The
engines idle modes are determined though inputs to the EEC which calculates the
required fuel flow supplied by the Hydro Mechanical Unit. (HMU)
Normal inputs to the
EEC are:
- ADIRU (P0, PT, TAT)
- DEU (flaps, gear, air/grnd, bleed, etc.)
- Engine sensors (several output pressures and RPM’s)
- Thrust Lever Angle (idle) wink emoticon
- ADIRU (P0, PT, TAT)
- DEU (flaps, gear, air/grnd, bleed, etc.)
- Engine sensors (several output pressures and RPM’s)
- Thrust Lever Angle (idle) wink emoticon
Extra inputs on the
ground:
- Outside air temperature
- Electrical power
- Bleed air demand
- Minimum fuel flow requirements
- Outside air temperature
- Electrical power
- Bleed air demand
- Minimum fuel flow requirements
Extra inputs in
flight:
- Anti-ice operation
- Flap position
- Altitude
- Anti-ice operation
- Flap position
- Altitude
Next the idle
operating modes explanation.
Ground
minimum idle:
After the engine is started on the ground the EEC determines a minimum idle RPM of the N2 spool which represents the operation of the engine (N1 is thrust) to a minimum requirement for operation of its components.
After the engine is started on the ground the EEC determines a minimum idle RPM of the N2 spool which represents the operation of the engine (N1 is thrust) to a minimum requirement for operation of its components.
These are identified
as:
- 58% N2 when TAT is < 52°C as a minimum for IDG operation
- 66% when TAT is >52°C to provide sufficient engine cooling
- Maintain a compressor discharge pressure to satisfy air supply to the aircraft environmental control system
- Maintain a fuel flow of at least 136 Kg/hari
- 58% N2 when TAT is < 52°C as a minimum for IDG operation
- 66% when TAT is >52°C to provide sufficient engine cooling
- Maintain a compressor discharge pressure to satisfy air supply to the aircraft environmental control system
- Maintain a fuel flow of at least 136 Kg/hari
Flight
minimum idle
In flight the EEC controls idle N2 RPM to be at least 72% as a minimum engine operational speed.
In flight the EEC controls idle N2 RPM to be at least 72% as a minimum engine operational speed.
Approach
idle
This idle function is selected by the EEC during certain phases of flight where the possibility exists to the need of a fast increase in RPM or better, to shorten spool-up time of the engines. Approach idle is a higher percentage of N2 (72 – 79% an increase of ± 1000 RPM) and related N1% in case of a go-around where a quick engine response is needed. Approach idle is selected by extending the flaps in the landing mode (>15°), or TAI with the thrust lever angle at idle.
This idle function is selected by the EEC during certain phases of flight where the possibility exists to the need of a fast increase in RPM or better, to shorten spool-up time of the engines. Approach idle is a higher percentage of N2 (72 – 79% an increase of ± 1000 RPM) and related N1% in case of a go-around where a quick engine response is needed. Approach idle is selected by extending the flaps in the landing mode (>15°), or TAI with the thrust lever angle at idle.
TAI
because when during the approach and icing conditions, a faster turning N1 fan
is subjected by a higher centrifugal force, reducing ice buildup on the fan
blades near the center of rotation.
