The Boeing CH-46 Sea Knight
The Boeing CH-46 Sea Knight is a medium-lift tandem rotor transport helicopter powered by twin turboshaft aircraft engines. And is used by the United States Marine Corps (USMC) to provide all-weather, day-or-night assault transport of combat troops, supplies, and equipment. The MV-22 Osprey replaced it. Additional tasks included combat support, search and rescue (SAR), support for forwarding refueling and rearming points, CASEVAC and Tactical Recovery of Aircraft and Personnel (TRAP).
The Sea Knight was also the U.S. Navy’s standard medium-lift utility helicopter until it was phased out for the MH-60S Nighthawk in the early 2000s. Canada also operated the Sea Knight, designated as CH-113, and used them in the SAR role until 2004. Other export customers include Japan, Sweden, and Saudi Arabia. The commercial version is the BV 107-II, commonly referred to simply as the “Vertol.”
A U.S. Marine watches two CH-46 Sea Knights, 2002
The CH-46 has tandem counter-rotating rotors powered by two GE T58 turboshaft engines. The engines are mounted on each side of the rear rotor pedestal with a driveshaft to the forward rotor. They couple the engines so either could power both rotors in an emergency. The rotors feature three blades and are folded for on-ship operations. The CH-46 has fixed tricycle landing gear, with twin wheels on all three landing gear legs. The wheels configuration causes a nose-up stance to facilitate cargo loading and unloading. The main gear, fitted in rear sponsons that also contain fuel tanks with a total capacity of 350 US gallons (1,438 L).
The CH-46 has a cargo bay with a rear loading ramp that could be removed or left open in flight for extended cargo or parachute drops. An internal winch is mounted in the forward cabin and can be used to pull external cargo on pallets into the aircraft via the ramp and rollers. A belly sling hook (cargo hook) rated at 10,000 lb. (4,500 kg), Could be attached for carrying external cargo. Although the hook is rated at 10,000 lb. (4,500 kg)., the limited power produced by the engines precludes the lifting of such weight. It usually has a crew of three, but can accommodate a larger crew depending on mission specifics. For example, a Search and Rescue variant will usually carry a crew of five (Pilot, Co-Pilot, Crew Chief, Swimmer, and Medic) to facilitate all aspects of such a mission. A pintle-mounted 0.50 in (12.7 mm) Browning machine gun, mounted on each side of the helicopter for self-defense. Service in Southeast Asia resulted in the addition of armor with the guns.
A flaming Marine CH-46 of HMM-265, after being hit by enemy AAA fire in “Helicopter Valley”, 15 July 1966
Known colloquially as the “Phrog,” the Sea Knight was used in all U.S. Marine operational environments between its introduction during the Vietnam War and its frontline retirement in 2014. The type’s longevity and reputation for reliability led to mantras such as “never trust a helicopter under 30”. CH-46s transported personnel, evacuated wounded, supplied forward arming and refueling points (FARP), performed vertical replenishment, search and rescue, recovered downed aircraft and crews and other tasks.
During the Vietnam War, the CH-46 was one of the prime US troop transport helicopters in the theater, slotting between the smaller Bell UH-1 Iroquois and larger Sikorsky CH-53 Sea Stallion. During the 1972 Easter Offensive, Sea Knights saw heavy use to convey the US and South Vietnamese ground forces to and around the front lines. Major technical problems plagued the CH-46 operations. The engines, being prone to foreign object damage (FOD ) ingested debris when hovering close to the ground, and subsequently suffering a compressor stall had a lifespan as little as 85 flight hours. On 21 July 1966, all CH-46s were grounded until more efficient filters had been fitted. By the end of US military operations in Vietnam, over a hundred Sea Knights had been lost to enemy fire.
In February 1968 the Marine Corps Development and Education Command obtained several CH-46s to perform herbicide dissemination tests using HIDAL (Helicopter, Insecticide Dispersal Apparatus, Liquid) systems; testing indicated the need for redesign and further study. Tandem-rotor helicopters were often used to transport nuclear warheads; the CH-46A was evaluated to deploy Naval Special Forces with the Special Atomic Demolition Munition (SADM). Nuclear Weapon Accident Exercise 1983 (NUWAX-83), simulating the crash of a Navy CH-46E carrying three nuclear warheads, was conducted at the Nevada Test Site on behalf of several federal agencies; the exercise, which used real radiological agents, was depicted in a Defense Nuclear Agency-produced
U.S. Marines load a simulated casualty onto a CH-46E during convoy operations training in May 2004.
The U.S. Marine Corps used the CH-46E Sea Knights during the 2003 invasion of Iraq. In one incident on 1 April 2003, Marine CH-46Es and CH-53Es carried U.S. Army Rangers and Special Operations troops on an extraction mission for captured Army Private Jessica Lynch from an Iraqi hospital. During the subsequent occupation of Iraq and counter-insurgency operations, the CH-46E was heavily used in the CASEVAC role, being required to maintain 24/7 availability regardless of conditions. According to authors Williamson Murray and Robert H Scales, the Sea Knight displayed serious reliability and maintenance problems during its deployment to Iraq, as well as “limited lift capabilities.” Following the loss of many US helicopters in the Iraqi theater, the Marines opted to equip their CH-46s with more advanced anti-missile countermeasures.