CH-46F Sea Knight
The Marine's CH-46F was similar to the CH-46D, having the same engine, rotor blades, and fuselage, but it contained additional electronic equipment and a slightly different instrument panel. A total of 174 were obtained by the USMC from July 1968 to February 1971. The CH-46F retained the T58-GE-10 turboshafts, but had revised avionics and other modifications. Ultimately all CH-46's in the fleet were "D"s in the Navy and "E"s in the USMC.
On 24 July 1968, still another version of the CH-46 was accepted at the Vertol plant in Morton. Bureau number 154845 looked exactly like the "D" on the outside. Even on the inside, most observers could see little difference. The new aircraft had the same performance and could lift the same amount as the "D" and for all practical purposes, was in fact the same-with one major exception.
The CH-46F, as it was designated, had provisions for the installation of the long-awaited Integrated Helicopter Avionics System (IHAS) which held promise of giving helicopters a true all-weather, low-level, formation flight capability. To an experienced CH-46 crew member, the most obvious difference in the new model was that the avionics compartments had space provided for the electronic components of the IHAS. In the cockpit, the radio control console between the pilots had been rearranged to leave room for the IHAS display. Once the contract for the instrument system had been awarded to Teledyne and the initial designs completed, a schedule was prepared in 1966 which called for the "navigation system of IHAS" to be installed " in the 360th aircraft delivered from the production line." It was anticipated that the first aircraft to be equipped should be ready in December 1967. Bureau number 154845 was that helicopter.
Once the "F" models were coming off the production line, NavAirSysCom confirmed to the Marine Corps that "earliest retrofit is planned to get this navigation capability in all aircraft." Before the first CH-46F could be delivered, the IHAS program was in trouble and Teledyne was recommending that only the Self Contained Navigation System (SCNS) portion of the system be installed. Continued delays in production of the electronics and constant increase in the cost of even the SCNS made the future of the CH-46F navigatio n system doubtful.
On 24 July 1968 the first CH-46F was accepted by the Marine Corps at the Vertol Plant in Morton, Pennsylvania. This model was designed to carry the long-awaited integrated helicopter avionics system (IHAS), which, however, quickly proved a failure in tests and was never installed. The end came when the SCNS blanked out all radio transmission from the helicopter. Five months of testing at Vertol in the first half of 1969 could not solve the problem. The CH-46F never went into operation with the IHAS or SCNS that were the sole reason for its new designation.
At 1100, 2 February 1971, the final production model of the CH-46F rolled out of the plant. Since 30 April 1962 when the first CH-46 had made its debut, a total of 624 A, D, and F models had been delivered to the Marines. The CH-46 had become, and remains, a versatile, hard working member of the vertical amphibious assault team.
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