AOPA Baron Wing Stain Traced To Leaking Bladder Patch

General Aviation Modifications Inc. (GAMI) says the gunk that smeared the underside of the left wing of the AOPA Beech Baron fuel test bed aircraft at AirVenture originated with a leaky patch in the 50-year-old bladder in the tank. In a report prepared by GAMI, the company said the mechanics who removed all four bladders from the Baron found the leak in an old patch on the ancient bladder that has been used to hold G100UL for the past nine months. Fuel then settled between the leaking bladder and "chafe tape" that is applied to the inside metal of the wing to protect the bladder from wearing against the metal. The fuel dissolved the glue on the tape and it became the sticky residue that dramatically appeared on the underside of the wing while the plane was on display at the show. There is 100LL in the right tank and AOPA is gathering comparison data on the use of the fuels in real-world conditions.

GAMI also stated that these types of fuel bladder leaks are relatively common in Beech Bonanzas and Barons operating on 100LL. The company said a pilot at GAMI’s booth at Oshkosh reported he had leaks in his Bonanza three times in three years.

The appearance of the stain on the underside of the wing at Oshkosh sparked intense online dialogue about the nature and impact of the apparent leak. In the report, GAMI noted there had also been minor leaks from the 100LL tank (which is 46 years old) and there was also evidence of leakage of 100LL from the left tank from before the side-by-side test. But GAMI said none of the leaks were related to its fuel or any other fuel eating the bladder material. It said G100UL was exhaustively tested, under FAA supervision, for compatibility with the bladder material during the STC process with no issues. AOPA left the Baron in Oshkosh after the show to have technicians determine the source of the leak. GAMI says the plane is now in Virginia and will get new fuel tanks, which was supposed to happen before the fuel test began but was deferred because the parts weren't available.