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AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
NAVIGATION - EVALUATION OF POSITION ACCURACY
A318/A319/A320/A321 FLEET DSC-22_20-20-20 P 2/16
FCOM 19 AUG 10
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.
If above 0.28 nm, the FMS rejects the
GPS position.
IRS/DME/DME Moves toward 0.28 nm. EPU decreases from 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.
GENERAL
Applicable to:
,
,
MSN,,
4617,
The FMGS 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 0.05 nm.
IRS/DME/DME 0.27 nm - 0.37 nm.
IRS/VOR/DME 0.30 nm - 0.42 nm. Dependent on the distance between the
aircraft and the VOR/DME.
IRS ONLY +6 kt for the first 40 min.
0 kt for the following 50 min.
+4 kt for the following 40 min.
0 kt for the following 45 min.
+2 kt after.
EPU increases continuously.
Note: After an IRS ‐ alignment, the EPU is set at 5 nm.
‐ At takeoff, the EPU is set at 0.2 nm.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
NAVIGATION - EVALUATION OF POSITION ACCURACY
A318/A319/A320/A321 FLEET DSC-22_20-20-20 P 3/16
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 specified 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
When one FMGC 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.
CAUTION "HIGH" or "LOW" on the PROG page indicates the FM position accuracy, based on
estimated uncertainty. The flight crew must periodically check this position accuracy.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
NAVIGATION - EVALUATION OF POSITION ACCURACY
A318/A319/A320/A321 FLEET DSC-22_20-20-20 P 4/16
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 specified RNP values of the navigation/approach
charts (if charts specify the RNP).
POSITION ACCURACY CRITERIA Defined by Airworthiness Authorities
FLIGHT AREA RNP VALUES
　
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