Limits and Abnormal Operations
Limits and Abnormal Operations tests the numbers and the decisions: what is continuous, what is transient, what requires a shutdown, and what must be recorded. Limits exist to protect turbine blades, casings and transmission components.
Core rules
- Limits are usually given for takeoff, maximum continuous, transient and starting, and differ by duration.
- TGT or EGT, torque, N1, N2, oil pressure, oil temperature and gas generator speed all have limits.
- Exceedances must be recorded with peak value and duration, then assessed against the maintenance manual.
- Abnormal conditions include hot start, hung start, surge, flameout, high vibration, chip warning and loss of oil pressure.
- A flameout may be followed by a relight attempt within the approved envelope; do not unload the rotor excessively.
- Transmission limits include torque, oil temperature and pressure, and freewheel or main gearbox abnormalities.
Worked example
The takeoff TGT limit is 850°C for 5 minutes. A recorder shows 870°C for 8 seconds during a rejected takeoff. This is an exceedance, but it is short and within a transient allowance only if the maintenance manual says so. Record 870°C and 8 s, notify maintenance, and complete the required inspection. Do not simply reset the recorder or continue as if nothing happened.
Traps
- Treating a transient limit as continuous.
- Using the wrong limit for the phase of flight.
- Not recording duration, only peak value.
- Continuing after a chip warning or low oil pressure.
- Assuming a relight is always permitted.