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area during winter.
The FCU, PFD, ISIS and CPCS are capable of operating at QNH/QFE up to 1 100 hPa, or
32.48 inHg.
The FMGS is currently limited to 1 050 hPa for DEST QNH entry on the MCDU PERF APPR page
(i.e. as long as the aircraft altitude remains above -1 000 ft standard pressure altitude).
When the Standard Pressure altitude becomes less than -1 000 ft STD, the FMS is no longer
capable to compute the aircraft position.
In addition, the ATC/TCAS operates only up to 1 050 hPa (that is as long as the aircraft altitude
remains above -1 000 ft standard pressure altitude).
Therefore, when using QNH, or QFE for QFE pin-programmed aircraft, for departure and arrival, the
crew should be aware of the following consequences, and should apply the following procedures.
It is necessary for the airline to obtain operational approval from its national airworthiness authorities.
CONSEQUENCES
Applicable to:
, ,
MSN
ON THE ATC-TCAS
For takeoff, approach and landing, the ATC altitude reporting and the TCAS TA/RA function may
generate erroneous altitude information and nuisance TCAS alerts for other aircraft, if the aircraft
standard altitude is below -1 000 ft standard pressure altitude.
To avoid this, it is recommended to set ALT RPTG to OFF when the QNH exceeds 1 050 hPa, and
to inform the ATC. As a consequence the TCAS reverts to STBY mode.
ON CABIN PRESSURIZATION
The CPCS normally uses the MCDU DEST QNH value to regulate cabin pressure during descent.
However, since DEST QNH entries on the MCDU are limited to 1 050 hPa, no DEST QNH
value should be entered during descent preparation, in order to avoid incorrect cabin pressure
regulation. As a backup, the CPCS will use the actual FCU barometric setting (when switching
from STD to Baro reference). In case of QFE use at arrival, the CPCS will erroneously use the
FCU-selected QFE as a QNH setting. To ensure correct re-pressurization of the cabin when QFE
is used, the Landing Field Elevation must be manually set to 0.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
PROCEDURES
SPECIAL OPERATIONS
OPERATIONS AT QNH ABOVE HPA
A318/A319/A320/A321 FLEET PRO-SPO-65 P 2/4
FCOM 19 AUG 10
Note: As no DEST QNH is entered, the FMS initially assumes that Standard barometric
reference will be kept down to destination for descent flight path calculations.
When QNH is set on the FCU, the aircraft and cabin altitude will be higher than expected
(the aircraft altitude can be up to 2 000 ft higher than expected). This will lead to a
higher descent rate, with a possible "CAB PR LO DIFF PR" ECAM caution, and possible
opening of the cabin pressure safety valve.
ON THE FMS
• Descent profile :
In the descent phase, when the crew switches from Standard to Barometric reference,
an altitude increase, greater than 1 000 ft will be induced. This results in a VDEV jump
(corresponding to the altitude difference), and a recalculation of FMS predictions.
Consequently, an altitude constraint, just below the Descent Transition Level may not be
satisfied, and actually flown with a positive error. This altitude difference will gradually be
zeroed, as the aircraft catches up with the descent profile.
• Approach :
When the Standard Pressure altitude becomes less than -1 000 ft STD, the FMS is no longer
capable to compute the aircraft position. The associated ND display (in ARC or NAV mode) will
subsequently be invalidated. Therefore, non-precision approaches must not be performed using
managed guidance. The flight crew must perform non-precision approaches using selected
lateral and vertical guidance, and raw data reference.
PROCEDURES
Applicable to:
, ,
MSN
FOR DEPARTURE
Before takeoff :
SET the ATC “ALT RPTG” to OFF (the TCAS reverts to STBY mode).
INFORM the ATC
After takeoff :
SET the ATC “ALT RPTG” to ON above 1 000 ft QNH, when time permits.
FOR APPROACH/LANDING
During descent preparation :
DO NOT INSERT a DEST QNH value on the MCDU PERF APPR page.
For QFE use only, SET the LDG ELEV selector to 0.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
PROCEDURES
SPECIAL OPERATIONS
OPERATIONS AT QNH ABOVE HPA
A318/A319/A320/A321 FLEET PRO-SPO-65 P 3/4
FCOM 19 AUG 10
Before the final approach :
SET the ATC “ALT RPTG” to OFF (the TCAS reverts to STBY mode).
INFORM the ATC.
FOR NON-PRECISION APPROACHES
Perform non-precision approaches using selected lateral and vertical guidance, and raw data
reference.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
PROCEDURES
SPECIAL OPERATIONS
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A320机组操作手册FLIGHT CREW OPERATING MANUAL 14(44)
