Proposed Bell 47 Blade Grip AD

Summary: This document is a superceding Airworthiness Directive (AD) to AD Final Rule No. 2000-SW-35-AD. This AD requires recurring eddy current inspections of the main rotor blade grip (grip) threads for a crack. If a crack is detected, this AD requires, before further flight, replacing the cracked grip with an airworthy grip. This AD also establishes a retirement life of 2,500 hours or 5,000 hours time-in-service (TIS) for each model grip.

Dates: Effective January 17, 2001, to all persons which contained the requirements of this AD.

Supplementary Information: The FAA issued Bell 47 Emergency AD 2000-18-51 and Final Rule AD 2000-SW-35-AD in response to the results of investigations of two Bell 47 helicopter accidents that occurred in Australia in May 1985 and in Canada in August 1998, which determined cracked main rotor blade grips were the cause of both accidents. The possibility of cracked grips on Bell 47 helicopters is a critical flight safety concern that has been addressed through the AD’s 2000-18-51 and 2000-SW-35-AD.

Since the unsafe condition described is likely to exist or develop on the Bell 47 helicopters models mentioned above using the same type of grips, the following inspection and TIS requirement shall be followed to prevent failure of a grip, loss of a main rotor blade, and subsequent loss of control of the helicopter.

Bell Helicopter Textron and other manufacturers, shall subject all newly manufactured main rotor blade grip (grip) threads to an eddy current inspection prior to releasing them for public use. These inspections are designed to ease Bell 47 operator fears of reported 70 percent failure rates of blade grips at low TIS hour levels. The results of the eddy current inspection will be provided as part of the sale paperwork to the buyer. Bell Helicopter Textron and other manufacturers, shall report all blade grips discovered with cracks to the FAA Rotorcraft Directorate, Rotorcraft Certification Office, ASW-170.

Bell 47 owners who have not complied with Emergency AD 2000-18-51 initial inspection requirements shall conduct either a liquid penetrant or eddy current inspection of the grip threads within 10 hours TIS for grips with 100 or more hours TIS or within 100 hours TIS since initial installation on any helicopter.

Thereafter, Bell 47 owners shall conduct an eddy current inspection procedure DOA/NDI/EC6 of the grip threads at the following intervals:

1. Wooden blades. Blade grip part numbers 47-120-135-1/2/3/5 and 47-120-252-7 not to exceed 200 hours TIS after initially installed. Thereafter, the eddy current inspections shall occur.during normal Bell 47 300 hour inspection cycles.

2. Blade grip part number 47-120-252-5 shall have a 300 hour TIS retirement life. Other than the initial manufacturer eddy current inspection, no additional eddy current inspections are required for this blade grip.

3. Metal blades. Blade grip part numbers 47-120-252-7/9/11 not to exceed 300 hours TIS after initially installed. Thereafter, the eddy current inspections shall occur during normal Bell 47 600 hour inspection cycles.

If a crack is detected, before further flight, replace the cracked grip with an airworthy grip.

Bell 47 owners shall report all blade grips discovered with cracks to the FAA Rotorcraft Directorate, Rotorcraft Certification Office, ASW-170.

Bell 47 blade grip part numbers 47-120-135-1/2/3/5 and 47-120-252-7 shall have a 2,500 hour TIS retirement life.

Bell 47 blade grip part numbers 47-120-252-7/9/11 shall have a 5,000 hour TIS retirement life.

Bell 47 blade grip part number 47-120-252-5 shall have a 300 hour TIS retirement life.

The FAA estimates 1,868 Bell 47 series helicopters of U.S. registry will be affected by this AD, that it will take approximately 20 work hours, including main rotor blade tracking, per helicopter to accomplish the inspection, and that the average labor rate is $60 per work hour. Required parts, if a grip needs to be replaced, will cost approximately $4,500 per grip (there are two grips on each helicopter). Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $10,200, assuming one inspection per helicopter and replacement of both grips on the helicopter.

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amend Part 39 of the federal Aviation Regulations (14 CFR Part 39) as follows: FAA ASW-100, Manager Rotorcraft Directorate can fill this part in per the above requirements.

Issued in Fort Worth, Texas on January 17, 2001

XXXXXXXXXX,

Manager, Rotorcraft Directorate, Aircraft Certification Service.