Fuel Tank Leaks
Fuel Tank Leaks: 
On the AA-1x series there are only 4 possible leak points from the wing spar tanks. Each end of the spar tube has a machined aluminum plug with an O-ring in a groove around the outside of the plug. The outboard plug is secured in place with 4 AN3 bolts which have special washers known as “Stat-o-seals”. The inboard plug is secured in place with either 1 or 2 AN3 bolts, depending on the year model. The same Stat-o-seals are used on the bolts at the inboard end. Deterioration of the O-rings or the rubber covered Stat-o-seals can result in leaks. At the inboard end of the spar tank a block of aluminum is bonded on the bottom of the spar and a hole through the spar and the bonded block allow for draining the sump. A short section of 1/4” rubber hose leads from the bonded block to a cast fitting and the drain valve. This hose can fail and leak the entire contents of the tank.
On the AA-5x series there are 4 access panels on the bottom of each wing that are sealed with a special “low adhesion” sealant. There has been an AD on the sealant used by the factory, and it is normal to require periodic re-sealing of the access covers. The wing ribs have a hole that is slightly larger than the wing spar tube. This leaves a gap of 1/16”-3/32” between the rib and the spar tube that the factory filled with a fillet of sealant. After 30+ years that fillet of sealant may leak as the wing flexes and stretches the sealant. The perimeter of the tank along all the bonded joints has been know to leak in the event of an incomplete bonded section or in the case of the purple glue on the late 74 through early 76 models, at areas of debonding. The fuel level sender on the inboard rib of the tank has a rubber gasket that deteriorates with age and can leak. The tank vent tube comes out both ends of the tank and can leak at the inboard end where some models have a section of rubber hose that connects to the next length of aluminum tubing. The AA-5x series can have tank leaks at the access covers, around the inboard and outboard spar to rib joint, at the fuel level sender gasket, the fuel pickup fittings and at bonded joints that are incomplete or failing. Its no wonder that the AA-5x have many more fuel leak problems than the AA-1x.
