V1 Decision Speed

[NikB]

Hi All

I had a good question asked by one of my students, and didn't know how to fully answer. Some research in the matter hasn't cleared things up either so perhaps you fellows can help me out.

The question goes something like this:
You have a light aircraft, taking off from a long dry runway, and the V1 is 120kts. Now you know, having flown the aircraft with a lot more weight, that the V1 at those higher weights is 140kts or so, sometimes more. Given the situation where you have a catastrophic engine failure with the lighter aircraft, at say 135kts, would you reject?

The obvious answer would be no, because then insurance wouldn't pay, and you better pray you don't have injuries or hull loss. However, it is technically possible, since the 120kt V1 is a minimum speed, to stop safely within the remaining runway. Would it be, to your best judgement, safer to reject, knowing full and well that the aircraft would stop safely within the runway?

Thank you for your answers in advance, I look forward to hearing your opinions on the matter.

[CHfour]

The take off performance category isn't mentioned but, assuming its cat C, it would be better to reject as there's no guarantee of SE capability until 200ft AGL. If the performance allows a much higher weight for the conditions you could check the figures for the heavier option and use the higher V1 but I'm not sure common sense is allowed these days.

[wiggy]

By the context I'd also assumed perf A and would certainly agree that the calculated /nominated V1 is the decision speed and you continue unless you literally cannot get airborne...

There is also the issue of (reduced) derated power for jet takeoffs (thrust amongst other things varying on aircraft weight) which complicates any thoughts of comparing performance across visits.

Above all If something happens above V1 but below Vr having a debate with the person in the other seat about "I know from a previous visit we can probably stop" perhaps followed by, " Ummm, is this a serious/catastrophic engine failure or not" is possibly not going to end well...so the KISS principle applies.

[FlyingStone]

If you are lighter than PLTOM, you will have better than minimum required performance in the event of engine failure, which should support the "go" option.

Rejecting a takeoff for a single engine failure of any kind after V1 is a VERY big no-no. How do you even figure out it is "catastrophic failure" or just a simple flameout, which would allow a restart and a non-eventful AEO return to the departure airfield? Surely as PF or PM you don't start diagnosing the type of engine failure during rotation?

There are situations where you may/should/could reject after V1, but all of them sort of follow the Boeing song "unable or unsafe to fly". Is the flight with one engine inop unsafe after V1 - no. Is the aircraft unable to fly with one engine inop after V1 - with the light weight, not even close.

[Piltdown Man]

Almost certainly you could stop. But that might be more riskier than continuing. For a start, you are not guaranteed to be in the same place on the runway to start the stop, the de-rate/flex may be so great that the slower acceleration performance might have put you further down the runway. Next, high speed rejects are not things you really want to do. Controllability, brake fires, steering problems are all problems you really don't want to deal with. It it better to fly single engine and then sort things out at your leisure. Lastly, pilots want things simple. Once you are past V1 you are flying. That is the script. So if you have an (even catastrophic) engine failure or fire you just carry on with the play as written and performed in the simulator. Only if the aircraft refuses to fly will I stay in the ground.

[BleedingAir]

For a start it's an unrealistic scenario, as a lightly loaded aircraft on a long, dry runway is not going to have a 15 knot split between V1 and Vr (assuming your 135 kt catastrophic engine failure occurred on the ground -- considering a reject after rotation for an engine failure is madness, assuming by the speeds we're talking jets).

Second, I really hope there are no crews out there discussing rejecting after V1 as a consideration in the scenario stated (engine failure). The speed is there for a reason, and as has been mentioned, the only legitimate reason for a post-V1 reject is the aeroplane being unsafe or unable to fly -- OEI does not fit these criteria. This has been studied for decades by people far more knowledgeable than myself, based on countless high speed rejects, and is not open to interpretation on the day.

[NikB]

Thank you for your replies everyone. A little more info as I might not have been 100% clear.
Yes I'm talking about class A, A320 to be exact, and yes about a derated calculation. Where I operate there actually is, for some reason, a huge margin between V1 and Vr at lighter weights (50T vs 70T), to the figure of 20kts. In fact today I saw V1 116, vr 137, v2 138, as calculated by the flysmart app.

I wouldn't think of rejecting after V1, and it is company policy to remove hands off throttles. However I've had many colleagues say they would because they think it's safer, up until Vr to reject and remain on ground. I tell them it's a bad idea, but I want to bring them technical arguments, other than just saying "No, it's what it says here and that's it".

Thanks again for your help

[FlyingStone]

However I've had many colleagues say they would because they think it's safer, up until Vr to reject and remain on ground. I tell them it's a bad idea, but I want to bring them technical arguments, other than just saying "No, it's what it says here and that's it".

If they are in the left or right seat of an airliner and still think that, it's time for a bit of change of scenery for you. Some people wouldn't accept that 1+1 is 2 even if somebody with PhD from mathematics explains them for hours on end why is that.

Write some CVs and wish them best of luck!

[Piltdown Man]

NikB - The technical argument is irrelevant. The important fact is that this is the way Performance A aircraft are flown. I'd even go so far as to say that intentionally flying an aircraft like this knowing that this is not the way things should be done is a criminal act. It is shame that we have to share the sky with morons who believe they know better. Stay well clear of muppets like these.

[Pugilistic Animus]

I think if you're forced to reject after V1 you're in pretty bad shape already. For example, I think if Concorde rejected after V1 it would have still been an unsurvivable and catastrophic accident.

[compressor stall]

As background thought, your EFB admin will be able to advise you how your V1 is calculated. Default settings can be: V1 Min, V1 Max, V1 Mean or optionally the ability to select a range of V1s.

It may be more appropriate in some airports to have a V1 Max, or at others a V1 Min. Your speeds almost certainly are using min V1 as IIRC that's just above Vmc for an A320.


You'd need to have a pretty bloody good reason to abort after V1, and an engine failure isn't one of them

[Judd]

You'd need to have a pretty bloody good reason to abort after V1, and an engine failure isn't one of themI think if you're forced to reject after V1 you're in pretty bad shape already
Agree. But there are always exceptions. But one captain did and his decision saved the lives of his 40 passengers and crew. Date 30 March 1998. Emerald Airways HS748 G-OJEM had just lifted off from Stansted runway 23 when No 2 engine suffered a catastrophic engine failure and fire in the engine nacelle.

The captain elected to set the aircraft back down on the remaining stretch of runway but it could not be halted before crossing the perimeter track and came to rest with the undercarriage nose wheel collapsed. The aircraft was burnt out and a total write-off but no serious injuries to the occupants.


I'd even go so far as to say that intentionally flying an aircraft like this knowing that this is not the way things should be done is a criminal act.


Agree. Depends on the circumstances at the time. See above incident

[compressor stall]

Didn't that go off into the weeds at 60+kts? IMHO that's a big call to say that the abort decision saved the lives of all the pax as this implies that they would have died had the takeoff been continued. And the aircraft was burned to the ground. 60kt runway excursions could end very very differently.

Yes, the fire might have burned the wing off in the circuit too. We'll never know. But I would argue that the statistics of a wing failing off / exploding after an engine failure and fire post V1 and continuing don't bear out the risk of conducting an airborne abort and overrun into the weeds / buildings / highways.

[Piltdown Man]

CS - I agree with you. Leeds United got very lucky that day. In the report you will read that in less than a second this captain determined that this failure would result in the mainspar being burnt through and that flight was not possible, so he snatched control from his F/O and crashed straight ahead. But it was the right hand engine that was on fire. He was also told this by his senior C/A who was sitting in the rear. To determine that the aircraft was in jeopardy he must have looked at the Mainspar Burn-through Indicator or there again, the passengers got very lucky. The AAIB did notice burn marks from the fire. But they also noted that landing after being airborne is not a recommended procedure, that this was an untrained and unrehearsed procedure, that absolutely no fire containment procedures were performed and that there was no evidence to suggest the wing spar would burn through. It is also telling that one this report took as long as is did to publish. I will speculate that certain some in the AAIB considered this a criminal act and therefore beyond their remit. It is also telling this company had its AOC pulled for a series of subsequent gaffs, oversights and near-misses. I'd suggest nowadays that such behaviour would result quite rightly in prosecution. Believe me, I normally defend fellow pilots, but not this one.

At V1 you decide to fly or stop.


ps. The moment my wife knew who was captain she said "He'll be on the telly tonight". She was spot on!

[oggers]

The Commander's decision to land the aircraft immediately on the runway remaining was sensible in the circumstances.

[Piltdown Man]

Absolutely, totally disagree! It was reckless if not criminal.

[oggers]

Not my opinion PM. What I wrote was a direct quote from the findings of the accident report.

[RAT 5]

I'm still curious how V1 = 116 & Vr = 137. That could have been a highly contaminated runway. 137Kts does not seem such a light a/c to a B737 pilot.

There are situations where you may/should/could reject after V1, but all of them sort of follow the Boeing song "unable or unsafe to fly"

B737. You are on a long runway; Vr is about halfway down, you attempt to rotate and nothing happens, the elevator is jammed. What do you do?

RTO?
Attempt to rotate on the trim?
Think WTF and depart off the end still pulling at high speed?

Just a little bar-room debate.

[Denti]

That scenario happened to a lufthansa, not the jammed elevator, just not enough authority to rotate. It was a combi variant and at the most forward position instead of an empty container there was one containing over 3 t of freight.

They rotated on trim, did a circuit and landed again, with a trim at the nose up limit if i recall correctly.

Anyway, large spreads between V1 and Vr are kinda common on the A320, especially on a wet runway. Usually the performance program offers a range of possible V1 speeds, and if one is go minded he will usually chose a lower one, although i would take care not toget too close to Vmcg personally.

[zoigberg]

rat5. For the bar room debate: Here's what moving away from the paper charts does for you.
Actual figures taken off our system for B737 300
I should add the figures don't fill me with glee but they are what they are.
LKPR RW 24
30C wet
QNH 1000
Wind calm
53000kg TOM

Derate to 20k thrust
39deg ass temp
Flap 1
V1 127 Vr 145 V2 151

And strangely enough when I look at fixing the flap at 1 with Improved climb selected I get same derate, a higher assumed temp and a V1 of 142. So.... in the original case the V1 figure of 127kt looks ... erm.... low.

I look forward to the bar room debate

[Piltdown Man]

oggers - I agree, but I don't have to agree with some aspects of this report. The phrase "was sensible in the circumstances" was not backed up by any fact or scientific analysis. As such it was merely opinion. So like the rest of us, the AAIB get things wrong every now and again. So I'll stick by my let's stop or go at V1. But are you prepared to say that it is perfectly alright to decide to stop or land back whenever you want, ie. V1 does not matter? In this website you have the opportunity to tell us how to fly. I'm sure others would like to read what you believe.

[oggers]

But are you prepared to say that it is perfectly alright to decide to stop or land back whenever you want, ie. V1 does not matter?

PM, it's a bit of a leap from the AAIB finding of "the Commander's decision to land the aircraft was sensible in the circumstances" to your question.