Case Description
During climb at approximately 20,000 feet, the flight crew reported power fluctuations on engine No.4.
The following parameters were observed:
RPM stable at 100%
Torque fluctuating ±5%
TIT fluctuating unexpectedly
Throttle movement had minimal effect on stabilizing engine power.
The TEMP DATUM Control Valve switch was set to AUTO.
Troubleshooting Investigation
Inspection of the temperature datum system showed unstable electrical signals from the thermocouple harness measuring turbine inlet temperature.
The fluctuating signal caused the temperature datum system to continuously adjust fuel flow.
Root Cause
Faulty thermocouple signal input to the Temperature Datum System caused unstable fuel correction commands.
Corrective Action
The thermocouple harness was replaced and the temperature datum system was recalibrated.
After corrective maintenance:
TIT stabilized
Engine power fluctuations disappeared
Lessons Learned
Accurate temperature signals are critical for proper operation of the Temperature Datum System. Faulty Thermocouples can lead to unstable fuel correction and engine performance fluctuations.