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ND/MCDU
A GPS PRIMARY message is displayed when GPS PRIMARY is again available. This message is clearable. A GPS PRIMARY LOST message is displayed when GPS PRIMARY is lost.
This message is clearable on MCDU but not on ND. When the class of navigation accuracy is downgraded from HIGH to LOW (LOW to HIGH), a NAV ACCUR DOWNGRADE (UPGRADE) is displayed on ND and MCDU
AIRCRAFT POSITION AWARENESS AND OPERATIONAL CONSEQUENCES
Applicable to: ALL
NAVIGATION ACCURACY INDICATIONS
The navigation accuracy indications are available on the MCDU PROG page. The following guidelines apply:
? If GPS PRIMARY is displayed, no navigation cross-check is required
? If GPS PRIMARY LOST, navigation crosscheck is required in climb, in cruise, about every 45 min,
before the Top Of Descent, reaching TMA and IAF and whenever a navigation doubt occurs.
? The crew will use, IRS only, LOW and NAV ACCUR DOWNGRAD messages as indications to trigger a navigation accuracy check.
NAVIGATION ACCURACY CROSSCHECK TECHNIQUE
The principle consists in comparing the FMS position with the RADIO position (aircraft real position).
 
SUPPLEMENTARY INFORMATION
NAVIGATION ACCURACY
 
Navigation accuracy cross check technique 1
 
There are two possible techniques:
? The flight crew inserts a radio ident in the MCDU PROG page that provides a bearing/distance in relation to the FMS position. They then compare these values with the raw data received from the navaid, that indicates the real position of the aircraft. This enables the flight crew to quantify the error ε.
? On the ND, the flight crew compares: The position of the needle and its associated DME distance (the real position of the aircraft) with the position of the navaid symbol and its associated distance, indicated by the range markers (these markers provide a bearing/distance, in relation to the FMS position).
Navigation accuracy cross check technique 2
 
 
SUPPLEMENTARY INFORMATION
NAVIGATION ACCURACY
 
OPERATIONAL CONSEQUENCES
The result of the crosscheck of the navigation accuracy determines the pilot's strategy for using the ND display, the AP/FD modes and the EGPWS.
 ND AP/FD mode EGPWS
 PF PNF  
GPS PRIMARY - Arc or Rose NAV with
raw data when required Lateral and vertical
managed modes ON
GPS
PRIMARY
LOST Or
No GPS Cruise Navigation
accuracy check
positive (≤ 3 nm) Arc or Rose NAV with
raw data when required Lateral and vertical
managed modes ON
  Navigation
accuracy check
negative (> 3 nm) ARC or ROSE NAV
may be used with care
and with raw data Lateral and vertical
managed modes with
care with raw data OFF
　
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本文鏈接地址：A330/A340 機組訓練手冊 FCTM Flight Crew Training Manual 2(67)