737 Classic Reject or Continue?
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737 Classic Reject or Continue?
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
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
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'.......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.........'
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.........'
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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:
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):
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.
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.
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.
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.
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.
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.
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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
Not wanting to cause too much thread drift but what are people's views on this?
B&S
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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.
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.
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.
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.
Boeing have already issued guidence. If you have just the amber reverser unlocked light you should continue.
They have two notes in the QRH
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.
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.
"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 a cock up during the high speed abort; likely according to the stats.
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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.
You would be mad to reject.
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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.
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.
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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!
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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.
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.
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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.
Stick with the perceived wisdom. You can't outguess Boeing.
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Reverser unlock light
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
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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
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Even a genuine reverser application could be handled and dealt with.
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.
Last edited by Stan Woolley; 14th Oct 2008 at 07:14.
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Has a real reverser deployment in flight ever happened. if so what happend?
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 and here.
edit:
Just noticed another thread here on tech log discussing the Lauda crash:
767 Thrust Reversers
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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.
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.
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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)
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)