View Full Version : 747-400 Overspeed Warning

6th Oct 2003, 11:02
I've always assumed that you will get an overspeed warning when you exceed flap limits (i.e. when you fly into the upper red band on the airspeed tape during approach).... perhaps because of my overfamiliarity with a certain 744 desktop simulator :} ... yet I am unable to find any official Boeing manuals which state this is the case.

Do you only get warnings if you exceed the normal flaps-up Vmo/Mmo (ignoring 5th Pod and Gear Down Dispatch switches for the moment)?


P.S. Are there any Boeings programmed to give you flap limit overspeed warnings? (767, 737NG, 777, etc?)

6th Oct 2003, 11:08
In response to your last question; not to my knowledge, you certainly won't get it on the 757/767.
I've always been under the impression that the clacker/overspeed warning is for Vmo/Mmo exceedances only.


6th Oct 2003, 21:11
Can't speak for the 744 but on the 75/76 the overspeed discrete is supplied from the Vmo/Mmo calculator within the DADC. This does not have any flap position input into it.

There is not a flap position input at the Clacker/Wailer, or the master warning module to modify the o/speed discrete either so I would say that avoiding a flap overspeed is down to good airmanship.

Of course there is a flap load relief system which operates but only for full flap positions (flap 30) driving the flaps to flap 25 if airspeed exceeds 170kts.

7th Oct 2003, 07:56
the 747-400 does have flap load relief through the entire airspeed range for the flaps. we apply hydraulic pressure and pitot statics in the hangar and ramp up airspeed - the flaps have strict airspeed tolerances in which to move up (can get these from the Maintenance manual if you really want them) - there is no warning in the flight deck when this happens, the system is entirely automatic.

If you exceed the red line on the PFD tape in normal clean flying conditions, you will get a red overspeed warning on EICAS, a red master warning (line of sight) light and an aural warning.

7th Oct 2003, 16:29
Thanks for the feedback, gents. The system wasn't as smart as I originally thought it was.

Moo.... Our 400 manuals say that Flap Load Relief is only for Flaps 25 and 30. There is an Advisory message "}Flap Relief", but no warning related to Flap Load Relief. I believe the EICAS flap indicator will change to indicate that flap position disagrees with flap lever position (similar to the change when the reversers are deployed).


P.S. (Edit) I've just been told that the KLM AOM has this to say:


This alert is displayed when the airspeed exceeds Vmo/Vmmo

Reduce airspeed or adjust flap/gear position whichever is applicable"

Why would it tell you to adjust your flaps or gear if the warning was not dependent on configuration?

7th Oct 2003, 18:10
I'm back in work on friday, i'll check our maintenance manual just to make sure.

p.s. these are BA aircraft, so this could possibly be an customer option?

8th Oct 2003, 17:14
"p.s. these are BA aircraft, so this could possibly be an customer option?"

I think this would be unlikely, Moo. I have access to your manuals by the way, but a fresh set of eyes might spot something.

BTW, had a look at your Wiring Schematics today, but I can't say I found anything to help.

Our flap load relief system will run the TE flaps from 30 to 25 and then to 20 if necessary, but that's about it. No LE stuff.