airstairs 'MAINT' Switch - Procedure for use? Nothing in AMM

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airstairs 'MAINT' Switch - Procedure for use? Nothing in AMM

Postby JetA1 » 03 Nov 2019, 14:26

Hello guys.

Looking for any reference to the red guarded MAINT switch on the fwd air stairs of NG aircraft.

I am aware it bypasses sensors/switches but cannot find a procedure for its use?

Nothing in my MEL or AMM. Just normal/stby operation or manual stow procedure.

Is this switch not for use other than workshops?

Thanks!
JetA1
 
Posts: 9
Joined: 31 Jul 2019, 13:53

Re: airstairs 'MAINT' Switch - Procedure for use? Nothing in

Postby maro12 » 03 Nov 2019, 18:05

Good Day JetA1,

Ref.AMM SDS 52-61-00 Pg.38, 46, 64 (latest Revision; pages numbers might slightly differ dependent on your airline config, but description is there)

You can use this switch if there is a fault in the retraction protection circuits.

As example: when you are on line, ac about to depart and airstairs will not retract (will not start retracting in case of S1, S2, S10 or will stop at the moment when lower ladder already folded in case of S11), before you will execute manual retraction procedure you try to operate this switch. If the cause of malfunction is S1, S2, S10, S11 when you activate Maintenance Switch S14 airstairs should retract.

!Make sure though that handrails are properly stowed, and lower ladder is up and locked.!

I encourage you to read through SDS part of the AMM.

Best Regards,
Maro12
maro12
 
Posts: 107
Joined: 05 Oct 2008, 01:51

Re: airstairs 'MAINT' Switch - Procedure for use? Nothing in

Postby JetA1 » 05 Nov 2019, 13:22

Thanks for the reply.

So it is mentioned in part 1 (SDS) but no procedure/task specifying when or how to use the switch in part 2 of the AMM?

Also with my companies MEL if the air stairs are to be locked out, the procedure is specified as aa manual stow.
This makes the maint switch a little pointless in my eyes - You can stow the stairs if there is a fault however to MEL them you need to manual stow/lock out anyway.

Maybe other procedures vary at differing company?

Thanks!
JetA1
 
Posts: 9
Joined: 31 Jul 2019, 13:53

Re: airstairs 'MAINT' Switch - Procedure for use? Nothing in

Postby maro12 » 05 Nov 2019, 22:01

You need to discuss it with people which write procedures in your company and ask their approach.

When you operate Maintenance Switch to bypass faulty "safety circuit" and airstairs retract, are they really unserviceable? If I remember correctly S1, S2, S10, S11 are only in the ground path for retract coils of airstairs motors relays, and if any of them would be faulty it would not affect extension sequence (This is from top of my head, please anyone correct me if I am wrong).

Therefore why would you like to lockout or MEL airstairs then?

But as I said this is the question for people who write your procedures.

AMM is selection of instructions provided by OEM. Once you know any system in depth you realise there are a lot of ways to meet your task requirements not covered by AMM, FIM etc. Sometimes you need to use your knowledge, experience and engineering judgement accompanied by common sense.

Best Regards,
Maro12
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