The Jet Fuel Starter (JFS) is a simple, scaled down jet engine (often called as APU - Auxuliary Power Unit - in civilian aviation) fitted centrally between the two engines - see (15) on the figure below. It is used to start the two engines (in fact it's the only way of starting them).

The JFS can start either engine, but not both simultaneously. The JFS itself is started by accumulated hydraulic pressure. There are two hydraulic accumulators which are automatically charged during flight by the utility hydraulic system or manually by a hand pump. Fuel is provided by the aircraft's main fuel system, ignition and electrical power are provided by the JFS generator (permanent magnet). The JFS has its exhaust on the bottom fuselage of the aircraft, behind the central external hardpoint (SUU-73/A pylon). The location of the JFS intake and exhausts are illustrated on the following figure.

Pilot Controls

The JFS is activated via a handle and a switch on the pilot's right hand console. See the illustration below.

The JFS starter switch (1) has positions of ON and OFF. For the JFS to be engaged this switch has to be put into ON position. Although the JFS shuts itself down automatically, it can be manually shut down by placing the switch to OFF position at any time during operation.

The JFS control handle (2) is used to discharge the hydraulic accumulator(s) to actually start the JFS. Pulling the handle straight out discharges one accumulator. Rotating the handle 45 degrees counterclockwise and pulling discharges both accumulators (or the remaining one if one has been already discharged). The handle is spring loaded to return to its normal position.

The JFS ready light (3) indicates if the JFS is ready to be engaged. The light goes out when the JFS is shut down.

A 'JFS LOW' caution appears on the caution display on MPD/ MPCD if either JFS accumulator pressure is too low.

Engine Start

The engine startup sequence is roughly the following (respective controls are referenced by their numbers on the illustration above):

• Turn the JFS starter switch on.
• Pull the JFS control handle.
• Engage the first engine by pulling its respective fingerlift on the throttle (see article on throttles in the 'Cockpit' section in the left menu). As a standard operating procedure, the right engine should be started first so that a hydraulic pump operated by the right engine can be checked. The fingerlift on the front of the throttle engages the JFS connection to the engines.
• Wait until the JFS spins the right engine to 20% rpm. Engine rpm can be monitored on the Engine Monitoring Display ( EMD) on the front dashboard above the right knee of the pilot (see article on the engines in the 'Engines' section in the left menu).
• Push the throttle forward out of NULL and into IDLE. The digital electronic engine control ( DEEC) takes over from there.
• Monitor the rpm and FTIT (Fan Turbine Inlet Temperature) on the EMD during the process to ensure there is not a hot start or other malfunction. PW-220 hot-start FTIT limit is 680 Celsius, while the same limit for PW-229 is 800 Celsius.
• As the engine spins up past 56% rpm the right generator comes on-line and the right engine intake ramp, which has been locked in the full-up position, slams to the full down position (this scares a lot of first-time passengers in the back seat!)
• Test fire sensor loops (see article on the Fire Warning/Extinguishing System in the 'Engines' section in the left menu).
• Repeat the same process for the left engine.

Since the JFS is a jet engine in itself, extra care should be taken not to be within the reach of its air intake and its hot exhaust gases when the JFS is running. The 'danger' zone is a 4 feet circle around the intake and two 20 degree cones from the JFS exhausts to the engine tail cones (see illustration below).

The JFS automatically shuts down when the second engine reaches approx. 50% rpm. Note that on aircraft 86-0183 thru 87-0200 a manual JFS shutdown may result in the CAS and MPDP temporarily dropping off the line.

The JFS may be used during flight to perform a JFS assisted restart (special operating procedures apply to this).

Engine Shutdown

Complete engine shutdown can be accomplished from the front cockpit only. However if over the left wing access door is used for engine shutdown, the engines can be positioned to IDLE from the rear cockpit as well to reduce danger of intake suction. The engine shutdown procedure is the following:

• Depress the left and right engine fire extinguisher buttons. This action closes the engine fuel shutoff and bleed air. Note, that the JFS should be running to provide 28 volt DC power for operation of the AMAD fire extinguisher system.
• If the JFS is running, push the AMAD fire button to close the JFS fuel shut-off relay.
• Raise fingerlifts on throttle and pull back throttles to below IDLE.
• Release fingerlifts and pull throttle back to OFF.

Limitations

There are certain limitations regarding JFS usage. These can be summarized as follows:

• Maximum 10 seconds (15 seconds if temperature is below 0 Fahrenheit) between JFS start initiation and ready light.
• Starter engagement time shall not exceed 90 seconds, except if a hot-start occurs, when this time may be extended to 150 seconds.
• Minimum 10 seconds between first engine at idle speed and engagement for second engine start. If the engine engagement time exceeds 90 seconds, wait 20 seconds before again engaging or shutting down the JFS.

Sources

• F-15E Flight Manual TO 1F-15E-1 (courtesy of eFlightManuals.com)
• Special thanks to USAF Capt. Randall 'Hacker' Haskin

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