B 737 Trailing Flap Assymetry

[JABBARA]

For those like me, whose native language is not English, even some simple points can be somehow confusing. So, I kindly expect someone to clarify those quotations from B737 QRH for me.

" TE FLAP ASSYMETRY
Condition: An uncommanded roll occurs when a new flap selection is made and/or a difference between the left
and right flap indication is observed.

FLAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SET

Move flap lever to the detent nearest the smallest actual
flap position"


Now,

Case 1: When retracting flaps from 5 to 1, TE flap indicator needles splitted; one of the needles is very close to 5 and the other needle is slightly away from 5 but still closer to 5 than 2. Where should I place the flap lever ?


Case 2: When extending flaps from 1 to 5, TE flap indicator needles splitted; one of the needles is very close to 2 and the other needle is slightly away from 2 but still closer to 2 than 1. Where should I place the flap lever ?

Best Regards

[B73C]

My take on the text:

Case 1: I say select Flap 5, since it is the smallest "ACTUAL" flap position. While 2 is a smaller setting, it's not "ACTUALLY" at that setting.

Case 2: While neither flap is at 1, I would say reselect 1 since both are closest to that setting. It's also the smallest setting you can select with both beyond Flap 1.

Since the text stipulates "Move flap lever to the detent nearest the smallest actual flap position" I say reselect the lowest flap setting that one pointer is actually at (or very close to...). "Actual flap position" is open to interpretation, I think, but that's how I read it.

My $.02...

[JABBARA]

Thank you B73 C

But I think your answer for case 2 is not answering to the question which I tried to describe.

[Jet2]

I've always read this in the way that what Boeing are saying is that you should position the flap lever to the detent that corresponds with the lowest of the split needles on the flap position indicator. So:

Case 1: The lever should be positioned to flap 5 because that is where the lower of the two indicator needles is closest to.

Case 2: The lever should be positioned to flap 2 because that is where the lower of the two indicator needles is closest to.

I think this is what B73C was saying in other words. Hope this helps.

[Sawbones]

Case 1 = select 5
Case 2 = select 1 .... most definately.

Perhaps it will help you to think ... always take the most conservative approach. For example, in case 2, you know with certainty that the flaps are at least at 1, likely more than that, but assuming they are at 1 will be the conservative for approach speed calculations.

Sawbones (former B737 Instructor/Check Captain)

[Blacksheep]

I'm not sure the wording of the procedure is correct. That example of moving from flaps 5 to flaps 1. You are selecting flaps up and get an asymmetry. There's little point in continuing retracting the flaps. Logic dictates that in the event of an asymmetry you should select back towards the last position the flaps passed through before the asymmetry became apparent.

In any case, the flap asymmetry system is designed to lock out the flaps and prevent further movement. In either direction.