737NG BUFFET ALERT - only with flaps up?

[pilotho]

So I'm led to believe that this alert only occurs on the scratchpad when the flaps are up.

I understand this alert means that the buffet protection can not be met and that you would need to change your aircraft's airspeed, altitude etc.

The question is though, why does this alert not occur with flaps down?

I have done it many times in a class D simulator and this is indeed the case.

[B737900er]

Ive had it twice on take off, and still can't work out why.

[eagleflier]

B737900er Ive had it twice on take off, and still can't work out why.


How can you have it on take off if the alert only pops up with flaps up. Do you take off with flaps up?

[RAT 5]

More to the point how the hell did you get it on takeoff? What were you doing?

[B737900er]

I had it on a flaps 5'take off from a very long runway and the departure was bumpy. It flickered on the CDU for no longer than 2 seconds.

This happened over two years ago (so can't remember the exact details) so it may have happened just after flaps up.

I still don't understand why it happened.

[Skyjob]

A known problem to NG operators, report it to your engineers and appropriate measures can be taken to prevent reoccurrence.

[latetonite]

Probably cause you have autoslats available when having any flaps extended.

[rudderrudderrat]

Hi pilotho,
why does this alert not occur with flaps down?
If you have a look at this Boeing document: http://www.theairlinepilots.com/forumarchive/quickref/stall.pdf, on page 36 it quotes the minimum V2 margin over the stall and on pages 46 onwards gives examples of various aircraft types and their margins. You will note that the margin is only around 13% for some aircraft!

The buffet margin when clean and in the cruise is normally 30%. Therefore to avoid unnecessary distractions on take off and departure, the software is written so as not to advise you of reduced margin when you have flaps out.

The buffet warning margin may be changed to suit the operator. We used to "fudge" our cruise C of G (if conditions were smooth) to reduce the buffet margin to 25% and at high weights, permit an earlier climb . We were then limited to a smaller bank angle.

[pilotho]

Thanks rudderrudderrat.

It would make sense to inhibit that alert during take off and landing when the stick shaker would be pretty obvious something is wrong!