Calling V1 early
Join Date: Jun 2001
Location: UK
Posts: 1,178
Likes: 0
Received 0 Likes
on
0 Posts
Astonishing level of varied 'understanding'!
Please see http://www.ais.org.uk/aes/pubs/aip/pdf/aic/4P182.PDF
which is UK CAA AIC 141/1998 (Pink 182) - still current.
Then perhaps the mis-informed will stay quiet!
Please see http://www.ais.org.uk/aes/pubs/aip/pdf/aic/4P182.PDF
which is UK CAA AIC 141/1998 (Pink 182) - still current.
Then perhaps the mis-informed will stay quiet!
Last edited by FlapsOne; 30th Jan 2006 at 19:26.
Join Date: Jun 2000
Location: Canada
Posts: 819
Likes: 0
Received 0 Likes
on
0 Posts
Rainboe
I am by no means an expert, but I believe you'll find that V1 calculations involve no additional increments. They are de facto performance calculations, under standard WAT conditions. Your statement, "I always understood a couple of seconds thinking time were already built into V1 calculations" refers, in fact, to the 'after V1' reaction buffers to bring the aeroplane to a stop.
It is my understanding that there was a one second, plus buffer, plus another second, plus buffer to get it stopped. This accounted for recognition AT V1, closing the thrust levers, apply max. braking and allow for spoilers up, plus an additional factor to stop. Under FAR 25 Amendment 42 an additional 2 seconds was added to the calculation of the Balanced Field calculation, which I suppose affects the initial V1 calculation.
Boeing has an excellent download called Takeoff Safety Traing Aid which explains everything in clear and uncertain terms.
Great discussion.
Empty Cruise
Thanks for the reference. I appreciate your trouble and truly must remember our friends who operate under the JARs. I stand better informed thanks to you.
cheers,
Willie
I am by no means an expert, but I believe you'll find that V1 calculations involve no additional increments. They are de facto performance calculations, under standard WAT conditions. Your statement, "I always understood a couple of seconds thinking time were already built into V1 calculations" refers, in fact, to the 'after V1' reaction buffers to bring the aeroplane to a stop.
It is my understanding that there was a one second, plus buffer, plus another second, plus buffer to get it stopped. This accounted for recognition AT V1, closing the thrust levers, apply max. braking and allow for spoilers up, plus an additional factor to stop. Under FAR 25 Amendment 42 an additional 2 seconds was added to the calculation of the Balanced Field calculation, which I suppose affects the initial V1 calculation.
Boeing has an excellent download called Takeoff Safety Traing Aid which explains everything in clear and uncertain terms.
Great discussion.
Empty Cruise
Thanks for the reference. I appreciate your trouble and truly must remember our friends who operate under the JARs. I stand better informed thanks to you.
cheers,
Willie
Moderator
An important subject and one needing lots of airing in places such as this. May I summarise the basics as discussed so far ...
(a) performance can be approached theoretically, in which case the numbers are all good fun and can be run to whatever accuracy is considered pleasing to the eye. Alternatively, one can look at the real world and note that the distribution curve shows up a degree of variability in achieved performance when compared to calculated. He who blindly puts all faith in charts beyond a reasonable scatter accuracy lives with the potential for excitement .. ie a little bit for mum and the kids in usually a good idea.
(b) the discussion so far shows clearly the variability in knowledge within the Industry on matters technical.
(c) the line pilot generally will not know whether the go or stop case is limiting or closer to being limiting for the particular takeoff on the day in question. Consider quizzing your ops engineering folk for runways which you might consider to be more exciting than others.
(d) Vmcg is a real limit and can make for exciting times if abused. Consider that the transition from easy directional control to loss of control may manifest itself in the space of several knots and the rate of onset of control problems is fast as the failure speed decreases.
Keep in mind that real world Vmcg (as opposed to the certification animal) is very crosswind dependent (typically 0.5 kt/kt for twins increasing to something in excess of 1 kt/kt for 4-engined beasties). This is made more interesting when one considers that the certification value usually is based on zero wind (7 kts under the old British standards). The certification value is there more for line in the sand purposes but, if you happen to be near or at the limit on the day, that doesn't help you much.
Taking an arbitrary decision to reduce the go decision to a speed significantly below V1 may be hazardous, especially for low weight, low altitude, low OAT takeoffs. Keep in mind that our simulator experience is a two-edged sword and that the great majority of simulator failure training exercises are done under non-limiting handling conditions .. this can create an unjustified comfort zone .. this is especially the case for aircraft where Vmcg is not usually a critical takeoff limitation.
(e) history suggests that more people have trouble with high speed aborts than they do with high speed continued takeoffs.
(f) current thinking (and this has been the case for quite some years) is that if you haven't initiated the stop BY V1 (ie the first abort action has been executed - normally brakes full on) then you keep going (unless there is a real perception that the aircraft will not fly). Particularly with older certifications initiating the stop after "deciding" at V1 (if the ASDA is, in fact, limiting) might be a bit worrying. Keep in mind that, in the real world, the bit of the runway on which you are hoping to stop is the bit on which umpteen thousands of tyres have left a thick film of rubber over the past however many months/years since it was all cleaned off .....
(g) the pilot who doesn't monitor his own instruments during the takeoff is asking for a surprise sooner or later.
(h) there is some fat in accel-stop scheduling (which varies with certification basis) but not a great deal (amendment 42 sought to redress this problem to some extent).
(i) the calculations should be made for the ambient conditions, not standard day. An earlier poster's reference to WAT conditions left me a little confused .. perhaps he might add some additional commentary ?
(j) being able to justify one's actions at the investigation is an important part of the plan. If you think you won't be able to, then maybe you ought not to be about to do whatever it is you are contemplating ... ?
(a) performance can be approached theoretically, in which case the numbers are all good fun and can be run to whatever accuracy is considered pleasing to the eye. Alternatively, one can look at the real world and note that the distribution curve shows up a degree of variability in achieved performance when compared to calculated. He who blindly puts all faith in charts beyond a reasonable scatter accuracy lives with the potential for excitement .. ie a little bit for mum and the kids in usually a good idea.
(b) the discussion so far shows clearly the variability in knowledge within the Industry on matters technical.
(c) the line pilot generally will not know whether the go or stop case is limiting or closer to being limiting for the particular takeoff on the day in question. Consider quizzing your ops engineering folk for runways which you might consider to be more exciting than others.
(d) Vmcg is a real limit and can make for exciting times if abused. Consider that the transition from easy directional control to loss of control may manifest itself in the space of several knots and the rate of onset of control problems is fast as the failure speed decreases.
Keep in mind that real world Vmcg (as opposed to the certification animal) is very crosswind dependent (typically 0.5 kt/kt for twins increasing to something in excess of 1 kt/kt for 4-engined beasties). This is made more interesting when one considers that the certification value usually is based on zero wind (7 kts under the old British standards). The certification value is there more for line in the sand purposes but, if you happen to be near or at the limit on the day, that doesn't help you much.
Taking an arbitrary decision to reduce the go decision to a speed significantly below V1 may be hazardous, especially for low weight, low altitude, low OAT takeoffs. Keep in mind that our simulator experience is a two-edged sword and that the great majority of simulator failure training exercises are done under non-limiting handling conditions .. this can create an unjustified comfort zone .. this is especially the case for aircraft where Vmcg is not usually a critical takeoff limitation.
(e) history suggests that more people have trouble with high speed aborts than they do with high speed continued takeoffs.
(f) current thinking (and this has been the case for quite some years) is that if you haven't initiated the stop BY V1 (ie the first abort action has been executed - normally brakes full on) then you keep going (unless there is a real perception that the aircraft will not fly). Particularly with older certifications initiating the stop after "deciding" at V1 (if the ASDA is, in fact, limiting) might be a bit worrying. Keep in mind that, in the real world, the bit of the runway on which you are hoping to stop is the bit on which umpteen thousands of tyres have left a thick film of rubber over the past however many months/years since it was all cleaned off .....
(g) the pilot who doesn't monitor his own instruments during the takeoff is asking for a surprise sooner or later.
(h) there is some fat in accel-stop scheduling (which varies with certification basis) but not a great deal (amendment 42 sought to redress this problem to some extent).
(i) the calculations should be made for the ambient conditions, not standard day. An earlier poster's reference to WAT conditions left me a little confused .. perhaps he might add some additional commentary ?
(j) being able to justify one's actions at the investigation is an important part of the plan. If you think you won't be able to, then maybe you ought not to be about to do whatever it is you are contemplating ... ?
Join Date: Jul 2000
Location: Smogsville
Posts: 1,424
Likes: 0
Received 0 Likes
on
0 Posts
Warning Toxic!
Disgusted of Tunbridge
Disgusted of Tunbridge
Join Date: Jan 2005
Location: Hampshire, UK
Posts: 4,011
Likes: 0
Received 0 Likes
on
0 Posts
Willie, what part of <<"By that I mean the call 'V1' is made, and you decide immediately Go/No Go. Then a few seconds are allowed for to get the thrust levers back to idle, select reverse and make sure autobrakes and speedbrakes deploy. Simple as that, tamper with it and you are at a lawyers mercy.'>> do you not understand? You have repeated what I said above!
Join Date: Sep 1999
Location: ME
Posts: 5,502
Likes: 0
Received 0 Likes
on
0 Posts
Willie Everlearn,
I suggest you check out FAA AC91-6B regarding contaminated runways using a 15ft screen height and reverser thrust.
Rainboe, the FAA certified the B747-400 using the constant velocity transition method for the accelerate stop. Basically, Vef is 1 second prior to V1, then they use the demonstrated brake, spoiler , reverse time FOLLOWED by 2 Seconds at a constant velocity before the aircraft is assumed to be decelerating.....
This method applied to the 737-300/400/500. B757-200, B767-200/300 and B747-400. The following are the various methods used by Boeing:
Willie Everlearn, you just explained how the B707,B727,B737-100/200, B747-100/200/300 were certified.
Mutt
Mutt
I suggest you check out FAA AC91-6B regarding contaminated runways using a 15ft screen height and reverser thrust.
Rainboe, the FAA certified the B747-400 using the constant velocity transition method for the accelerate stop. Basically, Vef is 1 second prior to V1, then they use the demonstrated brake, spoiler , reverse time FOLLOWED by 2 Seconds at a constant velocity before the aircraft is assumed to be decelerating.....
This method applied to the 737-300/400/500. B757-200, B767-200/300 and B747-400. The following are the various methods used by Boeing:
Willie Everlearn, you just explained how the B707,B727,B737-100/200, B747-100/200/300 were certified.
Mutt
Mutt
Join Date: Apr 2000
Location: 30 West
Age: 65
Posts: 926
Likes: 0
Received 0 Likes
on
0 Posts
Wait until you see what the Airbus does !
Longer runways, always goes for incresed V2 which drags V1 up with it. the number of times we look at remaining runway at V1 and go - Naaaah, that wouldn't have worked !
Don't always but blind faith in the V speeds either - we had a certain desert destination where luck features a lot - back in 2001, our perf people omitted the aerodrome elevation of over 2,000' in the perf calcs for a whole season !
They were interesting departures
Longer runways, always goes for incresed V2 which drags V1 up with it. the number of times we look at remaining runway at V1 and go - Naaaah, that wouldn't have worked !
Don't always but blind faith in the V speeds either - we had a certain desert destination where luck features a lot - back in 2001, our perf people omitted the aerodrome elevation of over 2,000' in the perf calcs for a whole season !
They were interesting departures
I have found this thread to be quite educational. Thank you all. I think J.T.'s summary brought many of the good points made into a unified, or at least more easily recognizable statement on the importance of understanding takeoff performance data to a somewhat more advanced level than is provided by typical type training. As illustrated by mutt's point about the differences in certification methodology used in the certification of older vs newer aircraft, It seems that it would be useful to learn what assumptions were made in the performance data for each specific type we fly. It's nice to know what margins are and are not built in. Since this is outside the normal curriculum of a standard type training course, I'll consider it to be an advanced learning assignment which may come in handy someday on a limiting runway. Once again, thanks.
Best regards,
Westhawk
Best regards,
Westhawk
Join Date: Apr 2004
Location: Europe
Posts: 467
Likes: 0
Received 0 Likes
on
0 Posts
Hey there, some of you might be surprised, but modern airplanes do have automatic call function, ergo V1 call is made automatically by nice synthetic voice. All you have to do is decide. I personally will stick to most common Airbus philosophy: up to 100 kt Stop minded, above GO minded, unless severe damage, fire (all mentioned in the airbus manual). I agree that a stop decision near V1 is more critical, as its been proven by statistic, but if its necessary to stop, then do it.
Cheers.
Cheers.
There is no argument in my mind that the book figures are valid and correct.
While I respect the book V1 and I know that fudge factors and decision times have been built into those V speeds, the experience of observing many botched aborts in simulator prof checks and when training for type ratings has convinced me there is a theoretical world and a real world when it comes to lightning fast decision making with an event close to V1. And we all know you have to be real quick and perfect on a balanced field length abort. Few pilots are both.
Certainly V1 must be correctly bugged using the book figure. And V1 is called when it arrives but once I pass beyond 15 knots below V1 and heading fast towards the bugged V1, I can afford to relax a little as I know the danger of a botched abort is less because I ain't stopping for no man - unless it is a catastrophic event where continuing is not on. Of course commonsense prevails when it comes to Vmcg. Its called playing the statistics, I suppose.
While I respect the book V1 and I know that fudge factors and decision times have been built into those V speeds, the experience of observing many botched aborts in simulator prof checks and when training for type ratings has convinced me there is a theoretical world and a real world when it comes to lightning fast decision making with an event close to V1. And we all know you have to be real quick and perfect on a balanced field length abort. Few pilots are both.
Certainly V1 must be correctly bugged using the book figure. And V1 is called when it arrives but once I pass beyond 15 knots below V1 and heading fast towards the bugged V1, I can afford to relax a little as I know the danger of a botched abort is less because I ain't stopping for no man - unless it is a catastrophic event where continuing is not on. Of course commonsense prevails when it comes to Vmcg. Its called playing the statistics, I suppose.
Join Date: Jun 2001
Location: In da north country
Age: 62
Posts: 452
Likes: 0
Received 0 Likes
on
0 Posts
Our company flys classic 747's. However, we use a bit of wisdom from the -400 in our thinking. Above 80 knots, the front C&W panel is blanked out. Boeing thinks that anything on that panel is not worth rejecting for over 80 knots. So, we keep this in our thinking while in the sim and try to use it on the line.
So, that leaves an engine failure or a fire to think about, or something really obscure.
At V-1, our hands come off the throttles, feet off the brakes.
Boeing says that the v-1 decision can be made at v-1 and that allows for the few seconds it takes to make a decision.
Well, our policy is , at V1, hands come off the throttles, were going. Our OPS system has made things very scary. it basically turns every runway into a balanced field, except for when your really light.
Don't make up your own rules, that will get you into trouble!
I'm just a line pilot, and I like to learn from other folks misfortunes.
So, that leaves an engine failure or a fire to think about, or something really obscure.
At V-1, our hands come off the throttles, feet off the brakes.
Boeing says that the v-1 decision can be made at v-1 and that allows for the few seconds it takes to make a decision.
Well, our policy is , at V1, hands come off the throttles, were going. Our OPS system has made things very scary. it basically turns every runway into a balanced field, except for when your really light.
Don't make up your own rules, that will get you into trouble!
I'm just a line pilot, and I like to learn from other folks misfortunes.
Join Date: Sep 2005
Location: No one's home...
Posts: 416
Likes: 0
Received 0 Likes
on
0 Posts
It would seem that first one has to define how V1 was computed. I have seen numerous methods to calculate V1 including min V1s.
Second, a high speed RTO is always a problem. It is probably the most dangerous thing that faces a pilot and is seldom done correctly. Studies have shown in most cases the pilot fails to use maximum braking rendering the numbers invalid. Unless you can shove a phonebook under your butt when you are standing on the brakes, you are probably not getting max braking. This of course discounts using autobrakes.
Even with autobrakes, many times an aviator will disconnect the brakes when s/he feels the situation is under control and unfortunately this is when they are entering the latter portion of the runway where once again you are getting into the rubber build-ups.
At or near V1, the airplane is accelerating at about 5-7kts per second and in an earlier report (PSM+ICR) it discussed how many simulator events were created not from actual data but what was supposed to be. In talking to a few aviators who had blown tires or blown engines, they said the same thing, "It was nothing like the sim!" Having landing with a disconnected nosewheel pin (727 many years ago) when we landed the airplane shook like a wet dog and I had no idea of what was going on. Had this happened on takeoff, I imagine I would have had great concern about whether or not it would fly.
The V1 -kt call has worked at my old house (now retired) and I would imagine that more than V1 or V1-5kts the best plan would be to know what you are going to do as you near V1, execute it flawlessly and then lift a glass to expert airmanship.
Second, a high speed RTO is always a problem. It is probably the most dangerous thing that faces a pilot and is seldom done correctly. Studies have shown in most cases the pilot fails to use maximum braking rendering the numbers invalid. Unless you can shove a phonebook under your butt when you are standing on the brakes, you are probably not getting max braking. This of course discounts using autobrakes.
Even with autobrakes, many times an aviator will disconnect the brakes when s/he feels the situation is under control and unfortunately this is when they are entering the latter portion of the runway where once again you are getting into the rubber build-ups.
At or near V1, the airplane is accelerating at about 5-7kts per second and in an earlier report (PSM+ICR) it discussed how many simulator events were created not from actual data but what was supposed to be. In talking to a few aviators who had blown tires or blown engines, they said the same thing, "It was nothing like the sim!" Having landing with a disconnected nosewheel pin (727 many years ago) when we landed the airplane shook like a wet dog and I had no idea of what was going on. Had this happened on takeoff, I imagine I would have had great concern about whether or not it would fly.
The V1 -kt call has worked at my old house (now retired) and I would imagine that more than V1 or V1-5kts the best plan would be to know what you are going to do as you near V1, execute it flawlessly and then lift a glass to expert airmanship.
Wileydog3 raises another critical factor in this discussion and that is that the braking technique on a rejected take-off has to be accomplished perfectly.
I did my DC-10 conversion at DFW and our very, very wise instructor used to set up an exercise on a short runway at Waco. Provided that FULL braking was applied at V1 it was JUST possible to stop the aeroplane before going off the end.
In order to achieve FULL braking it is necessary to have the rudder pedals right back so that it is possible to get your full body weight on to the brakes.
If you are the sort of chap that likes to have your rudders adjusted forward then you are for sure going to cock it up for your ankle muscles simply cannot get FULL brake pressure on in time if at all.
Think on that before you next go flying.
I did my DC-10 conversion at DFW and our very, very wise instructor used to set up an exercise on a short runway at Waco. Provided that FULL braking was applied at V1 it was JUST possible to stop the aeroplane before going off the end.
In order to achieve FULL braking it is necessary to have the rudder pedals right back so that it is possible to get your full body weight on to the brakes.
If you are the sort of chap that likes to have your rudders adjusted forward then you are for sure going to cock it up for your ankle muscles simply cannot get FULL brake pressure on in time if at all.
Think on that before you next go flying.
Join Date: Apr 2005
Location: uk
Posts: 260
Likes: 0
Received 0 Likes
on
0 Posts
From UKCAA-AIC 151/1993 :-
V1 must be respected as the latest speed by which a decision to stop must have been taken to assure a stopping capability within the distance available on a limiting runway.
It is not the speed called at which the PF decides to reject the take-off and use the appropriate procedure. In other words when V1 is called (human or automatic voice) the decision must be to GO.
The JAR accelerate-stop definition differs from the FAR definition in that the JAR includes the stopway in the calculation, whereas the FAR determines that the aircraft will stop on the runway itself.
In JAR's a 1.5 to 2 second "thinking time" is included in the V1 calculation.
If V1 is called early (beware the lawyers if is is found to be a factor in an accident!) then it is not guaranteed that the a/c will achieve lift-off before the end of the runway, following a power-plant failure nor achieve the 35' screen height (15' if wet or contminated conditions).
V1 and its' definition has been argued since long ago and will be argued for a long time yet. The 'sense' in the GO decision, when above Vmcg but below V1 may be obvious but ill-advised. Stick to SOP's and if you don't, be prepared with a good defence!!
V1 must be respected as the latest speed by which a decision to stop must have been taken to assure a stopping capability within the distance available on a limiting runway.
It is not the speed called at which the PF decides to reject the take-off and use the appropriate procedure. In other words when V1 is called (human or automatic voice) the decision must be to GO.
The JAR accelerate-stop definition differs from the FAR definition in that the JAR includes the stopway in the calculation, whereas the FAR determines that the aircraft will stop on the runway itself.
In JAR's a 1.5 to 2 second "thinking time" is included in the V1 calculation.
If V1 is called early (beware the lawyers if is is found to be a factor in an accident!) then it is not guaranteed that the a/c will achieve lift-off before the end of the runway, following a power-plant failure nor achieve the 35' screen height (15' if wet or contminated conditions).
V1 and its' definition has been argued since long ago and will be argued for a long time yet. The 'sense' in the GO decision, when above Vmcg but below V1 may be obvious but ill-advised. Stick to SOP's and if you don't, be prepared with a good defence!!
Join Date: Sep 1998
Location: EU
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
I have always quietly planned on continuing the take off from 15 knots below the published and bugged V1 - unless the event is catastrophic
Of course commonsense prevails when it comes to Vmcg.
I think we all understand your concerns, but I still think you are on very thin ice.
Moderator
Time for the next summary ... and the thread is developing very nicely, I believe.
(a) the detail of the certification basis for V1 has evolved over the years and can be studied via the reg changes and the flight test guide for those who are interested (FAR25). That is, V1 for a B707 means something a bit different to what applies for the latest offering from the OEMs.
(b) early aircraft are PARTICULARLY accel-stop critical on limiting runways. Effectively, there is near nil room for the pilot to think about what he is doing at the time .. lest he desire a near guaranteed overrun.
(c) amendment 42 addressed a gaping deficiency but is not the comfort zone which some might suppose. Consider two (2) seconds at, say, 150 kt .. equivalent to around 150 metres (if I have my conversions lined up correctly). That's still around 500 ft (in real numbers) but not very far in real runway eaten up at V1 terms .... so one needs to be very focussed.
(d) "V1 is the speed where the first actions to abort the T/O should be initiated" ... NO. He who follows this point of view sets himself up for needless excitement. As a general rule, if it isn't already stopping by V1, then it's going .. especially for the earlier aircraft.
(e) it is a lemma that the calculations are only as good as the quality of the information fed into the sums.
(f) it would be nice if pilots knew all the ins and outs of the basis for performance calculations. Unfortunately that is unlikely ever to be the case. Some of us, either due to interest or employment, end up with a bit more knowledge than most pilots. Mutt, for instance, is an experienced operations engineer rated on most (and possibly all) of the aircraft for which he crunches the numbers. Centaurus, while having a piloting background, possesses a knowledge base on this subject far greater than the great majority of pilots. I would suggest that, in respect of his reference to "V1 - 15", he is probably suggesting that he starts to become GO-minded at that delta.
(g) for the accel-stop manoeuvre, the brakes MUST be full deflection (assuming the Type has anti-skid) until the aircraft HAS stopped ... one needs to be VERY careful about releasing any pressure until the aircraft has actually stopped. Human estimation of speed under significant acceleration is not good.
(h) the point about AEO/OEI is very important. Other than for some later aircraft, all the accel-stop data is predicated solely on a fuel cut failure at the scheduled speed .. which history tells us is not the usual case facing our hapless pilot during the real world event.
(i) query ? FAR 25.109 appears not to support the contention that "the JAR accelerate-stop definition differs from the FAR definition in that the JAR includes the stopway in the calculation, whereas the FAR determines that the aircraft will stop on the runway itself". Perhaps the poster might give us some further guidance as to the origin of his assertion ?
(j) for those who might seek to develop their own techniques, it needs to be kept firmly in mind that the CVR/DFDR history on most modern aircraft may just bring you unstuck at the enquiry ....
Ref (i) I have now had a chance to search for the AIC referred to and cannot find a link to it. Can the poster provide one, please ?
(a) the detail of the certification basis for V1 has evolved over the years and can be studied via the reg changes and the flight test guide for those who are interested (FAR25). That is, V1 for a B707 means something a bit different to what applies for the latest offering from the OEMs.
(b) early aircraft are PARTICULARLY accel-stop critical on limiting runways. Effectively, there is near nil room for the pilot to think about what he is doing at the time .. lest he desire a near guaranteed overrun.
(c) amendment 42 addressed a gaping deficiency but is not the comfort zone which some might suppose. Consider two (2) seconds at, say, 150 kt .. equivalent to around 150 metres (if I have my conversions lined up correctly). That's still around 500 ft (in real numbers) but not very far in real runway eaten up at V1 terms .... so one needs to be very focussed.
(d) "V1 is the speed where the first actions to abort the T/O should be initiated" ... NO. He who follows this point of view sets himself up for needless excitement. As a general rule, if it isn't already stopping by V1, then it's going .. especially for the earlier aircraft.
(e) it is a lemma that the calculations are only as good as the quality of the information fed into the sums.
(f) it would be nice if pilots knew all the ins and outs of the basis for performance calculations. Unfortunately that is unlikely ever to be the case. Some of us, either due to interest or employment, end up with a bit more knowledge than most pilots. Mutt, for instance, is an experienced operations engineer rated on most (and possibly all) of the aircraft for which he crunches the numbers. Centaurus, while having a piloting background, possesses a knowledge base on this subject far greater than the great majority of pilots. I would suggest that, in respect of his reference to "V1 - 15", he is probably suggesting that he starts to become GO-minded at that delta.
(g) for the accel-stop manoeuvre, the brakes MUST be full deflection (assuming the Type has anti-skid) until the aircraft HAS stopped ... one needs to be VERY careful about releasing any pressure until the aircraft has actually stopped. Human estimation of speed under significant acceleration is not good.
(h) the point about AEO/OEI is very important. Other than for some later aircraft, all the accel-stop data is predicated solely on a fuel cut failure at the scheduled speed .. which history tells us is not the usual case facing our hapless pilot during the real world event.
(i) query ? FAR 25.109 appears not to support the contention that "the JAR accelerate-stop definition differs from the FAR definition in that the JAR includes the stopway in the calculation, whereas the FAR determines that the aircraft will stop on the runway itself". Perhaps the poster might give us some further guidance as to the origin of his assertion ?
(j) for those who might seek to develop their own techniques, it needs to be kept firmly in mind that the CVR/DFDR history on most modern aircraft may just bring you unstuck at the enquiry ....
Ref (i) I have now had a chance to search for the AIC referred to and cannot find a link to it. Can the poster provide one, please ?
Last edited by john_tullamarine; 31st Jan 2006 at 03:59.
A couple of notes from the peanut gallery:
In the mighty C-5, the engineers spent probably 20 minutes computing every detaicl on every take-off including Vmcg (corrected for xwind, just about 1 kt/kt), refusal speed and distance, and (of all things) take-off ground run. I cannot explain the reason for the last one other than it was surprisingly close to critical field length with zero height at DER. But, for a pilot that read and understood the data, no excuse for not having a full idea of what was going to happen when. So underpowered was the plane, we frequently made WAT-limited take-offs, esp in the Gulf.
I thought it was all interesting but rather pedantic....until I saw the data confirmed by a functional test or two. Limiting take-off at Sig to the east, just a couple of knots prior to V1, we were struck by a flock of birds, the A/C elected to stop. And stop we did, the end of the runway was not visible from the jump seat between the seats. Another time, landing on RCR 5 braking poor, the computed landing distance was 5000 feet on a 7000 foot runway. Standing on the brakes and I mean standing, we came to halt at the 2000 feet remaining marker. Guys, when the data says it will do it, it will, if you do your part.
On other thing, I always instructed new pilots that if they needed max anti-skid braking, they best plan on STANDING on the brakes like they did for a full power standing take-off. We did those too. Saved the guy at Sigonella.
Thanks J_T for the excellent thread guidance.
GF
In the mighty C-5, the engineers spent probably 20 minutes computing every detaicl on every take-off including Vmcg (corrected for xwind, just about 1 kt/kt), refusal speed and distance, and (of all things) take-off ground run. I cannot explain the reason for the last one other than it was surprisingly close to critical field length with zero height at DER. But, for a pilot that read and understood the data, no excuse for not having a full idea of what was going to happen when. So underpowered was the plane, we frequently made WAT-limited take-offs, esp in the Gulf.
I thought it was all interesting but rather pedantic....until I saw the data confirmed by a functional test or two. Limiting take-off at Sig to the east, just a couple of knots prior to V1, we were struck by a flock of birds, the A/C elected to stop. And stop we did, the end of the runway was not visible from the jump seat between the seats. Another time, landing on RCR 5 braking poor, the computed landing distance was 5000 feet on a 7000 foot runway. Standing on the brakes and I mean standing, we came to halt at the 2000 feet remaining marker. Guys, when the data says it will do it, it will, if you do your part.
On other thing, I always instructed new pilots that if they needed max anti-skid braking, they best plan on STANDING on the brakes like they did for a full power standing take-off. We did those too. Saved the guy at Sigonella.
Thanks J_T for the excellent thread guidance.
GF
Join Date: Sep 1999
Location: ME
Posts: 5,502
Likes: 0
Received 0 Likes
on
0 Posts
The JAR accelerate-stop definition differs from the FAR definition in that the JAR includes the stopway in the calculation, whereas the FAR determines that the aircraft will stop on the runway itself.
If V1 is called early (beware the lawyers if is is found to be a factor in an accident!) then it is not guaranteed that the a/c will achieve lift-off before the end of the runway, following a power-plant failure nor achieve the 35' screen height (15' if wet or contminated conditions).
Mutt
Moderator
... and (of all things) take-off ground run .... I have no idea of the C5's certification basis but this is similar to the civil TORR parameter (except that, for civil certification it includes a portion of the takeoff rotation air distance - usually 50 percent). The purpose is to give some comfort that, for an unbalanced takeoff, the bird will actually be off the ground before it is in the weeds at the far end ...
Join Date: Jan 2006
Location: Mumbai
Posts: 35
Likes: 0
Received 0 Likes
on
0 Posts
Early V1
FAA has changed the definition of V1 in Far part 1 to read as follows:
1) V1 means the maximum speed in the take off at which the pilot must take the first action(eg apply brakes, reduce thrust,deploy speed brakes) to stop the airplane within the accelerate stop distance;and,
2)V1 also means the MINIMUM speed in the take off, following a failure of a critical engine at which the pilot can the take off and achieve the required height above the takeoff surface within the takeoff distance.
Point number 2 in the definition makes it clear that, following an engine failure if a decision to continue is made prior to V1 the required height above take off surface will be compromised.
1) V1 means the maximum speed in the take off at which the pilot must take the first action(eg apply brakes, reduce thrust,deploy speed brakes) to stop the airplane within the accelerate stop distance;and,
2)V1 also means the MINIMUM speed in the take off, following a failure of a critical engine at which the pilot can the take off and achieve the required height above the takeoff surface within the takeoff distance.
Point number 2 in the definition makes it clear that, following an engine failure if a decision to continue is made prior to V1 the required height above take off surface will be compromised.