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Frank M
21st Oct 2003, 00:00
Hi all,

When looking at a failure in the Antiskid system on our aircraft (B767) we also looked at the possibility to deactivate a brake using either of two methods :

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Brake deactivation/disconnect tool
Capping of brake line
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Now I've heard that this brake deactivation tool actually does allow use of that brake in case a very heavy brake demand is present. Can anybody please explain (in simple terms....) how this is achieved.

The T/O performance penalties are also very different for the two options (3000 kg vs 25000 kg), so I'm quite sure the tool somehow lets you use that brake in case of a Rejected T/O.

Thanks in advance for the reply!

Frank.

mono
21st Oct 2003, 01:22
Just a quick reply here, will try to get a more detailed answer later.

From memory, the brake disconnect tool goes into the NORMAL brake line at the normal brake control module. In effect NORMAL brake pressure is prevented from operating the deactivated brake.

However ALTERNATE brake pressure can still operate the relevant brake. Under usual circumstances this this means the brakes are operated (by the alt system) on gear retraction.

So, the rule of thumb is........

Brake leaking or hoses leaking, cap the line (upstream of the leak of course)

Speed transducer u/s or a/skid problem, De-activate via disconnect tool.

You may find the extra penalty for a capped brake is in fact due to t/o performance not brake efficiency as if the brake is capped then the gear must remain down for 2 mins prior to retraction to ensure wheel rundown.

This may be wrong of course as I don't have a DDG or MEL to hand to check my data.

Frank M
21st Oct 2003, 06:19
Hi mono,

Ofcourse it is because of leaving the gear down..... I hadn't looked that far yet. Thanks for pointing that out ! Our MEL indeed states that we should leave the gear down for at least two minutes.....

Thanks for your quick reply !

Frank.