H-46 Service Life

The first flight of the CH-46A took place in August of 1962, and it entered fleet service in November 1964. Operating in Southeast Asia, the Sea Knight was outfitted with weapons and armor, along with higher-powered engines for the CH-46D models. After the last CH-46 was built in 1971, 524 Sea Knights had been inducted into the fleet.

The overall goal of the modification budget in FY2007 is to keep the H-46 a viable platform until a replacement aircraft can be fielded. H-46 helicopters are used by the Marine Corps for troop transport and Search and Rescue missions. USMC inventory as of 2007 was 220 CH-46E + 3 HH-46D (24 of the 220 CH-46E's are reserve aircraft. The original Design Service Life was 10,000 hours. It was subsequently extended to 12,500 hours 18 Dec 1992 and 15,000 hours 16 Feb 1996. Aircraft will continue to be flown past 15,000 flight hours on an Age Exploration program.

The Navy Air Systems Command ordered the grounding of all CH-46 helicopters on 18 August 2002 as a precaution after discovery of a crack in a rotor component of a Sea Knight at the Cherry Point Marine Corps Air Station in North Carolina. A similar problem was found a few days later in a CH-46 deployed aboard the amphibious assault ship Belleau Wood in the Persian Gulf area. Inspection of all 291 CH-46 Sea Knight helicopters in the Navy and Marine Corps found only one with a flaw of the kind that triggered the temporary grounding of the fleet, and the full fleet was returned to service.

The H-46 helicopter is nearing the end of its originally planned service life. Several dynamic components failed between 1988 and 1990 due to fatigue. Engineering Change Proposal (ECP)-556 incorporates design improvements to the critical safety items, which have been evident by in-service failure and flight strain survey. The changes increase thickness of critical sections and make other specific changes to increase resistance to fatigue damage. The major components include the forward and aft rotor heads, the forward and aft transmissions, the mixbox, aft vertical rotor shaft, the swashplates, synchronizing shafts, and accessory gear box. ECP-558 changes configuration of the Aircraft Flight Control System (AFCS), which reduces flight, loads on critical components. The H-46 previously used the MD-1 and AHRS gyroscopes for pitch and roll rate input to the AFCS. These gyroscopes originally designed for indication systems only and do not provide adequate input for pitch and roll rate to the AFCS. DCU was directed by Chief of Naval Operations (CNO) letter 13100 serial 504E/OU603293 dated 30 Aug 90 and approved by ASN (RDA) by Program Management Proposal (PMP) 90-7 on 18 Jan 1990.

In 2006, the average age of the H-46 helicopter was 39 years,and CH-46E squadrons deployed in support of GWOT have been flying in excess of 400% of planned utilization rate, creating a set of conditions that jeopardize the safety and reliability of the H-46 fleet. The H-46 Geriatric Aircraft Safety and Sustainment Program is driven by the H-46 Age Exploration Program, Systems Safety Working Group and other Fleet forums and provides redesign and modernization efforts [as of early 2008]:

1. Redesigned and modernized wiring harnesses in airframe areas subject to high levels of heat, sand contamination and/or vibration. 2. Redesigned and modernized hydraulics subsystems using common or COTS components.

3. Redesigned and improved portions of airframe structure subject to high levels of fatigue, corrosion and other stress.

4. Improved and modernized critical avionics, aircraft survival equipment (ASE) and other aircraft systems to resolve obsolescence, reliability or safety issues using common, previously qualified or COTS solutions. This initiative replaces components that are no longer supported in the supply system or are high maintenance degraders with modern, digital components maximizing commonality with other Naval aircraft to improve reliability,increase functionality and capabilities.

5. Non-recurring engineering (NRE) is underway for Infrared Suppression System for the Aircraft. 6. Non-recurring engineering (NRE) is underway for Ramp Gun Mounts.

7. Non-recurring engineering (NRE) is underway for Wire Strike Protection.

Non-recurring engineering (NRE) efforts were underway in early 2008. Contracts for Integration testing, prototype kits and production options will be awarded in FY2008. Prototype kit validation and verification will be performed in FY2008 and production installs will commence in FY2009.