Aborting T/O after v1...question?
02-17-2008, 07:14 PM
#81
Che Guevara
Joined APC: Aug 2005
Posts: 6,408
A couple of points to add:
In my 8 (short) years of flying transport cat aircraft, I have yet to be able to figure out "exactly" how much runway I'm going to need without going to the books. When you're zipping down the pavement at 110+ knots can you really tell if you're going to stop if you hit the brakes?
In my 8 (short) years of flying transport cat aircraft, I have yet to be able to figure out "exactly" how much runway I'm going to need without going to the books. When you're zipping down the pavement at 110+ knots can you really tell if you're going to stop if you hit the brakes?
02-17-2008, 07:18 PM
#82
Che Guevara
Joined APC: Aug 2005
Posts: 6,408
Otherwise after v1 you're better off going, as previously mentioned you'll be at a much lower energy level when you come back around for landing. At 120+ knots is not the time to say hmmm...i think....it might be ..... better to.... stop on the runway. now you're aborting from an even higher speed.
02-17-2008, 07:44 PM
#83
Gets Weekends Off
Joined APC: Dec 2007
Posts: 829
The argument that "past V1, we are going flying, period" shows a distinct lack of thought on what it means to be at V1. As previously mentioned, V1 is:
1) The maximum speed by which a rejected takeoff must be initiated to assure that a safe stop can be completed within the remaining runway ... and stopway.
2) The minimum speed that assures takeoff can be safely completed within the remaining runway ... and clearway, after failure of the most critical engine at a designated speed.
3) The single speed that permits a successful stop or continued takeoff when operating at the minimum allowable field length for a particular weight.
In no case will V1 be greater than Vr. In cases where V1 would otherwise be greater than Vr (i.e. on a ridiculously long runway), V1=Vr. On shorter and/or contaminated runways, there is an ever increasing V1/Vr split (V1 then Vr). On longer runways, especially when V1=Vr, the excess runway remianing after accelerating to V1 then stopping can be referred to as Stop Margin. If the stop margin is 10,000', any aborts after V1 will exceed the V1 abort distance and work into that 10,000'; and the greater the abort speed, the greater the portion of the remaining 10,000' will be used.
If you are at or slightly past V1 with a large stop margin, a decision to abort can be made and you will most likely remain on the runway.
While it is true that high speed aborts are statistically more dangerous than take-off continued, there are variables that must be considered. As TOGW increases and T/O speeds are generally increased; the energy that must be dissipated in the abort increases. That means that aborting in a fully loaded 747 is different than aborting in a fully loaded CRJ. Besides the TOGW increase multiple, you must also consider the generally higher speeds of the 747 than the CRJ. As KE = 1/2mv(2), the difference in KE is going to be the difference in mass times the difference in ground speed squared. While we can all agree that the braking system of a 747 is more capable than that of a CRJ, it isn't that many times more capable. Let's call the ratio of braking capability and 1/2mv(2) excess braking capability. Given the modern anti-skid on both aircraft and stopping capability of modern brake ssytems, the excess braking capability of a CRJ is actually greater than the excess braking capability of a 747 when the full KE is considered. Don't believe it, watch a few landings and see if the CRJ's don't turn off at an intersection well before the heavies. All that being said, rules of thumb that apply to 747 and MD-11 aborts don't necessarily transfer to CRJs and King Air's.
The answer to the question is the heart of two things: why you get paid for your experience, and why there is no substitute for experience. Everything we do is risk management. Given the scenario, it was far less risky to stop and ground egress than it was to take an active fire into the air. Make the wx bad, and the decision to stop is even wiser. Shorten the runway and make the wx CAVU, it starts to become less risky (relatively speaking) to go flying. Change the variables, and you change the answer. There is rarely such a black and white answer in aviation as "past V1, I am going, period." If you believe that statement without a conscious review and evaluation of the facts of the scenario, then you need more of that experience.
1) The maximum speed by which a rejected takeoff must be initiated to assure that a safe stop can be completed within the remaining runway ... and stopway.
2) The minimum speed that assures takeoff can be safely completed within the remaining runway ... and clearway, after failure of the most critical engine at a designated speed.
3) The single speed that permits a successful stop or continued takeoff when operating at the minimum allowable field length for a particular weight.
In no case will V1 be greater than Vr. In cases where V1 would otherwise be greater than Vr (i.e. on a ridiculously long runway), V1=Vr. On shorter and/or contaminated runways, there is an ever increasing V1/Vr split (V1 then Vr). On longer runways, especially when V1=Vr, the excess runway remianing after accelerating to V1 then stopping can be referred to as Stop Margin. If the stop margin is 10,000', any aborts after V1 will exceed the V1 abort distance and work into that 10,000'; and the greater the abort speed, the greater the portion of the remaining 10,000' will be used.
If you are at or slightly past V1 with a large stop margin, a decision to abort can be made and you will most likely remain on the runway.
While it is true that high speed aborts are statistically more dangerous than take-off continued, there are variables that must be considered. As TOGW increases and T/O speeds are generally increased; the energy that must be dissipated in the abort increases. That means that aborting in a fully loaded 747 is different than aborting in a fully loaded CRJ. Besides the TOGW increase multiple, you must also consider the generally higher speeds of the 747 than the CRJ. As KE = 1/2mv(2), the difference in KE is going to be the difference in mass times the difference in ground speed squared. While we can all agree that the braking system of a 747 is more capable than that of a CRJ, it isn't that many times more capable. Let's call the ratio of braking capability and 1/2mv(2) excess braking capability. Given the modern anti-skid on both aircraft and stopping capability of modern brake ssytems, the excess braking capability of a CRJ is actually greater than the excess braking capability of a 747 when the full KE is considered. Don't believe it, watch a few landings and see if the CRJ's don't turn off at an intersection well before the heavies. All that being said, rules of thumb that apply to 747 and MD-11 aborts don't necessarily transfer to CRJs and King Air's.
The answer to the question is the heart of two things: why you get paid for your experience, and why there is no substitute for experience. Everything we do is risk management. Given the scenario, it was far less risky to stop and ground egress than it was to take an active fire into the air. Make the wx bad, and the decision to stop is even wiser. Shorten the runway and make the wx CAVU, it starts to become less risky (relatively speaking) to go flying. Change the variables, and you change the answer. There is rarely such a black and white answer in aviation as "past V1, I am going, period." If you believe that statement without a conscious review and evaluation of the facts of the scenario, then you need more of that experience.
Last edited by LivingInMEM; 02-17-2008 at 07:51 PM. Reason: spelling
02-17-2008, 08:55 PM
#84
Gets Weekends Off
Joined APC: Dec 2005
Position: Leftof longitudinal
Posts: 1,899
Well you can land an erj at 130kts and stop her in 2500ft. So if I'm at 110+ I'd say yes. Again it's all situation dependent but that's part of knowing your aircraft. I know that if I stand on the breaks and put the reversers on that you'll have to fight to stay upright in your seat. A heavy 737 or CRJ might be completely different, it's the pilot's call that's why he's paid the big bucks.
02-17-2008, 09:14 PM
#85
Che Guevara
Joined APC: Aug 2005
Posts: 6,408
Your right, each type a/c is different. Curious if that 2500 ft is at MGTOW? Planes act a whole lot different when maximum braking between MGTOW and your normal landing weight. Don't know about RJ's, but on the 8 it is "scary"different if you are 100,000lbs apart. Takes way longer and expect burning tires when stopped. Know RJ spread would be alot less, but I remember the CL at Teterboro that did the RTO (wouldn't rotate) awhile back and went into the warehouse.
02-18-2008, 05:29 AM
#86
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Joined APC: May 2006
Posts: 394
02-18-2008, 07:03 AM
#88
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Joined APC: Dec 2006
Position: I was acquired, Not Hired
Posts: 1,784
Thanks to the original poster for bringing this up. This is a very informative post.
Just my two cents worth...
In the posting above by LivinginMEM, the quote, "The argument that "past V1, we are going flying, period" shows a distinct lack of thought on what it means to be at V1"...probaby summarizes this debate the best, IMHO.
Here's my viewpoint, we all know what the definition of V1 is, but do we know how we derive it's value ?
For example, at my earlier days at TWA we used a perfromance vendor that would give us V1 values for a max thrust departure on the 757 (PW2037 engines) with a spread of typically 10-15 knots from VR. When we switched over to American Airlines' perfromance vendor using the same flap settings the spread was narrower, typically 5-7 knots between V1 and VR. Taken one step further, many of those former TWA 757s are in service for Delta Airlines with winglets and, I would presume Delta has their own performance vendor and let's say for argument's sake that their spread between V1 and Vr is different than both American's and TWA's.
Why is that ? Same flap setting, all three scenarios include max thrust, and the engines are the same. Additionally, all three performance vendors had their software approved by the FAA.
So take the scenario one step further, take the same 757 and have it depart from let's say DFW. If it were possible, have the three (3) 757s brand new from Boeing, with three test pilots crews but departing using TWA's takeoff numbers, one with American's and one with Delta's.
Each of them will get an engine fire at 125 knots, the TWA airplane has a V1 of 120, the AA at 130, the Delta 127. All three will have a rotation speed of about 135 knots and a V2 at 140 knots.
So here we go, TWA gets the fire at 125 knots and they elect to fly. AA gets the fire at 125 knots they reject, and Delta gets the fire at 125 knots and this time they elect to abort, but with two knots difference between the fire and V1 it's a real nail bitter for anyone.
So with two and a half different outcomes, who did the right thing with the exact same airplane and the same scenario ?
All three did.
Tying this back to the original post, let's say you're in a Shorts 360. You're V Speeds are 115/120/125. You're taking off out of JFK on runway 31L which at full length is 14572 ft and it is 95 degrees F and you have 36 pax (26,453 lbs). Ok, so at 118 knots you get an engine fire and you elect to fly. You manually shut down the engine, feather the prop, RTOP the good engine and all you get is 576 feet of altitude and you're pointed at the Empire State Building. Or taken the scenario in the other direction, you abort with 12,000 feet of runway remaining at a speed of 120 knots.
Take that same scenario and now you're in a 747-100 with Pratt engines. At MGTOW, same temperature, and a full load of everything; your V speeds are somewhere in the 165/175/188 range as a guess. At 163 knots, you get a fire and elect to reject, you may get it the plane stopped before you get to the employee parking lot of Lefferts and you probably will thermally melt half your tires and run the risk of a fire.
Next topic, then i'll wrap it up. If you reject after V1 in an airline/type rating checkride you will probably fail your checkride. The reason is, checkrides are for the most part a planned event where there is a desired outcome based on a training syllabus. In addition, if you reject after V1 and wreck the plane, you won't have a leg to stand on at the hearing.
Now to tie in with what LivinginMEM said and my two cents worth. There is a reason Capt's are paid the big bucks because they are risk manager's which have to evaluate unique situations and resolve them. Some of them have the luxary of all day (passengers arriving late and missing their connections) and some split second which coincides with this posting.
Training allows you to successfully complete training events, checkrides and such which have more or less planned outcomes. Experience on the other hand coupled with training allows you to deal with all the other situations whose outcomes are less than planned.
My final thought, before every takeoff, before every landing take a few seconds and evaluate what the situation is. Stack the deck in your favor proactively, "...should we use max thrust, should we ask for the longest runway, should we take a runway better aligned with the wind since it has ice on it, etc". When we lower the risk, then we create options, as opposed to being like a trained robot with only one option, whereas; once you hear, "V1...engine fire..." we have no doubt no matter the scenario, that we are going flying.
Your mileage may vary....below is a 54 second, youtube clip about a high speed abort in a 747. I'm sure on paper, the numbers told the Capt that he had more than enough room to stop in the event of an engine problem before V1. I'm pretty sure the reject was started before V1, if you have different facts, please feel free to correct my post.
FF
http://www.youtube.com/watch?v=MH9_4...eature=related
Just my two cents worth...
In the posting above by LivinginMEM, the quote, "The argument that "past V1, we are going flying, period" shows a distinct lack of thought on what it means to be at V1"...probaby summarizes this debate the best, IMHO.
Here's my viewpoint, we all know what the definition of V1 is, but do we know how we derive it's value ?
For example, at my earlier days at TWA we used a perfromance vendor that would give us V1 values for a max thrust departure on the 757 (PW2037 engines) with a spread of typically 10-15 knots from VR. When we switched over to American Airlines' perfromance vendor using the same flap settings the spread was narrower, typically 5-7 knots between V1 and VR. Taken one step further, many of those former TWA 757s are in service for Delta Airlines with winglets and, I would presume Delta has their own performance vendor and let's say for argument's sake that their spread between V1 and Vr is different than both American's and TWA's.
Why is that ? Same flap setting, all three scenarios include max thrust, and the engines are the same. Additionally, all three performance vendors had their software approved by the FAA.
So take the scenario one step further, take the same 757 and have it depart from let's say DFW. If it were possible, have the three (3) 757s brand new from Boeing, with three test pilots crews but departing using TWA's takeoff numbers, one with American's and one with Delta's.
Each of them will get an engine fire at 125 knots, the TWA airplane has a V1 of 120, the AA at 130, the Delta 127. All three will have a rotation speed of about 135 knots and a V2 at 140 knots.
So here we go, TWA gets the fire at 125 knots and they elect to fly. AA gets the fire at 125 knots they reject, and Delta gets the fire at 125 knots and this time they elect to abort, but with two knots difference between the fire and V1 it's a real nail bitter for anyone.
So with two and a half different outcomes, who did the right thing with the exact same airplane and the same scenario ?
All three did.
Tying this back to the original post, let's say you're in a Shorts 360. You're V Speeds are 115/120/125. You're taking off out of JFK on runway 31L which at full length is 14572 ft and it is 95 degrees F and you have 36 pax (26,453 lbs). Ok, so at 118 knots you get an engine fire and you elect to fly. You manually shut down the engine, feather the prop, RTOP the good engine and all you get is 576 feet of altitude and you're pointed at the Empire State Building. Or taken the scenario in the other direction, you abort with 12,000 feet of runway remaining at a speed of 120 knots.
Take that same scenario and now you're in a 747-100 with Pratt engines. At MGTOW, same temperature, and a full load of everything; your V speeds are somewhere in the 165/175/188 range as a guess. At 163 knots, you get a fire and elect to reject, you may get it the plane stopped before you get to the employee parking lot of Lefferts and you probably will thermally melt half your tires and run the risk of a fire.
Next topic, then i'll wrap it up. If you reject after V1 in an airline/type rating checkride you will probably fail your checkride. The reason is, checkrides are for the most part a planned event where there is a desired outcome based on a training syllabus. In addition, if you reject after V1 and wreck the plane, you won't have a leg to stand on at the hearing.
Now to tie in with what LivinginMEM said and my two cents worth. There is a reason Capt's are paid the big bucks because they are risk manager's which have to evaluate unique situations and resolve them. Some of them have the luxary of all day (passengers arriving late and missing their connections) and some split second which coincides with this posting.
Training allows you to successfully complete training events, checkrides and such which have more or less planned outcomes. Experience on the other hand coupled with training allows you to deal with all the other situations whose outcomes are less than planned.
My final thought, before every takeoff, before every landing take a few seconds and evaluate what the situation is. Stack the deck in your favor proactively, "...should we use max thrust, should we ask for the longest runway, should we take a runway better aligned with the wind since it has ice on it, etc". When we lower the risk, then we create options, as opposed to being like a trained robot with only one option, whereas; once you hear, "V1...engine fire..." we have no doubt no matter the scenario, that we are going flying.
Your mileage may vary....below is a 54 second, youtube clip about a high speed abort in a 747. I'm sure on paper, the numbers told the Capt that he had more than enough room to stop in the event of an engine problem before V1. I'm pretty sure the reject was started before V1, if you have different facts, please feel free to correct my post.
FF
http://www.youtube.com/watch?v=MH9_4...eature=related
Last edited by FliFast; 02-18-2008 at 05:11 PM. Reason: Sobreity
02-18-2008, 10:36 AM
#89
Gets Weekends Off
Joined APC: Jun 2006
Position: CL605 PIC
Posts: 187
When I was sitting through basic systems training as a new-hire about 1 1/2 years ago, we had a discussion about this very topic, and the most senior ground instructor in the training center was brought into the class to answer some questions.
As some people have said in this thread already, most regional airlines (including us at XJT) claim to use balanced field numbers when calculating the takeoff performance data for all runways system-wide.
This is complete and utter b/s.
Somebody mentioned that their CRJ V1 and Vr numbers are often quite far apart, and i know this to be the case in larger jets like the 747. In our E-145 and E-135 aircraft, V1 and Vr are always the same.
Recently I was flying back to IAH from CRW (a 2.5 hour flight requiring nearly 10000 lbs of fuel) in a 135. It's a 6300ft runway at 1000' MSL which requires a flaps 18 takeoff (instead of the normal flaps 9).
This airport is built on top of a large hill, with sharp drop-offs on all sides including either end of this short runway.
Even with the flaps 18 takeoff, our V1 and Vr speeds were reached with much less than 2000' remaining on that runway. If this field was balanced, then I'll be a monkey's uncle...
There is NO WAY on earth that we could have even come close to stopping the airplane even at 10 knots below V1.
This is not a one off situation, either. Many times on shorter runways the end of the runway is fast approaching when the "V1, rotate" call is made leaving me thanking my lucky stars we hadn't had an engine failure or some other reason to have made a high speed abort...
Balanced... My arse...
As some people have said in this thread already, most regional airlines (including us at XJT) claim to use balanced field numbers when calculating the takeoff performance data for all runways system-wide.
This is complete and utter b/s.
Somebody mentioned that their CRJ V1 and Vr numbers are often quite far apart, and i know this to be the case in larger jets like the 747. In our E-145 and E-135 aircraft, V1 and Vr are always the same.
Recently I was flying back to IAH from CRW (a 2.5 hour flight requiring nearly 10000 lbs of fuel) in a 135. It's a 6300ft runway at 1000' MSL which requires a flaps 18 takeoff (instead of the normal flaps 9).
This airport is built on top of a large hill, with sharp drop-offs on all sides including either end of this short runway.
Even with the flaps 18 takeoff, our V1 and Vr speeds were reached with much less than 2000' remaining on that runway. If this field was balanced, then I'll be a monkey's uncle...
There is NO WAY on earth that we could have even come close to stopping the airplane even at 10 knots below V1.
This is not a one off situation, either. Many times on shorter runways the end of the runway is fast approaching when the "V1, rotate" call is made leaving me thanking my lucky stars we hadn't had an engine failure or some other reason to have made a high speed abort...
Balanced... My arse...
02-18-2008, 01:32 PM
#90
Gets Weekends Off
Joined APC: Jan 2008
Posts: 888
I agree with FliFast, the original question involved a training event v1 cut. If you aren't in upgrade training trying to prove you can think outside the box and consider other variables, the guys doing initial training just want to see you fly come back around and land, when you aborted you ruined his syllibus b/c he was supposed to either teach you or test you on single engine performance etc.
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