Heating And Cooling

The following information is derived from the FAAs Service Difficulty Reports and Aviation Maintenance Alerts.


Diamond DA40F

Failed Carburetor Heat Control Arm

A mechanic found the same problem on two identical aircraft:, “The carburetor heat control arm (p/n: D4F-7326-12-00-1) broke off the carburetor air box, causing uncontrolled selection of carburetor heat versus ram (cold) air intake.” The


mechanic recommends installing thicker material on the carburetor heat control arm lever, or a different welding/heat treating process, or a different attachment provision altogether.

Part Total Times: 12.7 and 30.9 hours.

Diamond DA40F

Failed Electrical Fuel Pump

Before the next students flight, the electric fuel pump (Dukes p/n 5100-00-20 installed on a Lycoming O360A4M) was found inoperative. Inadequate cooling is believed to be the source of the malfunction. The submitter suggests providing ram air for proper cooling of the fuel pump and motor.

Nine pumps installed on four identical aircraft were discovered failed. Time in service ranged from 102.3 hours to 593.2 hours and averaged 317.2 hours since overhaul.

Part Total Time: Various.

Mooney M20D

Inaccurate Fuel Gauge

This aircrafts fuel gauge indication is approximately 2.5-3.0 gallons higher than what is in the tank. (Left fuel gauge p/n: 5643860; left fuel tank transmitter p/n: 5642354)

Part Total Time: 5103.7 hours.

Lycoming TIO-540-AJ1A

Loose Exhaust Stacks

During a 100-hour inspection, the #2 cylinders exhaust stack was found pulled down approximately 1/16 inch. Further investigation found the number 1, 3, 5 and 6 engine cylinder exhaust stacks also pulled down, but not as much. When the cylinder was removed, the lower forward, -inch stud nut was found undertorqued and the forward two studs were below recommended torque. New, oversized studs (0.003″) were installed per Lycomings recommendations.

After installing a new #2 cylinder and new exhaust crossover pipe, tightening the exhaust flange nuts does not stop exhaust leakage on all studs; on some, the nut bottoms out on the threads. After tightening, the previously affected exhaust flange areas have come loose again after 50 hours time in service. Exhaust assembly p/n: 40B222318.

Part Total Time: 98.1 hours.

Sensenich S76EM And S74DM Propellers

Cracked Spinner Assemblies

Several forward spinner bulkheads were found cracked through the mount bolt holes. Affected were four Maule MXT-7-180 airplanes powered by a Lycoming O-360-C4F, and one Maule MXT-7-160 with a Lycoming O-320-B2D.

Part Total Times: 225.0 (avg.; S76) and 3600.0 hours (avg., S74).


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