Operationally unnecessary use of autobrakes for landing
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We must ensure the differences between steel and carbon are understood including the taxi techniques.
Steel and carbon have different unique properties relating to brake wear and heating up/cooling down.
If properly understood the taxi technique differs from when using steel to carbon brakes.
Note brake fans are not fitted to many commercial airliners, when they are it is for good reasons, to be used...
Regarding leaving idle reverse selected for taxi, not a good idea, as forward thrust vectors are required on many occasions, to start or keep the aircraft moving. Is the author of the post suggesting pilots use forward thrust to start moving then select reverse idle while in forward motion and cancel the reversers thrust each time to use forward thrust again for its next requirement?
Steel and carbon have different unique properties relating to brake wear and heating up/cooling down.
If properly understood the taxi technique differs from when using steel to carbon brakes.
Note brake fans are not fitted to many commercial airliners, when they are it is for good reasons, to be used...
Regarding leaving idle reverse selected for taxi, not a good idea, as forward thrust vectors are required on many occasions, to start or keep the aircraft moving. Is the author of the post suggesting pilots use forward thrust to start moving then select reverse idle while in forward motion and cancel the reversers thrust each time to use forward thrust again for its next requirement?
The European Action Plan for the Prevention of Runway Excursions discusses a proposed change to operational rules where the use of autobrake enables an exemption from the 15% additive to the expected landing distance (page 79).
Does anyone know if this proposal has been progressed; is any operator using this exemption?
The logic supporting the proposal is confusing. Previous paragraphs explain that the 15% margin provides some protection for the variability in normal operations – speed, flare, touchdown positon, reported runway condition, whereas the exemption suggests that the use of autobrake replaces most variability, although any difference in operation might only be the time and consistency of brake application.
The rationale states that pilots can always intervene when required yet fails to suggest how such a need be judged, or appreciate that max pilot braking might not make up any shortfall in landing distance if the landing was fast and/or long which the 15% margin might have mitigated.
Does anyone know if this proposal has been progressed; is any operator using this exemption?
The logic supporting the proposal is confusing. Previous paragraphs explain that the 15% margin provides some protection for the variability in normal operations – speed, flare, touchdown positon, reported runway condition, whereas the exemption suggests that the use of autobrake replaces most variability, although any difference in operation might only be the time and consistency of brake application.
The rationale states that pilots can always intervene when required yet fails to suggest how such a need be judged, or appreciate that max pilot braking might not make up any shortfall in landing distance if the landing was fast and/or long which the 15% margin might have mitigated.
Last edited by alf5071h; 29th Sep 2014 at 20:33. Reason: typo
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Is the author of the post suggesting pilots use forward thrust to start moving then select reverse idle while in forward motion and cancel the reversers thrust each time to use forward thrust again for its next requirement?
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Autobrakes are useful to maintain more constant pressure which will reduce wear on carbon brakes. However, one must be careful to not take them off, then "roll to the end" in a misplaced effort to "save the brakes" as that actually increases the brake wear. There is little training on this issue, but the difference between steel and carbon brakes should be understood as Skyjob indicated above.
However, the caveat is that it depends on where you might turn off. If I need to get to a spot near the far end of the runway, I would leave them off and roll down to the end then plan a consistent application to attain taxi speed for the turn off rather than have autobrakes on by rote and then turn them off to roll down to the end. That is one application that is a waste of brake life!
However, the caveat is that it depends on where you might turn off. If I need to get to a spot near the far end of the runway, I would leave them off and roll down to the end then plan a consistent application to attain taxi speed for the turn off rather than have autobrakes on by rote and then turn them off to roll down to the end. That is one application that is a waste of brake life!
Last edited by Shem Malmquist; 1st Oct 2014 at 12:40.
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If carbon brakes wear less when warm turning the brake cooling fans(if installed) on unnecessarily might lead to increased brake wear.
SOP's should address this.
SOP's should address this.
Last edited by misd-agin; 30th Sep 2014 at 14:58. Reason: added 'on'
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If carbon brakes wear less when warm turning the brake cooling fans(if installed) on unnecessarily might lead to increased brake wear.
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At my last airline: Memos from Chief Pilot would encourage minimum use of reverse, and maximum use of autobrakes.
Reverse uses more fuel, which comes from Flight Operation's budget, whereas autobrakes cause brake wear (Engineering's budget!)
Reverse uses more fuel, which comes from Flight Operation's budget, whereas autobrakes cause brake wear (Engineering's budget!)
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Idle reverse uses little, if any, more fuel.
Whether or not you use Autobrakes is a matter of SOP plus the specific environment for each landing. If SOP says ALWAYS use them, then ALWAYS use them. If SOP says NEVER use them, then NEVER use them. Brake life considerations are then not yours, but the company's.
When you have the discretion to use them or not, simply have a general scheme in mind: Minimum runway/rollout length and/or maximum landing weight for NOT using them. Then when you get the performance data for the next landing, decide on whether to use them, which setting to use, abd when to revert to manual.
Know your airplane and its capabilities, as well as your own.
Whether or not you use Autobrakes is a matter of SOP plus the specific environment for each landing. If SOP says ALWAYS use them, then ALWAYS use them. If SOP says NEVER use them, then NEVER use them. Brake life considerations are then not yours, but the company's.
When you have the discretion to use them or not, simply have a general scheme in mind: Minimum runway/rollout length and/or maximum landing weight for NOT using them. Then when you get the performance data for the next landing, decide on whether to use them, which setting to use, abd when to revert to manual.
Know your airplane and its capabilities, as well as your own.
If the braking efficiency of carbon brakes gets better the hotter they are, then is there an argument for deliberately "dragging" the brakes when taxiing for take off to heat them up so that in event of a high speed rejected take off the already hot brakes will permit greater stopping capability?
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No. I've seen a brake overtemp on taxi in a 744 due to a new guy with heavy feet taxiing the diagonal length of DFW...
On an RTO the brakes will heat up instantly. The brakes still have a finite energy absorption capacity, so deliberately heating them up in advance is NOT a good idea.
On an RTO the brakes will heat up instantly. The brakes still have a finite energy absorption capacity, so deliberately heating them up in advance is NOT a good idea.
