Fuel Caps

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


Beech C90A King Air

Worn Right Fuel Cap

Crew noticed fuel leaking from right outboard wing fuel cap. Aircraft returned to departure airport and the fuel cap was replaced with a new cap. The aircraft has since flown multiple legs with no defects noted.

Part total time: Unknown

Beech 300 King Air

Obstructed Fuel Cap

Crew noticed fuel streaming from the right main fuel cap. Maintenance found fuel cap lanyard on top of flange.

Part total time: Unknown

Cessna 172 Skyhawk

Vented Fuel Cap Failure

Pilot made a precautionary landing due to a rough-running engine. Pilot checked fuel and heard a “wooshing” sound when opening the right fuel cap. Pilot thought he corrected a venting problem and took off. Aircraft lost power on climb-out. Investigation revealed plugged main fuel system vent line, plugged vent interconnect line at left tank and a restricted right tank vented fuel cap.

Part total time: 2500.0 hours

Diamond DA40

Broken Fuel Cap

During a 100-hour inspection of the fuel cap and fuel cell area, a piece of plastic was found in the fuel filling area. After inspecting the fuel cap, the piece of plastic was confirmed to come from the plastic part of the fuel cap.

Part total time: 993.0 hours

Diamond DA42NG

Internal Fuel Cap Failure

Wing fuel cap internal black plastic rib breaks off inside the lower fuel cap retainer assembly.

Part total time: 990.0 hours

Piper PA-31-350 Navajo Chieftain

Missing Fuel Cap

Left inboard fuel cap was missing and all fuel siphoned out of tank, causing left engine to fail. Auxiliary tank was selected and engine restarted. Located and examined the missing fuel cap; no defects were noted.

Part total time: Unknown

Van’s RV12 Experimental

Plugged Fuel Cap

Pilot reported rpm loss on takeoff roll and aborted attempt. Same behavior observed after carburetor overhaul. Pilot also reports he smells fuel eachtime he aborts a takeoff. While the airplane is sitting in the sun, the fuel system goes into auto-siphon at the tank vent. Opening the gas cap stops the siphoning.

The gas cap vent had been sealed. We removed the sealant and all issues went away. Manufacturer had changed vent systems and the hole was plugged to prevent rain water from entering fuel.

Part total time: 0.0 hours


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