A total of ten development aircraft were built, five in the UK and five in Italy. These were not classed as prototypes, but this is in effect what they were.

PP1, the British basic systems development aircraft, first flew on October 9th 1987 at Yeovil. It was allocated the UK military serial ZF641.

PP2, the Italian basic systems development aircraft, first flew on November 26th 1987. It received the Italian military serial MMX600.

PP3 was the first commercial development aircraft, built by Westland. It first flew from Yeovil on September 30th 1988 carrying the civil serial G-EHIL. It also received the UK military serial ZH647.

PP4, the naval common systems development aircraft, made its maiden flight from Yeovil on June 15th 1989. It carried the UK military serial ZF644.

PP6, the Italian Navy mission systems development aircraft, flew on April 26th 1989 at Milan. It carried the Italian military serial MMX605, and also the civil serial I-RAIA.

PP5, the RN mission systems development aircraft, flew on October 24th 1989 at Yeovil as ZF649. Sea-going trials, including sonobuoy release, were completed in December 1992. It was fitted with the full Merlin avionics suite by early 1996.

PP7, the first military-utility rear-ramp version, made its maiden flight on December 18th 1989 at Milan. This initially had the civil serial I-HIOI.

PP8, the civilian passenger variant, flew on April 24th 1990 at Yeovil. This had the civil serial G-OIOI and also the military ZJ116. It appeared at Farnborough in September 1990.

In June 1990 the Rolls-Royce Turbomeca RTM322 was selected as the powerplant for the Royal Navy's aircraft. In September the General Eletric T700-GE-T6A was selected for the Italian Navy version.

PP2 carried out deck trials on INS Grecale and Maestrale in July 1990.

PP5 made the first landing by an EH101 on a warship on November 15th 1990, when it landed on HMS Norfolk off the Dorset coast. The aircraft was flown by Westland CTP Colin Hague

PP9, the second military-utility version with a rear ramp, flew on January 16th 1991 at Milan. This had the Italian civil serial I-LIOI.

PP10 was the static test airframe, built in Italy.

By September 1992 PP1 had flown 375 hours. It was fitted with the T700 turboshaft and a 3878-kW main gearbox.

PP2 crashed near Cameri in Italy on January 21st 1993 during noise measurement trials after an uncommanded application of the rotor brake in flight. The resulting friction caused several parts of the drive system to melt. The four people on board were killed. They were Raffaele Longobardi, Gilberto Tintori, Stefano Novelli and Massimo Colombo.

PP4 flew with three RTM322 engines on July 6th 1993. This was the start of a 2-year program of ground running and 160 flight hours.

PP3 carried out icing trials at CFB Shearwater for five months from November 1993. It also carried out weapons trials as ZH647 in 1993.

In October 1994 the passenger transport and rear-ramp versions of the EH101 received civil certification.

PP4 crashed near Chard, Dorset, on April 7th 1995 during a planned test flight to an altitude of 3650m at Yeovil. Test pilot John Dickens was at the controls. All four crew members parachuted to safety. It had flown 385 sorties, totalling 463 hours. After the loss of PP4, PP5 became the second RTM322 test bed.

PP9 carried out hot-and-high trials at Mesa, Arizona during 1995.

A 6000-hour EH.101 intensive flight operations programme began in early 1996, with PP8 and PP9 operating from Brindisi in Italy.

PP7 was damaged in an accident in Italy on August 20th 1996 - it turned over after the tail rotor drive failed on landing. It was repaired, and was airworthy again on January 21st 1999. The first production Royal Navy Merlin (ZH821) was diverted to the flight development program as a result of this accident. It flew a 200-hour program which ended in July 1998.

PP1 was tested on DTEO Boscombe Down's Rolling Platform Facility during the summer of 1997. The purpose of the tests was to establish the reliable operation of the automatic blade and tail folding mechanisms in the (simulated) worst sea states that the Merlin is designed to operate in.

RN02 undertook a series of temperature trials at DTEO Boscombe Down in September 1997.

In February 1998 GKN Westland and Agusta carried out a series of trials to demonstrate the EH101's growth potential. These included flights with a civil utility machine in Italy at take-off weights up to 15500kg - 900kg more than the present maximum. This extra capacity could accomodate enough fuel to give the EH101 a range of almost 2000 km.

In March 1998 all the gearboxes from PP8 were stripped out for its 1000-hour inspection, and reassembled without needing any replacement parts.

PP1 (ZF641) arrived at RNAS Culdrose during July 1998 for ground handling trials.

By the end of August 1998, PP8 and PP9 had flown over 1000 sorties for 2500 hours at Brindisi in Italy as part of a 6000-hour intensive flight operations (civil and military) programme. On September 14th the two aircraft flew to Aberdeen for the second phase of the programme, which was carried out in the hostile North Sea environment.

At June 1999 the two aircraft had reached 3500 hours, and also met the UK MoD's mean time between attributable failures requirement. PP8 spent a week in southwest England on a demonstration tour, and PP9 attended the Finnish Air Show and also visited bases in Denmark and Sweden en route.

Merlin HM.1 ZH827 flew on the Farnborough 1998 trade days, and I-LIOI (PP9) was in the static display.

The first Merlin HC.3 (ZJ117) for the RAF made its maiden flight at Yeovil on December 24th 1998. It was followed by ZJ118 on June 14th 1999.

PP3 was grounded on February 12th 1999 after 581 flights, and a total flight time of 653 hours. Following the removal of essential spares, it was stored at the Yeovil factory before being handed over to The Helicopter Museum at Weston-super-Mare on November 26th 1999.

By the beginning of August 1999 the EH101 fleet had accumulated 10084 flying hours. Of this total, the pre-production aircraft accounted for 8300 hours, Royal Navy 700M squadron over 700 hours and the first two Merlin HC.3s 110 hours.

Merlin HC.3 ZJ117 visited its future operating base (RAF Benson) on August 5th 1999.

EH101 PP9 made the type's first Atlantic crossing between August 30th and September 1st 1999, routing via the Faeroes, Iceland and Greenland. Total flying time for the 4000km flight was under 18 hours. The aircraft appeared at the Nova Scotia International Air Show.

PP9 returned to its Aberdeen base on September 29th, after clocking up 110 flying hours and more than 12800 km on its North American trip.

Development aircraft PP7 was allocated the UK military serial ZK101 in October 1999, for cold-weather trials in Canada.

During November 1999, Merlins ZH822 and ZH823 flown by Royal Navy operational development crews carried out trials of the FLASH active dipping sonar at a DERA site in the Outer Hebrides.

Also in November 1999 aircraft PP8 successfully completed a series of landings on a North Sea oil platform, 256km off the Scottish coast.

On December 1st 1999 EH101 PP7 (ZK101) made its first flight in snow conditions from Shearwater, Nova Scotia. It subsequently flew 25 times in conditions ranging from moderate to heavy snow in temperatures down to -6 degrees C. In addition, the first civil aircraft (I-AGWH) was at Fairbanks, Alaska, undertaking cold-weather trials in temperatures down to -32 degrees C.

As at mid-February 2000, the EH101 fleet had accumulated over 12000 flying hours, the equivalent of 30 years flying for a typical military helicopter.

It was announced on May 15th 2000 that EH101 PP9 had completed a 1750km simulated search-and-rescue mission lasting more than 8 hours. The aircraft took off at an all-up weight of 15600kg with 5500kg of fuel in internal and auxiliary tanks. After climbing to 2000ft, one of the aircraft's engines was shut down and it settled into a cruise at 200 knots. At 750km from base the helicopter hovered out of ground effect for 30 minutes, as if performing a rescue, before returning to base.

On October 17th 2000 it was announced that a Merlin HC.3 had completed a series of troop loading trials in a tactical environment on Salisbury Plain.

QinetiQ successfully completed a 3-week sea trial exploring operating limits (SHOL) for the Merlin HM.1 helicopter in early 2002. The trials were carried out over a three-week period, operating from HMS "Ark Royal" in the South-West Approaches. During the trials the aircraft flew for over 70 hours, completed 25 sorties and made 75 deck landings.

On June 3rd 2003 the UK MoD announced that Lockheed Martin UK Ltd had been selected as preferred contractor on a two year programme to assess possible upgrades to the Merlin Mk1 helicopter. Westland Helicopters Ltd will be a strategic sub-contractor in a partnership which will investigate how best to sustain Merlin's capabilities to meet the defence challenges of the next two to three decades.

Called Merlin Capability Sustainment Plus, the programme will build on significant operational experience (including the recent Gulf conflict) and technological advances since the aircraft was originally developed. The Assessment Phase, costing some £18 million, will investigate the most cost-effective way to sustain Merlin's capability across a broad range of roles including anti-submarine and surface warfare, and also the scope for enhancements to broaden the utility and versatility of the aircraft, particularly in surface surveillance, building on experience in the Gulf.

On July 8th 2003 EH101 PP9/I-LIOI arrived at Lockheed Martin's Systems Integration facility in Owego, New York. It was used to demonstrate to U.S. government customers how the American-built US101 medium-lift helicopter can be configured for different missions. The test bed will further support the low risk involved in transitioning the EH101 platform to fly the President of the United States and rescue military personnel.

On November 3rd 2004 the US101 demonstrator (previously serialled I-AGWH) arrived at the Lockheed Martin facility at Owego, NY. The aircraft validated the superior performance and reliability of its three GE CT7-8E engines and demonstrated the clarity of the updated Smiths Industries cockpit displays.

On January 11th 2005 John Howarth, Merlin Programme Manager at the UK MoD, officially switched on the EH101 Helicopter Electro-Mechanical Actuation Technology (HEAT) Integration Rig at AgustaWestland’s Yeovil facility. The HEAT system provides, for the first time on a helicopter, an all-electric primary flight control system including electro-mechanical actuators. It also enables the primary and secondary hydraulic systems, accessory gearbox and much of the mechanical flight control system to be deleted from the helicopter, thereby simplifying the aircraft configuration. The benefits of the system include reduced weight and cost of ownership while increasing reliability, survivability and safety. HEAT will also facilitate embodiment of Advanced Control Technology capabilities, including use of active side-stick controllers, and represents a major step towards an "all-electric" rotorcraft.

The key technology challenge associated with the project is electro-mechanical actuation, now made possible by the use of powerful DC brushless motors, high speed motor control and a quadruplex fly-by-wire primary flight control system. The application of a novel, flight-critical, technology in this challenging project demands particularly rigorous design and qualification processes. The system Integration Rig will undertake an extensive qualification and test programme of the HEAT system prior to it commencing its flight test programme. The integration rig replicates an existing EH101 in order to fully validate and verify the HEAT system. The rig can be "flown" from a replica cockpit, powered by a representative electrical & generation system and loaded to replicate flight loads based on flight test data.

On June 10th 2005 the first VH-71 Test Vehicle (TV1) arrived at Lockheed Martin's Systems Integration facility in Owego, New York. This aircraft is actually MM81495 leased from the Italian Navy; the three 'real' test vehicles will not be delivered until spring 2007.

On November 2nd 2005 MM81495 in the guise of TV1 arrived at Pax River to begin familiarization training for pilots and maintainers.

On September 26th 2006 EH101 G-17-510 (US101 demonstrator), fitted with new technology British Experimental Rotor Programme (BERP) IV main rotor blades, more powerful CT7-8E engines and a new integrated cockpit display system, made its first flight at Yeovil.

The more powerful General Electric CT7-8E engines, rated at 2,527 shp (1884 kW) each for take-off, provide 12 percent more power than previous CT7-family engines, increasing the EH101’s payload by at least 2,000 pounds while operating on hot days at high altitudes. Following an extensive flight test programme, utilising a US101 test aircraft, development flying for the CT7-8E engines is complete.

The new fully integrated flight and mission cockpit display system utilizes five 10 in x 8 in LCD main displays that give EH101 pilots 70 percent more display area enhancing their management of flight, system and mission data. The same large area displays are being introduced into the Royal Navy’s EH101 Merlin MCSP aircraft.

On February 13th 2008 a Merlin HC.3 (probably ZJ117) carried out the first-ever air-to-air refuelling by a British helicopter when it took on fuel from an Italian Air Force C-130J tanker over southern England. The AgustaWestland and RAF test pilots successfully plugged the helicopter's refueling probe to each of the tanker's two wing station drogues on the first attempt. The sorties were flown at an altitude of 4,000 ft at a speed of 127 knots. All trial objectives were achieved up to the Merlin's maximum flying weight of 34,400 lbs. This test demonstrated a key capability of the HH-71 candidate for the USAF CSAR-X contract.

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© David Hastings