General Aviation Modifications Inc. (GAMI) has traced the source of a stain on the underside of the AOPA Beech Baron fuel test bed aircraft to a leaky patch in a 50-year-old bladder in the tank. According to a report prepared by GAMI, mechanics who removed all four bladders from the Baron discovered the leak in an old patch on the aged bladder that had been used to hold G100UL for the past nine months.
Fuel settled between the leaking bladder and “chafe tape” applied to protect the bladder from wearing against the metal inside the wing. The fuel dissolved the glue on the tape, creating a sticky residue that appeared on the underside of the wing while the plane was displayed at AirVenture. The right tank contains 100LL, and AOPA is collecting comparison data on both fuels under real-world conditions.
GAMI stated that such fuel bladder leaks are relatively common in Beech Bonanzas and Barons operating on 100LL. A pilot at GAMI’s booth at Oshkosh reported experiencing leaks in his Bonanza three times over three years.
The appearance of the stain at Oshkosh sparked significant online discussion about its nature and impact. GAMI’s report noted minor leaks from both tanks, which are decades old, but emphasized that none were related to its fuel or any other fuel damaging the bladder material. G100UL underwent exhaustive testing under FAA supervision for compatibility with bladder material during its STC process without issues.
AOPA left the Baron in Oshkosh after AirVenture for technicians to determine the leak’s source. The plane is now in Virginia and will receive new fuel tanks, which was initially planned before testing began but was deferred due to parts unavailability.
