- Models
- 47, 47B, 47B3, 47D, 47D1, 47E and 18 more
- Registered aircraft
- 490 matched by model
- Product
- Aircraft · Rotorcraft
Unofficial copy of the text in the FAA’s Dynamic Regulatory System. The FAA’s own copy is the authoritative one. DRS record last changed May 30, 2024.
Copies of the files this page was built from, with their SHA-256. Retrieved October 18, 2026.
| File | Size | SHA-256 | Original |
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| FAA DRS HTML | 21 KB | 348f0870…2df6f90 | FAA DRS (API key needed) |
On this page
The airworthiness directive
55-16-01 BELL: Applies to All Model 47 Helicopters With 47-641-025-1 or 47-641-057- 1 Tail Rotor Hubs, and All Spares.
Compliance required prior to next flight.
Recent serious accidents have been caused by failure of the tail rotor hubs P/N 47-641- 025-1 and 47-641-057-1. Imperfections such as corrosion, tool marks, scratches, and pitting in the fillet set up stress concentrations which cause failure of the hub spindle. Consequently, immediate and complete inspection of the fillet area of the tail rotor hub must be accomplished as follows:
1. Inspect the inboard fillet area on both spindles of the hub for accuracy of the radius using a 10-power magnifying glass. Fillets must have a true continuous radius all around the spindles and also must have a smooth machine finish free of corrosion and pitting. When inspected under a magnifying glass, tool marks appear greatly exaggerated, and by a smooth machine finish is meant having extremely fine, uniform, closely-spacedand uninterrupted tool marks. No copper plating is allowed in the fillet.
2. Hubs not meeting these requirements must be replaced.
(Bell Service Bulletin No. 96, Revision B dated July 15, 1955, covers this subject.)
(This covers the same inspection as the CAA telegram of July 13, 1955.)
Affected TCDS · 3
The type certificate data sheets for the models this AD names, matched by model and maker.
Registered aircraft · 490
Registered aircraft whose airframe or engine model this AD names. Matched by model only, so check each against the AD’s applicability.
| 1946 | 1 |
|---|---|
| 1947 | 10 |
| 1948 | 5 |
| 1949 | 3 |
| 1950 | 2 |
| 1951 | 7 |
| 1952 | 8 |
| 1953 | 8 |
| 1954 | 9 |
| 1955 | 7 |
| 1956 | 19 |
| 1957 | 18 |
| 1958 | 18 |
| 1959 | 10 |
| 1960 | 10 |
| 1961 | 9 |
| 1962 | 12 |
| 1963 | 20 |
| 1964 | 18 |
| 1965 | 20 |
| 1966 | 33 |
| 1967 | 28 |
| 1968 | 20 |
| 1969 | 12 |
| 1970 | 8 |
| 1971 | 12 |
| 1972 | 14 |
| 1973 | 10 |
| 1974 | 4 |
| 1975 | 2 |
| 1976 | 1 |
| 1979 | 1 |
| 1980 | 1 |
| 1981 | 1 |
| 2010 | 1 |
128 with no year recorded