- 8 -
been maintained, failure of the propeller as subsequently happened would not have occurred.
Blade retention failure of the windmilling No. 4 propeller occurred when the aircraft was at approximately 9,000 feet altitude and at nearly the maximum permitted airspeed. According to information from the propeller manufacturer, based on the calculated blade retention strength and tests of the propeller, failure of this nature would be expected under approximately these circumstances. There were no indications of faulty material or workmanship.
Failure to obtain power from the No. 3 engine and the subsequent fire warning after leveling off at the lower altitude were the direct result of damage inflicted by the No. 2 blade of the No. 4 propeller when it became detached.
Findings
On the basis of all available evidence the Board finds that:
1. The aircraft and both pilots were properly certificated for the flight involved.
2. The aircraft was loaded within allowable limits as to the amount and distribution of weight.
3. Weather was not a factor in this accident.
4. The driven bevel gear bushing of the bevel box drive turned and became displaced.
5. The driven bevel gear of the bevel box drive then failed from fatigue,
