 'initiate' the abort at V1...and still have runway to get it stopped. "Initiate" means, you recognize the need to reject the takeoff (at V1), and promptly do the drill. Again, under the old certification standards, you don't have this.....under the old standards, you really need to have the stopping process going for you as you reach V1.
I can't remember exactly when this certification change occurred, but I'm thinking it was around the early nineties. Again, not sure about the 737NG, as it may still be certified under the original 737 certification rules.
From a practical standpoint, we're talking about only a couple of knots. Sure, as stated above, screen height is affected to some degree, but not significantly...i.e. not nearly the difference of 35 feet vs. 15 feet (dry vs. wet).
Of course, this is all based upon a 'balanced field length'. Some might define 'balanced field length' as "You're dead if you stop; you're dead if you go!" Again, in practice, if bad things happen near V1, you need to be "go minded" as Boeing and Airbus (both) recommend. Who defines 'near V1' is why we have stripes on our shoulders.
Fly safe,
Pantload
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Boeing Go /No Go videos
Part 1
http://www.youtube.com/watch?v=raCnJgDnijw
Part 2
http://www.youtube.com/watch?v=WhVVA...eature=related
3 Seconds decision time....?
Accelerate stop go distance remaining of less than 6ft
....that could prove interesting
Part 1
http://www.youtube.com/watch?v=raCnJgDnijw
Part 2
http://www.youtube.com/watch?v=WhVVA...eature=related
3 Seconds decision time....?
Accelerate stop go distance remaining of less than 6ft
....that could prove interesting
Thread Starter
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Taking the liberty of knocking of 3-5 kts from your performance calculation, to my opinion defeats the whole purpose of calculation.
If you move your V1, it will help you to stop, but it won't help you if you continue your takeoff with an engine failure that could have happened between that -5kts and V1. So what do you do when you are obstacle limited but have enough runway in front of you. Do you call V1 after V1 ?
I'd rather get off the runway while on the ground, than hit the building while in the air.
These procedures go against the whole performance calculation that was designed by the builders engineers, and give the freedom to airlines and pilots to interpret a given situation to their own standard.
Where do you draw the line ?
If you move your V1, it will help you to stop, but it won't help you if you continue your takeoff with an engine failure that could have happened between that -5kts and V1. So what do you do when you are obstacle limited but have enough runway in front of you. Do you call V1 after V1 ?
I'd rather get off the runway while on the ground, than hit the building while in the air.
These procedures go against the whole performance calculation that was designed by the builders engineers, and give the freedom to airlines and pilots to interpret a given situation to their own standard.
Where do you draw the line ?
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V1 is scheduled after Vef. The time gap depends on the certification standard. The gap is already in the calculation so you need to make the first action to stop at or before V1.
If you make the decision to go before V1 you will compromise your screen height.
If you make the first action to stop after V1 you will compromise your stopping distance.
This is for the engine failure case only, and when at your max take off weight balanced field length limited.
Other cases will be different.
It is possible to include stopping distance allowance to hedge the stopping case and of course line up allowance must be used where necessary.
It's just not black and white.
If you make the decision to go before V1 you will compromise your screen height.
If you make the first action to stop after V1 you will compromise your stopping distance.
This is for the engine failure case only, and when at your max take off weight balanced field length limited.
Other cases will be different.
It is possible to include stopping distance allowance to hedge the stopping case and of course line up allowance must be used where necessary.
It's just not black and white.
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I totally agree with TQ.
If you choose to tweak the numbers for a balanced T/O, then you better think about the other end of that equation too.
If you continue with an EF at V1-5, then you need abit more than your ASD to get to your 15' screenheight at rwy end.
If you choose to tweak the numbers for a balanced T/O, then you better think about the other end of that equation too.
If you continue with an EF at V1-5, then you need abit more than your ASD to get to your 15' screenheight at rwy end.
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Interesting...
Well, you are not knocking off 3 to 5 knots from your calculations. You're simply calling V1 in a timely manner to ensure that you do not initiate the rejected takeoff at a speed above V1. In point of fact, you're respecting V1, not changing, modifying, etc.
Again, the issue is dependent on when the aircraft was certified. Under the old certification, you really don't want to allow the aircraft to attain a speed above V1 before the stopping actions are initiated. If you call V1 at V1...have an engine failure at V1...and you try to stop (assuming you're field-length limited), you've got a problem....because, before you know it, you're going V1 plus a couple...then, you initiate the rejected takeoff drill....BIG PROBLEMS!!!!!
We're talking only a second or two in time.....makes a big difference for 'stopping'...not much difference in 'going'. According to engineering data, even if you lose an engine at, say, V1 minus 2 or V1 minus 3...and continue the takeoff...you'll find the reduction in screen height is reduced minimally...like maybe ten or so feet. (Still above the 15 foot wet-runway figure)
But, if you lose one at V1 minus 2, and you try to stop...you'd better hope you do things very quickly...you'd better hope the brakes are in good shape (not worn to just above minimum limits)...you'd better hope the runway surface at the other end of the runway is not contaminated...or full of rubber or other crap....in other words....if you reject at V1 (and you're field-length limited), things have to be perfect for you to stop before the end of the runway.
In contrast, losing one at V1 minus 2 and continuing the takeoff will have minimal consequences. This is why the manufacturers say, as you approach V1, you need to be more 'go minded' and less 'stop minded'.
PantLoad
Again, the issue is dependent on when the aircraft was certified. Under the old certification, you really don't want to allow the aircraft to attain a speed above V1 before the stopping actions are initiated. If you call V1 at V1...have an engine failure at V1...and you try to stop (assuming you're field-length limited), you've got a problem....because, before you know it, you're going V1 plus a couple...then, you initiate the rejected takeoff drill....BIG PROBLEMS!!!!!
We're talking only a second or two in time.....makes a big difference for 'stopping'...not much difference in 'going'. According to engineering data, even if you lose an engine at, say, V1 minus 2 or V1 minus 3...and continue the takeoff...you'll find the reduction in screen height is reduced minimally...like maybe ten or so feet. (Still above the 15 foot wet-runway figure)
But, if you lose one at V1 minus 2, and you try to stop...you'd better hope you do things very quickly...you'd better hope the brakes are in good shape (not worn to just above minimum limits)...you'd better hope the runway surface at the other end of the runway is not contaminated...or full of rubber or other crap....in other words....if you reject at V1 (and you're field-length limited), things have to be perfect for you to stop before the end of the runway.
In contrast, losing one at V1 minus 2 and continuing the takeoff will have minimal consequences. This is why the manufacturers say, as you approach V1, you need to be more 'go minded' and less 'stop minded'.
PantLoad
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which has been the main argument against flex for some time.
You're on the ignore list as of...now.
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Re all those discussing "reaction times". You emphatically do not have two seconds reaction time at V1.
25.107(a)(2) requires that V1 be not less than Vef (engine failure) plus pilot reaction time.
Therefore the reaction is to the engine failure - not to the point at which V1 is attained. And the time is not necessarily two seconds either - it's however long the test pilots took during certification testing. (AC25-7A directs that the time used for calcs be not less than one second).
The notion of a two second reaction time is likely coming from a reading of 25.109, which states ...
Yet a review of AC25-7A reveals that it states quite categorically that the 2 second distance allowance is not a "pilot reaction" time and must not be considered as extending the decision-making and reacting process past V1 ...
(Section 11(c)(3) of AC25-7A chg1, page 80-6, for those who wish to see it in its full context)
So AT V1 you MUST have taken the first action to stop the plane (if you're going to abort) and you have two further seconds to complete ALL the actions required to stop the plane if you are to achieve the OEM's calculated stopping performance. Any slower timings and you are not guaranteed to remain on pavement.
=====
Given all that, it makes perfect sense for the V1 call-out to begin before V1 - for it to be useful, the fact that V1 has been passed must be processed by the PF at the point of V1, if not before. If the PNF starts to call "Vee-one" as V1 is attained then by the time he has finished, and the PF has processed the info - perhaps 0.5 seconds for reasonable human reaction times - it's already too late.
25.107(a)(2) requires that V1 be not less than Vef (engine failure) plus pilot reaction time.
Therefore the reaction is to the engine failure - not to the point at which V1 is attained. And the time is not necessarily two seconds either - it's however long the test pilots took during certification testing. (AC25-7A directs that the time used for calcs be not less than one second).
The notion of a two second reaction time is likely coming from a reading of 25.109, which states ...
§ 25.109 Accelerate-stop distance.
(a) The accelerate-stop distance on a dry runway is the greater of the following distances:
(1) The sum of the distances necessary to—
(i) Accelerate the airplane from a standing start with all engines operating to VEFfor takeoff from a dry runway;
(ii) Allow the airplane to accelerate from VEF to the highest speed reached during the rejected takeoff, assuming the critical engine fails at VEFand the pilot takes the first action to reject the takeoff at the V1for takeoff from a dry runway; and
(iii) Come to a full stop on a dry runway from the speed reached as prescribed in paragraph (a)(1)(ii) of this section; plus
(iv) A distance equivalent to 2 seconds at the V1for takeoff from a dry runway.
(a) The accelerate-stop distance on a dry runway is the greater of the following distances:
(1) The sum of the distances necessary to—
(i) Accelerate the airplane from a standing start with all engines operating to VEFfor takeoff from a dry runway;
(ii) Allow the airplane to accelerate from VEF to the highest speed reached during the rejected takeoff, assuming the critical engine fails at VEFand the pilot takes the first action to reject the takeoff at the V1for takeoff from a dry runway; and
(iii) Come to a full stop on a dry runway from the speed reached as prescribed in paragraph (a)(1)(ii) of this section; plus
(iv) A distance equivalent to 2 seconds at the V1for takeoff from a dry runway.
.... Thus it can be seen that V1 is not only intended to be at the end of the decision process, but it also includes the time it takes for the pilot to perform the first action to stop the airplane. The purpose of the time delays is to allow sufficient time (and distance) for a pilot, in actual operations, to accomplish the procedures for stopping the airplane. The time delays are not intended to allow extra time for making a decision to stop as the airplane passes through V1. ...
So AT V1 you MUST have taken the first action to stop the plane (if you're going to abort) and you have two further seconds to complete ALL the actions required to stop the plane if you are to achieve the OEM's calculated stopping performance. Any slower timings and you are not guaranteed to remain on pavement.
=====
Given all that, it makes perfect sense for the V1 call-out to begin before V1 - for it to be useful, the fact that V1 has been passed must be processed by the PF at the point of V1, if not before. If the PNF starts to call "Vee-one" as V1 is attained then by the time he has finished, and the PF has processed the info - perhaps 0.5 seconds for reasonable human reaction times - it's already too late.
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@PantLoad:
While a perfectly respectable hope - any margin is worth having in a max energy RTO - the numbers are, at least in theory, good for "fully worn" brakes, and must be demonstrated with 90% worn brakes in the max KE case.
you'd better hope the brakes are in good shape (not worn to just above minimum limits)...
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Question????
Mad Flt Scientist:
With regard to brake condition at the beginning of the RTO, is the old certification standard with worn brakes? I have to research this, because I thought the old standard was with new brakes...the new standard is with (I can't remember)...either 50% or worn-to-limits brakes.
Please correct me...I'm not sure...but, I'm thinking that was changed, too, along with the V1 standard. (You usually have a pretty good handle on details like this.)
PantLoad
With regard to brake condition at the beginning of the RTO, is the old certification standard with worn brakes? I have to research this, because I thought the old standard was with new brakes...the new standard is with (I can't remember)...either 50% or worn-to-limits brakes.
Please correct me...I'm not sure...but, I'm thinking that was changed, too, along with the V1 standard. (You usually have a pretty good handle on details like this.)
PantLoad
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Sorry, I missed that your whole post had an "old cert rules" qualifier in the second para.
The new rules require worn-to-limit brakes (or a correction to that state). As to the old regs ... wait one.
OK, the max KE demo with 90% worn brakes came in with Amdt 25-92 in 1998. Prior to that the Accel-Stop para (25.109) had NO max KE requirement. (Though other paras may have applied, at least in part - 25.1301 "performs its intended function" comes immediately to mind as one candidate para)
The fully worn requirement is actually 25.101(i) and also came in with Amdt 25-92. Again, one could have argued about other regs. But there's nothing explicit.
The new rules require worn-to-limit brakes (or a correction to that state). As to the old regs ... wait one.
OK, the max KE demo with 90% worn brakes came in with Amdt 25-92 in 1998. Prior to that the Accel-Stop para (25.109) had NO max KE requirement. (Though other paras may have applied, at least in part - 25.1301 "performs its intended function" comes immediately to mind as one candidate para)
The fully worn requirement is actually 25.101(i) and also came in with Amdt 25-92. Again, one could have argued about other regs. But there's nothing explicit.
Last edited by Mad (Flt) Scientist; 28th May 2008 at 20:54.
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Mad Flt Scientist
Yep, you came through again!!!! Thanks. You're usually very good for posting the details.
It was in the early nineties, as I recall, a major carrier in the U.S. had an RTO accident...short/wet runway, non-standard grooving, a lot of rubber at the end...anyway, while they hung the captain, a lot of procedures changed. One new procedure that was implemented was that of a reduced V1 when on wet runways. Of course, another change in the SOPs was that of calling V1 five knots early...stressing the importance of (in the case of rejecting the takeoff) beginning the RTO procedure no later than V1 (in essence, not allowing the aircraft to accelerate above V1).
I remember the political nonsense (feel free to substitute another eight-letter word), as I was at the seminar held by Boeing that addressed this particular accident.
At the end of the seminar, there was a Q & A session...a couple of Boeing test pilots and engineers were running this thing...and, I had a bunch of questions...several questions they didn't like hearing, much less answering. My relationship with my company (my job) and with Boeing were never the same after that. In fact, my boss explicitly told me in front of everyone to sit down and shut up.
But, while the captain of the aircraft involved in the accident certainly had some blame coming to him, he was the victim of a stacked deck of cards against him. I had to make that point to Boeing. (Of course, they already knew this...I just wanted them to know that we all knew it, too!)
The accident was a fatal one...the captain has to live with this for the rest of his life. But, as a result, several SOPs have changed; runways are now getting standard grooving; runways are being steam cleaned more often. And, hopefully, things like this will not happen again.
Thank you, again, for this post and all your other posts which are quite informative.
Fly safe,
PantLoad
It was in the early nineties, as I recall, a major carrier in the U.S. had an RTO accident...short/wet runway, non-standard grooving, a lot of rubber at the end...anyway, while they hung the captain, a lot of procedures changed. One new procedure that was implemented was that of a reduced V1 when on wet runways. Of course, another change in the SOPs was that of calling V1 five knots early...stressing the importance of (in the case of rejecting the takeoff) beginning the RTO procedure no later than V1 (in essence, not allowing the aircraft to accelerate above V1).
I remember the political nonsense (feel free to substitute another eight-letter word), as I was at the seminar held by Boeing that addressed this particular accident.
At the end of the seminar, there was a Q & A session...a couple of Boeing test pilots and engineers were running this thing...and, I had a bunch of questions...several questions they didn't like hearing, much less answering. My relationship with my company (my job) and with Boeing were never the same after that. In fact, my boss explicitly told me in front of everyone to sit down and shut up.
But, while the captain of the aircraft involved in the accident certainly had some blame coming to him, he was the victim of a stacked deck of cards against him. I had to make that point to Boeing. (Of course, they already knew this...I just wanted them to know that we all knew it, too!)
The accident was a fatal one...the captain has to live with this for the rest of his life. But, as a result, several SOPs have changed; runways are now getting standard grooving; runways are being steam cleaned more often. And, hopefully, things like this will not happen again.
Thank you, again, for this post and all your other posts which are quite informative.
Fly safe,
PantLoad
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CattleFlyer - All I said is if something doesn't feel right during a Flex takeoff you can go to TOGA at anytime. Additional thrust is available and I will use it if necessary. I have not read your previous posts but you seem to point out that Flex takeoff are not safe - wrong. Read more about balance fields. You will have a better understanding of the concept of V1.
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Flight testing has no such thing, nor do the certification rules. And, as explained above, the flight manual is predicated on not just recognition but reaction having started at V1. Which means if AT V1 is when you start the "V1 process", you're already behind the aircraft.
It's very simple.
Pilots with zero reaction time, able to pronounce "vee-one" in zero seconds are right to call V1 at the time they see their ASI pass through one.
Others, who somehow fail to meet the criteria have to cater for it. Personally I call "GO!" 3kt before V1, per SOP.
Pilots with zero reaction time, able to pronounce "vee-one" in zero seconds are right to call V1 at the time they see their ASI pass through one.
Others, who somehow fail to meet the criteria have to cater for it. Personally I call "GO!" 3kt before V1, per SOP.
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Why would anyone with 200 pasengers in the back, intentialy choose to risk thier lives by flying right to the edge of being able to reject a flight safely?
Overunning into the wall, going off into the bay, off the cliff or into some houses doesn't seem like a fair trade off to save on some fuel.
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I thought I had heard all the calls that airlines make, but calling the target attitude during the rotate call is surely one of the most ridiculous ones out there. The attitude changes that much to have to have a reminder at a time when the pilots should be concentrating on their job of flying the airplane? For the 2 minutes or so a modern pilot actually flies, that is? And will the PNF be smart enough to adjust the figure for an engine failure? And what about the flight director, which has been programmed to give the best attitude soon after lift off anyway? Is the PF so ignorant he even needs this call? If he does not know what attitude to rotate to what is he doing in the seat?
Talk about flying with your tongue! What would you do if there was a genuine need to make a callout of a malfunction or error? The pilot is already expecting the garbage call, and will tune it out. If the PNF is wrapped up in this call, will she see anything going wrong elsewhere?
Keep the calls to a minimum. Only call when there is a non-standard situation, so the call will be heard and listened to. Extraneous calls of the bleeding obvious reduce safety by being a distraction and reducing situational awareness.
I surely wish the airlines would stop mucking about with the manufacturers' operational procedures.
Talk about flying with your tongue! What would you do if there was a genuine need to make a callout of a malfunction or error? The pilot is already expecting the garbage call, and will tune it out. If the PNF is wrapped up in this call, will she see anything going wrong elsewhere?
Keep the calls to a minimum. Only call when there is a non-standard situation, so the call will be heard and listened to. Extraneous calls of the bleeding obvious reduce safety by being a distraction and reducing situational awareness.
I surely wish the airlines would stop mucking about with the manufacturers' operational procedures.