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assess the GPS PRIMARY status at destination or alternate.
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).
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
NAVIGATION ACCURACY
A330/A340 FLEET SI-030 P 5/8
FCTM 17 JUN 09
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
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
NAVIGATION ACCURACY
A330/A340 FLEET SI-030 P 6/8
FCTM 17 JUN 09
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
PF PNF
AP/FD mode EGPWS
GPS PRIMARY - Arc or Rose NAV with
raw data when required
Lateral and vertical
managed modes
ON
Navigation
accuracy check
positive (≤ 3 nm)
Arc or Rose NAV with
raw data when required
Lateral and vertical
managed modes
Cruise 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
Navigation
accuracy check
positive (≤ 1 nm)
Arc or Rose NAV
with raw data
Lateral and vertical
managed modes
ON
GPS
PRIMARY
LOST Or
No GPS
Approach(1)
Navigation
accuracy check
negative (>1 nm)
ROSE VOR or
ILS as required
Lateral and vertical
selected modes
OFF
(1) A GPS-defined Non-Precision Approach must be interrupted, if the GPS PRIMARY LOST message is displayed.
POSITION UPDATE
In the case of an obvious and major map shift, indicated by messages, such as "CHECK A/C
POSITION, FM1/FM2 POS MISMATCH", the aircraft position may be updated on the MCDU
PROG page. There are two possible techniques:
The recommended technique is to update the FMS over a beacon by pressing the UPDATE
prompt once estimating that the aircraft overflies the beacon using the associated needle. The
potential error induced is approximately 4 to 5 nm. When the position update is achieved, the
EPE is automatically set to a higher value and the navigation accuracy is low.
The second technique consists of updating the FM position, when flying over a
Point/Bearing/Distance (P/B/D) with reference to beacon raw data (Needle + Distance) rather
than the beacon itself. The potential for error is far less when the distance is greater than 60 nm.
The flight crew will keep in mind the potential 180 ° error on bearing.
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
NAVIGATION ACCURACY
A330/A340 FLEET SI-030 P 7/8
FCTM 17 JUN 09
FM position update in flight
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
NAVIGATION ACCURACY
　
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