.
FAA considers the Engine failure condition as a remote event, and defers FTE OEI evaluation to the Operational approval. This means that the published RNP level for FAA certification is determined basically with All Engines Operative (AEO). During the operational demonstration, the Airline is expected to demonstrate that the
engine failure will be contained within the ±2xRNP limit.
.
EASA considers that FTE OEI has to be evaluated during certification, to
demonstrate that the engine failure will be contained within the ±1xRNP limit. This FTE OEI must not be determined statistically but deterministically considering the worst case (tight turns, adverse wind conditions).
EASA standard for RNP AR also requires the aircraft manufacturer to reassess the effects of aircraft system failures in RNP AR environment to demonstrate that the probable failures (probability >10-5/procedure) can be contained within ±1xRNP, including the failure of:
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RNP systems
.
Flight controls
.
Flight Guidance
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3. The RNP Concept
EASA also requires that:
- The remote system failures (probability from 10-5/ to 10-7/procedure) can be contained
within ±2xRNP,
- The aircraft remains maneuverable for a safe extraction after extremely remote system failures (probability from10-7 to10-9/procedure).
Pending further harmonization and maturity of the RNP AR standards, the EASA compromise is to allow the aircraft manufacturer to document both :
.
RNP levels associated to the TSE in normal conditions, and
.
RNP levels associated to the TSE with OEI or following probable/remote system failures.
The vertical navigation requirements for RNP AR (SAAAR) are similar to those of the MASPS (described in §3.3).
The vertical system error includes altimetry error (assuming the temperature and lapse rates of the International Standard Atmosphere), the effect of along-track-error, system computation error, data resolution error, and flight technical error. The vertical system error with a 99.7% probability must be lower than the value given in the following formula (in feet):
Component of the WPT
FTEz ASE navigation error resolution error
where . is the vertical navigation (VNAV) flight path angle, h is the height of the local altimetry reporting station and Δh is the height of the aircraft above the reporting station. The FTEz does not need to be determined statistically if the fixed 75ft value is established as an operational limit for maximal vertical deviation.
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