Flap Limit Protection on 747 'Classic'

[PistonTwin]

I am aware that the 'Fast/Slow' pointer on the ADI in the Classic is driven by the difference between the Command Airspeed Bug and the Captain's ASI.

I was wondering whether or not anyone knows where the Flap Limit Protection system gets it's airspeed information from?

And while I am here, does anyone know where it is written that the overspeed warning system senses whether or not there is fuel in reserves 2 and 3? This enables it to sound the overspeed clacker at either 342KIAS or Vmo, independent of the Aux/Norm switch selection on the ASI.

Thanks in advance.

[SixDemonBag]

Did you just start in QF did you?

[gas path]

Flap limit protection from 3 off capsules in the crawlway sensing pitot pressure, active when flap lever at 25 or 30 units.
Will retract the t/e flaps from 30 to 25 to 20 depending on the overspeed.
Early a/c only had one q switch and only retracted the flaps from 30 to 25 units.

Reserve fuel overspeed warning from fuel level float switches in reserve tanks 2 and 3 when either tank not empty.
mm 34-14-00

[PistonTwin]

Gas Path:

So the system senses the pitot pressure directly and doesn't take an input from the CADC?

Thanks for the info. I couldn't find the reserve fuel information anywhere!

[gas path]

No, just the switches in the flap lever, the 3 q pots, the flap load relief light on p2 and the load relief actuator.
The flap lever switches are to arm the system and prevent it operating unless the t/e flaps are selected to greater than 20 units.
Pitot pressure comes from the aux pitot no1 (l/h side lower)

[PistonTwin]

Gas Path:

Excellent, thanks for your help. I will have to get my hands on one of the maintenance manuals and have a look now. Should be interesting trying to track one of those down!