B737-800 MEL: Auto Speed Brake System INOP

[Bobermo]

Hi all,

Today I was flying a B737-800 with the Auto Speed Brake System INOP. We applied the procedures described in the MEL but couldn't understand the following point A.

(O)OPERATIONS
Reduce performance limited weights by the following:
A. Takeoff field length limit weight and brake energy limit weight: 1044kg
B. Landing field length limit weight based on auto speed brakes: 5897kg


Point B is logical because we manually have to raise the speedbrake on landing, this requires time so we have to cater for more landing distance required.

Point A I don't understand, because if we do an RTO the speedbrake already has to be raised manually in accordance with Boeing procedures. So why are we more limited on the Takeoff field length weight and brake energy limit weight?

Hope someone can point me in the right direction

[PPRuNeUser0190]

If I remember correctly it has nothing to do with a time delay. Whenever the auto system is inop spoiler deflection is less than normal requiring a performance penalty.

[latetonite]

That is for the SP and -900 ER version.

[Bobermo]

Thank you for the replies and still hoping for an answer!

[underfire]

I believe you have to manually raise the lever to get max angle on the ground/wing spoilers on an RTO. Then there is MTOW and MLW.

[PPRuNeUser0190]

I can't find the reference any more but I'm pretty sure it has to do with the angle of the spoilers being less than normal during RTO & landing. As latetonite mentioned it is only applicable on B737SFP & B737-900.

Our fleet has both SFP & non-SFP B737 and the performance penalty you mention is only applicable on the SFP B737.

[Bobermo]

That seems to be the answer, the aircraft we flew was a SFP B737, in the MEL for our normal 737's the penalty is not there.

However, I cannot find any reference in the manuals (FCOM/AFM) about this feature.. The only comment is : "Following an all flaps up (no flap) landing, the SPEED BRAKE lever will not move beyond the FLIGHT DETENT and the spoilers will not fully deploy." This comment does not affect the takeoff or RTO. Anyone can point me to the correct reference in the manual?

[Yeelep]

On the SFP/ER the spoilers are mechanical/hydraulic between down and flight detent. Between flight and up they are electro/hydraulic. When the auto speedbrake circuit breaker is pulled/collared as part of the MEL the solenoid operated valves for the flight spoilers are disabled. So instead of having full travel of 56 deg. for spoilers 2,3,10,11 and 65 deg. for 4,5,8,9 you only have 19.5/24.5 deg.

[de facto]

Thanks for the info Yeelep.

[Capt Chambo]

On the SFP/ER the spoilers are mechanical/hydraulic between down and flight detent. Between flight and up they are electro/hydraulic. When the auto speedbrake circuit breaker is pulled/collared as part of the MEL the solenoid operated valves for the flight spoilers are disabled. So instead of having full travel of 56 deg. for spoilers 2,3,10,11 and 65 deg. for 4,5,8,9 you only have 19.5/24.5 deg.

It's answers like this that keep me coming back to PPRuNe.

Thank you

[underfire]

When the auto speedbrake circuit breaker is pulled/collared as part of the MEL the solenoid operated valves for the flight spoilers are disabled. So instead of having full travel of 56 deg. for spoilers 2,3,10,11 and 65 deg. for 4,5,8,9 you only have 19.5/24.5 deg.

Just to clarify, this appears to say that with auto speedbrake off, spoilers are disabled and you have min spoilers? Dont you have max angle with auto off?

[73qanda]

Reduce performance limited weights by the following:
A. Takeoff field length limit weight and brake energy limit weight: 1044kg
B. Landing field length limit weight based on auto speed brakes: 5897kg

So instead of having full travel of 56 deg. for spoilers 2,3,10,11 and 65 deg. for 4,5,8,9 you only have 19.5/24.5 deg.

I have a question; if the 'SPEEDBRAKE DO NOT ARM' light illuminates in flight and the QRH checklist is run, there is no reference to reduced performance on the runway. Is this because the CB has not been collared?
Or is there a chance ( depending on the failure) that runway performance may be reduced ?
Thanks for the good info,
Qanda

[Yeelep]

Just to clarify, this appears to say that with auto speedbrake off, spoilers are disabled and you have min spoilers? Dont you have max angle with auto off?
26th Jul 2016 20:55

If you were to land without auto speedbrakes armed, they would operate normally when you manually move the speedbrake handle to up.

I have a question; if the 'SPEEDBRAKE DO NOT ARM' light illuminates in flight and the QRH checklist is run, there is no reference to reduced performance on the runway. Is this because the CB has not been collared?

The SPEEDBRAKE ARM/SPEEDBRAKE DO NOT ARM lights are powered through the auto speedbrake CB, so if the CB has popped or has been pulled/collared you won't get any lights. So if the SPEED BRAKE DO NOT ARM light is on, there is power through the CB and therefore power to the spoiler solenoid operated valves.

[framer]

Thanks yeelep, learnt something reading this.

[D-OCHO]

Point A I don't understand, because if we do an RTO the speedbrake already has to be raised manually in accordance with Boeing procedures. So why are we more limited on the Takeoff field length weight and brake energy limit weight

From the FCOM:

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

So yes the Boeing RTO procedure is a backup for the automatic procedure.