It's been a few years, but this is what I remember from memory
The aircraft is powered by four Allison T56-A-15 turboprop engines. The basic engine consists of two major assemblies - a power section and a reduction gear assembly - that are attached to each other by an extension shaft assembly and two supporting struts. The engine is provided with fuel, oil, starting, ignition, and control systems. The engine operates at a constant speed; therefore, engine power is related to TIT that varies according to the rate of fuel flow. An increase in fuel flow causes an increase in TIT and a corresponding increase in energy available at the turbine. The turbine then absorbs more energy and transmits it to the propeller in the form of torque. In order to absorb the increased torque, the propeller increases blade angle to maintain constant engine rpm. A decrease in torque results in a decrease in propeller blade angle to maintain engine speed. Thrust is obtained from the propeller, and a small amount of additional thrust (approximately 10 percent at takeoff) is created by the tailpipe exhaust.
ENGINE CONTROLS AND CONTROL SYSTEMS
Throttles
The throttles are quadrant mounted on the flight control pedestal. Throttle movements are transmitted through mechanical linkage to an engine-mounted coordinator. The coordinator transmits the movements through mechanical linkage to the propeller and to the engine fuel control, and it also actuates switches and a potentiometer which affect electronic temperature datum control system operation. Each throttle has two distinct ranges of movement, taxi and flight, which are separated by a stop. Both ranges are used for ground operation, but the taxi range must not be used in flight. In the taxi range, the throttle position selects a propeller blade angle and a corresponding rate of fuel flow. In the flight (governing) range, throttle position selects a rate of fuel flow, and the propeller governor controls propeller blade angle. The throttles have four placarded positions as follows:
1. MAXIMUM REVERSE - (0° travel) gives maximum reverse thrust with engine power approximately 40 percent of take-off power.
2. GROUND IDLE - (Approximately 18 ° travel) is a detent position. This is the ground starting position at which blade angle is set for minimum thrust.
Note
Throttles must not be moved out of GROUND IDLE detent during ground starting because the resultant increase in propeller blade angle might overload the starter, reducing the rate of engine acceleration.
3. FLIGHT IDLE - (34° travel) is the transition point between the taxi and flight (governing) ranges. A step in the quadrant limits aft travel of the throttle at this position until the throttle is lifted.
4. TAKE-OFF - (90° travel) is the maximum power position.
The throttle quadrant is also divided into two unmarked ranges with respect to control of the electronic temperature datum control system. The crossover point is at 65° throttle travel, at which point the switches in the coordinator are actuated. Below this point, the electronic temperature datum control system is limiting turbine inlet temperature. Above this point, it is controlling turbine inlet temperature if the TD valve switches are in the AUTO position.
Engine Condition Levers
Four pedestal-mounted, condition levers are primarily controls for engine starting and stopping and propeller feathering and unfeathering. They actuate both mechanical linkages and switches that provide electrical control. Each lever has four placarded positions as follows:
1. RUN is a detent position. At this position, the lever closes a switch that places engine fuel and ignition systems under control of the speed-sensitive control.
2. AIR START is a position attained by holding the lever forward against spring tension. In this position, the lever closes the same switch closed by placing the lever at RUN, and in addition closes a switch that causes the propeller feathering pump to operate.
3. GROUND STOP is a detent position. In this position, the lever actuates a switch that causes the electrical fuel shutoff valve on the engine fuel control to close only if the landing gear touchdown switches are closed. The switch also closes the nacelle preheat control circuit making this system operable.
4. FEATHER - A detent position. When the lever is pulled toward this position, mechanical linkages transmit the motion to the engine-mounted coordinator and from the coordinator to the propeller and the shutoff valve on the engine fuel control. Switches are also actuated by the lever as it is pulled aft. The results of moving the lever to FEATHER are the following:
a. The propeller receives a feather signal and mechanically and electrically energizes the feather solenoid valve.
b. The fuel shutoff valve on the engine fuel control is closed both mechanically and electrically.
c. The propeller feathering pump is turned on.
d. The nacelle preheat system remains operable only when the aircraft is on the ground (if installed).
CAUTION
When pulling a condition lever to FEATHER, pull it all the way to the detent to assure that the propeller is fully fathered when the engine fuel is shut off. If the lever is left at midposition, and the NTS is inoperative, an engine decoupling is possible.
PROPELLER SPEED CONTROL SYSTEM
The speed of the propeller is controlled by the propeller governing system and the synchrophasing system.
PROPELLER GOVERNING SYSTEM
The principal function of the propeller governing system is to maintain constant engine operating rpm. Propeller governing is accomplished by the action of the flyweight speed-sensing pilot valve.
SYNCHROPHASING SYSTEM
The synchrophasing system is an electronic system for controlling the blade position relation between all four engines.
ELECTRONIC PROPELLER GOVERNING
The synchrophaser electronic unit provides circuits for the following governing functions: speed stabilization (derivative), throttle anticipation, and synchrophasing. The propeller mechanical governor will hold a constant speed in the flight range but throttle changes will cause the governor to overspeed or underspeed while trying to compensate for the change in power.
NTS LOCKOUT SYSTEM
The propeller is equipped with a lockout system to deactivate the NTS system for throttle settings below flight idle. When the throttle is moved below flight idle, a cam moves the actuator away from the NTS plunger and renders the system inoperative. This is necessary to prevent a propeller from receiving a possible negative torque signal at high landing speeds when the throttles are moved toward reverse, with resultant asymmetrical power problems.
PROPELLER CONTROLS
Throttles
Each throttle is mechanically linked through the engine coordinator to an input shaft on the propeller control assembly. When the throttle is in the governing range, between FLIGHT IDLE and TAKE-OFF positions, the input shaft rotates with throttle movement but has no effect on propeller speed. When the throttle is in the range below FLIGHT IDLE, any movement of the throttle is transmitted to the speed sensing pilot valve to increase or decrease blade angle. The maximum negative blade angle is obtained when the throttle is at MAXIMUM REVERSE. Approximate minimum thrust angle is obtained when the throttle is at GROUND IDLE. When the throttle is moved below FLIGHT IDLE, a cam locks out tie NTS system and a switch interrupts synchrophaser signals to the propeller.
Engine Condition Levers
The engine condition levers serve primarily as feathering and unfeathering controls. Each lever is mechanically linked to the engine coordinator, which transmits the motion of the lever to the propeller linkage only when it is moved to the FEATHER position. When pulled to FEATHER, the condition lever also actuates switches to turn on the electrically driven auxiliary pump in the propeller control assembly, and the propeller blades are moved to the feather angle, For unfeathering, the engine condition lever is held in the AIR START position. A switch is actuated to turn on the propeller auxiliary pump, and the pump continues to operate as long as the lever is held in this position, When the engine condition lever is in the AIR-START position and the auxiliary pump is operating, fluid is routed to the aft side of the dome assembly piston to move the blades to low-pitch angle. When the condition lever is in GROUND STOP or RUN positions, the propeller is controlled normally and the lever has no effect on its operation.