View Full Version : 747-200 Flap Ld Relief

3rd Oct 2004, 21:36
Tell me how FLAP LD RELIEF works.

Flaps 30 you're good at 180 kts, but the LD RELIEF kicks back to Flap 25 if you're above 169 kts. ??? Does it care if you're accelerating or slowing? What's the "logic", and what's the "Q" switch?


gas path
4th Oct 2004, 14:03
The q switch(es) is(are) measuring airspeed. It depends on the airplane line no.
The later -200 a/c had 2 or 3 q switches 1st s/w activated at 25 units repositions to 20 and back to 25 with reducing a/spd. With flap lever at 30 2n/d s/w is activated and the flaps are driven to 25 units or 20 units depending on a/spd., reducing spd repositions flaps back to 25 or 30 units.
The actual a/spds I'd have to go look up!

4th Oct 2004, 15:07
Typically, Flaps limit speeds are 180kts for Flaps 30, and 205kts for Flaps 25.

The Flap Load Relief System is not active when trailing edge flaps are lowered electrically, and Flaps 30 limit speed would then be 160kts.

6th Oct 2004, 01:30
I appreciate all the input.

What's not clear is - the flaps 30 limit speed is 180 kts, BUT if you're over 169 kts, the FLAP LD RELIEF kicks the flaps back to Flap 25.

So is the "limit" really 169?

Must be something I'm missing. :confused:

gas path
6th Oct 2004, 09:11
Must be something I'm missing.
No I don't think so, it's just the tolerances built into the system.

7th Oct 2004, 00:18
No I don't think so, it's just the tolerances built into the system.



fire wall
7th Oct 2004, 12:02
Flap load relief light illuminates to indicate the IAS is approaching the limit for the selected flap setting.....common misconception.....it does not indicate the flaps have blown back.....YET!

If F30 is selected the TE flap will blow back to F25 at 183 kts IAS
As the speed reduces the flap will then run automatically to F30 at 165 kts.

If F25 is selected the TE flap will auto run back to F20 at IAS 208 kts and auto extend back to the F25 posn at 191 kts IAS..........

It is written in a confusing manner, if you think of it as I have written above then hopefully all will be clear.......I did say hopefully!

7th Oct 2004, 17:35
That makes a lot more sense to me.

Thanks :ok:

7th Oct 2004, 17:37
I wouldn't worry about it if your flying Classics in the EU because within a year you will only have flaps 25 for landing. :E

9th Oct 2004, 00:43
Our company rarely uses flaps 30 except for abnormal conditions. Flaps 25 is our normal operation and not just for noise abatement but some believe it's easier on the Old birds skeleton.:ok:

9th Oct 2004, 03:00
Good info Smokie.