Says Daily Rotor Check Procedures In Maintenance Manual Should Be Revised

The NTSB Tuesday released identical recommendations concerning some model Eurocotpers to the FAA and EASA.  The board said the two bodies should require Eurocopter to revise its aircraft maintenance manual for all helicopters equipped with part number 355A11-0020 and/or 355A11-0030 main rotor blades to include, as part of the daily flight-related check, specific visual inspections of the trailing edge of the blades, upper and lower skin surfaces for cracks and surface deterioration and/or disfiguration. Eurocopter’s EC-130 aircraft maintenance manual (AMM) specifies visual inspection of the main rotor blades as part of the daily flight-related check for “security, general coating, tabs, and polyurethane protection condition (visual check for de-bonding, scratches, crack, impact and distortions). No erosion holes on leading edge steel strip, no gaps nor impact.”

Eurocopter EC-130

Once the Eurocopter aircraft maintenance manual is revised, the board recommends that operators of all Eurocopter helicopters equipped with part number 355A11-0020 and/or 355A11-0030 main rotor blades be notified that they should revise their maintenance manuals to include specific daily visual inspections of the trailing edge of the blades, upper and lower skin surfaces for cracks and
surface deterioration and/or disfiguration.

On July 7, 2007, about 1651 EDT, a Eurocopter EC-130-B4 helicopter, N453AE, operated by Liberty Helicopters, Inc., experienced an in-flight separation of a section of one of the main rotor blades during flight and sustained substantial damage during an emergency descent and subsequent autorotation into the Hudson River in New York. The commercial pilot and seven passengers were uninjured. No flight plan was filed with the Federal Aviation Administration (FAA) for the 14 Code of Federal Regulations Part 135 and 136 sightseeing flight, nor was one required. Visual meteorological conditions prevailed at the time of the accident.

NTSB Image

The NTSB determined that the probable cause of this accident was the fatigue fracture and in-flight separation of a section of the composite main rotor blade trailing edge aft of the spar, due to inadequate manufacture, and the manufacturer’s failure to detect an out-of-specification deviation in the rotor blade’s trailing-edge roving.

The NTSB notes that the misalignment of the trailing-edge roving fibers7 occurred during manufacturing, when the fibers likely shifted during the curing process. Because the unidirectional fibers of the roving were not properly aligned (were not parallel) in the spanwise direction of the blade, a localized stiffness change occurred at the trailing edge. The misalignment of the fibers reduced the local load-carrying capacity of the roving, and the loads were transferred to the skin, which started cracking. According to a stress calculation conducted by Eurocopter, the skin is more susceptible to cracks than the trailing-edge roving and will start to fracture before the roving. The blades on the accident helicopter had not previously had any cracking issues.

FMI: www.ntsb.gov