Originally Posted by
A33Zab
Airbus used calculation for FPA = arc tan(Vzbi/GS)
Vzbi = baro-inertial Vertical Speed
(inertial for accuracy in dynamic maneuvers & baro for stability in time)
GS = Groundspeed
Vzbi is computed from Vacc (Vertical acceleration from IR), Hi (Inertial altitude from IR) and Hb (Baro altitude from ADR).
Just read this with great interest.
So the Airbus makes a trigonometric calculation to computes its FPA based on an IR based angle zero, the horizon.
If the Horizon is IR based, and the other variables all IR based, with just a small component of ADR based barometric Pressure Altitude to give the IR based vertical acceleration some stability in time (exactly like the Airbus vertical speed indicator), do you think that the PFA must be corrected when being used in cold temperature operations ?
In practical terms, if one wants to do a 3 degree approach but has to cross the FAF at an indicated altitude higher than the published altitude to compensate for temperature, the apparent flight path angle may be 3.2 degrees based on indicated temperature but the real angle based on true altitude remains the same at 3 degrees.
Considering that the Airbus is using trigonometry to compute an angle based mostly on IR data, should the FPA selected by the pilot be the real angle (3 degrees) or the apparent angle (3.2 degrees)