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 EH101 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 blade design
(British experimental rotor project), 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 EH101 is powered by either three Rolls-Royce/Turbomeca RTM322 turboshafts
(the same engines used in the UK's AH64 Apache
), or three 1,491 kW General Electric
CT7-6 turboshafts (Italy
, 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 EH101 to hover reliably in winds of over 80 km/h.
Weapon and defensive systems
A chin FLIR
is fitted to some variants. The EH101 (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.
EH101 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 EH101 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 EH101 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 later 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 so far 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 Arabian Gulf.
Royal Air Force
RAF ordered 22 transport helicopters designated Merlin HC3, the first of which entered service with No. 28 Squadron RAF, based at RAF Benson, in January 2001.
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.
The first operational deployment was to the Balkans in early 2003. They are currently deployed to southern Iraq as part of Operation Telic.
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:
- 8 anti-surface and anti-submarine (ASW)
- 4 (+2) early-warning (AEW)
- 4 utility aircraft
- 4 (+2) ASH (Amphibious Support Helicopter)
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 1st 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 EH101 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 security 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.
Portuguese Air Force
The Portuguese Air Force
has operated EH101 Merlins since 24 February 2005, in transport, search and rescue (SAR), combat search and rescue (CSAR), fisheries surveillance (SIFICAP) 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 EH101 is search and rescue in Portugal's expansive maritime zone. EH-101s are on constant alert at three bases: Montijo (near Lisbon, Portugal), Lajes (Azores) and Porto Santo (Madeira).
Japan Maritime Self-Defense Force
The Japan Maritime Self-Defense Force
ordered 14 aircraft in 2003 to use in both the MCM (Mine Clearing Mission) and transport roles. The MCH-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.
Merlin HM1Merlin HC3Merlin HC3ACH-148 Petrel
: 33 originally ordered by the Canadian Forces
, reduced to 28 and later cancelled.CH-149 Cormorant
: Search and rescue
variant for the Canadian Forces
(14 in service).VH-71 Kestrel
variant intended to serve as the US Presidential helicopter
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.
- 21 January 1993 - Italian development Merlin PP2 (MMX600) crashed near Novara-Cameri airfield in Italy after an uncommanded application of the rotor brake in flight - four killed.
- 17 April 1995 - British development Merlin PP4 (ZF644) crashed near Yarcombe in Dorset, England.
- 20 August 1996 - Italian development Merlin PP7 (I-HIOI) was damaged in an accident when it turned over after the tail rotor drive failed on landing. The helicopter was repaired.
- 27 October 2000 - British Royal Navy Merlin (ZH844) ditched near the Isle of Skye, Scotland after a hydraulic fire caused by the rotor brake being partially engaged.
- 30 March 2004 - British Royal Navy Merlin (ZH859) crashed on take-off from RNAS Culdrose due to tail rotor hub cracking.
- June 2007, during an airshow in the Irish city of Galway, a door detached from a hovering RAF Merlin and fell into the crowd of spectators below injuring three people. Investigators have concluded "...that a member(s) of the public had tampered with an emergency door handle, while the helicopter was being viewed at the static display park".
- 15 November 2007 - During a medical evacuation in the island of São Jorge, Açores, Portugal, a Portuguese Air Force Merlin caused injuries to five people when it suddenly and unexpectedly climbed by one meter in the middle of the embarking procedures. The pilot was then able to recover the control of the helicopter minimizing the damages. According to the air force spokesperson, this kind of incident is unheard of.
Specifications (Merlin HM1)