A/C Braking System Redesign
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A/C Braking System Redesign
Hi Guys.
You may or may not be aware of the accident in Manchester last Tuesday, when an Aer Arann ATR was approaching stand and failed to stop at its stop bar. It continued for several feet beyond it resulting in a collision with ground equipment. It would appear that the driver had lost all hydraulic pressure and was unable to apply any pressure to the brakes. Photos on the R & N forum would suggest that the a/c suffered a total and catastrophic loss of hydraulic pressure.
If that proves to be the cause of the accident, is there not a case for aircraft brakes to be redesigned so that hydraulic pressure keeps the brakes in the off position so that in the event that total hydraulic pressure is lost, the brakes would automatically engage?.
The ATR braking system would appear to have quite a lot of redundancy built in and has tried to cover all eventualities – two systems Blue and Green, DC elec pump in the event of failure of the AC system, cross feed from one to the other, accumulators in the event of the loss of pressure and an emergency brake.
None of the above will work if the hydraulic line fractures at or close to the calipers.
Cheers
You may or may not be aware of the accident in Manchester last Tuesday, when an Aer Arann ATR was approaching stand and failed to stop at its stop bar. It continued for several feet beyond it resulting in a collision with ground equipment. It would appear that the driver had lost all hydraulic pressure and was unable to apply any pressure to the brakes. Photos on the R & N forum would suggest that the a/c suffered a total and catastrophic loss of hydraulic pressure.
If that proves to be the cause of the accident, is there not a case for aircraft brakes to be redesigned so that hydraulic pressure keeps the brakes in the off position so that in the event that total hydraulic pressure is lost, the brakes would automatically engage?.
The ATR braking system would appear to have quite a lot of redundancy built in and has tried to cover all eventualities – two systems Blue and Green, DC elec pump in the event of failure of the AC system, cross feed from one to the other, accumulators in the event of the loss of pressure and an emergency brake.
None of the above will work if the hydraulic line fractures at or close to the calipers.
Cheers
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Point taken on the bigger tins but on the ATR, both lines are fed from a common tank.
Its is the same for most of the prop Cat B's. As can be seen from the photo's, these a/c are capable of doing a lot of damage when out of control and luck played a big part in the fact the no one was injured.
http://www.pprune.org/airlines-airpo...anchester.html
Its is the same for most of the prop Cat B's. As can be seen from the photo's, these a/c are capable of doing a lot of damage when out of control and luck played a big part in the fact the no one was injured.
http://www.pprune.org/airlines-airpo...anchester.html
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if you can show me a case where both lines on both gears ( total of 4 lines) have failed at the same time due to fatigue etc.
we are not talking about the main supply line from a reservior - the OP said "if the hydraulic line fractures at or close to the calipers"
we are not talking about the main supply line from a reservior - the OP said "if the hydraulic line fractures at or close to the calipers"
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You're replaced the case where total loos of hydraulics (at the brakes) means total loss of braking.
You've also replaced the case where loss of hydraulics in one system (at the brakes) means loss of the corresponding braking capability.
But you've now added the case that loss of hydraulic pressure (at the brakes) means inadvertent brake application - either on a system-by-system basis or as a total system.
Cases that would have to be addressed include hyd failure on TO causing full brake application of the corresponding brakes, with the performance impact (and associated hazards), the handling impact of possibly asymmetric brakes (depending on where the hyd failure occurs) and the risk to the brake of overheating and of tyre burst.
Since the existing cert rules more than adequately address the case of single hyd loss leading to associated braking loss, all that this proposal mitigates is the total braking failure case, which is a very improbable case (perhaps even "extremely improbable" in which case the certification is trivial). But now there's a whole bunch of single failures resulting in inadvertent brake application. Loss of one hyd system is typically a 10e-4 to 10e-5 per FH event, so that inadvertent braking is going to be pretty frequent - certainly I'd be concerned that the new risks are more dangerous than the case being mitigated.
if you can show me a case where both lines on both gears ( total of 4 lines) have failed at the same time due to fatigue etc.
Yes, I have never heard of all brakes failing. I've had them fail completely on one truck due to a couple of wheels coming apart, and another company 747 went off the end of the runway in the Middle East on takeoff for the same reason.
