68-25-04: Nose Steering Relief Valve

68-25-04 VICKERS: Amendment 39-691. Applies to Viscount Models 744, 745D and 810 Series Airplane. Compliance required as indicated unless already accomplished. To prevent fatigue failure of the nose wheel steering twin relief valve, P/N 70026 Sh. 35 at the valve body halves P/N 70026, Part 251 and Part 253, accomplish the following: (a) Inspect the valve body halves as specified in paragraph (b) at the following times: (1) Valves having less than 14,650 hours time in service on the effective date of the AD must be inspected prior to the accumulation of 15,000 hours time in service and thereafter at intervals not to exceed 2500 hours time in service. (2) Valves that have accumulated 14,650 or more but less than 20,000 hours time in service on the effective date of this AD must be inspected within the next 350 hours time in service and thereafter at intervals not to exceed 2500 hours time in service. (3) Valves that have accumulated 20,000 or more but lessthat 22,800 hours time in service on the effective date of this AD must be inspected within the next 350 hours time in service and thereafter at intervals not to exceed 1000 hours time in service. (4) Valves that have accumulated 22,800 or more hours time in service on the effective date of this AD must be inspected within the next 350 hours time in service. (b) Inspect the valve body halves for cracks at the fluid transfer holes by a dye penetrant method in accordance with British Aircraft Corporation Viscount Preliminary Technical Leaflet No. 265 Issue 2 (700 Series) or No. 128 Issue 2 (810 Series) or later ARB approved issue or an FAA approved equivalent. (c) Replace the valve body halves in accordance with paragraph (d) at the following times: (1) If cracks are found during the inspections required by paragraph (a), replace the valve body halves prior to further flight. (2) If no cracks are found during the inspections required by paragraph (a), replace the valve body halves as follows: (i) Valves having less than 14,650 hours time in service on the effective date of this AD, must be replaced before the accumulation of 20,000 hours time in service. (ii) Valves having 14,650 or more but less than 22,800 hours time in service on the effective date of this AD must be replaced before the accumulation of 23,500. (iii) Valves having 22,800 or more hours time in service on the effective date of this AD must be replaced within the next 750 hours time in service after the effective date of this AD. (d) Replace valve body halves with parts having the same part numbers which have been inspected and found to have no cracks or with new valve body halves P/N 70026-637-639. (e) Valves of the same part numbers used as replacements must continue to be inspected in accordance with paragraph (a) and replaced in accordance with paragraph (c). Compliance with the inspection and replacement requirements of this AD may be discontinued when new valves P/N 70026-637-639 are incorporated. This amendment becomes effective January 7, 1969.