Unlike reciprocating engine aircraft, the turbojet powered aircraft does not require a preflight runup unless it is necessary to investigate a suspected malfunction. Before starting, all protective covers and air inlet duct covers should be removed. If possible, the aircraft should be headed into the wind to obtain better cooling, faster starting, and smoother engine performance. It is especially important that the aircraft be headed into the wind if the engine is to be trimmed.
The runup area around the aircraft should be cleared of both personnel and loose equipment.
The turbojet engine intake and exhaust hazard areas are illustrated in figure 11-1. Care should also be taken to ensure that the runup area is clear of all items such as nuts, bolts, rocks, rags, or other loose debris.
A great number of very serious accidents occur involving personnel in the vicinity of turbojet engine air inlets. Extreme caution should be exercised when starting turbojet aircraft.
The aircraft fuel sumps should be checked for water or ice, and the engine air inlet should be inspected for general condition and the presence of foreign objects. The forward compressor blades and the compressor inlet guide vanes should be visually inspected for nicks and other damage.
If possible, the compressor should be checked for free rotation by turning the compressor blades by hand.
All engine controls should be operated, and engine instruments and warning lights should be checked for proper operation.
Starting a Turbojet Engine
The following procedures are typical of those used to start many turbojet engines. There are, however, wide variations in the starting procedures used for turbojet engines, and no attempt should be made to use these procedures in the actual starting of an engine. These procedures are presented only as a general guide for familiarization with typical procedures and methods. In the starting of all turbojet engines, refer to the detailed procedures contained in the applicable manufacturer's instructions or their approved equivalent.
Most turbojet engines can be started by either air turbine or combustion-type starters. Air turbine starters use compressed air from an external source. This source may be a ground cart unit or air bled from another engine on the aircraft that is in operation. Combustion starters are small gas turbine engines that obtain power from expanding gases generated in the starter's combustion chamber. These hot gases are produced by the burning of fuel and air or, in some cases, a slow burning solid or liquid monopropellant specially compounded for such starter units.
Fuel is turned on either by moving the power lever to "idle" position or by opening a fuel shutoff valve. If an air turbine starter is used, the engine should start or "light up" within approximately 20 seconds after the fuel is turned on. This is an arbitrarily chosen time interval that, if exceeded, indicates a malfunction has occurred and the start should be discontinued. After the cause of the trouble has been removed, another start may be made. If a combustion starter is used, the 20 second interval need not be observed, since starter operation will discontinue automatically after a predetermined time interval. The following procedures are useful only as a general guide, and are included to show the sequence of events in starting a turbojet engine.
1. Move power lever to "off" position unless the engine is equipped
with thrust reverser. If the engine is so equipped, place the power lever
in the "idle" position.
2. Turn on electrical power to engine.
3. Turn fuel system shutoff switch to "fuel on" position.
4. Turn fuel boost pump switch on.
5. A fuel inlet pressure indicator reading of 5 psi ensures fuel is being delivered to engine fuel pump inlet.
6. Turn engine starter switch on; when engine begins to rotate, check for oil pressure rise.
7. Turn ignition switch on after engine begins to rotate.
8. Move throttle to idle (if engine is not equipped with thrust reverser).
9. Engine start (light up) is indicated by a rise in exhaust gas temperature.
10. After engine stabilizes at idle, ensure that none of the engine limits are exceeded.
11. Turn engine starter switch off after start.
12. Turn ignition switch off.
Unsatisfactory Turbojet Starts
1. Hot Starts.
A hot start occurs when the engine starts, but the exhaust gas temperature exceeds specified limits. This is usually caused by an excessively rich fuel/air mixture entering the combustion chamber. The fuel to the engine should be shut off immediately.
2. False or Hung Start.
False or hung starts occur when the engine starts normally but the rpm remains at some low value rather than increasing to the normal starting rpm. This is often the result of insufficient power to the starter, or the starter cutting off before the engine starts self-accelerating. In this case, the engine should be shut down.
3. Engine Will Not Start.
The engine will not start within the prescribed time limit. It can be caused by lack of fuel to the engine, insufficient or no electrical power, or malfunctions in the ignition system. If the engine fails to start within the prescribed time, it should be shut down.
In all cases of unsatisfactory starts the fuel and ignition should be turned off. Continue rotating the compressor for approximately 15 seconds to remove accumulated fuel from the engine. If unable to motor (rotate) the engine, allow a 30 second fuel draining period before attempting another start.