Auto speedbrake retraction

[MasterBates]

Anybody know a logical explanation why on earth (so to speak) the speedbrakes don´t auto-retract on Boeing© built jets when full thrust is applied in the air. It does on ground, but why not up there.
Got this thought from the nostalgic 757 rememberance in "Rumours and news". From the letters there one might think an dear old auntie is already dead.
:p
MB.

ad nauseam

[B73567AMT]

The Speedbrakes will only Auto Retract on the ground if they have been automatically extended.
Speedbrakes cannot be automatically deployed in flight, so they cannot be automatically retracted.

[MasterBates]

Yes, I know that ( I do fly the darn thing).
I´m just wandering about the logic behind that design. The thought behind the decision to NOT let it retract in air, upon full throttle setting. This would only require very primitive software, and can hardly be a design enigma.
Just thinking about the philosophi.
MB
;)

[Shore Guy]

On the B-757……a story I heard is that in original airplanes, the engines did not have the “automatic” idle bump up with engine anti ice on. The throttles had to be manually moved to a higher minimum thrust to satisfy min N1/N2 for anti-ice. Hence, no auto stow of speedbrakes with throttle out of idle.

[Max Angle]

The fact that the speedbrakes remained extended with TOGA selected was cited as contributing factor in the AA Cali crash. Whilst is was accepted that are situations that require the speedbrakes to be deployed above idle thrust they could find no reasons why they would needed at very high power settings. A recommendation was included that suggested this feature be included in future designs. I believe that the B777 still does not have this feature, all Airbus FBW aircraft do feature auto retract with power settings of MCT and above.

Report available here:

http://sunnyday.mit.edu/accidents/calirep.html

[LEM]

Boeing says autoretraction would cause unwanted pitch change upon application of full thrust.

Ridiculous answer!

Autoretraction should be a must as a safety feature, as demonstrated by the Cali crash.

Guess what's the real reason for not installing such a feature?


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[mono]

Firstly, auto speedbrake is not a function of software. It is actually a quite simple circuit where a bi-directional actuator, actuated by air ground logic and thrust lever position is operated. A secondary circuit using thrust reverser lever position will also deploy the speedbrakes if the T/R is deployed.

As for a modification to enable them to be stowed on application of t/o thrust. I don't think it would be too expensive. Fag pack calculations lead me to feel a second actuator would be required (as B73567AMT says the current actuator needs to be extended in order to auto retract) which would be operated by a microswitch on the throttle switch pack (it is possible a spare already exists I don't have the WDM to hand) It would need to be bolted to structure and could drive through the 'no back' clutch already used in the existing installation (to allow over ride by crew in the event of a runaway/UCM). So total cost 1 actuator, 1 (possibly 2) microswitches, about 100' of wire (22awg for control and 18awg for power) and a few hours on the drawing board for a designer and a few hours for the STC or type approval from the FAA/CAA. It's not a complicated circuit as no air/ground interface is required, full thrust apeedbrakes down and that's it. It wouldn't interfere with the ground autodeployment function as this too will stow the speed brakes if full thrust is commanded and the a/c is on the ground.

As for why it was not incorporated in the first place, remember the 757/767 was first conceived in the 1970's and auto deployment/stowage of ground speedbrakes was at the time quite an innovation. they didn't want to get ahead of themselves by thinking about air operations too.

[BizJetJock]

Citations had auto speedbrake retraction in 1972. It's not that new!!

[Phoenix_X]

It's never bothered Boeing that they are 20 years behind on other aircraft manufacturers ;)