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Latest AAIB Report 12/2011 - Inadvertent brake application by PF on take off roll.

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Latest AAIB Report 12/2011 - Inadvertent brake application by PF on take off roll.

Old 10th Dec 2011, 10:42
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Latest AAIB Report 12/2011 - Inadvertent brake application by PF on take off roll.

http://www.aaib.gov.uk/cms_resources...DM%2012-11.pdf



Interesting incident just published caused by captain inadvertently applying brakes during take off roll. Aircraft did not respond to elevator at VR and copilot took it upon himself to close throttles and initiate rejected take off.

The brake pressure being applied unknowingly by the captain caused the nose wheel to be firmly attached to the runway until at VR when the nose down moment was so strong that up full elevator was unable to raise the nose more than a couple of degrees. The copilot thought the aircraft was un-flyable and whipped the thrust levers closed.

In the 737 simulator some years ago, we were practicing rejected take off procedures with two 200 hour cadets from Indonesia. Although both cadets performed each rejected take off correctly, one cadet frequently over-ran the runway.

During one take off run, it was noticed by the simulator instructor watching a selected page on the instructor screen that intermittent partial brake pressure was being applied (between 100 and 250 PSI) during the roll conducted by that cadet. This suggested he probably had his toes on the brakes without being aware of it. In turn, this extended the take off roll and invalidated the performance. Due to cultural mores he refused to believe it was his fault and denied inadvertently applying slight brakes.

When his crash mate was placed in the instructor seat and told to report what he saw on the brakes pressure display, only then was the cadet convinced he was at fault. No problems after that.

The AAIB report above is most instructive because it quantifies brake pedal angle with brake pressure applied. This revealed that the elevator was ineffective in raising the nose because of the down pressure on the nosewheel caused by partial braking.

Presumably this could happen on any aircraft depending on geometry and other factors. Indeed, like the subject aircraft in the AAIB incident report, this could persuade a pilot to abort after VR if he thought the aircraft was unflyable.

Of course, its a bit late to say to the PF "get your size 10's off the bloody brakes" if the aircraft was not responding to elevator control at VR. But an interesting discussion nonetheless if only because because there have been accidents due to the PF riding brakes inadvertently during take off.

Last edited by Tee Emm; 10th Dec 2011 at 10:53.
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Old 10th Dec 2011, 11:18
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I had some difficulty with that link so try this one.

Air Accidents Investigation: Download PDF document
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Old 10th Dec 2011, 15:16
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Obviously not the best practice :
When using the rudder pedals the commanderís technique was to place his feet on the pedals with his heels clear of the floor, so that the rudder was operated with the heels and the brakes by flexing forward the toe end of the foot.
That one makes more sense :
His feet would be positioned so that the ball of the foot rested on the lower part of the pedal (the rudder bar) with the heels on the floor, unless braking was required in which case he would lift his feet up so that he could apply the brakes.
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Old 10th Dec 2011, 15:56
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Presumably this could happen on any aircraft depending on geometry and other factors.
Yes! And I'm a big BACK TO BASICS kind of pilot.

**Heels on the FLOOR for every takeoff please**

This should be taught at the beginning of every pilots career.
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Old 10th Dec 2011, 16:01
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The fundamental problem with the type involved, and several others, is the angle at which the pedal resides, which makes inadvertent brake application much more likely than it should be.

Of course, the footwell is an area where space is often at a premium, but there should be no excuse for a pedal design which makes it difficult to have the feet positioned on the pedals to permit accurate brake application only when it is conscious.

The absence of a relevant certification standard, lack of dialogue between designers and ergonomics experts, lack of awareness of the problem (probably by everyone), and a ready acceptance of shoddy work in this specific aspect of design by too many folk involved in test and development, have all played their parts.

This idea that heels should rest on the floor only holds water if you assume that you will never reject at speed in a crosswind or with an engine failure, or that the autobrake (if fitted) is utterly reliable.

Otherwise, the motion required to reposition the foot (feet) on the pedal(s) necessarily involves reducing rudder force to zero, even if only momentarily. This destabilises the trajectory and causes big problems.

A combination of properly-designed pedals and some sort of acceleration monitoring (called for over many years but only now looking like a reality on some very modern types) is the answer, not a dictat to pilots that they should risk their aircraft by using a technique which deprives them of immediate access to their brakes.

Last edited by frontlefthamster; 10th Dec 2011 at 17:22.
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Old 10th Dec 2011, 17:24
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Otherwise, the motion required to reposition the foot (feet) on the pedal(s) necessarily involves reducing rudder force to zero, even if only momentarily. This destabilises the trajectory and causes big problems.
Do you have reports or anecdotes in mind which would support the mention of big problems ?
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Old 10th Dec 2011, 17:28
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How about if you "reject at speed in a crosswind or with an engine failure"?
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Old 10th Dec 2011, 17:41
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My best evidence, personally observed, is from seeing 'heels on the floor' pilots reject in the sim, especially with strong crosswind or a nasty swing such as from N1 seizure at a moderate speed on aircraft with wing-mounted engines.

This latter case can be particularly exciting if executed below the min speed for autobrake engagement... As one pilot put it in the debrief, "I realised I could keep straight but not stop, or had to decide to lose directional control to get to the brakes..."

If stopping suddenly is a possible operational requirement, it's up to the designers et al to provide an environment which allows the pilots to do that. In fact, some discussion here is of work-arounds to cheat the poor design, and that's bad news wherever you find it.

That some manufacturers put non-slip material or features on the pedals shows me that they don't believe sliding feet on them deliberately is part of the pilot's task either...
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Old 10th Dec 2011, 17:54
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My best evidence, personally observed, is from seeing 'heels on the floor' pilots reject in the sim, especially with strong crosswind or a nasty swing such as from N1 seizure at a moderate speed on aircraft with wing-mounted engines.
Yes, different strokes for..., my feet are off the floor for takeoff and landing, works good, lasts a long time (AB).
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Old 11th Dec 2011, 00:33
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Originally Posted by frontlefthamster
This latter case can be particularly exciting if executed below the min speed for autobrake engagement... As one pilot put it in the debrief, "I realised I could keep straight but not stop, or had to decide to lose directional control to get to the brakes..."
It is a fact there is a transition to take place, I agree.

Now, what's behind the words to lose directional control or big problems ?
Is it a very temporary and limited variation of the heading or is it enough to put a wheel off ?

Are we aware of reports recommending to keep the heels clear of the floor ?
The present report does not recommend either to keep the heels on the floor, but it could easily have done so ...

On my side, the heels have always been on the floor as long as braking was not applied, works good as well.
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Old 11th Dec 2011, 04:54
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This incident should be proof enough of the inadvisability of the 'heels on the rudder pedals' steering technique.


It is simply too easy to apply the brakes inadvertently.



When you need to use the brakes move your feet up to use them, yes this may be a difficult transition sometimes in heavy crosswinds but it's one we all have to do and with care it's not a problem.
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Old 11th Dec 2011, 05:02
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For me it depends. In an Airbus with the giant pedals it is feet all the way up for takeoff and landing. In a Boeing it is heels on the floor until brakes needed. About equal time in each and never any problems with x winds, engine faliures, or rejects.
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Old 11th Dec 2011, 06:26
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During a reject after a sudden cut at/close to V1 with a big boot of rudder to keep straight, I would find it very hard to slide my feet up the pedals to apply maximum braking. I would venture to suggest that it is almost impossible to "slide one's feet up" the pedals whilst applying any reasonable steering force; I would have to virtually pull my feet completely off the pedals first. Obviously, rather undesirable on a balanced-field reject. As far as I am concerned, wherever your feet are at the failure is where they are going to stay for the reject.

On all takeoffs my feet are right up ready. These incidents do however reinforce the need to keep one's toes off the brakes, wherever you have your feet.
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Old 11th Dec 2011, 08:05
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Hi Capn Bloggs,

Surely it depends on the features installed on the aircraft? Most modern manufacturers have bothered to fit autobrakes. Why not use that feature and avoid running the risk of applying the brakes unintentionally during the 99.99% of your successful take offs?

Have you never come across a low experience pilot, who didn't have their heels on the floor, and who applied the brakes unintentionally during the rudder control check during taxy?

If the RTO is performed below the autobrake threshold speed, then there is plenty of runway ahead and time to sort out your feet transition from floor to brakes.
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Old 11th Dec 2011, 08:24
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I subscribe to heels on the rudder bars and toes held clear of the brakes, until needed.

A recent landing performed by Bloggs (not Capt Bloggs) saw full left rudder and close to 200 degrees brake temp on the right bogie. IMHO Bloggs couldn't apply symmetrical braking because the left leg was fully extended and not able to provide much braking, whilst the right foot did most of the braking.

An illuminating lesson for both of us.
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Old 11th Dec 2011, 12:19
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On all takeoffs my feet are right up ready.
I thought a recent Boeing document recommended pilots should be Go-minded rather than REJECT minded - due to the propensity of pilots to abort unnecessarily. The general rule in the 737 FCTM was to use 80 knots as a trigger to stopping for any master caution. In that case why have your feet "ready" on the brakes when there is no problem with pulling up.

Above 80 knots the advice is to keep on going depending on the problem and in any case that is why the RTO is installed on most modern jet transports. It is the instinctive reaction at high speed where an unnecessary abort becomes dangerous if the statistics are to be believed. Keep your toes on the bottom of the rudder pedals and your heels on the floor has served the test of time
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Old 12th Dec 2011, 00:32
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Progress

Clarrie,

I guess they don't teach them to adjust the pedals to allow full brake with full rudder anymore...probably interferes with their social life!

Stay Alive,
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Old 12th Dec 2011, 02:07
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Originally Posted by CONF iture View Post
Do you have reports or anecdotes in mind which would support the mention of big problems ?
I have heels off the floor for every takeoff. Here is a classic example of why...

The brakes are operated by applying pressure to the top of the rudder pedals. The brakes can be operated from either the left or the right pilot seat through the dual rudder pedal system.

Examination of the rudder pedals by TSB investigators determined that, with the feet placed with the heels on the floor, very little pressure could be applied to the tops of the pedals to operate the brakes. It was possible to position the feet higher on the pedals so that the rudders could be operated without exerting pressure on the brakes, while also permitting the brakes to
be operated simultaneously with deflection of the rudder pedals.

The pressure exerted by the FOís foot against the right rudder pedal prevented repositioning the foot higher on the pedal to operate the brake. The FO was unable to operate the brake for directional control because he was unable to release the pressure on the rudder pedal without losing the directional control provided by the rudder.


Findings as to Causes and Contributing Factors

1. The aircraft was operating in environmental conditions conducive to snow
penetration into the brake assemblies during ground operations at Kenora.
2. The brake assemblies on the left main landing gear froze, preventing the wheels from
rotating during the landing roll at Dryden.
3. The first officerís foot position and pressure application on the rudder pedals prevented effective use of differential braking and nosewheel steering to maintain directional control of the aircraft after landing.

Findings as to Risk

1. Although the practice of pilots placing their feet on the rudder pedals with their heels on the floor reduces the risk of tire damage from an unintentional brake application, the practice creates a risk that pilots will not be able to use the brakes to maintain directional control.



http://tsb.gc.ca/eng/rapports-report...6/a04c0016.pdf
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Old 12th Dec 2011, 02:58
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Thanks a lot for the link punkalouver.
Interesting.
Once again excellent report by the Canadians.

Now, we have 2 reports that contradict themselves, and for good reasons.

No wonder my SOP and FCTM don't address the subject ... blamed if you do and blamed if you don't.
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Old 12th Dec 2011, 03:04
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I would be interested to see if there are any operators that teach this 'heels on the rudder pedals' technique.


I know it's not a Boeing procedure and I think it's disadvantages far outweigh any gains.
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