B737-300 Flap retract "F" Speed question
 

The flap retract speed from flap 1 to flap up (shown as an "F" symbol on the B737-300 simulator) appears to be up to 20 knots lower than another identical simulator down the road. Both have similar thrust ratings (I think) and the weight used is 50 tonnes.

The simulator down the road has the F symbol on the ADI very close to the block speed for 50 tonnes as one would expect, whereas in the first simulator the F symbol hovers around 168 knots at the moment of flap actuation from flap 1 to up. Seems an unusually low speed at which to start retraction from flap one to flap up. After all, retraction from flap 5 to flap 1 is done at a standard speed of V2 plus 15 - so why not a standard F speed?

It was explained to me that the difference was due to a pin option which permits an angle of bank change from 27 degrees to 33 degrees and thus a lower G margin is involved. Sorry to sound so vague but I am trying to remember exactly what the techs told me.

I would have thought that an identical aircraft (or simulator in this case) at the same parameters of weight, OAT, and altitude, would be required by certification to have the same safe flap retract speed. After all, the same block speeds apply - so why not same F symbol speed?

Hello Centaurus,

Slightly off topic, just think this may help a little bit. The new (not so new) block speed does not apply for flap retraction except when the FMC is not working. The 'f' speed is the maneuvering speed for the weight (if you have entered the weight correctly) and by definition (where we fly over here) it gives you the ability to bank 25 degrees with 15 degrees protection. I do not know how they programmed the first simulator but I agree with you, 168 knots 'f' speed for flaps 1 is, I think too low.

BTW, maybe if you have a look at the top of the yellow bar, it will give you further indication as to what they have programmed.

Cheers