B737 Speed Brake Lever

[LEM]

We don't get many details in the manuals about the speed brake lever.
When it moves automatically (upon landing if armed, upon reverse selection, upon thrust lever advancing if already extended), is it due to some sort of electric clutch?
Will it work if landing on battery only?

Thanks in advance

[Flying_Tuur]

My following 'theory' is just a guess, so please don't shoot me if I'm wrong..

On the classic, I don't thing the automatic speed brake lever will work on landing on BAT only, since the air/ground logic is not working on Bat only???

On the NG, all will work ok because air/ground logic will work and you have the needed hydraulics???

I stand to be corrected, just taking conclusions out of the All Generators Inop tables out of the B737 Cockpit Companion. (p62 - 63)

Hope someone will come up with a confirmation of this rather than to be corrected...

Nice question though!!

FT

[HotDog]

Only know about the classic 747 system but I presume it would be the same on the 737 Boeing. The speed brake lever is controlled by the auto speed brake actuator in response to gear tilt, thrust lever and reverse thrust signal inputs. As far as I know, it is not powered by the battery bus.

[QAVION]

"....is it due to some sort of electric clutch?"

The speedbrake lever is driven by an electric actuator during auto-ops, but there is a "no-back brake" which allows the pilot to move the lever without actually moving the actuator.

Logic for activation is similar in some respects, but not in others, to other Boeings. For activation on landing, Air Ground signals (Or wheel spin-up) and Radio Altimeter signals are required. Ground spoilers also need a mechanical input from the right hand strut.

Looking at the 737NG wiring schematics, the electric actuator is driven by Section 2 of the 28Vdc Bus (which I believe is only powered by the main AC busses (rectified, of course). However, I think the clincher is the "less than 10 feet" input from the Rad Alts (via the Flight Control Computers). This seems to be the final barrier to activation. Rad Alts, of course, do not run on batteries, so I really don't think you will get the Auto Speedbrake to operate without the main busses powered (As always, I stand to be corrected). :D

Sections of the Air/Ground system on some aircraft can be powered by the battery, so the wheel spin-up logic may not be required. Spin-up logic comes from the Antiskid System (Power for this system would also have to be looked into if the Air/Ground system malfunctioned).

Hope this helps.
Regards.
Q.

[av8boy]

I love PPRuNe. Biggest hangar in the world and always something to learn.

Dave :ok:

[LEM]

Thanks for your replies, gentlemen.

Flying_Tuur, on classics too the air/ground relay works on battery only.
But when it comes to speed brake lever electric actuator, I guess it's not powered.

QAVION, on classics radio altimeter is not required for auto speed brakes (but allows reverser deployement below 10ft...);
Inboard antiskid is OK on battery only.

The speedbrake lever is driven by an electric actuator during auto-ops, but there is a "no-back brake" which allows the pilot to move the lever without actually moving the actuator.
It is this electric actuator which I'd like to see with X-rays...
Is it a clutch?
Regarding the second part of your sentence, I don't understando!
Could you explain better?
Thanks, mate.

[QAVION]

"It is this electric actuator which I'd like to see with X-rays...
Is it a clutch?"

The actuator itself is simply a motor which drives a pushrod which is attached to the very complex Speedbrake lever assembly (under the floor, forward of the throttle stand). The assembly contains the no-back brake, I read. The pictures I have of this assembly look like a car crash... and are not very revealing at all. There is a resistive brake pad in there somewhere (to stop the lever sliding about when no forces are being applied to it).

"Regarding the second part of your sentence, I don't understand!
Could you explain better?"

I may have to hand you over to my Airframe colleagues at this point in time... I was basically quoting/paraphrasing what was written in the D&O in the Boeing 737NG Maintenance Manual.

"Speedbrake Lever Brake

The lever brake receives inputs from the speedbrake lever and the auto speedbrake actuator. The lever brake uses these inputs to move the forward drum. (Sidenote: the drum has steel cables on it which go to the wheel well to activate the spoilers).

The lever brake has a no-back brake assembly. This permits movement of the auto speedbrake actuator to backdrive the speedbrake lever, but prevents the speedbrake lever from driving the auto speedbrake actuator. It also permits the pilot to override the position of the auto speedbrake actuator"

Double Dutch, I know, if you haven't got a decent picture of the speedbrake assembly. Other Boeings have similar assemblies... Perhaps someone has a picture of one of these which is clearer than the 737 one?

Anyway, it works... most of the time ;)

Cheers.
Q.

P.S. (final of many edits) That last sentence in that BMM quote sounds like the speedbrake actuator position is being moved by the pilot, but later on in the manual, it indicates that this is not really the case. The pilot is actually overriding the command set by the actuator, not actually moving the pushrod position of the actuator.

[LEM]

Thanks, QAVION!

[wellthis]

As you know there are 2 panels of flight spoilers and 2 panels of ground spoilers on each wing. Upon landing and provided the AUTO SPEED BRAKE is armed, with thrust levers at idle and wheel spin-up to 60 kts on any two main wheels (if one should land with a bit of slip in X-wind) the 2 flight spoilers on each side extend. When the right main gear is compressed (AIR/GND sensor), the ground spoilers also extend.

It is of interest to note that if one should land with a right X-wind, all boards extend pretty much instantly creating more drag to bring the other wing down quicker making for a firmer landing than in a left X-wind-it could be used as an excuse anyway! Hope this helps.

[fruitloop]

wellthis.Said.Quote "As you know there are 2 panels of flight spoilers and 2 panels of ground spoilers on each wing.

I hope your refering to a -200

[LEM]

Yes wellthis is talking about -200's.
The logic is pretty much the same on classics.
I'll just add that should one forget to arm the speedbrakes before landing, they will extend anyway upon reverse selection.