CH-46E Sea Knight

MV-22 Ospreys replaced the Marines’ last squadron of CH-46E helicopters in April 2015, officially ending the Sea Knight’s 50-year run as the troop and supply transport workhorse of the Corps. Marine Medium Helicopter Squadron 164 received the first Sea Knights assigned to the West Coast in early 1965 and introduced the medium-lift helicopter to combat in Vietnam in 1966. Parts of the squadron also flew missions in the evacuation of Saigon, making it the first in and last out of the Southeast Asian country.

More than 600 CH-46s, affectionately known as “Battle Phrogs,” were produced over the years, but by 2015, just two remained. One was destined to join dozens of others in the “boneyard,” a storage space for retired aircraft, while the other — a shiny green model that flew missions in Vietnam — went to the National Museum of the Marine Corps in Quantico, Va.

The mission of the CH-46E Sea Knight helicopter in a Marine Medium Helicopter (HMM) squadron is to provide all-weather, day/night, night vision goggle (NVG) assault transport of combat troops, supplies, and equipment during amphibious and subsequent operations ashore. Troop assault is the primary function and the movement of supplies and equipment is secondary. Additional tasks are: combat and assault support for evacuation operations and other maritime special operations; over-water search and rescue augmentation; support for mobile forward refueling and rearming points; aeromedical evacuation of casualties from the field to suitable medical facilities.

The final upgrade-the CH-46E-came with increased power and fuel capacity. The CH-46E Sea Knight helicopter provides all-weather, day-or-night assault transport of combat troops, supplies and equipment. Troop assault is the primary function and the movement of supplies and equipment is secondary. Additional tasks may be assigned, such as combat support, search and rescue, support for forward refueling and rearming points, aeromedical evacuation of casualties from the field and recovery of aircraft and personnel.

Marine Aviation plays a crucial role in the MAGTF's ability to conduct Maneuver Warfare. The CH-46E mission is to support the MAGTF Commander by providing assault support transport of combat troops, supplies and equipment, day or night under all weather conditions during expeditionary, joint or combined operations. The ultimate goal of Marine Aviation is to attain the highest possible combat readiness to support Expeditionary Maneuver Warfare while at the same time preserving and conserving our Marines and equipment. Embedded within combat readiness is the ability to rapidly, effectively, and efficiently deploy on short notice and the ability to quickly and effectively plan for crises and/or contingency operations thereby ensuring Marine Aviation remains ready for combat when and where the need arises.

CH-46E Squadron are authorized: 12 aircraft; 28 Pilots/19 Crew Chiefs/19 Aerial Gunner/Observers. A standard CH-46 crew consists of 2 Pilots, one Crew Chief, and an AG/O. A core capable squadron is able to sustain 20 sorties on a daily basis during contingency/combat operations. The above sortie rates are based on 1.5 hour average sortie duration and assumes > 70 percent FMC aircraft and > 90 percent T/O aircrew. If unit FMC aircraft < 70 percent or assigned crew < 90 percent T/O, core capability will be degraded by a like percentage. A core capable squadron is able to accomplish all tasks designated in the unit METL from a main base, expeditionary base, and/or carrier/amphibious platform (as appropriate per aircraft/system). To make a CH-46E fly, it takes an average of 26 maintenance-hours for every flight hour.

The CH-46E Sea Knight is a tandem-rotor transport helicopter of 20,800 lbs normal gross weight, powered by two T58-GE-16 turboshaft engines. The primary mission of the CH-46E is to rapidly deploy up to 25 combat troops and/or supplies from assault landing craft or from established airfields to forward staging areas having limited maintenance and logistic support, under VFR or IFR weather conditions. Alternative uses include medical evacuation, general cargo transportation, and external cargo missions.

The mechanical control system of the CH-46E transmits cockpit control motions through a series of push rods, bellcranks, mix units and cables to the swashplate assembly of each rotor. Swashplate motion acts through the pitch links to generate rotor blade pitch changes proportional to control motion. Forward control stick motion reduces forward rotor collective pitch and increases aft rotor collective pitch, causing a nose down helicopter response. Right control stick motion increases right cyclic pitch on both rotors, resulting in a right roll response. Right pedal motion increases right cyclic pitch on the forward rotor and left cyclic pitch on the aft rotor, causing a nose right helicopter response. Upward motion "of the collective lever increases collective pitch equally on both rotors, causing the helicopter to climb. Opposite cockpit control motions cause opposite rotor pitch changes and opposite helicopter responses.

The Automatic Flight Control System [AFCS] of the CH-46E consists of two simple speed trim systems, a 3-axis SAS and a 4-axis ATS. Each system consists of one or more sensors which generate signals proportional to helicopter airspeed, attitude, rate, etc., gain and shaping networks which process these signals, and one or more actuators which convert the processed signals into control system inputs. Originally, 10,000 flight hours meant the aircraft's life was over, but NADEP's work is excellent, and they have found this number of flight hours doesn't affect the life of the airframe as harshly as first thought.

The CH-46E Engine Reliability Program (ERIP) is essential in order to maintain the CH-46E as a viable and supportable airframe until it is fully replaced by the MV-22 Osprey. By replacing the T58-GE-16 engine core and accessories, ERIP will prevent the downward trend in engine health, increase engine reliability, and restore operational power margins, while providing a significant reduction in fleet labor and support costs. Other modernization efforts include replacing an antiquated engine control system with a much simplified, highly reliable commercial-off-the-shelf (COTS) system reducing the number of components from 12 to 5. The last of more than 400 T58 engine gas path modules was delivered in March 2007 during the 50th anniversary celebration of the T58 engine. General Electric, working with the CH-46E program office, delivered these upgraded modules under budget and ahead of schedule to the U.S. Marine Corps completing a $300 million, seven year upgrade program for the CH-46E Sea Knight helicopter.

The T58-GE-16A ERIP is meant to extend the time between engine removals and sustain the rated power of the Sea Knight engine. The upgrade incorporates a new compressor, combustor and high-pressure turbine, plus modifications to the power turbine and engine accessory package. Another way was discovered to extend the life of the engines. A Titanium Nitride (TiN) coating process for the compressor blades was identified and added into ERIP process. The coating reduces blade erosion and improves engine time-on-wing thereby reducing maintenance time and costs. The 1,870 shaft horse power rating of the T58-GE-16A engine remains unchanged. However, tighter production tolerances have given the upgraded engines' average power margins more than seven percent of specification power - more than twice the margin of typical production engines. The higher power margins will help preserve full rated power over the service life of the upgraded engine and will improve performance in hot weather and high altitude emergencies.

A new Aircraft Integrated Maintenance System (AIMS) is also being fielded, which provides real time onboard rotor track and balance and engine setup capability and divests several pieces of expensive support equipment. AIMS monitors aircraft vibration data and key engine parameters real time to facilitate maintenance and provide limit warnings.

Sustainability efforts include the replacement of several key wiring harnesses suffering from age and degradation. The CH-46E will continue to play a vital role in support of the Global War on Terrorism, therefore Aircraft Survivability Equipment Systems are being upgraded, including the missile warning system, countermeasures dispensing system, and IR missile jamming system to mitigate enemy threats. Numerous weight reduction initiatives are also underway targeting 1000 pounds of payload recovery. Lightweight ceramic armor has been procured to replace the original steel armor. A contract has been awarded for lightweight armored crashworthy seats, which will be introduced into the fleet in 2006. CH-46E readiness and utilization rates are at historic highs and the efforts underway will help it safely and effectively perform the mission until retirement.

On 06 September 1996 a Marine One CH-46E helicopter's front rotor blade struck a light pole which was adjacent to the aircraft parking area at the Orlando, Florida, Executive Airport while enroute to a presidential lift site. It was ground taxiing to park for refueling under the direction of an airport taxi director at the time of the mishap. The aircraft turned on its side following the incident, and was destroyed by fire soon thereafter. All aboard regresses safely prior to the fire. This mishap is still under investigation. However, it is probable that a loss of situational awareness caused the aircrew to taxi too close to the light pole. The subsequent rotor blade damage induced extreme vibrations and structural damage that resulted in the aircraft rolling over and burning. Immediately following notification of this mishap, the Commanding Officer of HMX-1 issued an additional ground taxi policy requiring all crews operating at civilian fields to have their crew chiefs assist local civilian taxi directors.