ERA10LA357

The airplane had just been fueled by the lineman at the fixed-base operator (FBO), who secured the fuel caps after the service. During the climb after takeoff, the right-wing fuel cap came off of the wing, remaining attached only by the chain. An estimated 11 gallons of fuel was siphoned from the wing before the pilot returned to the airport and taxied back to the FBO. The pilot secured the cap and conducted a visual inspection of the right wing, before attempting to start the engine again. The right engine backfired, followed by a loud bang and whoosh sound; flames then rose from the right wing. A postaccident examination of the right wing revealed that the internal blast was a result of the backfire igniting fuel vapors that remained after the siphoning. The blast caused the upper wing skin to expand and separate from the retaining rivets. A soot trail originated at the exhaust pipes and traveled in an aft direction to the trailing edge of the wing. Examination of the fuel cap revealed that the outer o-ring was dry and cracked, a washer was missing, the cap leaked under pressure, and that the force required to secure the cap exceeded the manufacturer’s specification. The airplane’s maintenance records did not indicate the last time the fuel cap was overhauled. Fuel cap maintenance is permissible by a Federal Aviation Administration (FAA) certified airframe mechanic or by an FAA-approved overhaul facility. While the cap’s manufacturer has standards on the required forces to secure the fuel cap lock tab and a leak testing process, the airplane’s maintenance manual does not mention either. As a result of separate investigations, the airplane’s manufacturer has included in applicable airplanes’ maintenance manuals the following verbiage: “Note: Inspect the fuel filler cap outer o-ring for flexibility, splits cracks or distortion. If the o-ring is damaged in any way replace or overhaul the fuel cap.”

On July 11, 2010, at about 0915 eastern daylight time, a Beechcraft, BE-58, N405RW, owned and operated by private individuals, sustained substantial damage during a right engine start at the LaGrange-Callaway Airport (LGC), Lagrange, Georgia. The pilot was not injured. Visual meteorological conditions prevailed for the Title 14 Code of Federal Regulations Part 91, personal flight. The pilot stated that the lineman filled both wings to full capacity and secured both fuel caps. His preflight visually showed both caps in place. Following the takeoff from runway 31, at approximately 700 feet above the ground, the fuel cap on the right wing released from the opening and remained attached to the airplane by the retaining chain. Fuel was observed coming from the opening. The pilot initiated a return to LGC. With no traffic and no wind at the time, he landed on runway 13 and returned to the ramp. At the ramp, both engines were shut down as he met the lineman. He exited the airplane, secured the right fuel cap and visually observed that the upper and lower wing had no sign of fuel spillage. The lineman stated he observed the pilot re-secured the fuel cap on the right wing after his return and declined a top off of the right wing fuel tank. About 10 minutes from the time the airplane returned, the pilot boarded the aircraft and started the left engine then proceeded to start the right engine. The engine backfired on startup and a loud bang and whoosh sound was heard; flames rose from the right wing. The pilot continued cranking the engine and completed the emergency procedure for an engine fire during start. The propeller wash extinguished the flames quickly except for a small flame at the aileron linkage area, which the lineman extinguished with a fire extinguisher. The pilot shut down the engines and exited the aircraft. The airplane was examined by a Federal Aviation Administration (FAA) inspector and a representative from the airplane’s manufacturer. An estimated 11 gallons of fuel vented from the wing filler neck during the air turn back. Examination of the right wing revealed the blast was internal causing the upper wing skin to expand and separate from the retaining rivets. A soot trail originated at the exhaust pipes and traveled in an aft direction to the trailing edge of the wing. The wing exhibited upper and lower skin panel bulging and upper skin panel wrinkling. The majority of the damage was centered in the area around the aileron bell crank box structure. Several rivets separated and damaged the wing rib area. The aileron exhibited a bulged out area with soot near the outboard aileron hinge. The airplane’s fuel boost pumps were operated and no leaks were noted at the time. The left fuel cap was removed and it appeared to work properly. The right fuel cap was removed and it did not operate properly The locking tab could be lowered without the fuel cap being attached to the filler opening. The lanyard retaining clip was installed backwards.In addition the wing examination revealed that the right wing navigational light power wire was rubbing on a lightning hole and the landing light wires were chafing on the edge of a lighting hole. The right wing fuel vent lines were not secured with a clamp. Three inspection panels were observed with small amounts of fuel residue on the outside of the panels. The right wing’s fuel cap was tested and examined at a FAA certified overhaul facility with National Transportation Safety Board oversight. The outer o-ring was dry and cracked. The fuel cap leaked under pressure and exceeded the cap’s manufacture’s specification for the force required to close and secure the right fuel cap lock tab. The force to release (unlock) the fuel cap tab was below the cap’s manufacture’s specification. When the right fuel cap was disassembled a washer was missing. The fuel cap was reassembled with all the required parts and properly adjusted. The cap’s manufacturer specified forces to secure and unlock the tab were obtained at reexamination and the fuel cap did not leak during the second pressure test. The 1978 Beechcraft Baron 58 last annual inspection, reported by the pilot, was on July 7, 2009, the airplane had a total time of 3,139 hours. A review of the airplane’s maintenance records by the FAA did not reveal the last time the right fuel cap underwent maintenance or was overhauled. The fuel cap maintenance can be accomplished by a FAA certified airframe mechanic or by a FAA approved overhaul facility. The investigation discovered that the airplane manufacturers maintenance manual does not provide the forces required to open and close for the accident part number fuel cap. The cap’s manufacturer calls for specific required forces to open and close the fuel cap lock tab during the overhaul process. In addition, the overhaul process requires a pressure leak check on the cap; the airplane’s manufacturer maintenance manual does not. The airplane’s manufacturer and the fuel cap manufacturer have recognized that the fuel cap replacement is treated as an on condition basis, though no specific condition is typically given. As a result of separate investigations, the airplane manufacturer believes it is appropriate to add instructions for the fuel cap to be overhauled or replace on the condition of outer o-ring needing to be replaced. The airplane manufacturer has included, to applicable airplane’s maintenance manuals the following verbiage: “Note: Inspect the fuel filler cap outer o-ring for flexibility, splits cracks or distortion. If the o-ring is damaged in any way replace or overhaul the fuel cap”. The airplane’s manufacturer published a Safety Communiqué, No 298, dated October 2008, advising the operators and maintenance personnel of the importance for proper interior wing inspection of those areas of concern such as those found during the wing examination. On December 2010, the airplane’s manufacturer issued Safety Communiqué, N.298 - Revision 1, addingadditional areas of concerns discovered during this investigation. The FAA published Special Airworthiness Information Bulletin (SAIB) CE-11-28, dated April 8, 2011, addressing the areas of concern as noted in the mentioned Safety Communiqués.