Winter is here and experience tells us that colder temperatures can cause problematic fuel control P3 drain leaks. Fuel control changes account for a large percentage of flight delays or cancellations on TFE731-powered aircraft. Most of the FCUs removed for fuel leakage through the P3 drain have revealed wear of the PLA shaft o-ring seals inside the FCU. Colder temperatures will contribute to the PLA shaft o-rings becoming hard and brittle and not sealing properly. Honeywell is aware of this problem and is working to redesign the PLA shaft to improve sealing and prevent leakage.
To avoid unnecessary flight cancellations, follow the fuel leakage limits found in the Engine Light Maintenance Manual (LMM).
The probability for FCU replacement is probably unavoidable but might be deferred to a more suitable timeframe if leakage limits aren’t exceeded.