The airplane incurred substantial damage at about 0915 Eastern time during a right engine start. The pilot was not injured. Visual conditions prevailed. After both wings were filled with fuel to capacity, the flight departed. At approximately 700 feet agl, the right-wing fuel cap released from its opening but remained attached by a chain. Fuel was observed coming from the opening. The pilot returned and landed, then taxied to the ramp. The pilot shut down both engines, then secured the right fuel cap and visually observed the upper and lower wing had no sign of fuel spillage. The pilot then returned to the cockpit and completed a normal left-engine start. At the initial right engine start, a loud bang and whoosh sound was heard. The pilot continued cranking the engine and completed the ” Emergency Procedure Checklist” for engine fire during start. The lineman stated about 5 to 10 minutes elapsed between the time the engines were shut down on returning to the ramp and the fire. As soon as the right engine started the fireball was seen. The pilot continued cranking the engine until the flame was gone. An initial examination of the right wing revealed the blast was internal, causing the upper wing skin to expand and separate from retaining rivets.
