After replacing the fuel control unit on an aircraft gas turbine engine, what must be done?

After replacing the fuel control unit on an aircraft gas turbine engine, what must be done?

• A. Check for leaks
• B. Retrim the engine
• C. Recalibrate fuel control
• D. Inspect combustion chamber

Answer: (B)

Replacing the fuel control unit changes the fuel metering characteristics, so the engine must be re-trimmed to align the fuel schedule with the new unit. Retrimming adjusts the fuel flow versus throttle demand so that the engine’s speed (N1 or N2) and performance points at idle, takeoff, and other operating conditions match the intended settings. This ensures stable, predictable response and prevents abnormal operation due to a mismatch between the new unit and the engine’s fuel schedule. While routine checks like leaks or chamber inspections are still important, they don’t correct the altered metering curve introduced by a new FCU, and recalibration of the fuel control may be included as part of the process, but retrimming is the essential step to restore proper operation.

Replacing the fuel control unit changes the fuel metering characteristics, so the engine must be re-trimmed to align the fuel schedule with the new unit. Retrimming adjusts the fuel flow versus throttle demand so that the engine’s speed (N1 or N2) and performance points at idle, takeoff, and other operating conditions match the intended settings. This ensures stable, predictable response and prevents abnormal operation due to a mismatch between the new unit and the engine’s fuel schedule. While routine checks like leaks or chamber inspections are still important, they don’t correct the altered metering curve introduced by a new FCU, and recalibration of the fuel control may be included as part of the process, but retrimming is the essential step to restore proper operation.