Page:CAB Accident Report, United Airlines Flight 21.pdf/47

- 43 - of the accessory shaft and the impeller blades were scarred slightly. The rear case was cracked at one carburetor support stud.

The carburetors, fuel pumps, propeller governors, vacuum pumps, spark plugs, and ignition harnesses from both engines were forwarded to United's shop at Cheyenne, in the custody of an Air Safety Investigator, for examination and bench-testing. The ignition harnesses were badly crushed by impact and while there was some damage to other parts, tests made in the laboratories proved that the functional characteristics were satisfactory and indicated that the part were operating normally at the time of the crash. The two accessory drive shafts taken from the engines were forwarded to the National Bureau of Standards for examination. The report of the Bureau indicates that no metallurgical defect contributed to the failure of the shafts and that the fractures were caused by the sudden stoppage of the rotation of the shafts.

The condition of the parts of both engines was strikingly similar, from which it may be concluded that both engines were operating in the same manner at the instant of impact. However, it is not possible to determine from the condition of the engines whether they were operating under power at the time of impact, as the windmilling of the propellers would have been sufficient to cause the observed amount of damage.

Propellers

The plane struck with the propeller shafts approximately vertical. Disassembly and inspections of the propellers showed the done assemblies, the spider assemblies, and the barrel assemblies to be in good condition.