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Priority Letter: Robinson Helicopter Company Model R44 Helicopters

File Language:
English


Details

  • Corporate Creators:
    United States. Department of Transportation. Federal Aviation Administration
  • Subject/TRT Terms:
  • Resource Type:
    Letter
  • Geographical Coverage:
    United States
  • Corporate Publisher:
    United States. Department of Transportation. Federal Aviation Administration
  • Abstract:
    This Priority Letter Airworthiness Directive (AD) is prompted by an inflight failure of the main rotor gearbox (gearbox) on a French-registered Model R44 helicopter which resulted in an accident. An inspection of the gearbox revealed that the 18 bolts securing the gear, part number (P/N) C146-3, to the gear carrier assembly (gear carrier), P/N C268-2, had lost clamping torque due to the differences in the mating surface finish of these components. As the rough surface of the gear seated into the smoother surface of the gear carrier, the bolts lost clamping torque, resulting in fretting and failure of the gear carrier. Inspections of two other gearboxes that were returned to the manufacturer for overhaul and maintenance revealed that the bolts securing the gear to the gear carrier had also lost clamping torque. Prior to October 31, 1995, Robinson Helicopter Company (Robinson) did not have a requirement in their receiving inspections to verify that the surface finish of the gear was completed in accordance with the type design. As a result, gears have been found to have an improper surface finish. This condition, if not corrected, could result in fatigue failure of the gear carrier within the gearbox, and subsequent loss of power to the main rotor which could lead to a forced landing. Since an unsafe condition has been identified that is likely to exist or develop on other Robinson Model R44 helicopters of the same type design, this AD requires, before further flight, an inspection of the gearbox for pitting, elongated holes, or machining grooves (which appear similar to grooves on a phonograph record) that can be felt with a fingernail, and replacement of the gearbox with an airworthy gearbox if pits greater than 0.001-inch deep, elongated holes, or machining grooves are discovered on a mating surface; and replacement of the 18 bolts that attach the gear to the gear carrier with NAS6606-5 bolts and spacers, P/N C130-29. This rule is issued under 49 U.S.C. Section 44701 (formerly section 601 of the Federal Aviation Act of 1958) pursuant to the authority delegated to me by the Administrator, and is effective immediately upon receipt of this priority letter.
  • Format:
    PDF
  • Collection(s):
  • Main Document Checksum:
    urn:sha-512:054eaa8e1c9c66b2b2017b3d62ab7d882b98c28df1b2aa162291ea7e1e738e695a73bc53d88f3b374ddd6556d3f5d272ebf18921eba0d2c9725a45f596bc4996
  • Download URL:
  • File Type:
    Filetype[PDF - 59.09 KB ]
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