737-700 Speedbrake question
 

Hi guys,

I have a small question from a certain 'quiz' that has produced different answers from different sources... Input appreciated! :}

In order for the speedbrake to automatically deploy on landing the following condition(s) must be satisified:

a) Speedbrake lever in the armed position
b) Both thrust levers retarded to IDLE
c) Wheel spinup > 60 knots
d) Both a) and b)

Cheers, :ok:

Screwballs

Ps. I've already handed my answers in and had them corrected so just looking for different opinions on the answer.

Speedbrake lever in the armed position

Flight spoilers come up at wheel spinup on any 2 main wheels

Ground spoilers come up when mechanical squat switch on right gear is compressed

If wheel spinup is not detected speedbrake lever will move to the up position and all spoilers will deploy after squat switch is compressed

I can't remember if it's the case in the NG (I think it is) but in the 3/4/500 the speedbrake (or should I say ground spoilers) will also automatically deploy on the ground if the reversers are unlocked, even if it is not armed.

TS6

I agree with you, Topslide6, even if the Speedbrake lever is in the down position the auto speedbrake system operates when you get:

• main landing gear wheels spin up (more than 60 knots)
• both thrust levers are retarded to IDLE
• reverse thrust levers are positioned for reverse thrust

So with that info, which answer is the best fit?

Screwballs

I know this the case if you reject the takeoff and use the reversers.

You don´t need the IDLE position, but it is near Idle.
TRA must be <44
TLA (thrust lever resolver angle)

• Maximum reverse thrust =TRA 8
• Idle reverse =TRA 24
• Idle = TRA 36 to 38
• Maximum climb = TRA 72
• Maximum take-Off/go-around = TRA 78
• Maximum certified thrust = TRA 82.5

Screwballs,

Personally, I would have said A and C are both correct but given that you can't choose both of those there isn't really a correct answer!! Maybe a typo on behalf of the question setter for answer 'D' perhaps?!

TR4A,

This is from memory and not from the manual but I believe that the action of pulling the reverser handles from their stowed position raises a 'switch' that lifts the speedbrake out of its down detent thereby deploying it. I think ;)

Funny one!

TS6

From the 800 FCOM
 

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 bypass valve and the ground spoilers deploy.
If the SPEED BRAKE lever is in the DOWN position during landing or rejected takeoff, the auto speed brake system operates when these conditions occur:
• main landing gear wheels spin up (more than 60 kts)
• both thrust levers are retarded to IDLE
• reverse thrust levers are positioned for reverse thrust.
The SPEED BRAKE lever automatically moves to the UP position and spoilers deploy.
After an RTO or landing, if either thrust lever is advanced, the SPEED BRAKE lever automatically moves to the DOWN detent and all spoiler panels retract. The spoiler panels may also be retracted by manually moving the SPEED BRAKE lever to the DOWN detent.

The answer?
 

So to AUTO deploy ....MUST be

a) Speedbrake lever in the armed position..... Must YES

b) Both thrust levers retarded to IDLE Must YES as even if you use reverse thrust that requires thrust to idle

c) Wheel spinup > 60 knots NO ( strut compression will deploy them)

d) Both a) and b) YES

So A B and D are correct and I would chose D as it is "more correct"