Piper PA-39 Twin Comanche C/R — Maintenance Manual

This Service Letter No. 851 from Piper Aircraft Co. addresses critical maintenance procedures for the PA-39 Twin Comanche C/R and other models. It consists of three parts, each focusing on different aspects of fuel system maintenance. The document emphasizes the importance of checking for fuel valve leaks and draining water contamination from fuel tanks to ensure safe operation. It is intended for aircraft owners and maintenance personnel, providing detailed instructions and compliance recommendations to maintain the aircraft's fuel system in optimal condition. The letter highlights the need for regular inspections and preventive measures to avoid potential engine issues due to fuel mismanagement or contamination.

• Perform fuel valve leak checks at least every 50 hours of operation.
• If fuel collected during the leak check exceeds 1/2 fluid ounce, the fuel valve may need cleaning or replacement.
• Drain fuel tanks before flight if water contamination is suspected, especially after freezing temperatures.
• Each fuel cell should be drained for 10-12 seconds to check for water contamination.
• Inspect fuel caps and drain tubes regularly to prevent water accumulation.