Slat retraction during reverse ops on 747

[bio161]

Hi all,

Could anyone explain me the reason why on the boeing 747 the inboard slats retract during reverse selection and extend again once the reverses are stowed?

Thanks all of you!

[spannersatcx]

to prevent damage from reverse thrust air throwing up debris and the direction of the air impinging on the leading edge flaps (not slats).

[MarkerInbound]

Both the inboard and midspan flaps retract durring reverser operation.

[Beeline]

Not on BA aircraft anymore!

[By George]

Beeline I presume that is as a result of BA56 out of Johannesburg. I understand the mod only applies to Rolls-Royce engines. I must admit I admire the BA crew on that one, great job and proves yet again the value of good old fashioned hand skills.

For those not familiar with the incident, during take-off a false reverse thrust signal retracted the leading edge sections during take-off. Around 160 knots if my memory is correct, very exciting when hot, high and heavy.

[NSEU]

Not on BA aircraft anymore!

I doubt that.

As far as I know, all 744s had a wiring modification so that the LE flaps won't retract due to indication problems. However, they will still respond to reverse lever input (>10 deg)

Our GE's and RR's have had this modification.

[NSEU]

Here's the Boeing Service Bulletin number: 747-78A2181

Google found this: http://www.skybrary.aero/bookshelf/books/1319.pdf

"This service bulletin will prevent the Group A leading (LE) flaps from automatically retracting if the flap control unit (FCU) receives dual REV Amber messages from the thrust reversers".

Unstow signals from symmetrical engines (two inboard or two outboard) previously triggered Group A (midspan and inboard) LE flap retraction.

[SMOC]

I thought the reason was for fatigue cracking of the variable camber flaps due to sonic vibration, retracting them unloads the the flap as it's no longer being bent into the shape of an airfoil. Think I read the SB after the company I worked for installed the system on some non RR classics a couple of decades ago.

[Slasher]

I presume that is as a result of BA56 out of Johannesburg

I didn't get to hear about that one, and I can't find any tech
analysis. Could anyone point me in the right direction at all?

Not current on the '47 anymore but wouldn't mind seeing the
story and system info on the occurrence.

Thanks.

[mm43]

This AVHerald Report has a good summary and includes QAR traces.

[Desert185]

bio161:

Could anyone explain me the reason why on the boeing 747 the inboard slats retract during reverse selection and extend again once the reverses are stowed?

I flew the 747 Classics from 1988 to 2007 with P&W engines. We never had that mod.