Hi all,
I have a question about the B737-800 FCOM text below. I have forwarded the question to our tech department but unfortunately they did not know they reason either so hoping to get some input here.
the operation of speedbrakes upon landing: the conditions mentioned below state that a wheel spin up is required and any gear strut compression for the flight spoilers and right main gear compression for the ground spoilers! However, when no wheel spin up is detected upon touchdown the flight spoilers still deploy on any gear compression and the ground spoilers deploy on right main gear compression!
So, what’s the difference between the two situations. Why is the wheel spin up required? As I read it, weather a wheel spin up is detected or not, the spoilers still deploy under the same conditions! Flight spoilers upon any gear strut compression, ground spoilers on right gear compression!
looking forward to some insight and thanks in advance!
Ground Operation
During landing, the auto speed brake system operates when these conditions
occur:
• SPEED BRAKE lever is in the ARMED position
• SPEED BRAKE ARMED light is illuminated
• radio altitude is less than 10 feet
• landing gear strut compresses on touchdown
Note: Compression of any landing gear strut enables the flight spoilers to deploy.
Compression of the right main landing gear strut enables the ground
spoilers to deploy.
• both thrust levers are retarded to IDLE
• main landing gear wheels spin up (more than 60 kts).
The SPEED BRAKE lever automatically moves to the UP position and the
spoilers deploy.
If a wheel spin-up signal is not detected, when the air/ground system senses
ground mode (any gear strut compresses) the SPEED BRAKE lever moves to the
UP position and flight spoiler panels deploy automatically. When the right main
landing gear strut compresses, a mechanical linkage opens the ground spoiler
interlock valve and the ground spoilers deploy.