Engine Fuel Control

STUDENT GUIDE T-39N/G NATOPS

C. Engine Fuel Control

1. An engine driven hydromechanical unit, controlled by a mechanical linkage to the

throttle, meters fuel to the engine.

2. A mechanical computer receives signals from compressor inlet pressure (PT2), engine

RPM, throttle position, and compressor discharge pressure (PT5) to meter fuel to meet required

thrust.

3. An engine driven, two element (centrifugal and gear) fuel pump supplies high pressure

fuel to the engine. Loss of the gear element of the fuel pump will result in flameout.

4. The centrifugal element has suction feed capabilities to at least 15,000' MSL if a wing

tank mounted boost pump fails, regardless of fuel temperature.

D. Oil system

1. Lubricates and cools the engine bearings. Engine oil pump is located on the engine

accessory gearbox.

2. Fuel/oil cooler maintains normal operating range of 40-120 C. Temperature is controlled

by adjusting fuel flow (via throttles). Primary purpose is to cool the oil.

3. Total capacity is 2.03 U.S. gallons; 1.6 U.S. gallons is full servicing.

4. Normal oil pressure is 40-50 psi with fluctuations of +5 psi; idle is 35 psi min.

5. OIL PRESS LOW light if the oil pressure falls below 28 psi. Check gauges to determine

affected engine then execute OIL PRESSURE (below 35 PSI) EP.

E. Ignition

1. Two igniters: Located in the No. 3 and No. 6 burner cans.

2. No. 3 igniter may spark continuously. No. 6 is duty cycle limited:

2 min ON, 3 min OFF

2 min ON, 23 min OFF

3. Red starter button(s) illuminate anytime igniter(s) are providing spark to engine.

4. SWITCH POSITION

a. CONTINUOUS: Constant power to the No.3 igniter only. Selected during:

(1) T/O (2) LDG, (3) flight in icing conditions, turbulence, or heavy precipitation,

or (4) anytime FUEL FILTER BLOCK caution light illuminates.

b. NORMAL: Powers BOTH igniters during: (1) engine start (from throttle

advancement to idle until 31-35% RPM), (2) with AIRSTART SWITCH in LH or

RH position, or (3)during stall warning.

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ENGINES