Arming 737 Speed Brake

[Cfm56]

I'd like to know from any UAL or any other 737 pilots if you have any limitation on arming the speed brake PRIOR to landing gear extension.

 

[Rudy]

No 737 I know of has this limitation...I fly at US and there's no such limitation here. The DC-9 was a different story. You were not supposed to arm the speedbrakes (spoilers?..I forget which applies to which machine) before lowering the gear. This is because under certain conditions, the wind blast on the gear could generate a "on the ground" signal, and the speedbrakes would inadvertantly deploy.

 

[lpbrian]

Not sure about that. I always thought spoilers on a DC-9/MD-80 were deployed on main wheel spin-up. The pilots handbook may indeed call for arming spoilers after gear down, but I don't think for the reasons you stated. BTW, inflight, they are called speedbrakes, on roll out, spoilers. Semantics.

 

[NWA/AMT]

Not sure about that. I always thought spoilers on a DC-9/MD-80 were deployed on main wheel spin-up.

[post="280998"][/post]​

On the DC-9/MD-80 they're deployed either through wheel spin-up as sensed by the anti-skid system or by WOW using the NLG ground sensing system. Any prohibition on arming them prior to gear extension may be to ensure full NLG strut extension to prevent uncommanded operation via ground sense either while the NLG is retracted or under air load during gear extension.

The maintenance manuals differentiate between the two functions of "speedbrake" and "spoiler" mainly by how they're actuated. When they're used as roll augmentation in flight it refers to them as "spoilers" and when operated by the handle, either in flight or on ground, as "speedbrakes".