Page:CAB Accident Report, Standard Airways Flight 388C.pdf/4

 4. The spark plugs in engines Nos. 3 and 4 were of a type not approved for use in the TC18DA series engines.

5. The timing ring lock nut of the left distributor of the No. 4 engine was not safetied.

6. The retaining nut of the No. 2 PRT on the No. 4 engine was not safetied.

Examination of the Curtiss Electric Propeller assemblies revealed extensive impact damage generally concentrated on the blades and slip ring assemblies. Other than the No. 3 propeller assembly, the remaining propellers showed no evidence of operating failure prior to impact. Propeller power unit settings indicated blade angles at impact at 27 degrees for propellers Nos. 1, 2, and 4. The No. 3 propeller was at a blade angle of plus one-degree; in the reverse pitch range. The specified low blade angle setting is 23.7 degrees.

Detailed examination of the No. 3 propeller power unit (S/N 165047, S/N 11819. S/N A-119) revealed the threaded brake cage of the pitch change motor was unscrewed three threads and that the two cage lock safety bolts were missing. The armature of the pitch change motor was free to rotate. A brake clearance measurement indicated the brake clearance to be .052 inches. Normal specified clearances; inspect .008 to .018, reset .008 to .012. Two of the brake cage locking bolt slots were worn excessively, with the wear pattern extending into the cage retaining threads. These worn areas were 5/16 and 21/64 of an inch in length and were diametrically opposed. The lower cage shoulder showed indication of wear by the locking bolts over a surface dimension of 13/32 and 17/32 of an inch. The outer diameter of the splined disc duplex brake plate assembly contained two areas of heavy battering. Two of the brake cage window struts showed indication of heavy battering in the unscrewed direction in the area above the normal position for the brake cage wrench. The brake facing was in place and its measured thickness was .214 to .216; (specified thickness .169 to .259). The power unit motor was energized and speed reducer operation was obtained. The limit switches functioned normally.

Inspection of the Nos. 1, 2, and 4 propeller power units revealed no evidence of operating distress prior to impact.

The last overhaul, subsequent inspection, and maintenance records pertaining to propeller power unit S/N 165047 were examined. It was determined that the last overhaul of this unit was accomplished on July 6, 1962, at which time a zero time since