-
VOR/DME/inertial,
-Inertial only.
. GPS/Inertial
The Inertial system (ADIRU) computes the hybrid GPS/Inertial position.
Hybrid signals from IRS/GPS are used to compute GPIRS position.
As long as GPS/Inertial mode is active and integrity is ensured, neither DME/DME nor
VOR/DME radio update is performed.
Different algorithms for GPS/Inertial integrity computation are available: NGC/Litton AIME,
Honeywell HIGH and RAIM.
With Honeywell HIGH, the integrity estimate (Hybrid- RAIM) is calculated by the ADIRU’s
using integrity parameters resulting from RAIM computation provided by the MMR plus Air
Data parameters for altitude aiding. The satellites exclusion is performed by the MMR.
With Litton AIME, the integrity estimate is calculated by the ADIRU’s using the AIME
algorithm. The satellites exclusion is performed by the ADIRS.
. Radio Navigation ( DME/DME/Inertial or VOR/DME/Inertial)
The FMS computes a DME/DME position, if two DME stations are correctly received and their relative geometry to the aircraft is adequate. Otherwise a VOR/DME position can be computed, if at least one VOR/DME station is received. The FMS uses the VOR bearing associated to the DME to compute a VOR/DME position. The FMS radio-updating is normally not suitable to support RNP AR operations. To avoid FMS radio updating if GPS PRIMARY is lost, the crew should deselect the radio navaid stations that would be tuned by the FMS. When basing its navigation on a single VOR/DME, the FMS position may become inaccurate depending on the quality of the ground station being used. For approaches where ground NAVAIDS are available and could be used by the FMS for radio updating in VOR/DME mode in case of GPS PRIMARY loss, those VOR/DME shall be de-selected by the crew prior starting approach using the Position Monitor Page . SEL NAVAIDS. This de-selection capability is limited to 6 NAVAIDS. If a deselected navaid can be used to support a contingency procedure, this navaid should be tuned for display only. With Honeywell FMS release 1A, it will be possible to inhibit any FMS radio update.
. Inertial only
The three ADIRU inputs are used and mixed together within each FMS to provide a MIX IRS
position.
In case of IRS failure, each FMS will use its on side IRS (or IRS3).
In Inertial only navigation the FMS position will drift with the drift rate of the triple mixed
position or the single IRS position. The last position bias computed between the GPIRS
position and the IRS or MIX IRS position remains constant.
The drift rate is small enough to allow the “ safe extraction” of the aircraft if a GPS PRIMARY
LOST alert appears during the approach.
5. The navigation and guidance system design
Getting to grips with RNP AR
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