Pressure Switches

The following information is derived from the FAA's Service Difficulty Reports and Aviation Maintenance Alerts.


Cessna 172R Skyhawk

Broken Oil Pressure Switch

During a private pilot checkride, the examiner noticed oil specks on the windshield and diverted for a precautionary landing. The dipstick indicated zero oil. Examination revealed the oil pressure switch had broken and three quarts of oil remained. An airworthiness directive requires switch replacement by 3000 hours. This failure occurred earlier than that.

Part total time: 2172.5 hours

Cessna 172S Skyhawk SP

Low Oil Pressure

Oil pressure switch failure caused erroneous low oil pressure annunciation and inoperative Hobbs meter. Replacing the switch with one from a different lot number resolved the problems.

Part total time: 66.0 hours

Cessna 337G Skymaster

Faulty Hydraulic Pressure Switch

After takeoff, the right main landing gear leg would not retract. The electric pump shut off, but did not pop the circuit breaker. The landing gear was extended using the emergency hand pump, followed by a safe landing. Examination revealed the hydraulic pressure switch would turn off the pump early. This overhauled switch was installed 20 hours previous.

Part total time: 20.0 hours

Beech B200CGT King Air

Fuel Pressure Switch

During preflight inspection, the copilot found the right fuel pressure CAS message would not extinguish. Troubleshooting revealed that the right fuel pressure switch was the issue. It was replaced with a new one and the aircraft was returned to service.

Part total time: 1409.0 hours

Beech B300 King Air

Failed Autofeather System

During the takeoff roll, the left autofeather armed annunciator failed to illuminate. Takeoff was aborted below 80 knots. The right high pressure switch was replaced and a successful check flight was performed.

Part total time: 2223.0 hours

Diamond DA40 Star

Leaking Hobbs Switch

Pressure switch controlling the Hobbs meter failed, allowing oil to flow out of the engine. The problem was found during a preflight inspection. Estimate that the aircraft would have lost a quart of oil an hour or more.

Part total time: 1201.0 hours

Pilatus PC-12/47E

Cycling fuel pumps

In cruise, both fuel pumps were cycling on and off at five-second intervals. Checklist actions had no effect. An unscheduled landing was safely made. The fuel system low pressure switch was removed and replaced. Leak and ops checks were satisfactory.

Part total time: 1749.0 hours


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