Airbus fbw SLATS/FLAPS JAMMED, OVERSPEED, VMAX and High Speed Protection
 

Hi
I'm getting very active in PPrune, lately…

In a case of, say, a flaps jammed situation, VMAX as displayed in the PFD is not correct. It reflects flaps lever position associated VMAX, Right?

Still, we can rely on the OVERSPEED warning because it is triggered at the correct actual VMO/MMO plus. Good.

Now, my question is: What happens if you deliberately fly (A/THR OFF) into PFD's VMAX and beyond? Will the AP trip off and/or the High Speed Protection kick in and pitch up to keep the airplane within the envelope (wrongly overriding me)? Or will it just fly until the real overspeed takes place and then the protection kicks in?

I can't find in the FCOMs which input the flight control computers (ELAC, PRIM) are using for that protection (the one that the PFD uses or the one that the OVERSPEED warning uses?) So I guess only an empirical experiment can solve my doubt, and It is till some time till my next sim.

Or some wise airman around here :8 can enlighten me

Thank you

V MAX display as you said comes from flap lever but actual speeds are calculated by FAC from calculation of Vs1g. FAC uses actual calculated speeds for protections. That's why I call V max, S and F speed displays as good time friends. The moment lever doesn't match the real position you need to ignore them. A380 it comes from actual surface position.

thank you vilas. the 380 is cool

Hi MB2002,
The AP will only disconnect and the aircraft pitch up for the high speed protection (green dashes in VMO / MMO tape). It will happily let you exceed all Flaps / slats speed limitations. E.g. If you accelerate too quickly with AP & A/T engaged whilst the Slats are being retracted to 0.

In the old days we used to control the rate of acceleration by retarding the TLs a bit and respecting the placarded speeds. Manual thrust control or selecting a sensible speed, when the AT is engaged, would earn you extra Brownie points.

When ALT* or ALT is engaged and ATHR is blue(armed) then there is no protection but if thrust is active (white) FMGS will limit the speed to VMAX. Also in SRS if thrust levers are left in TOGA at acceleration altitude FMGS will limit the speed to VMAX by increasing climb. Momentary over speed warning while retracting flaps to zero at high weights does not cause any structural problems.