Regulatory and Certification Policy
FAA issues final Bell 47 AD
On August 29, 2001, the FAA issued final AD 2001-17-17. The AD, intended to detect and correct cracks in Bell 47 main rotor blade grips, requires eddy current inspections at 300 hour intervals and places a service life of 1,200 hours on blade grips.
The importance to our members:
The AD affects more than 1,000 Bell 47 helicopters on the U.S. registry. Owners and operators of Bell 47s continue to voice serious concerns regarding repetitive inspection intervals, TIS limitations, and the availability of replacement parts.
- In August 2000, the FAA issued AD 2001-17-17 on Bell 47 main rotor grips. The emergency AD required repetitive inspection of main rotor blade grips for cracks and mandates retirement of blade grips with more than 1,200 hours time in service (TIS).
- The FAA cites accidents in Australia and Canada as primary cause for AD action.
- The following aircraft models are affected: Bell Helicopter Textron Model 47B, 47B-3, 47D, 47D-1, 47G, 47G-2, 47G2A, 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, and 47K
- The AD requires penetrant or eddy current inspections of the main rotor blade grips for cracks. If a crack is detected, the defective blade grip must be replace prior to further flight. The AD also establishes a blade grip retirement life of 1,200 hours TIS.
- Australian and Canadian airworthiness authorities, both of which are historically more conservative than the FAA when dealing with airworthiness concerns, have maintained their respective blade grip retirement times of in lieu of lowering the service life of the blade grip to the FAA's current 1,200 hours TIS level.
- According to a recent Experimental Aircraft Association (EAA) survey of Bell 47 owners, 99.9994% of grips inspected under AD 2000-18-51 passed inspection. Further, 57% of the grips reported in the survey have total times in excess of 1,200 hours TIS.
- In response to EAA's survey, numerous mechanics (most with at least two decades experience working on Bell 47 helicopters) stated that they had inspected hundreds of grips without seeing any cracks.
AOPA agrees that, in this particular situation, the potential for in-flight separation of a main rotor blade and subsequent loss of control of the helicopter warrants airworthiness action. However, AOPA maintains that repeated main rotor disassemble/reassembly at 200-hour TIS intervals may substantially increase the probability of induced, undetected damage to the main rotor system. Further, AOPA maintains that there is little data to substantiate the FAA's current mandatory 1,200 hour TIS blade grip retirement life. Further, AOPA recommends that the FAA continue to issue AMOCs allowing repetitive inspections in lieu of retirement at 1,200 hours TIS.
- On August 29, 2001, the FAA issued final AD 2001-17-17.
- On February 9, 2001, the FAA issued SAIB SW-01-13 announcing that they would consider limited changes to the compliance schedule of AD 2000-18-51 and will issue a revised AD in as few as 6 weeks.
- On January 29, 2001, AOPA participated in a meeting with the FAA, EAA, Bell and owners/operators of Bell 47 helicopters to discuss the issues surrounding the AD.
- On November 15, 2000, the FAA published AD 2000-18-51 in the Federal Register.
- On August 31, 2000, the FAA issued Emergency AD 2000-18-51.
- On March 29, 2001, the FAA proposed a revision to the current AD. The proposed revision contains the same provisions of the current AD while expanding its applicability to include two additional part number blade grips. The proposed revision also eliminates the dye penetrant inspection in lieu of a more effective eddy current inspection.