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AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
NAVIGATION - POSITION COMPUTATION
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A330/A340 FLEET DSC-22_20-20-10 P 10/10
FCOM 19 AUG 10
A330/A340 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
NAVIGATION - EVALUATION OF POSITION ACCURACY
A330/A340 FLEET DSC-22_20-20-20 P 1/8
FCOM 19 AUG 10
GENERAL
Applicable to:
The FMGES continuously computes an Estimated Position Uncertainty (EPU).
It is an estimate of how much the FM position diverged, and it is a function of the navigation mode
that the system uses.
CURRENT NAV MODE EPU
(RATE or THRESHOLD)
REMARK
IRS/GPS
(in meters)
FOM = Figure of Merit of GPS position.
If above 0.28 nm, the FMS rejects the GPS
position.
IRS/DME/DME Moves toward 0.28 nm. EPU decreases from the initial value to
0.28 nm.
IRS/VOR/DME 0.1 nm + 0.05 X DME DIST.
Minimum: 0.28 nm.
Dependent on the distance between the aircraft
and the VOR/DME.
IRS ONLY +8 kt for the first 21 min.
+2 kt after.
EPU increases continuously.
Note: After an IRS alignment or at takeoff, the EPU is set to 0.2 nm.
GENERAL
Applicable to: ,
The FMGES continuously computes an Estimated Position Uncertainty (EPU).
It is an estimate of how much the FM position diverged, and it is a function of the navigation mode
that the system uses.
CURRENT NAV MODE EPU
(RATE or THRESHOLD)
REMARK
IRS/GPS
(in meters)
FOM = Figure of Merit of GPS position.
If above 0.28 nm, the FMS rejects the GPS
position.
IRS/DME/DME Moves toward 0.28 nm. EPU decreases from the initial value to
0.28 nm.
IRS/VOR/DME 0.1 nm + 0.05 X DME DIST.
Minimum: 0.28 nm.
Dependent on the distance between the aircraft
and the VOR/DME.
IRS ONLY +8 kt for the first 30 min.
0 kt for the following 60 min.
+4 kt for the following 30 min.
0 kt for the following 60 min.
+2 kt after.
EPU increases continuously.
Note: After an IRS alignment or at takeoff, the EPU is set to 0.2 nm.
A330/A340 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
NAVIGATION - EVALUATION OF POSITION ACCURACY
A330/A340 FLEET DSC-22_20-20-20 P 2/8
FCOM 19 AUG 10
ESTIMATED POSITION UNCERTAINTY
Applicable to:
The FMS displays the EPU to the flight crew and compares it with the Required Navigation
Performance (RNP):
If the EPU does not exceed the RNP, accuracy is HIGH‐
If the‐ EPU exceeds the RNP, accuracy is LOW.
The RNP is displayed in the REQUIRED field of the PROG page. The displayed RNP is a default
value and it is possible for the flight crew to modify it.
When the "SYSTEM RNP IS XX.XX" message is displayed, the flight crew should verify the RNP
value that was manually entered in the REQUIRED field of the PROG page, and clear or modify it if
necessary.
This message is also displayed at the change of flight area if the new RNP (default value) is smaller
than the displayed RNP (manually entered).
The RNP value should be in accordance with the specific RNP values of the navigation/approach
charts (if charts specify the RNP).
POSITION ACCURACY CRITERIA Defined by Airworthiness Authorities
FLIGHT AREA RNP values
EN ROUTE 3.41 nm
TERMINAL 2.07 nm
APPROACH VOR/DME 0.61 nm
OTHER CASES 0.36 nm (1)
(1) The MCDU may display 0.37 nm due to the fact that the required position accuracy value, 0.366 nm , is rounded off.
When one FMGEC changes the NAV accuracy from LOW to HIGH (or HIGH to LOW), the MCDU
and the ND display the "NAV ACCUR UPGRAD" (or DOWNGRAD) message. These messages are
inhibited when the navigation mode is IRS/GPS.
A330/A340 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
NAVIGATION - EVALUATION OF POSITION ACCURACY
A330/A340 FLEET DSC-22_20-20-20 P 3/8
FCOM 19 AUG 10
When in IRS/GPS mode, the GPS PRIMARY status is related to integrity criterion: This is the
capability to detect a failure and provide appropriate warning of it. This criterion indicates the
confidence that the flight crew can have in the FMS position.
If the GPS PRIMARY status complies with this criterion, the "GPS PRIMARY" message is displayed
on the MCDU (PROG page, [5R] field and scratchpad) and temporarily on the ND. If the GPS
PRIMARY status no longer complies with this criterion (integrity lost), the GPS PRIMARY status is
lost and the MCDU and the ND display the "GPS PRIMARY LOST" message. It is possible to clear
the scratchpad message on the MCDU, but not on the ND.
　
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