**ON A/C ALL
FUEL FLOW INDICATING − DESCRIPTION AND OPERATION
1.
General
Fuel flow indicating for the engine fuel and control installation consists of two identical, but
independent fuel flow indicating systems, one for each engine. Each system consists of a fuel
flow transmitter connected to a fuel flow indicator. The transmitters are mounted on the
engine casings and the indicators are located on the engine instrument panel in the flight
compartment.
The electrical circuit for each engine is powered from the 28 V dc bus, and protected by a
5−ampere FUEL FLOW IND ENG 1 (C5) left main bus or FUEL FLOW IND ENG 2 (Q5) right
main bus circuit breaker.
2.
Description and Operation
Refer to Figure 1.
A.
Fuel Flow Transmitter
A fuel flow transmitter installation consisting of a transmitter and a mounting bracket
assembly is attached to the engine front inlet case rear flange at approximately 3 o’clock
(viewed from rear of engine). The transmitter is connected into engine metered fuel lines
between the hydromechanical fuel control unit (HMU) and the fuel manifold and nozzles
installation of each engine fuel system.
A directional arrow, on the transmitter casing, points away from the HMU and provides
indication of required fuel flow direction. The bracket assembly and the transmitter are
provided with an uneven bolting pattern to prevent incorrect installation.
The transmitter is of the rotating impeller type and is connected to the associated
indicator by electrical wiring.
B.
Fuel Flow Indicators
Refer to Figure 2 and Figure 3.
The fuel flow indicators are located on the engine instrument panel in the flight
compartment and are internally lighted by white lighting, powered from the 5 V dc lighting
system (refer to Chapter 33).
Each indicator receives an ac signal equivalent to fuel flow from its associated
transmitter and provides a fuel flow readout by means of a moving pointer against a fixed
dial and an equivalent digital display. A 0 to 5 V dc signal proportional to fuel flow is
relayed to the flight data recorder (refer to Chapter 31).
The digital display is of the 4−digit liquid crystal display (LCD) type. Pre mod 8−1/1101
aircraft incorporate a heater associated with LCD operation in each indicator. The
heaters are powered from the 28 V dc secondary buses, engine No. 1 IND LCD HTR
(S2) indicator heater from the left bus and engine No. 2 IND LCD HTR (A1) indicator
heater from the right bus (refer to Chapter 77). The heaters are temperature controlled to
ensure LCD operation at low temperature conditions in the flight compartment.
The indicator dial is marked FF PPH × 100 (KG/H × 100) and the scale is graduated in
major graduations in increments of 100 PPH (100 KG/H) between 0 and 1200 PPH (0
and 550 KG/H), with minor graduations in increments of 50 PPH (50 KG/H). Indicator for
engine No. 1 is powered by 28V dc L MAIN BUS (C5). Engine No. 2 by 28V dc R MAIN
BUS (Q5).
D
SERIES 100
AIRCRAFT MAINTENANCE MANUAL
MASTER
EFFECTIVITY: See Pageblock 73−32−00 page 1
73−32−00
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Dec 20/2004