Rejected Takeoff
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Rejected Takeoff
Have been looking at several Boeing QRH's recently re the RTO manoeuvre. There appears to be a major difference in the order of selecting "speedbrake up".
Some QRH's suggest ....close thrust levers, disconnect autothrottle, select speedbrake up...
Others suggest...close thrust levers, disengage autothrottle, apply maximum manual wheelbrakes or verify operation of RTO autobrakes. Raise speedbrake....
Any comments or links to articles re this topic most appreciated. Why does your company recommend one action before the other ??
Some QRH's suggest ....close thrust levers, disconnect autothrottle, select speedbrake up...
Others suggest...close thrust levers, disengage autothrottle, apply maximum manual wheelbrakes or verify operation of RTO autobrakes. Raise speedbrake....
Any comments or links to articles re this topic most appreciated. Why does your company recommend one action before the other ??
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By Company SOP ...
1) Thrust levers to idle.
2) Ensure A/T disconnect (if prior to "Throttle Hold" callout).
3) Speed brakes to Ground Detent
4) Monitor Auto Brake (max manual if "Auto Brake Disarm" callout).
5) Thrust reversers used as required.
2) Ensure A/T disconnect (if prior to "Throttle Hold" callout).
3) Speed brakes to Ground Detent
4) Monitor Auto Brake (max manual if "Auto Brake Disarm" callout).
5) Thrust reversers used as required.
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jet,
i must say the confusion lies in how to put it in written words. i believe the intend is to apply brakes AND raise speedbrakes SIMULTANEOUSLY. my previous experience tells me the tendency is to select reverse thrust AHEAD of speedbrake. I keep forcing myself but it still happen. guess needs more practise
SR
i must say the confusion lies in how to put it in written words. i believe the intend is to apply brakes AND raise speedbrakes SIMULTANEOUSLY. my previous experience tells me the tendency is to select reverse thrust AHEAD of speedbrake. I keep forcing myself but it still happen. guess needs more practise
SR
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as you know the original 'certification'required two'reliable'stopping devices-spoilers/brakes-to be deployed within about 3.5secs(depend on type/configuration-longer to recognise the centre engine failure)..Newer types(320)has auto spoiler extension(depending on occurence speed).
Depending on the 'test card'either 'brakes on/thrust levers close 'was the first 'action'
Cheers
Depending on the 'test card'either 'brakes on/thrust levers close 'was the first 'action'
Cheers
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This has been a bone of contention in various airlines I've worked for; types B737 and the B757/767 family.
Boeing say:
Close TL's etc etc,
Raise speed brake
Apply max reverse thrust.
etc. etc.
It does not say how to raise the speed brake. Some training dept's. insisted it was to be done manually BEFORE the T.R's were actioned. Others said that the raising of the T.R's to the interlock position would deploy the speed brake before the application of reverse thrust and thus satisfied the sequence of events by automatics. i.e. the way Boeing designed the system to be used.
It was a controversial point when changing companies. It is certainly more natural to apply T.R's immediately after closing the T.L's because that is where your hands are.
However, as often the case, getting a definitive answer from Boeing as to the correct method was impossible. They would not, according to the respective training depts, declare any preference but approved both methods.
Boeing say:
Close TL's etc etc,
Raise speed brake
Apply max reverse thrust.
etc. etc.
It does not say how to raise the speed brake. Some training dept's. insisted it was to be done manually BEFORE the T.R's were actioned. Others said that the raising of the T.R's to the interlock position would deploy the speed brake before the application of reverse thrust and thus satisfied the sequence of events by automatics. i.e. the way Boeing designed the system to be used.
It was a controversial point when changing companies. It is certainly more natural to apply T.R's immediately after closing the T.L's because that is where your hands are.
However, as often the case, getting a definitive answer from Boeing as to the correct method was impossible. They would not, according to the respective training depts, declare any preference but approved both methods.
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There might be some slight variations in sequence depending on the specific airplane’s automatics/certification, but the basic idea regarding commercial jetliners is to first get maximum weight on the wheels, since most (almost all) of the braking action comes from there. Once reverse thrust has spooled up, it may be quite ineffective anyway due to being at low speed already.
Therefore:
1. Stop the acceleration (close thrust levers)
2. Start wheelbraking and get weight on the wheels simultameously (brakes, speedbrakes)
3. Initiate reverse thrust
But then again, airlines differ in their utilization of automatics...
My personal view: If aborting (something serious wrong already), I wouldn’t rely too much on auto-features.
happy landings
dolly
Therefore:
1. Stop the acceleration (close thrust levers)
2. Start wheelbraking and get weight on the wheels simultameously (brakes, speedbrakes)
3. Initiate reverse thrust
But then again, airlines differ in their utilization of automatics...
My personal view: If aborting (something serious wrong already), I wouldn’t rely too much on auto-features.
happy landings
dolly
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Our sop's may differ from others, but on an RTO, the handling pilot closes the thrust levers, disconnecting the a/t, and simultaneously applying max foot braking (or monitor autobrakes). The non handler applies max reverse, and ENSURES the autospeedbrakes have deployed, if not they're deployed manually.
Hope this helps.
Hope this helps.
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I haven't checked in practice. But if you were to ARM the speedbrakes on the 737NG, 757, 767 before TO. They'd deploy automatically when the throttles are brought to idle and airspeed is what???(above 90 kts or so). It looks like most of the criteria for this to happen would be satisfied.
I don't know why it's not done on these aircraft? Any good reason?
I don't know why it's not done on these aircraft? Any good reason?
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Appreciate all the comments. Yes with RTO armed and above 90 knots the auto-speedbrkes "should" operate but many operators prefer to manually deploy the speedbrakes just in case. Had a peak in the 737NG FPPM and whilst there is a 4300kg penalty landing for the NG, there is no take off penalty at all if the Auto-Speedbrakes are u/s. Did I read this wrong ?
This all leads me to my next question then - what helps the most on an RTO - brakes (auto/manual), speedbrakes or thrust reversers ?
This all leads me to my next question then - what helps the most on an RTO - brakes (auto/manual), speedbrakes or thrust reversers ?
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On 75 and 76 the speedbrakes will deploy automatically if the thrust reversers are deployed and the a/c is on the ground (bogie tilt). At the same time the selection of reverse thrust combined with wheel speed above 90 kts will initiate RTO braking rate (i.e. max avail). This is all automatic. In the event of automatics failing it is important to consider that it will take about 2 seconds for the reversers to deploy so for me the sequence would be : - close throttles whilst disengaging A/T, deploy reversers whilst monitoring autobrake/applying brake, check/manually apply speedbrake, apply reverse thrust.
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originally posted by jetblues
That very much depends on the aircraft and the conditions.
TRs will be far more effective, proportionally, on a wet runway, and brakes less effective, due to loss of braking mu.
Aircraft with energy limited brakes, or torque limited brakes, may find brake contribution to the RTO greater at lighter weights, as brake fade may affect braking at heavier weights.
Effectiveness of spoilers depends obviously on number of panels.
Fo a given aircraft you can gauge the relative effectiveness of each system to the RTO by looking at the penalties for various failures in the flight manual, for landing distances. While not the complete story, that will give you a rough guide to the relative effectiveness of these devices.
This all leads me to my next question then - what helps the most on an RTO - brakes (auto/manual), speedbrakes or thrust reversers ?
TRs will be far more effective, proportionally, on a wet runway, and brakes less effective, due to loss of braking mu.
Aircraft with energy limited brakes, or torque limited brakes, may find brake contribution to the RTO greater at lighter weights, as brake fade may affect braking at heavier weights.
Effectiveness of spoilers depends obviously on number of panels.
Fo a given aircraft you can gauge the relative effectiveness of each system to the RTO by looking at the penalties for various failures in the flight manual, for landing distances. While not the complete story, that will give you a rough guide to the relative effectiveness of these devices.
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Is it not the case that in an RTO calculation the effect of T.R's is not considered? They are a bonus and deceleration is calculated using brakes and anti-skid. For the brakes to have their correct effectiveness the ground spoilers must be deployed.
While it is true that brakes will lose effectiveness on anything other than clean & dry, this is taken into account via the non-too accurate, (especially when contaminated) weight reduction calculation.
The brakes are generally very effective and thus there is a rapid deceleration causing the T.R's to lose effectiveness as speed reduces. Perhaps this is why they are treated as a bonus, except on slippery surfaces, when you would most likely be in the lap of the gods anyway.
While it is true that brakes will lose effectiveness on anything other than clean & dry, this is taken into account via the non-too accurate, (especially when contaminated) weight reduction calculation.
The brakes are generally very effective and thus there is a rapid deceleration causing the T.R's to lose effectiveness as speed reduces. Perhaps this is why they are treated as a bonus, except on slippery surfaces, when you would most likely be in the lap of the gods anyway.
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Yes, for the calculatyed & certified distance TRs are not considered.
But they are effective, nevertheless, and the question was asking which was more effective, not which were considered.
I don't know about other manufacturers, but the loss of braking mu is considered directly in calculating the distances on wet and contaminated surfaces for our manuals, and I believe that's what the regs require. Certainly it's rather more than a crude weight reduction.
(weight would only be reduced if one held the LFL or ALD constant, otherwise the distances just go up as the decel devices become less effective)
But they are effective, nevertheless, and the question was asking which was more effective, not which were considered.
I don't know about other manufacturers, but the loss of braking mu is considered directly in calculating the distances on wet and contaminated surfaces for our manuals, and I believe that's what the regs require. Certainly it's rather more than a crude weight reduction.
(weight would only be reduced if one held the LFL or ALD constant, otherwise the distances just go up as the decel devices become less effective)
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Thrust Reversers are not considered in RTO performance for the very good reason that they may not be useable. If you are rejecting the take off because you've lost an engine, and if the runway is wet/slippery with crosswind etc then controllability may be a serious issue. You might only be able to apply idle reverse on one engine at best (in the case of a twin).
It therefore makes perfect sense to consider this worst possible scenario during training and emphasise the order of actions to take maximum advantage of the reliable retardation systems you have. That means:
1) Thrust Idle
2) Brakes on (simultaneously)
3) Speedbrake deployed manually (have a look at the penalties for spoilers u/s for take off!)
4) Reverse Thrust (if available)
IMHO.
It therefore makes perfect sense to consider this worst possible scenario during training and emphasise the order of actions to take maximum advantage of the reliable retardation systems you have. That means:
1) Thrust Idle
2) Brakes on (simultaneously)
3) Speedbrake deployed manually (have a look at the penalties for spoilers u/s for take off!)
4) Reverse Thrust (if available)
IMHO.
Paxing All Over The World
From an outsider, or inside if I am riding with you that day ...
It is said here that TR is not of great use. I can understand that with a twin or triple engined machine, where the risk of off balance is great - is that the only reason for discounting it? Even at low speeds T.R. must have a reasonable impact on the forward speed?
Thanks.
It is said here that TR is not of great use. I can understand that with a twin or triple engined machine, where the risk of off balance is great - is that the only reason for discounting it? Even at low speeds T.R. must have a reasonable impact on the forward speed?
Thanks.
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Perhaps there is a case for saying that if we abort below the 80 knot call, deploying the speedbrake before reverse thrust is a better course of action as the reverse thrust has a lesser effect at lower speeds. If we abort between 80 knots and V1 then apply reverse thrust first (if available) then pull the speedbrake lever.
Having two procedures though depending on speed does also serve to complicate the matter I would have thought.
Thoughts from jet drivers (only humble ATPL student and FS 2000 737 add on driver myself!)
Having two procedures though depending on speed does also serve to complicate the matter I would have thought.
Thoughts from jet drivers (only humble ATPL student and FS 2000 737 add on driver myself!)
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Traditionally,the most reliable stopping device was credited to the spoilers(weight on wheels),the brakes didn't on wet surfaces.
JAR's give credence to Reverse thrust in the WET runway scanario,due to their improved reliablity.
ergo if reversers are only effective at HIGH speed and the Brakes are optimum on DRY surfaces,don't the spoilers still win??
Cheers
JAR's give credence to Reverse thrust in the WET runway scanario,due to their improved reliablity.
ergo if reversers are only effective at HIGH speed and the Brakes are optimum on DRY surfaces,don't the spoilers still win??
Cheers
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There's nothing inherent in TRs that causes them to lose effectiveness as speed reduces. What often causes this is a decision to schedule the maximum reverse thrust N1 (or EPR, for the Derby types) with speed, in order to reduce the risk of reingestion or loss of directional stability.
The spoilers, ON THEIR OWN, are probably the least useful of any of the devices, since they only create drag, which is less and less useful for stopping as the speed decreases - eventually you'd be relying on rolling friction to come to a halt. They are great for increasing the effectiveness of the brakes, by increasing the weight on the wheels, but that's really the brakes doing the work.
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.
The spoilers, ON THEIR OWN, are probably the least useful of any of the devices, since they only create drag, which is less and less useful for stopping as the speed decreases - eventually you'd be relying on rolling friction to come to a halt. They are great for increasing the effectiveness of the brakes, by increasing the weight on the wheels, but that's really the brakes doing the work.
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.
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Our SOP's on this changed last year. On our fleet (B757-200/-300) We used to rely on auto speedbrake. However following reccomendation from Boeing, following an incident with Airtours I think where it did not deploy, the SOP was changed. It is now....... Simultaneously close thrust levers (disengage autothrottle if required) apply max manual brakes or verify operation of RTO autobrakes. Raise speedbrake lever. Apply max reverse thrust consistent with conditions.
Eff Oh.
Eff Oh.