What Makes Up the Lycoming T53 TA-Series Fuel Control System?
The TA-series fuel control system consists of two (2) components:
1. The Main Fuel Regulator (FCU) is a pump/control package in one. Series TA-7 for the -13 and
-703 and Series TA-10 for the -11 engines respectively.
2. The Power Turbine Governor (PTG). Series PTG-3.
Each component is procured separately and each is handled as an individual unit in all phases of
maintenance. During installation, however, the power turbine governor mounts on and operates in
conjunction with the main fuel regulator.
The main fuel regulator has a splined driveshaft which engages in the accessories gear train,
connected to the gas producer turbine (N1). The power turbine governor is splined through the
engine torque meter rotary boost pump which is connected to the engine power turbine (N2).
What is Meant by A “Free Turbine” Engine?
A free turbine engine has no direct mechanical coupling between the two turbines:
1. The gas producer turbine (GP) drives the engine compressor/gas producer turbine. The gas
producer turbine is designated N1 speed.
2. Then power turbine drives the helicopter rotor though a gear reduction unit. The power
turbine speed is designated N2 speed.
➢ What Does the TA-Series Fuel Control System Do?
The TA-series fuel control system provides for total fuel management to regulate the
operation and performance of the Lycoming T53L13B and T53L703 series engines.
➢ What Does the Main Fuel Regulator do?
The fuel control is mechanically connected to the pilot’s twist grip and driven by the N1 accessory
gearbox. Engine control is accomplished by the output of the hydro mechanical computer which
accepts as input parameters gas producer speed (N1), free turbine speed (N2), ambient
temperature (T1), ambient pressure (P1), and main throttle position.
It controls the fuel flows during acceleration and deceleration and steady state conditions in
response to throttle command. It also provides a manual emergency back-up control system.
➢ What does the Power Turbine Governor Do?
The power turbine governor is mechanically connected to the pilot’s collective pitch control through a linear actuator. The actuator is operated electrically by the pilot’s beep trim switch which allows the pilot to make minor adjustments in N2 speed to compensate for aerodynamic and ambient conditions.
Being the helicopter is designed to operate with a constant rotor speed during flight, the governor
functions to maintain the power turbine speed constant under varying load conditions as established
by the collective pitch. In flight, the governor overrides the main fuel control to maintain the actual
rotor speed at the level selected by the pilot. Because the governor is sensitive to and controls the
speed of the engine power turbines, it is designated as the N2 control.
The above information is just a brief overview of the functions and interface of the fuel
control/governor in respect to the pilot and the engine operation. With a basic knowledge
of what happens during the engine operation with respect to the fuel control system allows
a better degree of proficiency when attempting to troubleshoot fuel system problems during
starting, steady state and accelerations.
Future editions of T53 engine tips will be added to facilitate further information and
answers to any questions or comments that arise on the forum.
Wayne Bond
Director, T53 Engine Program
M International, Inc.
