Screaming_Emu
Well-Known Member
I think the theory is that after you rotate, you won't be aborting. Which in this situation isn't entirely correct.
V1, Rotate- and the jet won't. You're the FO..
- Thread starter Firebird2XC
- Start date
I think the theory is that after you rotate, you won't be aborting. Which in this situation isn't entirely correct.
Screaming_Emu
Well-Known Member
Gotcha. The numbers are there, but the powers that be keep them secret...
That seems to be a trend. Our manuals are getting more and more dumbed down. One of our flight attendants had a misconception about what had to do with the railings for the air stairs before the door was closed. I got my manual out to make sure I wasn't the one screwing it up. Our manual basically said "you have rails on the air stairs."
Agreed... Normally for us though, Vr is typically 10 kts faster than V1. The time between V1 and Vr are definitely open to possible aborts when the aircraft is UNFLYABLE.
In the civil world, it's done a little differently than you and I did/do it military. You're thinking Situation 1/2/3 type thinking......where 1 is CFL is less than RL, 2 where they're equal, 3 where CFL exceeds RL. So not only are there Refusal Speeds (V1/S1, whatever), there's also Decision Speeds.
In civil, you can have so much runway available, that V1 climbs up to and eventually meets Vr. V1 never exceeds Vr (though it technically can), because you're getting airborne by then. Emu was making the good point that starts to talk to what you and I understand, in terms of knowing what that excess runway length is, and how it can help you for an abort past V1 if necessary.
Screaming_Emu
Well-Known Member
We very rarely have any kind of split. We will usually only see it on a contaminated runway. Even on most short runways you'll only see a few knots of split because our data includes stop ways off the end of the runway (which is pretty dumb in my opinion).
It happens so rarely that when PF and there is a large split I request that when the captain calls V1, he follows with "don't rotate." I'm a creature of habit and could see myself expecting V1 and Vr to be the same. "Then you're gonna have a bad time..."
Sounds like the with the military version, it's more "go" oriented, and more "stop" in civil then. If you're allowing RA drive V1, you're going to have a much longer time until reaching V1 in order to stop.
That's the thing, for you and me, we can have a Decision Speed which can be past Refusal Speed, CFL dependant. We aren't going to be able to stop, but we'll still be able to get airborne at that speed (not that it would matter with a plane that's incapable of flying; am only talking performance-wise), whereas civil, V1 will only go as high as Vr and not beyond (though it technically exists beyond, RA-dependant).
Actually, we don't ever let V1 pass Refusal. If V1 > Vrefusal, we reduce gross weight to make CFL equal to RA, therefore V1 = Vrefusal.
It sounds like from the civil standpoint thought, they aren't computing a true V1 as you and I know it. They're basing it off of Vrotate and the RA instead of CFL.
All of our numbers are based on reaching Vmcg as quickly as possible. Once there, it's safer to maintain thrust and take the aircraft airborne than it is to stop.
If civil is basing it more on the premise of maximizing time to abort, it makes sense to take V1 as high as Vrotate. The aircraft might be "flyable" sooner than the civil charted V1, but the pilot will have more time to decide on an abort.
Back in the day, if CFL exceeded RA, we could still go, pending we had higher level approval....ie- combat necessity. Made no sense to download bombs or munitions, or fuel if there was no airborne tanker and/or no time to go to one. That was all part of the risk. Too though, we had arresting cables and/or barriers, or drag chutes, to assist.
It sounds like from the civil standpoint thought, they aren't computing a true V1 as you and I know it. They're basing it off of Vrotate and the RA instead of CFL. [/quote]
Yes. V1 for civil, in some cases, can be artificial when it equals Vr (even though it could exceed it).......the example given where there's tons of RA, and CFL is far shorter than that.
Which makes sense for an E-6 and having the CFMs. For most tail-mounted or centerline thrust jets like MD-80, RJ, etc, Vmcg is likely not much of a factor (someone here can correct me if wrong).
Based on RA, yes......maximizing the time to abort prior to liftoff, when it equals Vr; but like the OP situation here.......knowing what the true maximization (what the "real" V1 is) for times when you have tons of RA beyond the CFL, and need to use it.
BEEF SUPREME
Well-Known Member
Not an airline pilot but this happened to me in a Citation 2. We picked up the airplane from a 10k hr check. The trim was rigged backwards. When I called V1, Rotate nothing happened. It was a very strange feeling and by the time I realized that we were not going to fly, somethings wrong we should abort and I should call abort the captain had already started to abort. In the short time it took us to recognize the problem and take action we had gone way over rotation speed. We used a lot of runway and the brakes were smoking as we taxied back into the ramp.
Just to address the armchair QB camp here at JC: 2 pilots and 3 mechanics, who rode along for the flight, thoroughly preflighted the aircraft. I ran the trim all the way forward and all the way back in the cockpit but not while anyone was looking at it. I set take off trim and looked at the trim tab. It was flush with the elevator and there was no indication of where it should have been.
One thing I am proud of is suggesting we use the longer runway which was a much longer taxi. Usually for a citation 2 a 7k foot runway is fine but after I mentioned that hey this thing was taken apart and put back together, we elected to use the 10k+ runway.
As we were stopping I looked out and watched the end of the short runway go by. Certainly things could have been much worse this day. I certainly don't feel good about picking up an aircraft from MX.
Just to address the armchair QB camp here at JC: 2 pilots and 3 mechanics, who rode along for the flight, thoroughly preflighted the aircraft. I ran the trim all the way forward and all the way back in the cockpit but not while anyone was looking at it. I set take off trim and looked at the trim tab. It was flush with the elevator and there was no indication of where it should have been.
One thing I am proud of is suggesting we use the longer runway which was a much longer taxi. Usually for a citation 2 a 7k foot runway is fine but after I mentioned that hey this thing was taken apart and put back together, we elected to use the 10k+ runway.
As we were stopping I looked out and watched the end of the short runway go by. Certainly things could have been much worse this day. I certainly don't feel good about picking up an aircraft from MX.
The C550 I fly, we have the same luxury of a long runway......almost 14,000'; so we get the same V1 = Vr darn-near all the time, with the "true" V1 being some high number somewhere......probably max tire speed or something.
Good job getting it done. Looks like the standard "3 second delay" that's figure into standard accelerate-stop calc's for the problem recognition to abort call and action, actually occurred.
BEEF SUPREME
Well-Known Member
The C550 I fly, we have the same luxury of a long runway......almost 14,000'; so we get the same V1 = Vr darn-near all the time, with the "true" V1 being some high number somewhere......probably max tire speed or something.
Good job getting it done. Looks like the standard "3 second delay" that's figure into standard accelerate-stop calc's for the problem recognition to abort call and action, actually occurred.
Well when you haul back on the yoke and nothing happens there certainly is a WTF moment. I certainly was not expecting that to happen and was never trained for anything like that. Of course I'm sure I had one of those slow motion perception moments.
Polar742
All the responsibility none of the authority
YOU aren't calculating a TRUE V1
In our world, V1 can have a multitude of factors used to calculate that number. V1 is merely a speed that takes in a number of factors, afterwhich, it has been determined to be safer to take a plane in the air than try to stop it on the ground.
In lieu of the original 0.000001% chance of the scenario that was the first post of this thread, (for my unofficial and off the cuff rule "Crash at the slowest speed possible" I'd probably take an airplane not wanting to fly on a 14,000' runway and stop, even if it's past V1. I figure that I'd do a better job slowing down, controlling and stopping the aircraft with minimal damage than taking a machine that DOES NOT want to fly into the air /ramble) V1 takes a number of factors, and indeed even at the same weight, due to environmental conditions (slick runway) you might have a different V1.
In the examples where V1 is equal to Vr, the concept is called "Balanced Field Length" in most cases. In this scenario, the distance from the point where take off thrust is set, you get to V1 and you stop or you get to V1 and fly to 35' is equal.
So, for the sake of simplicity, we'll use a 6000' runway. It takes 3000' to get to V1, initiate the abort, bring the machine to a stop on a dry runway you'll use, oddly today, 6000'. On the other hand, if you lose an engine at that point and continue the takeoff, you'll be 35' above the runway at 6000'. We'll say for instance, in this scenario that V1 and Vr are 155 kts.
This example is going to be way deep pretend, but let's assume we change absolutely nothing outside the runway condition. Let's look at the same runway, but it's got a bunch of packed snow on it. Doing the math, we find the jet at the same weight needs 4500' to stop - 1500' into the off road zone. We could a) make the jet lighter so it can maybe have 3000' to stop, as that's what it would take at the same weight as the example above - which means leaving money behind. or, b) we could back up the V1 to a point that if we closed the throttles, we'd get 4500' to stop. The jet won't fly any sooner, but it needs way more space to stop than a dry runway.
So in this instance our performance program decides we'll be at 120 kts 1500' down the runway. So now V1 is 120 kts, and Vr is still 155 kts.
What we've done is "unbalanced" the field meaning we've decided to take a much further distance to climb to 35' than the 6000' of runway. The airplane will still stop on the 6000' runway, but it might not make 35' until 7500' down from the takeoff end versus 6000' in the good weather example.
Kind of like when you see a 747 way at the far end of the runway just rotating and getting off the ground. Most folks are like "Well, I hope he doesn't have to stop now!", but in fact the decision to abort was made way before at the point where the brakes wouldn't haul the machine to a stop on the remaining concrete.
This is a very simplistic example, but I hope it illustrates the point well.
This is the last post-V1 abort I know of:
Polar,
Completely understand your explanation. The part that gets me is the acceptance of an "unbalanced" field. By "reducing" V1 based solely on the fact that you don't have the runway available and you don't want to leave "money" behind boggles the mind.
Granted, as MikeD and I were talking about, most of the info I work with is a Vmcg (Minimum Control Ground) problem with the four engine aircraft. However, I assume that even in the large two engine aircraft of the day, losing one of the motors during the takeoff still would still cause a Vmcg issue depending on just how big your rudder is.
For us, our balanced field length would be based on Vcef (Critical Engine Failure). On a nice day with some hefty crosswinds, we also need to consider Vmcg (Minimum Control Ground). Both of these are considered when we come up with our Critical Field Length (CFL); distance required to accelerate on four engines, lose a motor, and either continue or abort the takeoff. Once these is calculated, we pretty much forget about any "extra" runway ahead of us. If we have a 12,000 ft runway, but our CFL (Critical Field Length) is 7,000 ft, we're "never" going to use the extra 5,000 ft.
What I'm getting from all the "civil" explanations, and yours as well, is that V1 is only based on accelerate-stop speeds, what we would call Vrefusal. We as well, cannot have a V1 above Vrefusal, makes stopping sporty like you've said. But, if we don't reduce weight, now at our "V1," we may not have reached Vmcg or Vcef.
For us,
Normally, Vmcg < Vcef = V1 < Vrefusal and Vr (Balanced Field)
Heavy Crosswinds, Vcef < Vmcg = V1 < Vrefusal and Vr (Unbalanced, as it'll take less room to takeoff than it does to stop)
When do run into the Vcef < Vmcg area, we will reduce the thrust of our outboard engines to regain a balanced field length. However, we can only reduce our motors so much before the inboard engines become more critical and Vcef becomes driven by them. If we reduce them to the limit, we will remain on an "unbalanced" field.
Now, you can make the argument that you can use that extra 5,000 ft for stopping if need be. And that's where we fall into with the OP. If we have a failure AFTER V1 that makes the aircraft INCAPABLE of flight, we'll abort. The extra 5,000 will come in handy and, heck, we weren't going to fly anyways.
But, in all the examples ya'll have given, you base V1 essentially ONLY on the fact about possibly being able to stop in the runway available. While this is GREAT for stopping, it opens up the possibility that you'll be attempting to fly an aircraft, past V1, that is NOT safe to fly. If you lose a motor past your "reduced to carry all the money" V1, are you sure you'll be at or past Vmcg? If you don't have the rudder available, you just don't have it. This is where my sticking point is.
Sorry for the lengthy post, just feel like I'm missing part of the conversation somewhere.
Completely understand your explanation. The part that gets me is the acceptance of an "unbalanced" field. By "reducing" V1 based solely on the fact that you don't have the runway available and you don't want to leave "money" behind boggles the mind.
Granted, as MikeD and I were talking about, most of the info I work with is a Vmcg (Minimum Control Ground) problem with the four engine aircraft. However, I assume that even in the large two engine aircraft of the day, losing one of the motors during the takeoff still would still cause a Vmcg issue depending on just how big your rudder is.
For us, our balanced field length would be based on Vcef (Critical Engine Failure). On a nice day with some hefty crosswinds, we also need to consider Vmcg (Minimum Control Ground). Both of these are considered when we come up with our Critical Field Length (CFL); distance required to accelerate on four engines, lose a motor, and either continue or abort the takeoff. Once these is calculated, we pretty much forget about any "extra" runway ahead of us. If we have a 12,000 ft runway, but our CFL (Critical Field Length) is 7,000 ft, we're "never" going to use the extra 5,000 ft.
What I'm getting from all the "civil" explanations, and yours as well, is that V1 is only based on accelerate-stop speeds, what we would call Vrefusal. We as well, cannot have a V1 above Vrefusal, makes stopping sporty like you've said. But, if we don't reduce weight, now at our "V1," we may not have reached Vmcg or Vcef.
For us,
Normally, Vmcg < Vcef = V1 < Vrefusal and Vr (Balanced Field)
Heavy Crosswinds, Vcef < Vmcg = V1 < Vrefusal and Vr (Unbalanced, as it'll take less room to takeoff than it does to stop)
When do run into the Vcef < Vmcg area, we will reduce the thrust of our outboard engines to regain a balanced field length. However, we can only reduce our motors so much before the inboard engines become more critical and Vcef becomes driven by them. If we reduce them to the limit, we will remain on an "unbalanced" field.
Now, you can make the argument that you can use that extra 5,000 ft for stopping if need be. And that's where we fall into with the OP. If we have a failure AFTER V1 that makes the aircraft INCAPABLE of flight, we'll abort. The extra 5,000 will come in handy and, heck, we weren't going to fly anyways.
But, in all the examples ya'll have given, you base V1 essentially ONLY on the fact about possibly being able to stop in the runway available. While this is GREAT for stopping, it opens up the possibility that you'll be attempting to fly an aircraft, past V1, that is NOT safe to fly. If you lose a motor past your "reduced to carry all the money" V1, are you sure you'll be at or past Vmcg? If you don't have the rudder available, you just don't have it. This is where my sticking point is.
Sorry for the lengthy post, just feel like I'm missing part of the conversation somewhere.
Polar742
All the responsibility none of the authority
No worries.
The fact that "V1" means 2 different things in 2 different communities causes the issue. We do the same stuff you do for calculations, but we approach it from a different angle. The same issues are looked at, but they are presented way differently.
In civilian V1, when you lose an engine at or after V1, the aircraft is not only safe to fly, it's actually safer than stopping. Before V1 it is safer to stop the aircraft than fly. Mainly due to all the factors you pointed out in your post in regards to Vmcg, Vmca, braking ability, OEI controllability and OEI climb ability.
We can reduce V1, but usually only to the point where VMcg is not an issue.
It all works the same 2 engine or 4 engine under Part 25.
The fact that "V1" means 2 different things in 2 different communities causes the issue. We do the same stuff you do for calculations, but we approach it from a different angle. The same issues are looked at, but they are presented way differently.
In civilian V1, when you lose an engine at or after V1, the aircraft is not only safe to fly, it's actually safer than stopping. Before V1 it is safer to stop the aircraft than fly. Mainly due to all the factors you pointed out in your post in regards to Vmcg, Vmca, braking ability, OEI controllability and OEI climb ability.
We can reduce V1, but usually only to the point where VMcg is not an issue.
It all works the same 2 engine or 4 engine under Part 25.
Firebird2XC
Well-Known Member
Here's another thought-
What if it's not the airplane having a mechanical issue, but a problem with your payload and/or CG?
Depending on weather conditions such as Density Altitude, prevailing winds, windshear/microburst, things could also go very wrong during the takeoff roll.
I seems to me that many pilots assume that approach and landing is where things go really wrong, but takeoff accidents are definitely on the chart as well. That's another reason why a good FO is backing up the CA and carefully checking numbers. Even if it's just a "Captain's task" or something the Skipper usually does, learning the process and backing them up can be vital.
Example: Once, I noted that a station actually took the leeway of the difference between Takeoff Weight and Max Ramp Weight. We had to sit for ten minutes and burn off fuel.
Another time.. I ..heard.. of a station that "made a typo" on the fuel onboard in the Automated Weight and Balance software. The "typo" made their numbers work. Given the runway length and potential CG issues, the FARs were the least of my concern. The Laws of Physics took the forefront. Needless to say the crew took decisive action to correct the "typo" before pushback.
What if it's not the airplane having a mechanical issue, but a problem with your payload and/or CG?
Depending on weather conditions such as Density Altitude, prevailing winds, windshear/microburst, things could also go very wrong during the takeoff roll.
I seems to me that many pilots assume that approach and landing is where things go really wrong, but takeoff accidents are definitely on the chart as well. That's another reason why a good FO is backing up the CA and carefully checking numbers. Even if it's just a "Captain's task" or something the Skipper usually does, learning the process and backing them up can be vital.
Example: Once, I noted that a station actually took the leeway of the difference between Takeoff Weight and Max Ramp Weight. We had to sit for ten minutes and burn off fuel.
Another time.. I ..heard.. of a station that "made a typo" on the fuel onboard in the Automated Weight and Balance software. The "typo" made their numbers work. Given the runway length and potential CG issues, the FARs were the least of my concern. The Laws of Physics took the forefront. Needless to say the crew took decisive action to correct the "typo" before pushback.
jynxyjoe
Queso King
It seems like you are asking two questions. If the payload and CG are off by 1000lbs how much difference does it make on your V1, 3 knots? If you are out of CG and the plane rotates funny I find it unlikely any (non-ninja handed) pilot is going to really understand how screwed they are until the thing is in the air, so the question is moot.
DA and tailwinds are calculated on my airplane. Windshear / Microburst activity you are going NO-FLEX and I always rotate a little slower in those conditions as the book says to consider. I think we've all taken off enough times, as professional pilots, in areas of major windshear and microburst activity to realize it is just as random as a red light event would be and that we aren't (as professional aviators) going to wring our hands at what else can go wrong when your training says to do something. I blew an engine at V1- bad day. On top of that, in climbout I hit a microburst- bad day turned into real bad day. Statically, wildly unlikely. If the engine fails and at the same time you see the trees being flattened by wind at the end of the runway and you elect to keep it on the ground I'll back you up. If you elect to abort after V1 purposefully because of ATIS report of windshear during taxi I don't agree with the decision making.
It seems like you are cascading and confounding the question of a go or no go. This question, while paramount, is not the type of question you load up with as many factors as you can in hopes of stressing out a pilot, unless you are the screaming sim instructor for the beech 1900 back at Colgan. You have exceptionally limited time past V1 to make a decision to abort, but the odds are in your favor that if you fall back on training you'll be ok.
Firebird2XC
Well-Known Member
Eh, this really becomes clearer when you've flown the -145. The horizontal stab and elevator are small, and when the CG is more forward, you can tell. A 'forward caution zone' CG usually requires a more deliberate back pressure on the yoke, depending on the bellcrank mod.
I'm not entirely clear with the scenario I'm referencing, but it was inferred that some sort of forward CG issue could have been the problem- there just wasn't enough elevator authority. But I'm not totally sure what was being said there. The -145 has had a number of weird stab/elevator issues over the years. Now, we're required to apply nose down trim after rotation before we reach 160 knots, because after 160 knots, the stab actuator might have problems re-trimmin the stab, causing a serious control problem.
I'm sort of just spit-balling possible scenarios to consider at this point, mostly to get people asking questions.
jtrain609
Antisocial Monster
Holy crap, you ain't kidding. We don't have many of the old ones (only about 30 left in the fleet), and they fly like a mack truck. It always feels like the plane simply WON'T rotate with the original rigging. 135's leap off the runway, 145LR's are ok, and the 145XR's are finally dialed in properly.
Firebird2XC
Well-Known Member
It makes a difference. I wonder which mod the... uh.. hypothetical scenario had.