Quote:
Originally Posted by Linktrained
How much of an aircraft's flying is done with the Trim Tank "inoperative"?
Pretty rare, but I can still remember flying under MEL an entire week or so without it due to a defective trim tank isolation valve.
Happen to have deactivated a THS tank a few months ago, due to access panel leakage.
Repair interval Cat C (10 days), empty TT; manual closing and deactivating TT isolation & TT inlet valve to prevent fuel entering TT but to keep trim pipe with fuel for APU ops.
Crew selects TT Tank Feed switch to ISOL, 1% fuel to be increased due CG control not available.
Indeed very rare, it was the first time in our company.
@GB:
Is cg calculated based only on pre-takeoff W&B, or is it computed constantly from AOA, IAS, ALT and trim?
Flight preparation:
GROSS WEIGHT INSERTION (INIT B page) :
- ZFCG/ZFW --------------------- INSERT
- BLOCK FUEL--------------------- INSERT
Block fuel may be automatically computed by the FMGC, using the FLIGHT PLANNING function.
CAUTION:
Part of characteristic speeds, displayed on the PFD (green dot, F, S, VLS), are computed from
the ZFW and ZFCG entered by the crew on the MCDU. In addition, the pitch trim will be
automatically set to the takeoff position, according to the entered ZFWCG.
Therefore, this data must be carefully checked (Captain's responsibility).
The flight crew should insert the weights after completing all other insertions. This is to avoid cycles
of prediction computations at each change in flight plan, constraints, etc...
If ZFCG and ZFW are not available, it is acceptable to enter the expected values in order to obtain
predictions. Similarly, the flight crew may enter the expected fuel on board, if refueling has not been completed at that time.
If ZFCG, ZFW, and BLOCK FUEL are inserted, the FM will provide all predictions, as well as the EXTRA fuel, if any.
In Flight:
The FMGC uses the weight and center of gravity from the FCMC (Fuel Computer) when available.
The GW and CG computed by the FE part are used:
– as back-up in case of dual FCMC failure.
– to trigger the aft CG caution and warning signals (independently of the FCMC).
FE Weight computation (back up)
– When the aircraft is below 14625 feet and 255 knots :
GW = f(α, CAS, N1/EPR actual, CG from FE part, altitude)
– When the aircraft is above 14625 feet or 255 knots :
GW = TOGW − WFU
TOGW: takeoff gross weight
WFU: weight fuel used acquired from FADECs.
FE Center of gravity computation (back up/aft cg computation)
The CG is computed from the position of the horizontal stabilizer and is
function of the N1/EPR, Vc, ALT, MACH and GW from FE part.