Airworthiness Directive · Amendment 39-16740 · -13-p
MD Helicopters, Inc. Model MD900 Helicopters
Superseded. A later AD replaced this one: AD 2012-21-01. Comply with the one in force.
Model MD900 helicopters with main rotor lower hub assembly (lower hub), part number (P/N) 900R2101008-107, serial numbers (S/Ns) that begin with 5009, certificated in any category.
This amendment supersedes an existing airworthiness directive (AD) for MD Helicopters, Inc. (MDHI) Model MD900 helicopters. That AD currently requires visually inspecting the main rotor lower hub assembly (lower hub) for a crack, and if you find a crack, before further flight, replacing the unairworthy lower hub with an airworthy lower hub. Additionally, within 10 days of finding a cracked lower hub, the existing AD requires reporting the finding to the Los Angeles Aircraft Certification Office (LAACO). That AD was prompted by two reports of cracks detected in the hub in the area near the flex beam bolt hole locations during maintenance on two MDHI Model MD900 helicopters. Since we issued that AD, we determined that one manufacturer had incorrectly inserted flanged bushings into the lower hub bore that resulted in local corrosion, leading to fatigue cracking. Examination of lower hubs from the other manufacturer shows correct bushing installation. Therefore, this amendment limits the applicability to the affected lower hubs; retains the visual inspection but at a different compliance time; adds an eddy current inspection; retains the requirement to replace a cracked lower hub with an airworthy lower hub before further flight; and removes the requirement to report to the LAACO. The actions specified by this AD are intended to detect a crack in the lower hub and prevent failure of the lower hub and subsequent loss of control of the helicopter.
Within 100 hours time-in-service (TIS) or during the next annual inspection, whichever occurs first, unless done within the last 200 hours TIS:
(1) Visually inspect the sides and bottom of the area between the arms for the centering bearing and the areas adjacent to the bushings of the lower hub assembly for a crack. If there is a crack, before further flight, replace the lower hub with an airworthy lower hub.
(2) If the lower hub is not replaced as a result of the visual inspection required by paragraph (e)(1) of this AD, eddy current inspect the lower hub for a crack by following the Accomplishment Instructions, paragraphs 2.A(2) through 2.A.(10)., of MD Helicopters Inc. Service Bulletin SB900-117, dated January 14, 2011 (SB). If there is a crack, before further flight, replace the lower hub with an airworthy hub.
(f) The eddy current inspection required by paragraph (e)(2) of this AD must be done by a Level II technician with ASNT-TC-1A, CEN EN 4179, MIL-STD-410, NAS410, or equivalent certification in eddy current inspections. The technician must have done an eddy current inspection in the last 12 months.
