Included in this page are typical guidelines for locating engine malfunctions on most turbine engines. Since it would be impractical to list all the malfunctions that could occur, only the most common malfunctions are covered. A thorough knowledge of the engine systems, applied with logical reasoning, solves most problems that may occur.
Troubleshooting Turbojet Engines
Table enumerates some malfunctions that may be encountered. Possible causes and suggested actions are given in the adjacent columns. The malfunctions presented herein are solely for the purpose of illustration and should not be construed to have general application. For exact information about a specific engine model, consult the applicable manufacturer’s instructions.
| Indicated Malfunction | Probable Causes | Suggested Action |
|---|---|---|
| Engine has low rpm, exhaust gas temperature, and fuel flow when set to expected engine pressure ratio. | • Engine pressure ratio indication has high reading error. | • Check inlet pressure line from probe to transmitter for leaks. |
| • Check engine pressure ratio transmitter and indicator for accuracy. | ||
| Engine has high rpm, exhaust gas temperature, and fuel flow when set to expect engine pressure ration. | • Engine pressure ratio indication has low reading error due to: | |
| - Misaligned or cracked turbine discharge probe. | • Check probe condition. | |
| - Leak in turbine discharge pressure line from probe to transmitter. | • Pressure-test turbine discharge pressure line for leaks. | |
| - Inaccurate engine pressure ratio transmitter or indicator. - Carbon particles collected in turbine discharge pressure line or restrictor orifices. | • Check engine pressure ratio transmitter and indicator for accuracy. | |
| Engine has high exhaust gas temperature, low rpm, and high fuel flow at all engine pressure ratio settings. | • Possible turbine damage and/or loss of turbine efficiency. | • Confirm indication of turbine damage by: - Checking engine coast-down for abnormal noise and reduced time. - Visually inspect turbine area with strong light. |
| NOTE: Engines with damage in turbine section may have tendency to hang up during starting. | • If only exhaust gas temperature is high, other parameters normal, the problem may be thermocouple leads or instrument. | • Re-calibrate exhaust gas temperature instrumentation. |
| Engine vibrates throughout rpm range, but indicated amplitude reduces as rpm is reduced. | • Turbine damage. | • Check turbine as outlined in preceding item. |
| Engine vibrates at high rpm and fuel flow when compared to constant engine pressure ratio. | • Damage in compressor section. | • Check compressor section for damage. |
| Engine vibrates throughout rpm range, but is more pronounced in cruise or idle rpm range. | • Engine-mounted accessory such as constant-speed drive, generator, hydraulic pump, etc. | • Check each component in turn. |
| No change in power setting parameters, but oil temperature high. | • Engine main bearings. | • Check scavenge oil filters and magnetic plugs. |
| Engine has higher than normal exhaust gas temperature during takeoff, climb, and cruise. Rpm and fuel flow higher than normal. | • Engine bleed-air valve malfunction | • Check operation of bleed valve. |
| • Turbine discharge pressure probe or line to transmitter leaking. | • Check condition of probe and pressure line to transmitter. | |
| Engine has high exhaust gas temperature at target engine pressure ratio for takeoff. | • Engine out of trim. | • Check engine with jetcal. Re-trim as desired. |
| Engine rumbles during starting and at low power cruise conditions. | • Pressurizing and drain valve malfunction. | • Replace pressurizing and drain valves. |
| • Cracked air duct. | • Repair or replace duct. | |
| • Fuel control malfunction. | • Replace fuel control. | |
| Engine rpm hangs up during starting. | • Subzero ambient temperatures. | • If hang-up is due to low ambient temperature, engine usually can be started by turning on fuel booster pump or by positioning start lever to run earlier in the starting cycle. |
| • Compressor section damage. | • Check compressor for damage. | |
| • Turbine section damage. | • Inspect turbine for damage. | |
| High oil temperature. | • Scavenge pump failure. | • Check lubricating system and scavenge pumps. |
| • Fuel heater malfunction. | • Replace fuel heater. | |
| High oil consumption. | • Scavenge pump failure. | • Check scavenge pumps. |
| • High sump pressure. | • Check sump pressure as outlined in manufacturer’s maintenance manual. | |
| • Gearbox seal leakage. | • Check gearbox seal by pressurizing overboard vent. | |
| Overboard oil loss. | • Can be caused by high airflow through the tank, foaming oil, or unusual amounts of oil returned to the tank through the vent system. | • Check oil for foaming. • Vacuum-check sumps. • Check scavenge pumps. |
Troubleshooting turbojet engines
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