737 Classic Reject or Continue?

[Harry Cane]

Hello There,

Would like to hear different opinions about the following situation. During Toff roll say 10 to 5 Kts. prior to V1, the Reverser Unlocked light of one engine pops up.
Will you continue or reject?

As usual guys, thanks for the help.
H.C

[Rainboe]

'.......Above 80 kts, we will only stop for:
any fire warning
engine failure
control difficulty
runway obstruction
or
windshear ahead warning
otherwise we will continue with the take=off and deal with any other problems when the aeroplane has settled down and a roll mode is selected.........'

[NonFlushingLav]

Reject Reject Reject

[SNS3Guppy]

If you've got just the light with no other indications of a reverser deploying, then continue. If you've got other signs such as a control difficulty or difficulty maintaining the runway centerline, then you've already made your decision before initiating the takeoff. Reject.

If it happens at or after V1, you're going. Your calculated performance is predicated on this happening (loss of power).

Many reverse systems employ snatch-back cables which will rapidly pull one thrust lever to idle upon deployment of a reverser, depending on the type of reverser (fast enough it can break your finger or hand, too). With this in mind, while a reverser unlocked might sound like a disaster, it's hardly so, and amounts to little more than a power loss if you follow your procedure.

The decision to make is "do you have a controllable airplane?" If you're not getting secondary indications, if you're not getting directional control issues, then what you have is either a malfunctioning indication, or a problem that isn't worthy of risking a high speed rejected takeoff.

Furthermore, if your performance data has been planned using a reduced thrust takeoff, increasing thrust isn't necessary to meet the performance requirements at this stage, either...because the performance has been found to met all the applicable requirements for this departure using the value on your TOLD card or data card.

This has been the topic of a series of memos and discussion from our safety and training departments. A memo not long ago on the subject from our safety officer included some information on rejected takeoffs which may be of interest:

According to Boeing and the Flight Safety Foundation (FSF), approximately one in every 3,000 takeoffs is rejected. And, one third of those rejected takeoffs (RTOs) result in the aircraft leaving the runway. In the last 30 years, over 600 people have died as a direct result of unsuccessful RTOs. FSF claims that 80 percent of the overrun incidents could have been avoided with proper crew decisions and technique.

Although in training, the RTO is almost always initiated because of an engine failure, the large majority of RTOs on the line are not related to engine malfunctions. Boeing statistics show that only 26 percent of RTOs were for engine abnormalities, followed by 24 percent for tire/wheel failure and 13 percent for improper aircraft configuration. The remainder RTO’s were for a large variety of other reasons, such as bird strikes, improper crew coordination, ATC, etc.

Additionally, both Boeing and FSF report that the majority of aircraft involved in an RTO would have continued safely to landing had they not initiated the RTO. The number varies from 55 to 70 percent, according to the sources.



I think it's important to note that the second paragraph discusses different reasons for rejected takeoffs. It's not written to illustrate a wide vareity of reasons to reject a takeoff, but to point out that many rejected takeoffs are made for the wrong reasons, or unnecessarily.

The memo continues (with my emphasis):

Below 80 knots, Boeing recommends an RTO for: system failure(s), unusual noise or vibration, tire failure, abnormally slow acceleration, unsafe takeoff configuration warning, fire or fire warning, engine failure, or if the airplane is unsafe or unable to fly. The RTO below 80 knots should not result in runway overruns. Even at high gross weights, you should have the ability to stop on the runway.

Rejecting takeoffs above 80 knots is a completely different matter. Boeing limits the list of malfunctions worthy of an RTO between 80 knots and V1 to four conditions: fire or fire warning, engine failure, or if the airplane is unsafe or unable to fly.

Rejected takeoffs above V1 should not even be considered. The primary reason is that, all aircraft performance data is based on an RTO initiated below V1, thus making V1 your go no-go decision speed. An RTO initiated above V1 voids your computed stop margins. To further explain, if you have some condition that occurs after V1 that you believe makes the airplane unsafe or unable to fly, you will go off the end of the runway and you will substantially damage the aircraft (and possibly yourself) in the process. Again... You WILL damage the aircraft and yourself.


On our forward annunciator panel, we have a wide variety of malfunctions that can be announced. This includes loss of one of our four main hydraulic systems which provide aircraft control (we're not a 737), and engine oil pressure warnings. Company policy, with which I agree wholeheartedly, is that there are no annunciations on the forward caution panel worthy of a high speed rejected takeoff...which for us is anything above 80 knots.

Another point to consider are the limitations in continuing. I noted that performance when employing reduced thrust is predicated on completion of the takeoff with a failed engine, if one is unable to reach the point at which that occurence is planned (V1 or higher), then that concept is out the window. Further, if one has encountered a condition which makes the airplane unflyable, clearly going isn't an option...that's obvious enough it should go without saying. Limitations on power use, temperatures, speeds, etc...these are all to protect the future of the airplane...from the present until some undetermined point in time and space. However, if the future of the airplane is in jeopardy...in other words if one doesn't act to prevent the airplane from losing it's future...then the limitations are also out the window.

With THAT in mind, if you're having directional control issues with a deployed reverser and you're below V1, it's NOT the time to go pushing the power up (making directional control problems worse) and continuing the takeoff...if you can't control the airplane, then today isn't the day to fly. If you can control the airplane, then go fly get away from all those hard, dangerous objects on the ground. Handle it as an airborne emergency, and come back to a runway lined with people who wish to help you, considerably more runway ahead of you than when you had the indication at V1...and the equipment staged and ready to do the job.

[bucket_and_spade]

Some of our fleet have a predictive windshear system installed. Our company policy puts a predictive windshear warning together with the warnings we'd reject for between 80 knots and V1.

Not wanting to cause too much thread drift but what are people's views on this?

B&S

[SNS3Guppy]

B&S,

If that's your company policy, then your course would appear fairly clear. Predictive windshear is an additional tool that isn't available on all airplanes; as you note, it's applied in your own fleet selectively as equipped. There is no sense attempting to be airborne when that will place the flight in more jeopardy than might be experienced in a rejected takeoff.

[lomapaseo]

Im a strong believer in following published procedures as they are thought out in a non volatile atomosphere. What I read above are excellent examples.

I would however consider a reverser unlock light as equivalent to an engine failure in most installations. If there is a question about this then it's best to go back and ask the people that wrote the orriginal procedure for a review.

[c100driver]

Boeing have already issued guidence. If you have just the amber reverser unlocked light you should continue.


malfunctions worthy of an RTO between 80 knots and V1 to four conditions: fire or fire warning, engine failure, or if the airplane is unsafe or unable to fly.


They have two notes in the QRH


"Only multipule failures could allow the engine to go into reverse thrust"


"Unstowed reverser sleeves produce buffett, yaw, roll and increased airplane drag"

The probability of an actual reverser deployment is "unlikely" (Boeings words)

The probability of a cock up during the high speed abort; likely according to the stats.

[Rainboe]

Absolutely. The vast majority of reverser unlocked lights are likely to be false warnings. Greater hazard to abandon. Even a genuine reverser application could be handled and dealt with. You would be reasonable to assume that full reverse would not be applied, and you would be aware from many cues whether the indication was confirmed. Stick to the list!

You would be mad to reject.

[ajd1]

The original question said 5-10 kts before V1.
Much comment has ensued, but I guess that what the reverser is doing (or not doing) at that speed could well be totally different 20kts later.
Personally, I would probably reject the take-off, but I've the advantage of having seen inflight reverser deployment many times in the sim.
To say that you would be "mad" to reject is a bit unfair I think .... many factors, in addition to the fault itself, are in play ... for example,for a 733, even at MTOM, a V1 reject at LHR or MUC presents little problem, but would be a different story at LTN.

[Rainboe]

Nevertheless, the instructions from Boeing and what is taught to you throughout your training and in the simulator is to only reject aove 80 kts for those 4 or 5 items. A reverse indication is NOT one of them. Argue it with Boeing and see how far you get!

[SNS3Guppy]

What you see in the simulator isn't necessarily what you see in the airplane. I've seen airplanes in the sim stop flying and move backward in unrealistic and wild ways during a T/R deployment just after takeoff.

A few knots before V1, you get a light with no other indications...by the time you do something about it, you'll be past V1. The aircraft is fully controllable, still increasing in speed...yes, you'd be very foolish to reject.

Is your aircraft equipped with snatch-back cables that pull the thrust lever to idle in the event of a T/R deployment? Many are. If you have the light and no other indications, and the lever hasn't been pulled out of your hand to the idle stops, you don't have anything in evidence at that stage that demands rejecting the takeoff.

A low speed reject, perhaps. A high speed reject; unwise.

[Rainboe]

And the first part of the emergency briefing is 'up to 80 kts we may reject for many reasons. Announce the failure and be ready for a call from me of 'stop!' or 'continue!'....above 80kts.......'

Stick with the perceived wisdom. You can't outguess Boeing.

[SNS3Guppy]

LiveLeak.com - Raw Video Of Pilot Aborting Takeoff As Tires Catch Fire 26.09.2008 (http://www.liveleak.com/view?i=494_1223909509)

LiveLeak.com - Boeing 747-200F aborted takeoff (http://www.liveleak.com/view?i=3a1_1185485876)

[BelArgUSA]

The question is - reject for "reverser unlock LIGHT" ... ?
The answer is "NO" ... !
I had two or three such light problems in 707s... maybe close to V1...
Maybe on 727 or 747 as well.
Never did reject the takeoff. Were false warnings. Microswitch problem...
xxx
What would make me reject the T/O, is a sudden yaw, say 10 KIAS prior to V1.
That is not just a light... that is the real thing...
xxx
:*
Happy contrails

[Stan Woolley]

Even a genuine reverser application could be handled and dealt with.

Absolutely not true according to a BOEING test pilot who posted on an aviation website I read over ten years ago.Everyone was discussing how reverser deployment had been handled in the sim.

He came on and in a very professional way pointed out that if a deployment happened on takeoff you would be in very deep trouble.His name was Green if I recall correctly.

[ali1986]

Has a real reverser deployment in flight ever happened. if so what happend?

[TopSwiss 737]

Has a real reverser deployment in flight ever happened. if so what happend?

Yes it has.

A Lauda B767 climbing out of BKK encountered an inflight reverser deployment in May 1991... Resulted in a complete loss of control and subsequent airframe break up within seconds. Can not remember if the engine remained at climb thrust or power was reduced automatically as per system design.
Of course because of the high speed and altitude the forces involved are much different than the take off scenario originally being discussed in this thread....

Read more about this accident on airdisaster.com (http://www.airdisaster.com/cgi-bin/view_details.cgi?date=05261991&reg=OE-LAV&airline=Lauda+Air) and here (http://www.pilotfriend.com/disasters/crash/lauda004.htm).


edit:
Just noticed another thread here on tech log discussing the Lauda crash:
767 Thrust Reversers (http://www.pprune.org/tech-log/346688-767-thrust-reversers.html)

[Rainboe]

Absolutely not true according to a BOEING test pilot who posted on an aviation website I read over ten years ago.Everyone was discussing how reverser deployment had been handled in the sim.

Because of various interlocks and protection systems, we are assured that inadvertent full power reverse is impossible. A full reverse scenario would be almost impossible to occur- an idle reverse scenario is far more likely, and that could be handled.

A single warning light indication is so overwhelmingly likely to be an indicator fault that in the absence of any other indication of reverse, I think it would be criminal to go rejecting at high speed.

[A Comfy Chair]

I'm with Rainboe and others that say "Go".

I can't speak for the 737, but the 744 and 767 Non Normal Checklists can give you a clue. They both clearly state that with just an indication (and no yaw, loss of airspeed, or buffet) that you operate the engine normally.

For the 767 at least, Boeing have stated that a reverser deploying in flight during takeoff and climb, and descent and landing, can be successfully managed.

The reasons for conducting a high speed abort are pretty clearly stated, and whilst you could argue that you thought the aircraft was unable to fly, I think that with no buffet or yaw, there would be no reason to think that to be the case. Far safer to continue the takeoff than to reject at high speed.

There is, of course, the other argument that what if your V1 was not Accel - Stop limited, and you had 2km of excess runway, but thats for another day (and thread) :}

[Rainboe]

The abort parameters are very strictly laid down, both for the sub-80kt case and the over-80kt/belowV1 case. It always bemuses me the number of people who come up with 'but I would do this if it happened'. I suppose they like being part of the accident statistics for discussion in Pprune! If the parameters are strictly laid down by companies with the bark of Boeing and presumably Airbus, who are these pilots that reckon they know better, and why do they think they are safe enough to fly passengers?

I see Post 2 of 'Abort Abort Abort!' has, not surprisingly, been removed.

[NonFlushingLav]

Corporate jet crashed due to two buckets opening up on take off...evidentely they had been locked out by maintanance, then closed. Pilot hopped in, took off, crashed. TR light for me, is an instant abort prior to V1...simply put, hitting the stow button might not work. In the sim a double TR deployment acts stupid, unrealistic, I think it can be flown with enough speed...but at lower speeds, trying to acclerate and fly out with all that drag prior to V1 is suicide in my opinion.

[PantLoad]

Gentlemen:

With regard to rejected takeoffs, Airbus has this to say:
-----------------------------------------------------------------------
ABOVE 100 KNOTS AND BELOW V1:

Rejecting the takeoff at these speeds is a more serious matter, particularly on slippery runways. It could lead to a hazardous situation, if the speed is approaching V1. At these speeds the captain should be "go- minded" and very few situations should lead to the decision to reject the takeoff:

1. Fire warning or severe damage.
2. Sudden loss of engine thrust.
3. Malfunctions or conditions that give unambiguous indications that the aircraft will not fly safely.
4. Any red ECAM warning.
5. Any amber ECAM caution listed below:
. F/CTL SIDESTICK FAULT
. ENG FAIL
. ENG REVERSER FAULT
. ENG REVERSE UNLOCKED

Exceeding the EGT red line or nose gear vibration should not result in the decision to reject the takeoff above 100 knots.

In case of tire failure bewteen V! minus 20 knots and V1:
Unless debris from the tires has caused serious engine anomalies, it is far better to get airborne, reduce the fuel load load, and land with the full runway available.

The V1 call has precedence over any other call.
-----------------------------------------------------------------------


Boeing may be different...it's been many years since I flew a Boeing, so I can't tell you what they say. But, this is the Airbus philosophy.


Fly safe,


PantLoad

[Rainboe]

Interesting. Slightly different philosophy, but not significantly different.

[Mach E Avelli]

In my view, not knowing whether the reverser has really unlocked or could unlock at any time falls into the 'it's better to be on the ground wishing you were up there, than being up there wishing you were on the ground' category. Having read all about the Lauda crash, I would reject up to V1 and cop the criticism from the armchair experts even if it did turn out to be nothing more than a faulty sensor.

[NonFlushingLav]

Mach E Velli +1 Couldn't have said it better...everyone on the ground alive, vs yet another pilot who thought he could fly the plane off to the scene of the accident. Yeah I will take a little flack from the Monday morning quaterbacks if the passengers are alive.

[SNS3Guppy]

You'd be copping a lot more than criticism if you rejected only to find you'd damaged the airplane...which is a big part of the reason that Boeing states one should NOT reject for a T/R indication in absence of vibration, directional control issues, or other indications that it's more than just a light.

Bear in mind that with the Lauda mishap, the airplane had already experienced 13 incidents of recorded T/R failures and failure messages in the months preceeding the crash. The crew had warnings for about ten minutes before the reverser deployed. Further, the event which occured where the subject of multiple later system changes and airworthiness directives...this isn't something to be expected or reasonably anticipated on other aircraft, or the same aircraft in the time since.

If you place the flight in jeopardy over what you think might happen, you accept a real risk and a high probability of damage, vs. a possibility which does not yet exist. When considering abnormalities or emergencies occuring during the high speed portion of the takeoff roll, in nearly all cases you are FAR better to continue the takeoff and treat the condition as an airborne emergency.

Whereas the engine may be shut down in very sort order, the threat of a T/R deployment isn't worthy of a high speed rejected takeoff if no other conditions exist at the time of the reverser indication.

If you want to compare the 767 mishap with the question central to the thread about identifying a problem a few knots before V1, you have to take into account the ten minutes the crew had to consider the abnormality announcement. Furthermore, the crew wasn't looking at an unlocked or T/R deployment condition immediately, but the same valve annunciations that had been occuring in the past; there's more history to what happened than simply someone saw a light and took action (or didn't).

[lomapaseo]

It sounds to me like a good idea to follow the recommended procedure for your specific aircraft. If life would be simpler to have a consistent procedure accross both Boeing and Airbus aircraft than just ask them for a rationale through your safety representative.

[A37575]

and a roll mode is selected

What on earth has a roll mode got to do with it? You have got ailerons - use them and forget about a god almighty rush to get the autoflight systems engaged. Flight directors are there as an aid - not the be all and end all of navigating the beast.

[Centaurus]

During Toff roll say 10 to 5 Kts. prior to V1, the Reverser Unlocked light of one engine pops up

If the thrust lever retards automatically then you are in reverse on that engine and you reject fast. If there is no movement of the thrust lever then you are in forward thrust and you continue. Sort the problem light when you get time. Any abort that close to a real V1 on a limiting runway length - especially if a wet runway, is asking for trouble. Sometimes you have to make a critical decision and wear it.

[Rainboe]

What on earth has a roll mode got to do with it? You have got ailerons - use them and forget about a god almighty rush to get the autoflight systems engaged. Flight directors are there as an aid - not the be all and end all of navigating the beast.

I'm afraid things have changed on the more modern aeroplanes! It is standard now with any defect you carry into the air to get the aeroplane settled in teh climb, gear up, and at 400' select a roll mode- Hdg or LNav as required. if you have an engine out, you are not allowed to turn, you must climb straight ahead unless specifically req'd on that runway to do otherwise. Contravene that and you look for another job.

Mach E Avelli:
In my view, not knowing whether the reverser has really unlocked or could unlock at any time falls into the 'it's better to be on the ground wishing you were up there, than being up there wishing you were on the ground' category.
Ignore your training and you will be looking for another job! You get trained, then come a problem and you throw it away and decide you know better than Mr. Boeing? How many Boeing aeroplanes have crashed with full reverse on take-off? Zero. How many Boeing aeroplanes have had false 'reverser unlocked' warning lights on take-off? Quite a few I would hazard a guess- I have had false reverse indications, but not on take-off. Boeing recommend that particular take-off briefing I outlined earlier. Why throw that away the first time you have (what you think is) an emergency? Foolhardy to abandon near V1 for a stupid false warning light! Wake up guys and reread your emergency briefing! Then for goodness sake stick to it! You do not know better!

Mach E Avelli- you aren't a prof pilot, are you? Have you been Boeing trained? If not, why are you involving yourself in this discussion without saying so? Do you think passing your opinion is advisable in a discussion of this nature?
'

[galdian]

Rainboe

Actually (at least on the NG) Boeing DOES allow (albeit implied, not explicit) a reject for something such as T/R:

The criteria in my company's manuals:
- engine fail
- engine fire
- predictive windshear
- if the aircraft is insafe, or unable, to fly.

Suspect T/R deployed would comfortably fit the last, of course more than happy for the techies to provide how successfully an aircraft will take-off and climb (or not) with a T/R deployed.

Would be interesting to ask those who have been there (maybe the Lauda boys??) what a real T/R deployment does to an aircraft - oops, sorry, they're too busy looking for another job.

Call me crazy but I go to work each day not worrying about whether I'll need to start looking for another job tomorrow but hoping to marry my training with a fair amount of commonsense regards what's happening around me in the real environment, not a simulator solely or the thoughts of the multitudes on Pprune and similar.

Partly to safeguard the aircraft and all the souls within, mainly to minimise all those pesky "reports to the company" you have to write when things don't quite line up as expected.

Cheers. :ok:

[SNS3Guppy]

Suspect T/R deployed would comfortably fit the last, of course more than happy for the techies to provide how successfully an aircraft will take-off and climb (or not) with a T/R deployed.


Have you looked at the procedure for inadvertant reverse thrust in flight?

A T/R light isn't a suspected T/R deployed. Not without secondary indications such as directional control issues, buffeting, vibration, etc. Further, if you're comparing the 767 to your 737, especially the 767 prior to introduction of the T/R AD's, then you're making an inappropriate comparison.

The criteria in my company's manuals:
- engine fail
- engine fire
- predictive windshear
- if the aircraft is insafe, or unable, to fly.


Is a T/R unlock light an engine failure? No.

Is a T/R unlock light an engine fire? No.

Is a T/R unlock light a predictive windshear warning? No.

Is a T/R unlock light an unsafe condition that makes the airplane unable to fly? Not according to Boeing.

By applying your own spin or interpretation, rather than the manufacturer, you risk making a high speed rejected takeoff and putting the flight in certain danger, rather than a perceived danger which does not exist...in other words, you're putting the flight in harms way...not avoiding a dangerous situation. When you see that light and it's not accompanied by movement of the thrust lever or by secondary (and obvious) indications that the T/R really is deployed, then you're creating a dangerous condition when one doesn't yet exist...in other words, there isn't a problem until you elect to make one by rejecting the takeoff unnecessarily.

[galdian]

OK

That's fair enough.

When all hell breakes loose we can each write our reports - and the aviation fraternity can learn from decisions made which will be good, or bad, or somewhere in-between.

RTO's, regardless of how close to V1, are still part of training - are they not??

Cheers :ok:

[c100driver]

Yes V1 aborts are part of the training but they still get cocked up with regularity outside of the simulator. A T/R light is just a light not an actual reverser deployment.

[Stan Woolley]

But it's a Boeing light!

How could it possibly be telling us something that isn't true? :\

[Harry Cane]

Thanks a lot guys for your different opinions about Reverser Unlocked light during takeoff roll. Just one thing I want to point out, and makes me rethink the subject over and over. That was the accident of a Fokker 100 in Sao Paulo (CGH) in 1986. The cause of the mishap was a Reverser Deployment after rotation with a fatal outcame.

Thanks again for the help,
H. C

[lomapaseo]

Thanks a lot guys for your different opinions about Reverser Unlocked light during takeoff roll. Just one thing I want to point out, and makes me rethink the subject over and over. That was the accident of a Fokker 100 in Sao Paulo (CGH) in 1986. The cause of the mishap was a Reverser Deployment after rotation with a fatal outcame.

Thanks again for the help,
H. C

I don't think that you have the details correct, but lets not let a single one-off event cloud the discussion.

The go-no-go decision needs to be appropriate for the aircraft type and experience both pro and Con. I just happen to be strongly on the side of following the manufacturers recommendations since they have access to all the data and recommended training material.

Also as I understand the original question it has to do with a warning light, and not necessarily with a mechanical outcome. However if you would like to expand the question then please be specific.

[SNS3Guppy]

Just one thing I want to point out, and makes me rethink the subject over and over. That was the accident of a Fokker 100 in Sao Paulo (CGH) in 1986. The cause of the mishap was a Reverser Deployment after rotation with a fatal outcame.


That particular incident really deserves it's own discussion. It wasn't a case of a reverser light illuminating prior to rotation. In the case of the fatal TAM flight, the autothrottle was engaged. The autothrottle attempted to retard power, and the first officer pushed it up twice, complicating the problem and making it worse. He was fighting the autothrottle which was attempting to adjust the thrust levers, and finally disengaged it and pushed up the power manually on both powerplants...sealing their fate.

The fact that the thrust reverser deployed wasn't what brought them down. it was their insistance on not recognizing that the reverser had deployed and repeatedly fighting the airplane while using the incorrect response. One has to recogize the problem that exists in the first place, in order to do something about it, and the crew wasn't aware that a reverser was deployed, at all. You really can't compare that situation to the discussion at hand.

With a reverser deployment, retarding the power on the affected engine is critical. There's really not much one can do that's worse than pushing the power up on the affected engine...repeatedly. It's a different topic than a rejected takeoff, however...and with a reverser unlock light on takeoff, we're not talking about an unsafe condition that places the ability of the airplane to fly in question. We're talking about a light, with no other indications. One can't handle an emergency that doesn't exist, and by rejecting the takeoff for that light, one is creating an emergency when one didn't exist.

Be careful of scars earned from battles in which you should never have fought.