737ng Alternate flap extension

[seifly]

Question was raised as to why we set the flap lever to flaps 15 when using the alternate flap extension.

[RAT 5]

If you mean why use F15 and not a greater setting; if a GA was required the TE flaps could only be retracted using the ALT system. This takes too long and so the extra drag remains too long for the performance gradient to be achieved. F15 is the normal GA selection so no problems.

[seifly]

No. My question was why move the lever at all as the flaps will extend using the alternate method. What is the reason for setting the lever to 15?

[RAT 5]

Ah Ha. RTFQ. I apologise. It could be a left over from B732. That could have been something to do with LE & TE sequencing and indications and in the various valve movements. I realise the LE's go to full ext immediately. That's more engineering 'under the floor boards' stuff. It also makes a non-normal configuration look more normal
However, on NG, the flap speed bug comes from the flap lever position and not the flap position. So on NG that is a good reason.

[seifly]

Thank you very much! As I had only known about the warning horn only.