The AgustaWestland AW101 (EH101 until June 2007) is a medium-lift helicopter for military applications but also marketed for civil use. The helicopter was developed as a joint venture between Westland Aircraft in the UK and Agusta in Italy (now merged as AgustaWestland). The aircraft is manufactured at the AgustaWestland factories in Yeovil, England and Vergiate, Italy. The name Merlin is used for AW101s in British, Danish and Portuguese military service.
In spring 1977, the UK Ministry of Defence issued a requirement for an anti-submarine warfare (ASW) helicopter to replace the Royal Navy's Westland Sea Kings. Westland responded with a design designated the WG.34 that was then approved for development. Meanwhile, the Marina Militare (Italian Navy) was also seeking a replacement for its (Agusta-built) Sea Kings, leading Agusta to discussions with Westland about the possibility of a joint development. This culminated in the joint venture being finalised in November 1979 and a new company (EH Industries Limited [EHI], based in London) being formed in June the following year to manage the project.
As the design studies progressed, EHI became aware of a broader market for an aircraft with the same capabilities as those required by the British and Italian navies. On 12 June 1981, the UK confirmed their participation, with an initial budget of £20 billion to develop nine pre-series examples. At the 1985 Paris Air Show at Le Bourget, Agusta showed a mock-up of a utility version of the new helicopter, leading to a more generalised design that could be customised. After a lengthy development, the first prototype flew on 9 October 1987.
EHI was renamed AgustaWestland International Limited in January 2004 when parent companies merged. Consequently, in June 2007, the EH101 was re-branded as the AW101.
The modular aluminium-lithium alloy fuselage structure is damage and crash resistant, with multiple primary and secondary load paths. Active vibration control of the structural response (ACSR) uses a vibration-cancelling technique to reduce the stress on the airframe. The AW101 is rated to operate in temperatures ranging from -40 to +50 °C. High flotation tyres permit operation from soft or rough terrain. The main rotor blades are a derivative of the BERP rotor blade design, which improves the aerodynamic efficiency at the blade tips, as well as reducing the blade's noise signature.
The cockpit is fitted with armoured seats for the crew, and can withstand an impact velocity of over 10 m/s. Dual flight controls are provided, though the EH-101 can be flown by a single person. The pilot's instrument displays include six full colour high-definition screens and an optional mission display. A digital map and Forward-Looking Infrared system display can also be installed.
The military version of the AW101 is powered by either three Rolls-Royce/Turbomeca RTM322 turboshafts (the same engines used in the UK's WAH-64 Apache) (UK, Japan, Denmark and Portugal), or three 1,491 kW General Electric CT7-6 turboshafts (Italy, Canada, Japan TMP). Engine inlet particle separator systems provide protection when operating in sandy environments. Each engine is supplied by a separate 1,074 litre self-sealing fuel tank using dual booster pumps. A fourth tank acts as a reservoir supply, topping up the main tanks during flight; while a fifth transfer tank can be added to increase range, as can airborne refuelling. The engines power an 18.59 metre diameter five-bladed main rotor. The rotor blades are constructed from carbon/glass with nomex honeycomb and rohacell foam, edged with titanium alloy. Computer control of the engines via the aircraft EECU's (electronic engine control unit) allows the AW101 to hover reliably in winds of over 80 km/h.
Weapon and defensive systems
A chin FLIR is fitted to some variants. The AW101 (excluding the ASM MK1) is equipped with Chaff and flare dispensers, directed infrared countermeasures (infrared jammers), ESM (electronic support measures, in the form of RF [radio frequency] heads), and a laser detection and warning system.
It has two hard points for weapon carriers, on which the HM Mk1 model can carry four Sting Ray torpedoes or Mk 11 Mod 3 depth charges, though at present cannot use the Sea Skua missile. The Mk1, Mk3 and 3a variants can mount General Purpose Machine Guns (GPMGs) in up to 5 locations in the main cabin pointing out of door and window apertures.
The AW101's fuselage has a volume of 31.91 m3 and the cargo compartment is 6.5 m in length, 2.3 m wide and 1.91 m high. The military version of the AW101 can accommodate up to 24 seated or 45 standing combat troops and their equipment. Alternative loads include a medical team and 16 stretchers, and cargo pallets. The cabin floor and rear ramp are fitted with flush tie-down points, a semi-automatic cargo release unit (SACRU). The ramp (1.91x2.3 m) can take a 3,050 kg load, allowing it to carry vehicles such as Land Rovers. A cargo hook under the fuselage can carry external loads of 5,440 kg via the use of a SACRU (semi auto cargo release unit). A rescue hoist and a hover trim controller are fitted at the cargo door.
The navigation system includes a GPS and inertial navigation system, VHF Omnidirectional Radio range (VOR) instrument landing system (ILS), tactical air navigation (TACAN) and automatic direction finding. The MK1 and MK3 are equipped with a DVS (Doppler velocity system) for when the exclusive use of the conventional pitot pressure instruments might be unreliable for gauging accurate airspeed. The AW101 is equipped with helicopter management, avionics and mission systems linked by two 1553B multiplex and ARINC 429 databuses. A Smiths Industries OMI SEP 20 automatic flight control system provides dual redundant digital control, giving autostabilisation and four-axis auto-pilot operation.
The RN's final order was for 44 ASW machines, originally designated Merlin HAS.1 but soon changed to Merlin HM1. The first fully operational Merlin was delivered on 17 May 1997, entering service on 2 June 2000. All aircraft were delivered by the end of 2002, and are operated by four Fleet Air Arm squadrons, all based at RNAS Culdrose in Cornwall: 814 NAS, 820 NAS, 824 NAS, 829 NAS and 700 NAS.
In March 2004, RN Merlins were grounded following an incident at RNAS Culdrose when the tail rotor failed on one of them. Investigations revealed that this was due to tail rotor hub manufacturing defects. Flights resumed the following year.
To date, ten Type 23 frigates have been refitted to accept the Merlin HM1.The Merlin HM1 has also been cleared to operate from the Royal Navy's aircraft carriers, amphibious assault ships and a number of RFA vessels including the Fort Victoria Class. The UK is considering the Merlin as a replacement for the Westland Sea King ASaC7 in the Airborne Early Warning (AEW) role.
Royal Navy Merlins have seen action in the Caribbean, on counter-narcotics and hurricane support duties. They have also been active in Iraq, providing support to British and coalition troops on the ground, as well as maritime security duties in the North Persian Gulf.
Royal Air Force
The type is equipped with extended-range fuel tanks and is capable of air-to-air refuelling; however, due to the lack of a suitable UK tanker aircraft, this capability has not been cleared for use. It also differs from the Royal Navy version by having double-wheel main landing gear, whereas the RN version only has a single wheel on each of the main gears.
To alleviate a shortfall in operational helicopters the British Ministry of Defence acquired six Merlins from Denmark in 2007. These were delivered to the RAF as the Merlin HC3A. As part of the deal, the UK Ministry of Defence has ordered six new-build replacements for the Royal Danish Air Force. In December 2007, a second Merlin squadron (No. 78 Squadron) was formed at Benson.
In 1997, the Italian Government ordered 20 EH101 helicopters with four options for the Italian Navy in the following variants:
The first Italian Navy production helicopter (MM81480) was first flown on 4 October 1999 and was officially presented to the Press on 6 December 1999 at the Agusta factory. Deliveries to the Italian Navy started at the beginning of 2001 and were completed by 2006. Italian EH101s operate from major surface units, aircraft carriers and amphibious assault ships.
Royal Danish Air Force
In 2001, the Royal Danish Air Force announced the purchase of eight EH101s for SAR duties and six tactical troop transports. The last of the 14 EH101s was delivered March 1 2007 and the first SAR EH101s became operational in late April 2007. The Danish Mk 512s have a MTOW of 15,600 kg.
In 2007, the British Ministry of Defence acquired the six troop transport EH101s from Denmark to alleviate a shortfall in British operational helicopters. In exchange, the British have ordered six new-build helicopters from AgustaWestland as replacements for the Royal Danish Air Force.
On 28 January 2008, one Danish AW101 broke the drive shaft from one engine to the gear box and made an emergency landing at Billund Airport. Following this incident the Danish fleet was grounded as a safety precaution. The incident caused some national debate about the future of the EH101 in Danish service and whether it made sense to acquire different helicopters since the EH101 had very low availability (roughly 30%) due to mechanical issues. AgustaWestland, in turn, blamed the Danes for ordering spare parts very late and not keeping enough staff to properly service the helicopters. In April 2008, RDAF reported considerable improvements in operational availability (over 50%), citing improved service form AW (speedy delivery of spare parts) and increased proficiency of groundcrews.
AW101 is a candidate for the Norwegian All Weather Search and Rescue Helicopter (NAWSARH) that is planned to replace the Westland Sea King Mk.43B of the Royal Norwegian Air Force in 2015. The other candidates for the NAWSARH contract of 10-12 helicopters are Bell Boeing V-22 Osprey, Eurocopter EC225, NHIndustries NH-90 and Sikorsky S-92.
Portuguese Air Force
The Portuguese Air Force has operated Merlins since 24 February 2005, in transport, search and rescue, combat search and rescue, fisheries surveillance and maritime surveillance missions. The 12 aircraft, in three versions, gradually replaced the Aérospatiale Puma in those roles. Portuguese Merlins are painted in a tactical green and brown camouflage.
The main role of the Portuguese AW101 is search and rescue in Portugal's maritime zone. EH-101s are on constant alert at three bases: Montijo (near Lisbon), Lajes Field, Azores and Porto Santo Island.
Japan Maritime Self-Defense Force
The Japan Maritime Self-Defense Force ordered 14 aircraft in 2003 to use in both the MCM (Mine Counter-Measures) and transport roles. The MCH-101 and CH-101 will replace the S-80-M-1 (MH-53E) for MCM, and the Sikorsky S-61 in a support role for Japanese Antarctic observations.
In November 2007, Algeria signed a contract for six AW101 helicopters. The first aircraft will be delivered in 2009, with further orders possible.
In mid-2008 it was revealed that a Saudi Arabian customer had ordered two VVIP AW101s.
The USMC has two AW101 VH-71 helicopters as part of its efforts to replace its Marine One helicopters. With the proposed elimination of further expenditures on the programme announced on 6 April 2009.
Law enforcement operators
Notable accidents and incidents
Five Merlins have been written-off and one damaged in accidents, of which three have been due to problems with the tail rotor hub cracking.
Specifications (Merlin HM1)
Published - July 2009
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