Rejected Takeoff

[jetblues]

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 ??

[Cross Check]

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.

[SuperRanger]

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

[m&v]

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:D

[18-Wheeler]

FWIW the 747 has had auto-spoiler extension on a rejected take-off since about 1970.

[RAT 5]

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.

[dolly737]

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

[ratarsedagain]

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.

[dvt]

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?

[jetblues]

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 ?

[mono]

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.

[Mad (Flt) Scientist]

originally posted by jetblues
This all leads me to my next question then - what helps the most on an RTO - brakes (auto/manual), speedbrakes or thrust reversers ?

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.

[RAT 5]

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.

[Mad (Flt) Scientist]

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)

[Idunno]

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.

[PAXboy]

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.

[timzsta]

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!)

[m&v]

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:confused: :confused:

[Mad (Flt) Scientist]

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.

[Eff Oh]

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.

[Idunno]

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.

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.

[jetblues]

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" ?

[Mad (Flt) Scientist]

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.

The advantage with the TR/brake only combo is that the two decel devices are somewhat independent. Spoilers are pretty useless without brakes. I guess I meant to say that if I was only allowed ONE, it sure wouldn't be spoilers.

[x]

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.

[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.

[Tan]

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
:D

[None]

"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.

[LOKE]

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

[411A]

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?:E ;)

[LOKE]

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

[411A]

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

[18-Wheeler]

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.

[LOKE]

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

[411A]

LOKE,
Read 18-Wheelers post above...maybe you will get the picture.
Edited

[dolly737]

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

[Idunno]

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!?

[18-Wheeler]

Interesting figures Dolly.
I'm surprised at the amount of lift generated with the nosewheel on the ground though, I thought it would have been a lot less.

[Captain Stable]

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.

[Tan]

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?

[Menen]

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.

[jetblues]

Menen thanks for getting the topic back on track again.

Still looking for some "official" tech papers on the topic if anyone has these handy ?

[Ignition Override]

SuperRanger: It is a shame that we only practice aborts once per year in the sim.

However, if your preflight "flow" tells you to check the spoilers (while noticing fluc. in hydraulic pressures) and then to push the throttles forward, thereby retracting the gnd spoilers, you can modify this just a little bit and practice the motions of an abort each time you do the long preflight checklist, while pushing on the brake pedals. Just don't forget to reset the parking brakes!


This practice helps me in the sim, because the abort is less of a radical change to the normal landing where we almost never need to lift the spoiler handle-unless the FO makes a very smooth landing with some float and the wheels barely kisss the runway (2 main wheels spin-up to activate, before ground shift happens). They mostly make better landings than I do.:\

[RatherBeFlying]

Dolly737's data point shows the effect of spoilers at 135 kt, but it does not give the deck angle (which of course is of more interest with the spoilers down).

As airspeed reduces to headwind the drag contribution from the spoilers (and any lift) reduces with the square of the airspeed; so, to completely assess the effect of spoilers, one has to do an integration and I've been out of school too long to think of doing that.

But I do have to say that I have seen the effect of spoilers at low speed at a glider field. One day somebody landed a Pilatus, forgot the spoilers and came within a few yards of the fence at the end.:ooh:

So if spoilers make a big difference to the ground roll of a glider between 35 and 5 kt, they must also make a significant contribution on the big iron at low speed.

[john_tullamarine]

Considering glider vs big bird ... consider the comparative differences in

(a) spoiler frontal area and contribution to total airframe drag

(b) aircraft mass

and the usual observations are readily explained ...

The value of spoilers on the sailplane is seen in reverse .. very clearly ... on the odd occasion when the glider launches with the boards cracked and the tug pilot then has his work cut out and, perhaps, an unpleasant decision to make ...

[swish266]

On B767 "RTO" setting on autobrk selector is equal to "max manual braking" Boeing recomends not to disengage "RTO" IF IT IS DOING a good job coz it copes better with braking than the Best human can do and reduces the workload in a RTO situation. So the Best human can focus on things like maintaining the centerline... :cool: