BELL 47 TAIL ROTOR INFORMATION

FROM BHT

1. The Bell 47 was originally certified with wood tail rotor blades, and for the sake of this discussion these blades are not considered.
2. The first metal tail rotor hub and blade assembly used was the 47-641-058, which included blade 47-641-102 of various dash numbers.  Ordered as a blade set, the pair of blades was most recently identified as the 47-641-102-55 blade set.  This blade can be identified by a single bolt hole in the pitch horn portion of the blade root.  This set of blades installed on the hub assembly 47-641-058 which can be identified by the single 5/16 in. Delta Hinge bolt passing through the hub and tail rotor mast.  This is probably known colloquially as the early version metal blade configuration.
3. The second iteration of the metal tail rotor blade was the 47-642-102 also of various dash numbers, which installed on hub 47-641-104.  This hub can be identified by the existence of a pivoting trunnion that attached to the mast by means of a splined joint.  Ordered as a blade set, the latest part number was 47-642-102-77 blade set.  This blade is similar in appearance and profile to the above blade, but can be differentiated by the two bolt holes on the pitch horn portion of the blade root.  Together the combination resulted in hub and blade assembly 47-641-059, this combination is probably known as the intermediate tail rotor hub and blade assembly.
4. Service Bulletin 47-76-2 introduced the “206 style tail rotor hub and blade assembly 47-641-170,  consisting of blade 47-642-117 and hub assembly 47-641-170 both quite similar in appearance to the 206 style.  This installation is known to Bell as the improved tail rotor assembly and is probably known colloquially as the latest version tail rotor blade.  This is the only current spare configuration, and the only version approved by Bell for continued operation on any FAA certified Bell 47.

Operators who choose to continue in operation with the early version blades are accepting significant risk and have no course of litigation available resulting from any superceded tail rotor blade.  Another risk is that previously reported flight time may be fraudulent since only the improved tail rotor blade has been supplied by Bell since March 1976.  Additionally FAA AD 80-10-04 requires the removal from service of all 47-641-102 blades that are installed on a Lycoming engine-powered Bell 47.