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THIS IS AN UNCONTROLLED DOCUMENT.
THIS ELECTRONIC DOCUMENT MAY HAVE BEEN SUPERCEDED.
THE MOST CURRENT DOCUMENT INFORMATION IS AVAILABLE
FROM YOUR BELL HELICOPTER TEXTRON REPRESENTATIVE.
PRODUCT DATA JANUARY 2003
FADEC SYSTEM FEATURES OPERATION (continued)
The FADEC control system provides
automatic start sequencing and engine
control during the engine starting cycle.
This involves controlling fuel flow until
stabilized idle gas generator (NG) speed
is reached. Starting is initiated by the pilot
by placing the throttle in the ground idle
position and activating the start switch.
Once the required light off NG speed of 12%
is achieved (10% if ambient temperature
is less than 20°F), the FADEC introduces
fuel to the engine. The engine fuel flow is
then regulated to control the NG turbine
rate of acceleration (NDOT) and to maintain
a turbine temperature (MGT) limit while
AUTOMATIC START
The FADEC declares an engine flameout
by detecting an NG deceleration rate
greater than a predetermined flameout
boundary rate. The engine flameout is
enunciated to the aircraft via the ARINC-
429 data bus. Without pilot action, the
flamed out engine’s FADEC will initiate a
restart sequence, which includes
scheduling the appropriate restart fuel flow
as a function of operating and ambient
conditions and activating the ignition
system. Relight will be detected by the
FADEC and the turbine temperature will
be controlled. The engine will then smoothly
accelerate back to the commanded
operating condition. The Engine Out
discrete will turn off after a minimum NDOT
or increasing MGT is established. No pilot
action is required unless the engine fails
to relight by 50% gas generator speed (NG).
In the event of an unsuccessful relight, the
engine PLA (throttle) should be moved to
cutoff.
AUTORELIGHT
The FADEC detects engine surge by
comparing the rate of change of NG speed
to a predetermined boundary rate. If the
boundary is exceeded and MGT is
increasing, the surge will be detected and
recorded by the internal ECU EMS. The
surge will be recorded in the ECU’s memory
relative to the NG speed at which it
occurred. Without pilot action, the FADEC
will reduce fuel flow during the surge and
reduce the maximum acceleration schedule
during the current acceleration in order to
quickly recover from the surge. The FADEC
will then lower the acceleration schedule
at the NG where the surge occurred to avoid
subsequent surge. The acceleration
schedule is reset to the original schedule
at FADEC power up transition of the auto/
manual switch from manual mode to auto
mode.
SURGE DETECTION AND
RECOVERY
Automatic limiting functions accomplished
by the FADEC include turbine temperature
limiting, engine torque limiting, NG speed
limiting, and NP speed limiting.
The FADEC system interfaces to the MGT
harness to measure engine temperature.
When the engine is approaching its steady
state or transient temperature limit, the
FADEC reduces fuel flow to prevent limit
exceedance. A smooth, controlled
transition between governing and
temperature limiting is accomplished by the
FADEC.
The FADEC system interfaces to the TMOP
(torque meter oil pressure) torque sensor
to measure output shaft torque. The FADEC
reduces fuel flow in response to measured
torque to prevent limit exceedance.
EXCEEDANCE LIMITING
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