AD 70-10-08

70-10-08 BELL: Amendment 39-983 as amended by Amendment 39-1063 is further amended by Amendment 39-2642. Applies to all Model 47 Series helicopters certificated in all categories, equipped with metal tail rotor blades, P/N 47-642-102 and to all other helicopters equipped with metal tail rotor blades, P/N 47-642-102.

Compliance required as indicated.

To prevent failure of tail rotor blades due to fatigue cracks, accomplish the following:

(a) Before the first flight of each day and before the first flight after each refueling of the helicopter after the effective date of this AD, visually check for cracks and permanent deformation in the tail rotor grips in the area between Blade Station 2.7 and 3.7, in the tail rotor blade trailing edge between Blade Station 5.0 and 8.0, and at the area surrounding the rivets that attach the blade skin to the grip, using a three-power or higher magnifying glass. (Station 0 is the center of the tail rotor yoke.)

(b) Before the first flight of each day and before the first flight after each refueling of the helicopter after the effective date of this AD, visually check blades equipped with tabs, P/N 47-642-114, for deformation of the tabs or check the equivalent strike-detection device in a manner approved by the Chief, Engineering and Manufacturing Branch, Flight Standards Division, Southwest Region, FAA.

(c) Replace tail rotor blades having cracks or permanent deformation on skid- equipped helicopters before further flight.

(d) Replace tail rotor blades having cracks, permanent deformation, bent tabs, or strike indication from equivalent strike-detection device on float-equipped helicopters before further flight, except that blades with bent tabs or a strike-indication from the equivalent strike- detection device only may be flown for a period not to exceed 1.5 hours in accordance with FAR 21.197 to a base where the blade may be replaced.

(e) Within the next 300 blade hours' time in service after November 25, 1966, install tabs, P/N 47-642-114, on metal tail rotor blades, P/N 47-642-102, of float-equipped helicopters in accordance with Bell Service Letter No. 125 dated June 21, 1965, or an equivalent strike- detection device approved by the Chief, Engineering and Manufacturing Branch, Flight Standards Division, Southwest Region, FAA.

(f) Within 10 hours' time in service after the effective date of AD 68-02-03, provide a clear view of the tail rotor blade external critical areas in the manner prescribed in Bell Service Bulletin 143 SB, Revision D, dated January 23, 1968, or in a manner approved by the Chief, Engineering and Manufacturing Branch, Flight Standards Division, Southwest Region, FAA.

(g) The checks in (a) and (b) above may be performed by the pilot.

NOTE: For the requirements regarding the listing of compliance and method of compliance with this AD in the aircraft permanent maintenance record, see FAR 91.173.

(h) Inspect those tail rotor bladeshaving 300 or more hours' time in service on the effective date of AD 68-02-03 within 10 hours' time in service therefrom in accordance with the procedures listed below. Inspect those tail rotor blades having less than 300 hours' time in service before reaching 310 hours' time in service in accordance with the procedures listed below. Accomplish repetitive inspections in accordance with the procedures listed below at intervals of not more than 150 hours' time in service from the last inspection.

(1) Remove the tail rotor blade from the helicopter in accordance with the appropriate model maintenance and overhaul instruction manual.

(2) Remove the metal grease seal in the blade grip. If bonded, remove in the manner prescribed in Bell Service Bulletin 143SB, Revision D, dated January 23, 1968, or in a manner approved by the Chief, Engineering and Manufacturing Branch, Flight Standards Division, Southwest Region, FAA.

(3) Visually inspect internal surfaces of the bladegrip for cracks in the rivet area using a dental mirror and light or an equivalent inspection method approved by the Chief, Engineering and Manufacturing Branch, Flight Standards Division, Southwest Region, FAA.

(4) Visually inspect the internal surface of the grip for cracks and tool marks in the bearing relief under-cut radius using a dye penetrant or an equivalent inspection method approved by the Chief, Engineering and manufacturing Branch, Flight Standards Division, Southwest Region, FAA.

(5) Install a new metal grease seal, P/N 47-642-112 as required, in the blade grip in the manner described in Bell Service Bulletin 143 SB, Revision D, dated January 23, 1968, or in a manner approved by the Chief, Engineering and Manufacturing Branch, Flight Standards Division, Southwest Region, FAA.

(6) Reassemble, reinstall, balance and track metal tail rotor blades in accordance with the appropriate model maintenance and overhaul instruction manual.

(i) Remove and replace metal tail rotor blades with 500 or more hours' time in service on the effective date of AD 68-02-03, within 100 hours' time in service therefrom.

(j) Remove and replace metal tail rotor blades with less than 500 hours' time in service on the effective date of AD 68-02-03, prior to accumulating 600 hours' time in service.

(k) Remove and replace all subsequent replacement metal tail rotor blades prior to accumulating 600 hours' time in service.

(l) Within 25 hours' time in service after July 20, 1976, and, thereafter, at intervals not to exceed 25 hours' time in service from the last inspection, accomplish the following:

(1) Clean the blades' external surfaces of any visible residue.

(2) Inspect the blades trailing edge between Blade Station 5.0 and 8.0 for cracks, permanent deformation, and any nick or indentation, using a 10-power or higher magnifying glass.

(3) Inspect for cracks and permanent deformation in the tail rotor grips in the area between Blade Station 2.7 and 3.7 and at the areas surrounding the rivets that attach the blade skin to the grip, using a 10-power or higher magnifying glass.

(4) If cracks, permanent deformation, any nicks or indentations are found, replace the tail rotor blades before further flight.

(m) This AD is not applicable to Bell Model 47 series helicopters equipped with P/N 47-642-117 tail rotor blades.

Amendment 39-983 superseded Amendment 39-546 (33 F.R. 2885) AD 68-02-03 which became effective to all known United States operators of Bell Model 47 series helicopters upon receipt of individual copies mailed January 20, 1968, and to all other persons on February 13, 1968.

Amendment 39-983 became effective June 2, 1970. Amendment 39-1063 became effective August 15, 1970. This amendment 39-2642 becomes effective July 20, 1976.