A320 Pushbutton Switch failure - open or closed?
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Joined: May 2005
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From: On a good day - at sea
A320 Pushbutton Switch failure - open or closed?
Can a Pushbutton switch fail in flight in the closed position (leaving systems still powered)?
Our regulator has asked about A320 MEL 24-26-02 B and -03, OPERATIONS WITH THE COMMERCIAL PB SWITCH UNSERVICEABLE.
The MEL describes an alternate procedure for turning off the commercial power to be followed in place of the QRH direction ....."Commercial PB...OFF" in the Avionics Smoke procedure.
The point raised is, if the commercial PB switch failed in flight, and subsequent to that there was a requirement to follow the avionics smoke procedure, how would the flight crew know about the alternate procedure for shutting off commercial power ?
Does the commercial power PB switch fail "closed" ? It would appear that if the failure of that switch removed power from the commercial system, then there would be no requirement to follow the alternate procedure described in the MEL.
Our regulator has asked about A320 MEL 24-26-02 B and -03, OPERATIONS WITH THE COMMERCIAL PB SWITCH UNSERVICEABLE.
The MEL describes an alternate procedure for turning off the commercial power to be followed in place of the QRH direction ....."Commercial PB...OFF" in the Avionics Smoke procedure.
The point raised is, if the commercial PB switch failed in flight, and subsequent to that there was a requirement to follow the avionics smoke procedure, how would the flight crew know about the alternate procedure for shutting off commercial power ?
Does the commercial power PB switch fail "closed" ? It would appear that if the failure of that switch removed power from the commercial system, then there would be no requirement to follow the alternate procedure described in the MEL.
Joined: Sep 2009
Posts: 353
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From: bahrain
A pushbutton switch can get stuck and fail in either states closed or open, I have come across both cases.
That procedure is there to make sure the system is isolated, a defective system has to be isolated the legal way regardless of the condition of its pushbutton, you never know that faulty p/b in the open state at any time can fail in the closed again causing the system to switch on, therefore proper isolation is essential.
That alternate procedure is there to avoid any unprecedented events as such (push button reverting to closed state putting power back).
That procedure is there to make sure the system is isolated, a defective system has to be isolated the legal way regardless of the condition of its pushbutton, you never know that faulty p/b in the open state at any time can fail in the closed again causing the system to switch on, therefore proper isolation is essential.
That alternate procedure is there to avoid any unprecedented events as such (push button reverting to closed state putting power back).
Last edited by flame_bringer; 23rd May 2013 at 20:47.
