Aborting T/O after v1...question?
02-18-2008, 01:48 PM
#91
Tuk er jerbs!
Joined APC: Mar 2007
Position: B747 Left
Posts: 1,342
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, 02:23 PM
#92
Where's my Mai Tai?
Joined APC: Aug 2006
Position: fins to the left, fins to the right
Posts: 1,754
It's been over 9 years since I was on the 727, and I'm sure someone will correct me if I'm wrong, but I think the max effort stop at MTOW was less than 1500 feet. Everything melts but you can stop it. I know I've landed and stopped in less than 2250.
02-18-2008, 06:28 PM
#94
Chief Jeppesen Updater
Joined APC: Oct 2005
Position: Executive Transport Driver
Posts: 3,080
Out of curiousity, what does everybody use for performance data these days?
ACA used to use Jepp data, and then switched to AeroData performance. AD was superior in my opinion since it was run about 1 hour before launch and considered many various factors. We then used the lower of the AD V1 speed or the "book" V1 which might be significantly higher. AD numbers guaranteed both balanced field and SE takeoff performance at/above V1. (IE if the engine fails at a V1 of 85 knots on a contaminated runway, at the performance weight limit you still have enough runway to accelerate on 1 engine and takeoff).
ACA used to use Jepp data, and then switched to AeroData performance. AD was superior in my opinion since it was run about 1 hour before launch and considered many various factors. We then used the lower of the AD V1 speed or the "book" V1 which might be significantly higher. AD numbers guaranteed both balanced field and SE takeoff performance at/above V1. (IE if the engine fails at a V1 of 85 knots on a contaminated runway, at the performance weight limit you still have enough runway to accelerate on 1 engine and takeoff).
02-18-2008, 07:50 PM
#95
Gets Weekends Off
Joined APC: Aug 2007
Posts: 281
Doesn't matter how long the runway is, it is still only 150' (or whatever) wide. Many botched aborts or rejected takeoffs go off the side of the runway, not the end, especially when one pilot decides to use his experience to abort past V1 while the other pilot is following procedures and trying to continue flying.
At V1 you are already flying, the wheels just happen to still be on the ground. You'd rather have the whole runway to get her stopped than whatever happens to be remaining.
Of course, if you don't think the plane will fly, then you really don't have much choice, do you?
At V1 you are already flying, the wheels just happen to still be on the ground. You'd rather have the whole runway to get her stopped than whatever happens to be remaining.
Of course, if you don't think the plane will fly, then you really don't have much choice, do you?
02-18-2008, 09:22 PM
#96
Che Guevara
Joined APC: Aug 2005
Posts: 6,408
Doesn't matter how long the runway is, it is still only 150' (or whatever) wide. Many botched aborts or rejected takeoffs go off the side of the runway, not the end, especially when one pilot decides to use his experience to abort past V1 while the other pilot is following procedures and trying to continue flying.
At V1 you are already flying, the wheels just happen to still be on the ground. You'd rather have the whole runway to get her stopped than whatever happens to be remaining.
Of course, if you don't think the plane will fly, then you really don't have much choice, do you?
At V1 you are already flying, the wheels just happen to still be on the ground. You'd rather have the whole runway to get her stopped than whatever happens to be remaining.
Of course, if you don't think the plane will fly, then you really don't have much choice, do you?
02-18-2008, 10:18 PM
#97
Gets Weekends Off
Joined APC: Feb 2006
Position: DD->DH->RU/XE soon to be EV
Posts: 3,732
Out of curiousity, what does everybody use for performance data these days?
ACA used to use Jepp data, and then switched to AeroData performance. AD was superior in my opinion since it was run about 1 hour before launch and considered many various factors. We then used the lower of the AD V1 speed or the "book" V1 which might be significantly higher. AD numbers guaranteed both balanced field and SE takeoff performance at/above V1. (IE if the engine fails at a V1 of 85 knots on a contaminated runway, at the performance weight limit you still have enough runway to accelerate on 1 engine and takeoff).
ACA used to use Jepp data, and then switched to AeroData performance. AD was superior in my opinion since it was run about 1 hour before launch and considered many various factors. We then used the lower of the AD V1 speed or the "book" V1 which might be significantly higher. AD numbers guaranteed both balanced field and SE takeoff performance at/above V1. (IE if the engine fails at a V1 of 85 knots on a contaminated runway, at the performance weight limit you still have enough runway to accelerate on 1 engine and takeoff).
02-18-2008, 10:21 PM
#98
Gets Weekends Off
Joined APC: Feb 2006
Position: DD->DH->RU/XE soon to be EV
Posts: 3,732
How's hitting V1 at 115kts and stopping harder than landing at 125kts and stopping? The only way the other guy is still trying to fly is if there's a failure of communication. Plus the guy flying is the one making that decision. His hands are on the thrust levers and his feet are on the brakes. The only way the other guy should be "trying to fly" is if he's over there making the wrong callouts. His hands shouldn't be on the controls.
02-19-2008, 12:19 AM
#99
Gets Weekends Off
Joined APC: May 2007
Position: 330 FO
Posts: 584
How bout this one?
Good discussion and I'll add this.
Was flying with a LCA the other day and we were discussing this subject. He related the following actual event to me, what would you do?
You're taxiing out for takeoff. Airport is at or near mins. Wind shifts and they turn the airport around. You adjust your taxi and get to the end of the new deparure runway. You're cleared onto the rwy and cleared for takeoff. Right after V1 tower emphatically tells you to abort, not why....just "Delta 123 abort takeoff!!!"
Do you do it?
Well, this crew did and brought the jet to a stop just as a 737 still on approach from the opposite direction that tower had forgotten about broke through the ceiling dead ahead of them and initiated a go around.
Granted this scenario is surely rare but it does illustrate a situation where not only is your aircraft flyable, it has nothing wrong with it. Yet you take it flying and you may well have killed 2 planeloads.
Was flying with a LCA the other day and we were discussing this subject. He related the following actual event to me, what would you do?
You're taxiing out for takeoff. Airport is at or near mins. Wind shifts and they turn the airport around. You adjust your taxi and get to the end of the new deparure runway. You're cleared onto the rwy and cleared for takeoff. Right after V1 tower emphatically tells you to abort, not why....just "Delta 123 abort takeoff!!!"
Do you do it?
Well, this crew did and brought the jet to a stop just as a 737 still on approach from the opposite direction that tower had forgotten about broke through the ceiling dead ahead of them and initiated a go around.
Granted this scenario is surely rare but it does illustrate a situation where not only is your aircraft flyable, it has nothing wrong with it. Yet you take it flying and you may well have killed 2 planeloads.
02-19-2008, 07:10 AM
#100
Gets Weekends Off
Joined APC: May 2007
Position: A320 CA
Posts: 1,531
Actually in most airplanes and in ALL heavy's (at max gross), V1 doesn't mean you're flying. V1 can mean balance field length or Critical Engine Failure Speed or Vmcg or refusal speed occurred before Rotate and can be 40 knots or more before Vrotate....Vrotate is a fly speed, V1 is decision speed. No matter what you fly, V1 is not a "flying speed," it is a decision speed, even if it is co-located with Vrotate.
Last edited by blastoff; 02-19-2008 at 07:16 AM.
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