49-52-02 BELL: Applies to All Models 47B, 47B3, 47D, and 47D1 Series Helicopters.
Compliance required as indicated.
As a result of recent accidents, the following precautionary measures should be taken:
1. The main rotor hub (Bell P/N 47-120-136-1) must be replaced if it has been involved in an accident or sudden stoppage, for any reason, in which the following has occurred:
(a) One or both main rotor blades were damaged to the extent that the steel core shows through the wood at any point.
(b) A drag brace end fitting or the equalizer horn, or both, are damaged or distorted.
(Bell Service Bulletin No. 65, dated August 2, 1949, covers the subject of this portion of the directive.)
2. All aluminum main rotor hubs (Bell P/N 47-120-136-1) must be replaced after 600 hours of operation unless it is necessary to replace them sooner as a result of being affected by the requirements of paragraph 1. In order to assist those operators who possess a part which has over 600 hours accumulated at the time of receipt of this directive, the following latitude in replacing the parts is permitted:
Accumulated Time on Hub at Time of this Directive
Replacement Limit
0-500 hours
At 600 hours
501-800
Within the next 100 hours
801-899
At 900 hours
900 and up
Before the next flight
Hubs with less than 300 hours must be inspected visually (with a 10- to 20-power glass) at 300 hours, in addition to the inspections required by the manufacturers "Erection and Maintenance Manual" for the particular model. During this inspection, specific attention must be directed toward locating fatigue cracks in the shotpeened fillet radius, particularly on the leading edge side. The discovery of cracks in any portion of this radius is cause for immediate replacement of the part. In addition to the execution of the Form FAA 1226, "Malfunctioning and Defects Report," such a discovery should be reported immediately to the Bell Aircraft Corp., together with the number of hours accumulated on the hub, the serial number of the hub, model and serial number of the helicopter on which it was installed, and a statement to indicate whether or not the part had been involved in an accident such as described in paragraph 1.
This supersedes AD 49-35-02.