Fwd Left pax door indication

[Dunny]

Had an issue with a fwd entry door indicating on the door warning module on touchdown. (737-800)

Looking at the schematics the forward left entry door has both an entry door sensor S199, and entry door switch S1147.

Its the only door on the airplane with the extra switch.

Why doesn't the other doors have this additional switch ?

[maro12]

Good Day Dunny,

Ref.SB 737-52-1159 R01

Basically operators reported diversions and turnbacks due to Fwd Entry Door air leaks and airctaft not pressurizing. There was no indication on the door annunciator pnl that the door was not fully latched.

Adding S1147 prevents extinguishing of Fwd Entry Door light on door annunciator pnl when Fwd Entry Door are not fully latched.

Most probably operators reported that problem mostly on Fwd Entry Door, might be that Fwd Entry Door sometimes have to be opened/closed in rush by the crew before departure for operational reasons. I am sure that Boeing would prepare SB for other doors if needed/required.

Hope this helps.

Best Regards,
Maro12

[Dunny]

Thanks for the info

Surely the other doors get opened as much and are subject to as much wear

Just seems a tad strange that they only added it to one door.

[maro12]

Hello Dunny,

I am sure we all seen that the crew have to open Fwd Enrty Door again after boarding completed for different reasons. Accessing aircraft for maintenance usually through Fwd Entry Door, etc.

Best Regards,
Maro12

[sjap]

The fwd entry door is the biggest and heaviest one, and the hinges and mechanisms tend to wear out much more due to the heavy load of the door.
My experience is that it is possible to close the door, but due to the upper hinge wear the upper aft guide latch may be turned but not into the recess. So the door looks closed (from the inside) but the upper half is still an inch inward and not flush with the fuselage at the aft latch. The fwd latch is always ok, the aft upper latch isnt.
So you may close the door normally and it is still not flush at the upper half aft side.
That gives a false idea of a closed door while it is not. The original switch may then be closed so the cockpit crew thinks it is ok.

The others doors are much smaller and lighter and especially the aft doors move in a horizontal line which wears out the hinges much less.
The fwd rh door is smaller and lighter as well and so far it may not have caused so many issues with th hinges as the big lh fwd door,

So the extra switch is a typical boeing solution. Not making the hinges stronger but installing an extra switch to monitor the latch.

(do you remember the flap input cable switch at the aft rh side under the cabin floor on the 737 classic? Typical a boeing solution. Making a switch to monitor if the cable breaks giving you a flap bypass situation. pfff)
I always refer to this boeing solution: Its not looking for the headache cause but gives a pill against the headache. Problem solved.

[Dunny]

Good answer and makes sense now...