# AD 84-25-01: Main Gearbox Inspection - Type: Airworthiness directive - Status: Current - Products: Sikorsky S-61A, S-61D, S-61E, S-61L, S-61N, S-61NM, S-61R and S-61V - Effective: January 19, 1985 - Superseded by: Nothing supersedes this AD - Product type: Aircraft, Rotorcraft - Amendment: 39-4961 - Registered aircraft: 54 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/EF7D7D66052C900286256A33004DFA0E.0001 - DRS record last changed: May 30, 2024 - Page: https://openairdocs.org/ad/84-25-01 ## The airworthiness directive 84-25-01 SIKORSKY AIRCRAFT DIVISION: Amendment 39-4961. Applies to all Sikorsky Model S-61 series helicopters, certified in all categories, equipped with Part Number (P/N) S6135-20608-1 main transmission power input spur gears. Compliance is required as indicated (unless already accomplished). To intercept pending failure of either spur gear, P/N S6135-20608-1, in the main gearbox, accomplish the following: (a) On all helicopters equipped with a functioning cockpit main gearbox chip detecting system, visually inspect the main gearbox oil scavenge screen for steel particles within the next 10 hours time in service after the effective date of this AD and thereafter at intervals not to exceed 10 hours time in service from the last inspection. (b) On all helicopters not equipped with a cockpit main gearbox chip detecting system, visually inspect both the main gearbox chip detector and the oil scavenge screen for steel particles within the next 10 hours time in service after the effective date of this AD and thereafter at intervals not to exceed 10 hours time in service from the last inspection. (c) Any magnetic steel particles found by inspecting either the chip detector or the scavenge screen will require replacement of the main gearbox before further flight unless the particles are (1) fine hairline particles, or (2) confirmed as originating from components other than the spur gear. (d) If the inspections of paragraph (c) are inconclusive, the gearbox must be replaced or, at the option of the operator, the following maintenance tests may be conducted to evaluate the condition of the spur gear. (1) Drain and refill the gearbox with an approved lubricant. (2) Operate the helicopter at a safe height (below 5 feet), at a gross weight not less than 16,000 pounds, with a nominal neutral center of gravity, at 100 percent main rotor speed for one-half hour with one engine at 100 percent torque and the remaining engine at a torquelevel required to sustain safe hover. Repeat the procedure for one-half hour with the other engine at 100 percent torque and the remaining engine at a torque level required to sustain safe hover. (3) Inspect the gearbox scavenge screen and the magnetic chip detector and apply the inspection criteria of paragraph (c) and, if appropriate, reconduct the maintenance tests of paragraph (d) one time. Apply the inspection criteria of paragraph (c). NOTE: This procedure is not intended to authorize continued operation of the helicopter if any questionable safety condition is exposed by debris found when conducting these checks. (e) Replace spur gear P/N S6135-20608-1 with spur gear P/N S6135-20608-3 and comply with Sikorsky Overhaul and Repair Instruction 6135-342, Revision A, or later revision, or FAA-approved equivalent before further flight after December 30, 1986. The inspections of paragraphs (a), (b), and (c) may be discontinued for helicopters modified as required bythis paragraph. (f) Upon request, with substantiating data submitted through an FAA maintenance inspector, equivalent methods of compliance, adjustment in the inspection intervals, and adjustment in the replacement date may be approved by the Manager, Boston Aircraft Certification Office, FAA, New England Region. This amendment supersedes AD 83-17-04, Amendment 39-4706. This amendment becomes effective on January 19, 1985. ## Affected data sheets (2) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS 1H15](https://openairdocs.org/tcds/1H15): Sikorsky Aircraft; names 4 of 4 models: S-61R, S-61N, S-61L, S-61NM - [TCDS H2EA](https://openairdocs.org/tcds/H2EA): Sikorsky Aircraft Corporation; names 4 of 4 models: S-61A, S-61D, S-61V, S-61E ## Registered aircraft it may apply to (OpenAirDocs) Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment. - Aircraft: 54 (54 by airframe model, 0 by engine model) - Makers: Sikorsky 53, Carson Helicopters / Sikorsky 1 Models with the most aircraft: - [Sikorsky S-61N](https://openairdocs.org/model/sikorsky-s-61n): 45 aircraft (airframe model) - [Sikorsky S-61A](https://openairdocs.org/model/sikorsky-s-61a): 5 aircraft (airframe model) - [Sikorsky S-61L](https://openairdocs.org/model/sikorsky-s-61l): 1 aircraft (airframe model) - [Sikorsky S-61NM](https://openairdocs.org/model/sikorsky-s-61nm): 1 aircraft (airframe model) - [Sikorsky S-61R](https://openairdocs.org/model/sikorsky-s-61r): 1 aircraft (airframe model) - [Carson Helicopters / Sikorsky S61A](https://openairdocs.org/model/carson-helicopters-sikorsky-s61a): 1 aircraft (airframe model) All 6 models: https://openairdocs.org/ad/84-25-01/models.md Every aircraft: https://openairdocs.org/ad/84-25-01/aircraft.md Its text cites no advisory circulars or STCs. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.