. Extremely Remote failures are considered when the probability of occurrence is from 10 -7 to 10-9 per operation (based on a 15min exposure time). Sizing Extremely Remote failures considered are : double severe FMS reset, erroneous FMS position. For those failures, aircraft remains manoeuvrable for a safe extraction during a contingency procedure if corresponding procedure is published and made available to the flight crew.
All data of this paragraph are given for example. For a particular Airbus aircraft, the Airlines should refer to the aircraft Flight Manual and the associated ACD.
5. The navigation and guidance system design
Getting to grips with RNP AR
5. THE NAVIGATION AND GUIDANCE SYSTEM DESIGN
Only a navigation solution with IRS and GPS PRIMARY can meet all the requirements of RNP AR.
Consequently, it is essential to ensure that GPS PRIMARY will be available during the RNP procedure and to alert the flight crew of any loss of RNP capability.
As the FTE was demonstrated with AP ON, the AP guidance must be used in
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NAV and APP NAV for initial approach
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FINAL APP during the final approach
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NAV for missed approach and departure
The crew also needs to monitor the AP performance using the L/DEV and V/DEV indications on PFD, and the ND.
The detailed description of the navigation system and the automatic flight control system can be found in the FCOM.
5.1. NAVIGATION SYSTEM
5.1.1. AVAILABILITY OF GPS PRIMARY
The RNP capability depends on the availability of GPS/IRS integrity. For Aircraft equipped with Litton AIME or Honeywell HIGH ADIRU, the availability of GPS/IRS integrity has been demonstrated to be 100% in approach world-wide for GPS satellite constellation of 24 (or 23, see AFM) satellites. The use of a Ground-Based Prediction Program is only required when less than 24 (or 23 see AFM) satellites are operative, or RNP<0.3 is intended. However, in certain environments, such as mountainous terrain, a RNP ground-based predictive capability may be required to determine that the performance is adequate. In these cases, the appropriate Ground-Based Prediction Program (AIME or HIGH predictive tools) should be used to assure that the performance calculations are representative of those performed in the resident navigation software.
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5. The navigation and guidance system design
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5.1.2. A/C POSITION COMPUTATION
The estimation of the aircraft position is performed by the Flight Management System based on different sensors: Inertial (ADIRU), GPS, radio navigation (DME and VOR). The FMS computes the best aircraft position estimate based on the following hierarchy of navigation modes:
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