Rejected Takeoff
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If you had to choose one of the three systems to leave off the plane during design, I would suggest the spoilers would lose out.
Take the BAe146 for example....no thrust reversers fitted, but it has spoilers (and an airbrake too).
Many aircraft types have no reversers but do have spoilers.
I would have thought that choosing between the complexity and weight of a reverse thrust system - when compared to a spoiler system - would be a no brainer.
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Appreciate all the comments so far however are there any "technical" papers to back up the different company SOP's ?
Or is it simply how a Company chooses to interpret "Boeing SOP's" ?
Or is it simply how a Company chooses to interpret "Boeing SOP's" ?
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Fair point but
Can't agree with that statement, and the real world tends to back me up.
Take the BAe146 for example....no thrust reversers fitted, but it has spoilers (and an airbrake too).
Many aircraft types have no reversers but do have spoilers.
I would have thought that choosing between the complexity and weight of a reverse thrust system - when compared to a spoiler system - would be a no brainer.
Take the BAe146 for example....no thrust reversers fitted, but it has spoilers (and an airbrake too).
Many aircraft types have no reversers but do have spoilers.
I would have thought that choosing between the complexity and weight of a reverse thrust system - when compared to a spoiler system - would be a no brainer.
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As I understand it, the speedbrakes should be up before reverse thrust is initiated because asymmetric reverse thrust with speedbrakes down gives asymmetric lift dump. Asymmetric lift dump increases both drag and brake effectiveness on the affected side which may cause severe directional control problems. Regaining directional control may only be possible by disarming autobrakes and applying differential braking, a course of action especially undesirable following a high speed reject.
Asymmetric lift dump is, to the best of my knowledge, what caused the Airtours 757 previously mentioned to run off the side of the runway (although this incident was after landing following hydraulic failure rather than a rejected takeoff).
In certain Boeing aircraft, with the speedbrake down (i.e. not armed), raising either reverse thrust lever to the interlock stop mechanically moves the speedbrake into the armed position and it will then deploy if the autospeedbrake system is operative and the relevant conditions are satisified (which they should be following an RTO).
However, in the light of lessons learned from the Airtours incident, following an RTO or after landing with certain hydraulic failures (when asymmetric reverse thrust is especially likely and autospeedbrake may be inoperative), it is now considered preferable to manually raise the speedbrakes before selecting reverse thrust and not rely at all on the auto system.
Asymmetric lift dump is, to the best of my knowledge, what caused the Airtours 757 previously mentioned to run off the side of the runway (although this incident was after landing following hydraulic failure rather than a rejected takeoff).
In certain Boeing aircraft, with the speedbrake down (i.e. not armed), raising either reverse thrust lever to the interlock stop mechanically moves the speedbrake into the armed position and it will then deploy if the autospeedbrake system is operative and the relevant conditions are satisified (which they should be following an RTO).
However, in the light of lessons learned from the Airtours incident, following an RTO or after landing with certain hydraulic failures (when asymmetric reverse thrust is especially likely and autospeedbrake may be inoperative), it is now considered preferable to manually raise the speedbrakes before selecting reverse thrust and not rely at all on the auto system.
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Lets face facts here.
NOTHING stops an aeroplane like BRAKES, not reverse, not spoilers.
Close throttles, and at the same time, apply MAXIMUM braking force...all other actions are secondary.
Been this way for a long time...and not likely to change, younger guys notwithstanding.
NOTHING stops an aeroplane like BRAKES, not reverse, not spoilers.
Close throttles, and at the same time, apply MAXIMUM braking force...all other actions are secondary.
Been this way for a long time...and not likely to change, younger guys notwithstanding.
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Quote:
This all leads me to my next question then - what helps the most on an RTO - brakes (auto/manual), speed brakes or thrust reverses?
Hmm, I had a high speed RTO on a 767-200 out of CYYZ-LAX on a cold January dry runway morning a few years back. We experienced an engine failure at V1, did the RTO thing and came to a stop just as the good reverse came in. The bottom line, the brakes did the majority of the deceleration.
The biggest problem in all of this is the “shock factor” the rest is all training
This all leads me to my next question then - what helps the most on an RTO - brakes (auto/manual), speed brakes or thrust reverses?
Hmm, I had a high speed RTO on a 767-200 out of CYYZ-LAX on a cold January dry runway morning a few years back. We experienced an engine failure at V1, did the RTO thing and came to a stop just as the good reverse came in. The bottom line, the brakes did the majority of the deceleration.
The biggest problem in all of this is the “shock factor” the rest is all training
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"In certain Boeing aircraft, with the speedbrake down (i.e. not armed), raising either reverse thrust lever to the interlock stop mechanically moves the speedbrake into the armed position and it will then deploy if the autospeedbrake system is operative and the relevant conditions are satisified (which they should be following an RTO)."
The part of the quote that says "...if the autospeedbrake system is operative..." was a learning point a while back. The autospeedbrakes circuit breaker had been pulled and collared by maintenance due to a fault. We discussed whether the SBs would deploy upon selecting reverse after landing. They did not. We thought we had learned in training that the reverse levers would mechanically deploy the SBs. The way X describes it is the most accurate way of explaining it.
The part of the quote that says "...if the autospeedbrake system is operative..." was a learning point a while back. The autospeedbrakes circuit breaker had been pulled and collared by maintenance due to a fault. We discussed whether the SBs would deploy upon selecting reverse after landing. They did not. We thought we had learned in training that the reverse levers would mechanically deploy the SBs. The way X describes it is the most accurate way of explaining it.
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411A:
"Lets face facts here.
NOTHING stops an aeroplane like BRAKES, not reverse, not spoilers.
Close throttles, and at the same time, apply MAXIMUM braking force...all other actions are secondary.
Been this way for a long time...and not likely to change, younger guys notwithstanding."
Edited
BRAKES & Flt/Gnd Spoilers - it's the exact reason that most training manuals suggest that the spoilers are the one single item that the NFP backs the FP up on during an RTO.
You pay a heavey penalty just without the auto activation of the speed brake - this is nothing compared to what you suggest - just putting brakes on and forgetting the rest. Edited
LL
"Lets face facts here.
NOTHING stops an aeroplane like BRAKES, not reverse, not spoilers.
Close throttles, and at the same time, apply MAXIMUM braking force...all other actions are secondary.
Been this way for a long time...and not likely to change, younger guys notwithstanding."
Edited
BRAKES & Flt/Gnd Spoilers - it's the exact reason that most training manuals suggest that the spoilers are the one single item that the NFP backs the FP up on during an RTO.
You pay a heavey penalty just without the auto activation of the speed brake - this is nothing compared to what you suggest - just putting brakes on and forgetting the rest. Edited
LL
Last edited by Captain Stable; 23rd Apr 2003 at 16:44.
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LOKE,
Some older designs do not have auto-spoilers (suspect you are too young to know, but hey, thats alright).
Reverse thrust (by itself) does not stop aeroplanes (at least within the confines of most civil runways) and is not figured in the regulated stop distance anyway (FAA).
Ground spoilers without the application of auto/manual braking certainly does not stop aeroplanes.
Only one item that is available for the flight crews' use can positively stop the civil aeroplane...wheel braking.
Spoilers/reverse help, but cannot by themselves do the job.
Understand now?
Some older designs do not have auto-spoilers (suspect you are too young to know, but hey, thats alright).
Reverse thrust (by itself) does not stop aeroplanes (at least within the confines of most civil runways) and is not figured in the regulated stop distance anyway (FAA).
Ground spoilers without the application of auto/manual braking certainly does not stop aeroplanes.
Only one item that is available for the flight crews' use can positively stop the civil aeroplane...wheel braking.
Spoilers/reverse help, but cannot by themselves do the job.
Understand now?
Last edited by Captain Stable; 23rd Apr 2003 at 16:43.
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411A:
Uh - Yeah:
And the A/C that do have auto speed brake are heavily penalized by only the reduction in speed of getting out the speed brake manually.
I've seen lots and lots of aborts in the sim and guess what - never seen a single pilot forget the brakes!!! Seen a few forget the Speed Brake until they were reminded of it though.
The fact is that if you are Runway Length Limited and you do not get the speed brake out in a timely manner - auto or manually - you WILL go off the end of the runway!!! Edited
Do you understand now?
LL
Uh - Yeah:
And the A/C that do have auto speed brake are heavily penalized by only the reduction in speed of getting out the speed brake manually.
I've seen lots and lots of aborts in the sim and guess what - never seen a single pilot forget the brakes!!! Seen a few forget the Speed Brake until they were reminded of it though.
The fact is that if you are Runway Length Limited and you do not get the speed brake out in a timely manner - auto or manually - you WILL go off the end of the runway!!! Edited
Do you understand now?
LL
Last edited by Captain Stable; 23rd Apr 2003 at 16:43.
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Life in the sim...sometimes you get only half the picture.
LOKE,
Tell me LOKE, if after landing or following a rejected takeoff, you deploy spoilers only (no brakes), do you stop?
Yes, of course you do...when you run off the end of the runway into the grass.
Life in the simulator can be interesting...line operations are quite another.
Edited
Tell me LOKE, if after landing or following a rejected takeoff, you deploy spoilers only (no brakes), do you stop?
Yes, of course you do...when you run off the end of the runway into the grass.
Life in the simulator can be interesting...line operations are quite another.
Edited
Last edited by Captain Stable; 23rd Apr 2003 at 16:42.
Have to agree with 411A.
By a huge margin the brakes stop the plane. Adding spoilers makes them more effective at high speed for sure, but by far the number one priority is to get on the stoppers hard & fast.
Everything else is just a bonus.
By a huge margin the brakes stop the plane. Adding spoilers makes them more effective at high speed for sure, but by far the number one priority is to get on the stoppers hard & fast.
Everything else is just a bonus.
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411A
Tell me 411A, if during a rejected takeoff, when you are runway lenth limited, you do not deploy spoilers, only brakes, do you stop?
Yes, of course you do...when you run off the end of the runway into the grass.
Life at the end of performance calculations will determine what will happen. Can you name me a single overrun where the pilots forgot to use the brakes?
Edited
LL
Tell me 411A, if during a rejected takeoff, when you are runway lenth limited, you do not deploy spoilers, only brakes, do you stop?
Yes, of course you do...when you run off the end of the runway into the grass.
Life at the end of performance calculations will determine what will happen. Can you name me a single overrun where the pilots forgot to use the brakes?
Edited
LL
Last edited by Captain Stable; 23rd Apr 2003 at 16:42.
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Speedbrakes & Wheelbrakes:
FYI, may I provide some figures for a typical mid-size two-engine transport (RTO at 135KTAS):
Figures are lbs.
===================SpeedBrakes========
====================Dn=====Up=====Diff
Drag..............8.500...14.700..+73%
Lift.............52.000...-1.200.-102%
Load on Wheels..141.600..194.800..+38%
Braking Force....75.900...98.000..+29%
--------------------------------------
Max.Stop.Force...84.400..112.700..+34%
(brakes & drag)
Happy landings
dolly
FYI, may I provide some figures for a typical mid-size two-engine transport (RTO at 135KTAS):
Figures are lbs.
===================SpeedBrakes========
====================Dn=====Up=====Diff
Drag..............8.500...14.700..+73%
Lift.............52.000...-1.200.-102%
Load on Wheels..141.600..194.800..+38%
Braking Force....75.900...98.000..+29%
--------------------------------------
Max.Stop.Force...84.400..112.700..+34%
(brakes & drag)
Happy landings
dolly
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I'm beginning to suspect that 411A's statement is based on the startling misconception that SPOILERS are there only to add DRAG as a retardation action. Tell me he doesn't really think so!?
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I have deleted two posts from this topic and edited some personal comments out of several others. I have no wish whatsoever for Tech Log, one of the most useful forums on PPRuNe, to become a flame war area. Any repetition of the offences will be dealt with severely.
Please keep this forum for discussion on technical issues - leave attacking personalities out of it.
Please keep this forum for discussion on technical issues - leave attacking personalities out of it.
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Captain Stable
Well done, I was shocked to read how some posters were attacking others...
The Tech forum is suppose to be about helping others with a free exchange of ideas, experience and information..
Wow what ever happened to all that CRM training?
Well done, I was shocked to read how some posters were attacking others...
The Tech forum is suppose to be about helping others with a free exchange of ideas, experience and information..
Wow what ever happened to all that CRM training?
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Many years ago during our B737 endorsement with a Boeing instructor pilot, we were told that the purpose of immediate manual speed brakes (rather than count on the reverse thrust lever action to raise them), was to dump lift as well as create drag at high speed. He went on to say that the reverse thrust lever was a back-up in case the crew forgot to pull manual speed-brake. This instructor would go off his trolley if you forgot to raise the speed brakes manually on an abort.
He briefed us that Boeing never envisaged use of the reverse thrust levers alone as the prime means of raising the speed brakes in an abort. In any case it may be unhealthy to reverse an engine that is on fire if the abort was due to a fire warning. Thus if your company requires the use of reverse thrust lever actuation as the primary means of getting the speed brakes up, it is worth thinking about the engine fire case.
During simulator sessions we were shown an abort at high speed using max reverse thrust only. The purpose of this demonstration was to show the excellent initial retardation of reverse thrust and as the speed reduced below 100 knots the retardation was less and less until at 60 knots the aircraft kept on coasting down the runway and off the end while still making lots of noise at full reverse. We then saw an abort using maximum brake and speedbrake and the difference was phenomenal. All this on a dry runway. It is on a wet runway that reverse starts to come in on its own as the brakes don't get a good grip initially.
What we often see in the simulator is the pilot frantically attempting to haul through the interlocks into full reverse on an engine failure abort and failing to concentrate instead on maintaining maximum braking (if he has overridden the RTO function - which people sometimes do inadvertently while using rudder to keep straight on a single engine high speed abort).
As someone mentioned earlier, on a dry runway by the time you wind up into full reverse on the live engine, the brakes have done their job and the speed is down into the reverse useless range.
There are companies that have the PNF sharing the abort actions by being responsible for reverse thrust actuation and modulation of reverse. This might work well in a simulator where you know that aborts are bound to be practiced. In real life, however, I venture to argue that this is a recipe for confusion. Especially if the aircraft started to weather-cock off centre line requiring judicious reverse handling. A case of who's up who, and who is paying the rent!
A high speed abort may hopefully never happen in one's career but if it does it may well be the most critical instant decision that one ever has to make. I would also venture to say that during certification flight testing the test pilot personally takes all the required abort actions - I am sure he would not pass the responsibility of reverse handling during the abort to the co-pilot? In my book anyway, the abort is a one man handling operation with the other pilot monitoring.
He briefed us that Boeing never envisaged use of the reverse thrust levers alone as the prime means of raising the speed brakes in an abort. In any case it may be unhealthy to reverse an engine that is on fire if the abort was due to a fire warning. Thus if your company requires the use of reverse thrust lever actuation as the primary means of getting the speed brakes up, it is worth thinking about the engine fire case.
During simulator sessions we were shown an abort at high speed using max reverse thrust only. The purpose of this demonstration was to show the excellent initial retardation of reverse thrust and as the speed reduced below 100 knots the retardation was less and less until at 60 knots the aircraft kept on coasting down the runway and off the end while still making lots of noise at full reverse. We then saw an abort using maximum brake and speedbrake and the difference was phenomenal. All this on a dry runway. It is on a wet runway that reverse starts to come in on its own as the brakes don't get a good grip initially.
What we often see in the simulator is the pilot frantically attempting to haul through the interlocks into full reverse on an engine failure abort and failing to concentrate instead on maintaining maximum braking (if he has overridden the RTO function - which people sometimes do inadvertently while using rudder to keep straight on a single engine high speed abort).
As someone mentioned earlier, on a dry runway by the time you wind up into full reverse on the live engine, the brakes have done their job and the speed is down into the reverse useless range.
There are companies that have the PNF sharing the abort actions by being responsible for reverse thrust actuation and modulation of reverse. This might work well in a simulator where you know that aborts are bound to be practiced. In real life, however, I venture to argue that this is a recipe for confusion. Especially if the aircraft started to weather-cock off centre line requiring judicious reverse handling. A case of who's up who, and who is paying the rent!
A high speed abort may hopefully never happen in one's career but if it does it may well be the most critical instant decision that one ever has to make. I would also venture to say that during certification flight testing the test pilot personally takes all the required abort actions - I am sure he would not pass the responsibility of reverse handling during the abort to the co-pilot? In my book anyway, the abort is a one man handling operation with the other pilot monitoring.