Airworthiness Directive · Amendment 39-18993 · Main rotor head
MD Helicopters, Inc., Helicopters
This AD applies to Model MD900 helicopters with main rotor upper hub assembly (upper hub) part number 900R2101006-105, -107, -109, or -111 installed, certificated in any category.
We are superseding Airworthiness Directive (AD) 2014-16-01 for MD Helicopters, Inc. (MDHI), Model MD900 helicopters. AD 2014-16-01 required an eddy current inspection of the main rotor upper hub assembly (upper hub) for a crack. This AD requires additional inspections and replacing the fillet seal. This AD was prompted by three additional reports of upper hub cracks. The actions of this AD are intended to prevent an unsafe condition on these products.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
(1) Within 100 hours time-in-service (TIS), and thereafter at intervals not to exceed 100 hours TIS:
(i) Inspect the fillet seal around each flexbeam bolthole to determine whether it adheres properly to the hub or bushing or is missing. Indications of an improperly adhered seal include lifting, bubbling, peeling away, drying out, or cracking. If the fillet seal is not properly adhered or is missing, before further flight, replace the fillet seal with sealant C232 or equivalent by following the Accomplishment Instructions, paragraphs 2.D.(2) through 2.D.(5) and Figure 1, of MD Helicopters Service Bulletin SB900-125, dated February 19, 2016 (SB900-125).
(ii) Using a light and a 10X or higher power magnifying glass, inspect the area outside of the fillet seal around each flexbeam bolthole on the top of the upper hub assembly for a crack. If there is a crack, before further flight, replace the upper hub assembly.
(2) Within 12 months, and thereafter at intervals not to exceed 12 months:
(i) Remove the paint and primer from the area around each flexbeam bolthole on top of the upper hub. Remove the fillet seal from the mating surface of each bushing and the top of the upper hub.
(ii) Using a light and a 10X or higher power magnifying glass, inspect the area around each flexbeam bolthole for a crack. If there is a crack, before further flight, replace the upper hub assembly.
(iii) Inspect each lead leg shim and bushing for corrosion around the flexbeam boltholes on the bottom of the upper hub in the flexbeam pockets. If there is corrosion, before further flight:
(A) Remove the lead leg shim from the flexbeam pocket and clean the area adjacent to the flexbeam bolthole to remove any corrosion within maximum repair damage limits. If the corrosion exceeds maximum repair damage limits, replace the upper hub assembly.
(B) Using a light and a 10X or higher power magnifying glass, inspect the area around the flexbeam bolthole for a crack. If there is a crack, before further flight, replace the upper hub assembly.
(iv) Replace the fillet seal as described in paragraph (f)(1)(i) of this AD.
(3) Within 1,000 hours TIS, and thereafter at intervals not to exceed 1,000 hours TIS:
(i) Eddy current inspect the areas adjacent to each flexbeam bolthole, top and bottom, for a crack. This eddy current inspection must be performed by a Level II or higher technician with the American Society for Nondestructive Testing ASNT-TC-1A, European Committee for Standardization CEN EN 4179, Military Standard MIL-STD-410, National Aerospace Standard NAS410, or equivalent certification who has performed an eddy current inspection within the last 12 months. If there is a crack, before further flight, replace the upper hub assembly.
(ii) Replace the fillet seal as described in paragraph (f)(1)(i) of this AD.
