The AgustaWestland AW101 (previously EH101) 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 in Italy.


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.

The AW101 Merlin is well known for its extensive use of composite materials. 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-canceling 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 used by the UK, Japan, Denmark and Portugal; or three 1,491 kW General Electric CT7-6 turboshafts in Italy, Canada, and Japan. The Rolls-Royce RTM322 engine was specifically designed for the AW101, and was later used other helicopters such as the WAH-64 Apache. 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.

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 October 9 1987.