When close-in on a straight-in approach to runway 14, the pilot requested a 360 degree turn to lose altitude. During this turn the right wing struck the surface and was torn off. The aircraft slid along the ground on its right side, struck a rock outcrop, and came to rest 350 ft from the point of initial impact. Examination of the fuel system revealed that the fuel supply for the right engine was not transferring automatically to the no.4 cell which feeds the engine, but was spreading out by gravity to the other cells. This would be aggravated in a descent, and it is likely that the right engine flamed out during the turn due to fuel starvation. The flapper valves in no.4 and 5 tanks were not of the approved type and were not installed properly. The fuel injector nozzle in the fuel transfer system for the right engine was plugged due to the coarse mesh fuel strainers which allowed foreign particles to penetrate.