Overrun again
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Overrun again
Concern in regards to overuns following RTOs justifiable evokes debate. What changes to regulatory requirments for defining and calculating ASDR could be put foward??
Ur ideas please
Ur ideas please
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readbackcorrect,
It could all be achieved by legislation tomorrow by applying the same margins to Accelerate-Stop as presently exist for the continued Takeoff case.
Unfortunately, it would send all of the airlines bankrupt. No cynicism intended, that's the reality.
It could all be achieved by legislation tomorrow by applying the same margins to Accelerate-Stop as presently exist for the continued Takeoff case.
Unfortunately, it would send all of the airlines bankrupt. No cynicism intended, that's the reality.
Last edited by Old Smokey; 18th Aug 2004 at 12:55.
Paxing All Over The World
OK, as the outsider and non-pilot, I'll ask the dumb question.
Extending the runway would hurt everyone and be fed back to the airlines but you seem to be saying that the solution is directly within the airlines grasp and that they would have to pay the cost at first hand?
Extending the runway would hurt everyone and be fed back to the airlines but you seem to be saying that the solution is directly within the airlines grasp and that they would have to pay the cost at first hand?
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Just the thoughts of a mere ATPL theorist: Isn't it the case that if you reject the t/o before V1 you stop before the end, if not you overrun. It is my limited understanding that it must remain the Commander's choice if the t/o should be binned after V1 and accept the virtually certain overrun. Legislation cannot account for every circumstance that has yet to occur.
This is kinda difficult if you dont tell us if you are using JAR's or FAR's.
For me, i would like to see those nice people in the USA wake up and realize that it snows! Runways do become contaminated, airplanes dont like contamination, so airlines and manufacturers should be legally accountable for these conditions!
Then you could also add accounting for line up distances.
PAXBoy, extending the runway wont solve the problem as we will just reduce the aircrafts takeoff power for the actual weight and will end up using all of the newly available length!
Old Smokey, what margins are you talking about?
Mutt.
For me, i would like to see those nice people in the USA wake up and realize that it snows! Runways do become contaminated, airplanes dont like contamination, so airlines and manufacturers should be legally accountable for these conditions!
Then you could also add accounting for line up distances.
PAXBoy, extending the runway wont solve the problem as we will just reduce the aircrafts takeoff power for the actual weight and will end up using all of the newly available length!
Old Smokey, what margins are you talking about?
Mutt.
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from my limited experience on flight sim 2002 i found that due the acceleration of larger aircraft a rejected takeoff shouldnt even be considered say 10kts before v1. ?
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from my limited experience on flight sim 2002 i found that due the acceleration of larger aircraft a rejected takeoff shouldnt even be considered say 10kts before v1. ?
ASDR = Accelerator Stop Distance Required. Basically the shortest distance that your a/c requires on the this day on that runway to accelerate to V1 and then stop. If this is greater than the ADSA (distance available) then you need to loose some weight...somehow.
Last edited by High Wing Drifter; 19th Aug 2004 at 09:51.
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just found some more info, asdr allows for any abortion below v1 allowance of 3 secs (for appropriate action) and sufficient distance to stop.
Any one disagree
These are CASO reg ie older NZ stuff,
How does JAR or FAR differ?
Any one disagree
These are CASO reg ie older NZ stuff,
How does JAR or FAR differ?
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JAR assumes engine failure at Vef. V1 is Vef + 2secs to allow for reaction time (pending other limitations such as Vmcg). There is an additional 2sec allowance for the amount of time it takes to retard the throttles and other necessary stuff once the decision is made at V1.
Last edited by High Wing Drifter; 19th Aug 2004 at 11:17.
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Mutt,
My reference to - "the same margins to Accelerate-Stop as presently exist for the continued Takeoff case"
In applying the present legislation, the second segment climb utilises Nett performance data, whereas the accelerate-stop manoeuvre essentially uses Gross data. If the relatively simple case of a 1.6% Net gradient is required for a 2 engined aircraft, the aircraft must be capable of achieving a 2.4% Gross gradient, a Net Vs Gross performance delta of 0.8%, or put another way the aircraft only need achieve 2/3 of it's Gross performance capability to ensure obstacle clearance, i.e. 50% above minimum required. At higher gradients, it is well understood that, as the decrement is fixed, this actual percentage margin decreases, but remains substantial. Again, in the 3rd segment, Net level flight is assumed to commence at the horizontal point where the Gross gradient achieves acceleration altitude, i.e. at a lower altitude in the same ratio to Gross as in the 2nd segment case - a substantial margin.
Both of these (2nd and 3rd segments) examples illustrate significant margins above assumed (Net) performance.
For the Accelerate-Stop consideration, Gross performance is used throughout with considerably lower margins. The only significant margin is the certification requirement of keeping one means of retardation in reserve, typically Reverse Thrust. For most aircraft with which I'm familiar, this typically is ABOUT 15% of the ASDR, well short of the 50% example quoted for the 2 engined aircraft. Just about the only other margin is the pilot's ability to react in a lesser time than assumed for certification purposes, something which is rarely achieved.
Longer runways are prohibitively expensive, and, as you've said so eloquently, we would simply reduce thrust accordingly to take advantage of it. I would, both as an RTOW creator, and as a pilot.
My reference to - "the same margins to Accelerate-Stop as presently exist for the continued Takeoff case"
In applying the present legislation, the second segment climb utilises Nett performance data, whereas the accelerate-stop manoeuvre essentially uses Gross data. If the relatively simple case of a 1.6% Net gradient is required for a 2 engined aircraft, the aircraft must be capable of achieving a 2.4% Gross gradient, a Net Vs Gross performance delta of 0.8%, or put another way the aircraft only need achieve 2/3 of it's Gross performance capability to ensure obstacle clearance, i.e. 50% above minimum required. At higher gradients, it is well understood that, as the decrement is fixed, this actual percentage margin decreases, but remains substantial. Again, in the 3rd segment, Net level flight is assumed to commence at the horizontal point where the Gross gradient achieves acceleration altitude, i.e. at a lower altitude in the same ratio to Gross as in the 2nd segment case - a substantial margin.
Both of these (2nd and 3rd segments) examples illustrate significant margins above assumed (Net) performance.
For the Accelerate-Stop consideration, Gross performance is used throughout with considerably lower margins. The only significant margin is the certification requirement of keeping one means of retardation in reserve, typically Reverse Thrust. For most aircraft with which I'm familiar, this typically is ABOUT 15% of the ASDR, well short of the 50% example quoted for the 2 engined aircraft. Just about the only other margin is the pilot's ability to react in a lesser time than assumed for certification purposes, something which is rarely achieved.
Longer runways are prohibitively expensive, and, as you've said so eloquently, we would simply reduce thrust accordingly to take advantage of it. I would, both as an RTOW creator, and as a pilot.
Moderator
Some of the posters to this thread appear to have a Gospel-like belief in the wonders of V1 and this is a worry.
All certification performance is artificial in that the sums and the verifying tests are based on sets of assumptions which may, or may not, have all that much to do with real life.
If you are going to be serious about these things, then you need to know the ground rules and how the certification paddock was fenced.
This is made more difficult because the Design Standards are living, evolving documents .. ie, we can say that aircraft A, with frozen Design Standards appropriate to sometime 25 years ago, is a FAR 25 aircraft. Similarly, we can say that Aircraft B .. etc .. but with Standards appropriate to a year or so ago, is a FAR 25 aircraft. However, in the meantime, the Standards have changed more than quite a bit, so the two animals are quite different.
For those who don't have the detailed background knowledge, there is some merit in placing a degree of trust in the back room techo folk in the Regulator and the Operator.
Then again, the more knowledge the individual has, the better the likelihood that he/she can detect some of the occasions when it might not be sensible to trust too much in the information presented in the cockpit.
All certification performance is artificial in that the sums and the verifying tests are based on sets of assumptions which may, or may not, have all that much to do with real life.
If you are going to be serious about these things, then you need to know the ground rules and how the certification paddock was fenced.
This is made more difficult because the Design Standards are living, evolving documents .. ie, we can say that aircraft A, with frozen Design Standards appropriate to sometime 25 years ago, is a FAR 25 aircraft. Similarly, we can say that Aircraft B .. etc .. but with Standards appropriate to a year or so ago, is a FAR 25 aircraft. However, in the meantime, the Standards have changed more than quite a bit, so the two animals are quite different.
For those who don't have the detailed background knowledge, there is some merit in placing a degree of trust in the back room techo folk in the Regulator and the Operator.
Then again, the more knowledge the individual has, the better the likelihood that he/she can detect some of the occasions when it might not be sensible to trust too much in the information presented in the cockpit.
Old Smokey,
Very interesting view point with some excellent points to ponder! As you are well aware the whole concept of V1 and the timings associated with it have evolved over the years. With the present policy of accounting for worn brakes, VEF and the change in reaction timing, coupled with more realistic training devices such as Flight Simulator 2002, do you think that we have come far enough?
J_T,
I’m starting to get the impression that with the introduction of newer technology people are getting taught less about how an aircraft actually flies.
Mutt.
Very interesting view point with some excellent points to ponder! As you are well aware the whole concept of V1 and the timings associated with it have evolved over the years. With the present policy of accounting for worn brakes, VEF and the change in reaction timing, coupled with more realistic training devices such as Flight Simulator 2002
, do you think that we have come far enough?J_T,
I’m starting to get the impression that with the introduction of newer technology people are getting taught less about how an aircraft actually flies.
Mutt.
Perf A was sometime ago, and did'nt really understand anyway, but I think the original poster was getting a bit confused as to what an overrun is.
At V1 and a failure occurs, Ac can either Go or stop, the stop part means that it can come to a halt within the Accel Stop Dist Avail,,,ASDA and from hazey recolection this can include grass at the end of the runway,or some other semi prepared surface, forget the exact definition, but it will not always stop on the Black Stuff.
So just because aircraft left the runway at the end can mean it was stopped within the prescribed ASDA.
Besides as J T said, perf figures are for a prescribed set of circumstances, as you have to base them on something. It's just that it is pretty unlikely you will have those circumstances afffecting you on the day you hear ""RING RING" " V1", and as John Coleman said " What happened next"" answers to..
Ring Ring is the firebell by the way..
At V1 and a failure occurs, Ac can either Go or stop, the stop part means that it can come to a halt within the Accel Stop Dist Avail,,,ASDA and from hazey recolection this can include grass at the end of the runway,or some other semi prepared surface, forget the exact definition, but it will not always stop on the Black Stuff.
So just because aircraft left the runway at the end can mean it was stopped within the prescribed ASDA.
Besides as J T said, perf figures are for a prescribed set of circumstances, as you have to base them on something. It's just that it is pretty unlikely you will have those circumstances afffecting you on the day you hear ""RING RING" " V1", and as John Coleman said " What happened next"" answers to..
Ring Ring is the firebell by the way..
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Besides as J T said, perf figures are for a prescribed set of circumstances, as you have to base them on something. It's just that it is pretty unlikely you will have those circumstances afffecting you on the day you hear ""RING RING" " V1", and as John Coleman said " What happened next"" answers to..
