107
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THIS ELECTRONIC DOCUMENT MAY HAVE BEEN SUPERCEDED.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 overspeed test evaluates the ability
of the overspeed solenoid valve to shut off
fuel flow. This test is conducted at ground
idle to shut the engine down.
The pilot activates the overspeed test
switch. The FADEC energizes the
overspeed solenoid valve which closes and
shuts off the fuel. The overspeed light also
comes on.
OVERSPEED FUNCTIONAL TEST
The operational status of the overspeed
system is automatically and continually
monitored by the other ECU circuits to
detect latent failures that could result in
false trips or nonoperation should one or
more additional failures occur. Should a
failure be detected by the automatic test
or the continuous checks it will be
annunciated to the pilot by the ECU fail or
ECU degrade discretes. Any failure in a
redundant component that leaves the
system operational shall be annunciated
as “ECU Degraded” failure. Any failure that
disables the system completely shall be
annunciated as “ECU Failure”. This failure
information will be recorded by the ECU’s
EMS feature.
FAILURE ENUNCIATION
In auto mode, a software implemented
overspeed system is provided. Should the
software detect an NG speed above the NG
overspeed threshold, the ECU will activate
the overspeed solenoid valve and reduce
fuel flow to minimum flow. Once the NG
speed drops below the overspeed
threshold, the solenoid valve opens and
normal operation may resume.
The ECU contains a basic engine
monitoring system to record and store
engine and system fault information. The
information is recorded in nonvolatile
memory for retrieval by maintenance
personnel via RS-423 digital data
communication link to portable terminal.
The recorded parameters include:
•engine running time
•compressor module running time
•turbine module running time
•number of engine starts
•highest peak value and time exceeding
turbine speed limit (NG and NP)
•highest peak value and time exceeding
turbine run temperature limit (MGT)
•highest peak value and time exceeding
engine output shaft torque limit
•highest peak value and time exceeding
engine start temperature limit (MGT)
•occurrence of engine surge
To permit transfer of engine ECU’s from
one aircraft to another, data may be read
from and input to the ECU nonvolatile
memory via the RS-423 digital data link.
These data include:
•engine serial number
•ECU serial number
•compressor serial number
•NG turbine serial number
•NP serial number
ENGINE CONDITION
MONITORING
NG OVERSPEED
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