ENGINE POWER SETTING
--------------------------------------------------------------------------------
Two modes of power setting, EPR and N1 modes are used for engine control depending on the availability of air data inputs to the FADEC which are used for rating computation.
Two sources of air data are used by the FADEC :
- either engine data : P0 static pressure
P2 total air pressure
T2 total air temperature
- or ADIRS 1 or 2 data : Ps equal to engine P0
Pt equal to engine P2
Tt equal to engine T2
Thrust computation for both engines is mainly based on one ADIRS data. This ensures engine thrust symmetry.
A comparison between ADIRS 1, ADIRS 2 and engine data is made by the FADEC to determine the source to be validated and the mode to be used.
EPR MODE
EPR mode is the normal mode to control the thrust.
The required EPR is set by controlling the fuel flow.
The FADEC computes the command EPR as a function of :
Thrust Lever Angle (TLA)
Altitude
Mach number
Air data (static pressure, total air pressure/temperature)
Service bleed.
Note : During reverse operation, the thrust is controlled as a function of N1.
N1 MODE
In the event of no EPR available the affected FADEC will automatically revert to N1 mode.
At the reversion to N1 mode, an equivalent thrust to that achieved in EPR mode is provided until a thrust lever position change.
Autothrust control is no more available. ALPHA FLOOR protection is lost.
In case of dispatch in N1 mode, flex take-off is not available. ALPHA FLOOR protection is lost.
Depending on the failure case leading to EPR mode loss the FADEC will revert to either rated or unrated N1 mode.
RATED N1 MODE
An automatic reversion to rated N1 mode occurs when :
engine P2 and/or P5 are not available,
or, engine P2 lower than ADIRS Pt.
The FADEC will compute an EPR COMMAND depending on TLA, then convert it into a N1 COMMAND as a function of Mach.
The rated N1 mode can also be manually selected through the ENG N1 MODE pushbutton on the overhead panel.
UNRATED N1 MODE
An automatic reversion to unrated N1 mode occurs when :
engine P2 and ADIRS 1 + 2 Pt are not available,
or, engine T2 and ADIRS 1 + 2 Tt are not available,
or, engine P0 and ADIRS 1 + 2 Ps are not available.
The N1 is defined as a function of TLA and altitude and is limited by the FADEC to either the smaller of N1 max or N1 redline (if T2 is available) or N1 redline (if T2 is not available).
The N1 rating limit, N1 TLA and N1 max indications on ECAM E/WD are lost.
Phhhheeewww!
Regards.