55-16-01: Tail Rotor Hub Fillet
FAA order 55-16-01 is an airworthiness directive. The FAA's subject line: Tail Rotor Hub Fillet. It names Bell 47: about 478 aircraft on the U.S. register today, though an order usually covers particular versions or serial numbers rather than every one. System: rotorcraft systems.
What it applies to as the FAA lists it
- Kind of product
- Aircraft
- Makes
- Scotts-Bell 47 Inc
- Models
- 47, 47B, 47B3, 47D, 47D1, 47E, 47G, 47G-2, 47G-2A, 47G-2A-1, 47G-3, 47G-3B, 47G-3B-1, 47G-3B-2, 47G-3B-2A, 47G-4, 47G-4A, 47G-5, 47G-5A, 47H-1, 47J, 47J-2, 47J-2A, 47K
- On this site
- Bell 47 478 registered
Dates and paperwork
- Docket
- Unknown
- Status
- Current
- The FAA's document
- Read the order on the FAA's site
The order itself the regulatory text, as published
Show the full text (1,289 characters)
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.)
Related safety bulletins advice on the same designs, not orders
2001-02-09SW-01-13 ·
Source: FAA Dynamic Regulatory System, airworthiness directives. The FAA's document is the authority; the register counts are this site's, from the FAA register of November 6, 2026. Connections as data: /graph/directive/55-16-01.json · aircraft systems.