Chapter 11. Safety, Ground Operations, & Servicing

Turbofan Engines

Unlike reciprocation engine aircraft, the turbine-powered aircraft does not require a preflight run-up 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 run-up area around the aircraft should be cleared of both personnel and loose equipment. The turbofan engine intake and exhaust hazard areas are illustrated in Figure 11-17. Exercise care to ensure that the runup area is clear of all items, such as nuts, bolts, rocks, shop towels, or other loose debris (FOD). Many very serious accidents have occurred involving personnel in the vicinity of turbine engine air inlets. Use extreme caution when starting turbine aircraft.

Check the aircraft fuel sumps for water or ice, and inspect the engine air inlet for general condition and the presence of foreign objects. Visually inspect the fan blades, forward compressor blades, and the compressor inlet guide vanes for nicks and other damage. If possible, check the fan blades for free rotation by turning the fan blades by hand. All engine controls should be operated, and engine instruments and warning lights should be checked for proper operation.

Starting a Turbofan Engine

The following procedures are typical of those used to start many turbine engines. There are, however, wide variations in the starting procedures used for turbine 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 turbine engines, refer to the detailed procedures contained in the applicable manufacturer’s instructions or their approved equivalent.

Most turbofan engines can be started by either air turbine or electrical starters. Air-turbine starters use compressed air from an external source as discussed earlier. Fuel is turned on either by moving the start lever to “idle/start" position or by opening a fuel shutoff valve. If an air turbine starter is used, the engine should “light off" within a predetermined time after the fuel is turned on. This time interval, if exceeded, indicates a malfunction has occurred and the start should be discontinued.

Most turbofan engine controls consist of a power lever, reversing levers, and start levers. Newer aircraft have replaced the start levers with a fuel switch. [Figure 11-18] Turbofan engines also use all the normal instruments speeds, (percent of total rpm) exhaust gas temperature, fuel flow, oil pressure, and temperature. An instrument that measures the amount of thrust being delivered is the engine pressure ratio. This measures the ratio between the inlet pressure to the outlet pressure of the turbine.

The following procedures are useful only as a general guide, and are included to show the sequence of events in starting a turbofan engine.

  • If the engine is so equipped, place the power lever in the “idle" position.
  • Turn the fuel boost pump(s) switch on.
  • A fuel inlet pressure indicator reading ensures fuel is being delivered to engine fuel pump inlet.
  • Turn engine starter switch on; note that the engine rotates to a preset limit; check for oil pressure.
  • Turn ignition switch on. (This is usually accomplished by moving the start lever toward the “on" position. A micro switch connected to the leveler turns on the ignition.)
  • Move the start lever to “idle" or “start" position; this will start fuel flow into the engine.
  • Engine start (light off) is indicated by a rise in exhaust gas temperature.
  • If a two spool engine, check rotation of fan or N1.
  • Check for proper oil pressure.
  • Turn engine starter switch off at proper speeds.
  • After engine stabilizes at idle, ensure that none of the engine limits are exceeded.

Newer aircraft will drop off the starter automatically.

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