bustion camber and the other is at the aft end to ensure
2-3-29. FADEC Description.
714A Each engine is controlled by its own Full Authority
Digital Electronic control System (FADEC) which pro-
vides the following features:
Automatic start scheduling.
1 and 2 engine load sharing.
Power turbine speed governing.
Transient load anticipation (using rotor speed
and collective pitch rates).
Transient torque smoothing (using N2 rates).
Contingency power capability to meet aircraft de-
Acceleration and deceleration control.
Engine temperature limiting throughout the oper-
Compressor bleed band scheduling..
Fuel flow limiting.
Engine fail detection.
m. Power assurance test.
Engine history/fault recording.
Engine-to-engine communication (via data
Automatic switchover to reversionary backup in
the event of a FADEC primary system failure.
The FADEC provides automatic engine start, simulta-
neously sequencing ignition, start fuel, and stabilized
operation at idle. A data link between 1 and 2 engine
FADEC systems transmits signals to achieve load sha-
ring. It also provides control of N1 speed and NR (N2)
output shaft speed to maintain the rotor system at a near
constant RRPM throughout all flight power demand con-
ditions. FADEC provides smooth acceleration and over-
temperature protection when ECLs (both together) are
moved from GROUND to FLIGHT. Overtemperature
protection is provided (through the DECU temperature
limiting function) by control system thermocouple inter-
face at the power turbine inlet. The control system
compares PTIT temperature signals with reference limits
to calculate and provide appropriate N1 acceleration.
During starts, an absolute 816_C limit is set and if ex-
ceeded an engine out indication and shutdown will occur.
If compressor performance deteriorates for any reason,
surge detection automatically allows recovery from com-
pressor instability while protecting the engine from dam-
age due to overtemperature.
The FADEC system consists of:
The Digital Electronic Control Unit (DECU) in-
cludes a primary mode and a reversionary section for
backup (fig. 2-3-7).
(HMA), includes Hydromechanical Fuel Metering Unit
(HMU) and fuel pump unit for all fuel metering to support
both primary and reversionary fuel metering, a self-con-
tained alternator for powering the FADEC electronics, a
primary and revisionary compressor bleed air control,
and redundant speed sensing.
ENG COND panel (fig. 2-3-5).
FADEC control panel (fig. 2-3-6).
RPM INC/DEC (Beep) switch THRUST CONT
On 714A engine installations, engine beep
switches are only active when in reversionary mode.
Each switch is labeled NO. 1 or NO. 2 which
is used to adjust RRPM when in reversionary mode.
Operation of the beep switches on the
714A in the reversionary mode are the same as for the
712 except that each switch operates respective en-
gine independently. If only one engine is in reversionary
mode, the RRPM will not change, as it is governed by the
engine in primary mode.
2-3-30. Reversionary System. 714A
Aircrew should be alert to the possibility of
abrupt NR and engine power changes when
operating the FADEC in single or dual engine
REV mode (s).
The reversionary (backup mode) automatically takes
control of the engine if the primary mode fails or if se-
lected by the operator via the FADEC panel, REV switch.
When an engine is operating in reversionary mode,
FADEC provides engine and rotor control through N1
speed governor, beep control, and thrust pitch
When both engines are in reversionary mode, RRPM will
require more pilot attention since proportional rotor
speed governor will not hold speed as accurately as the
primary systems. With large collective changes, the rotor
speed can change up to $3 percent from a nominal
The reversionary system provides the following control
Automatic start sequencing including over tem-
perature protection, but not start abort.
Pilot controlled start fuel enrichment/derichment,
if required, through ECL modulation.
Ground idle set 55 "5 percent with ECL at GND.