A320 tachymeter

[Citation2]

Question for engineers:

On A320 when a single tachymeter is inoperative the aircraft is not dispatchable.Obviously the brake system would not be able to work without having a proper tachymeter but...
Having a look at brake system fault on a wheel , the brake can be deactivated on the affected wheel and the aircraft is dispatchable.

My question is , in case of tachymeter fault on one wheel , is it possile to deactivate the whole brake system on the affected wheel and dispatch the aircraft?

[Beeline]

If you have a Brake Fault it means look at the PFR and see what's wrong, 9/10 times it will be a BSCU Ch1 or 2 fault. Dispatchable.

If you have a Tachometer fault on both channels let's face it it is a Tachometer fault. No dispatch.

Maybe coincidence but if the clown who sent one of our aircraft back with a brake locked out after this exact fault is reading this prepare for a hammering because I have reported you for doing just that.

A new BSCU box has been released that is more sensitive to tachometer faults so those who are not aware be aware of this potential no dispatch condition. The tachometer gives a lot more info to systems other than just autobrake/anti skid. Don't lock the brake out and send it away. Pilots please do not accept.

Rant over

[Ollie Onion]

I assume that you can't just lock out the brake because this doesn't address the actual tacho fault. It could still play silly buggars with the rest of the braking systems by sending erroneous data. As with all things airbus it is amazing what other systems may be involved with the tacho, so treating a symptom like the brake instead of the actual fault is asking for trouble!

[Citation2]

Thanks for your input guys it makes sense.I totally agree to treat the failure independantly as no dispatch like stated in the MEL.Doing otherwise is a kind of arrangement not so compatible with aviation. But similarly when RA1 is inop which is a no go item , how would you see the swapping over? Legal or not?If RA2 replaces RA1 , now RA1 is working , would you accept such swapping not written in the holy books to dispatch the aircraft?If the tachymeter is so important that even a deactivated brake could not work without ,MMEL should state it as one of the condition to dispatch the aircraft with one brake deactivated. " brakes inop---condition of dispach tachymeter operative" or is it a miss?

Likwise if nothing is written about the swapping does that mean that you can or cannot do it?

[Beeline]

Think you are missing the point with so called work arounds.

In your RA example it usually is not the system that is a no dispatch as it is based on a redundancy architecture.

However the place in the rack is paramount due to the units wiring ie. power supply or as in the LGCIU1 example hard wired to the three greens. (plenty of threads on that one)!!

With the tachometer example again the BSCU uses the information for WHEEL SPEED and if the brake is released hence no dispatch. To be fair this is a recent addition that Airbus have obviously felt that 4 must be serviceable, we use to be able to dispatch with one inop.

A better work around would be to make the anti skid system u/s and tell the skipper he/she is on alternate braking at 1000 psi.

I doubt they will take it!

[Citation2]

Thanks for your inputs. At the end the best course of action is obviously follwing what MEL says.

[Beeline]

In your defence the MEL can also be very ambiguous. Not everything is black and white!

Be careful out there!