Commando Merlin

Ian Harding details the upgrade of the UK Merlin HC3 transport helicopter into one for naval service


Merlin HC4 ZJ122/F on a test flight from Yeovil.
Ian Harding

The Commando Helicopter Force (CHF) transition from Junglie Sea King to Junglie Merlin HC3 successfully completed with the move of 845 Naval Air Squadron from RAF Benson, Oxfordshire, to Royal Naval Air Station Yeovilton in June 2016. They are now in the midst of the Merlin HC4/HC4A (Commando Merlin) programme, which upgrades the Merlin HC3/HC3A to a fully shipmodified version known as the Commando Merlin. This is progressing well and the first upgraded Commando Merlin arrived at Royal Naval Air Station Yeovilton in Somerset on April 25 to commence operational evaluation. AIR International met with Leonardo Helicopters (LH) at its nearby Yeovil facility to find out about this major programme.

Merlin life sustainment programme

As the Westland Sea King HC4 Out of Service Date (OSD) approached in March 2016, the UK MoD announced during January 2014 that AgustaWestland (AW) (now LH) had been awarded the contract to convert 25 former RAF Merlin HC3/ HC3A helicopters for maritime operations. At this point, the process of transitioning these helicopters from the RAF to Royal Navy command (with CHF and 845 and 846 Naval Air Squadron respectively at Yeovilton) was already advanced.

Valued at approximately £455 million, the Merlin Life Sustainment Programme or MLSP has two primary elements: first, a life sustainment package to resolve legacy obsolescence out to the types planned 2030 OSD, similar to the major upgrade of 30 Merlin HM1 to HM2 standard completed by the company in July 2016; second, a ship optimisation package to enable the aircraft to operate more effectively from ships in the maritime environment. Leveraging from more than ten years of system design, development and operational evaluation that has transformed the HM2’s capabilities, coupled with that for the Wildcat, has been a clear benefit to all participants in this latest programme. This includes the tail fold system that was initially developed for Royal Navy’s HM1 and the Italian Navy AW101 programmes. The MLSP is therefore considered a low-risk technical upgrade.


The MLSP involves the upgrade of two variants, namely, 19 HC3 to HC4 standard and six HC3A to HC4A standard. The six HC3A aircraft were acquired by the MoD from Denmark in 2007. Having been purchased from AW approximately ten years after the UK received its Merlin HC3s, the six former Danish HC3As naturally incorporated a number of enhanced technical features over their UK counterparts, owing to their role as a specialist SAR platform. Whilst the two variants were both powered by Rolls-Royce Turbomeca RTM322 engines, they had different power rating structures, for example. The UK HC3 also had a four-tank fuel system compared to five for the former Danish HC3A, and the respective cockpit and window layouts were significantly different. Externally, the HC3A could be easily distinguished from the HC3 by its distinctive nose cone, which was designed to enable a laser obstacle avoidance system to be fitted in addition to a weather radar and electro-optical device. The MLSP addresses most of the variant differences that exist, but not all of them; we will consider these later. The MLSP contains two distinct conversion phases.

Phase 1

This phase saw seven aircraft converted to interim HC3 (also referred to as iMk3) standard to enable the CHF to maintain embarked operations and to bridge the capability gap between the Sea King OSD set for March 2016 and the service introduction of the Merlin HC4/HC4A in early 2018. The critical design review (CDR) for this upgrade was concluded by June 30, 2014, with the first aircraft ZJ122/F (c/n T1) arriving at LH facility in Yeovil for upgrade on October 23, 2014. Key features of this upgrade were:

Tail folded on the first Merlin HC4; the photos show the articulation of the tail fold mechanism.
Simon Pryor/Leonardo Helicopters

• Ground crew controlled folding main rotor head (non-folding tail)

• New fast roping and abseiling point

• Modified undercarriage for deck operations

• New aircraft lashing points for deck security

• Additional radio

The iHC3 first flight took place on March 24, 2015, six months before the aircraft’s initial release to service on September 30, 2015. Initial operating clearance was exactly one year after the aircraft’s first flight on March 24, 2016. All seven aircraft were delivered to the MoD and Royal Navy (845 and 846 NAS) ahead of a schedule that the MoD itself considered ‘demanding’. Since their validation these aircraft have continued to provide defence with a maritime counterterrorism capability.

Phase 2

This involves the conversion of 25 aircraft to full HC4/HC4A standard. The CDR for this phase was March 31, 2015, with the first aircraft (TI#1) arriving at Yeovil approximately four months later on August 5, 2015. Additional modifications made to the iHC3 focus primarily on the upgrade of the cockpit and ship optimisation. The modifications are as follows:

Key features of avionics design include upgraded aircraft management and mission computers, General Dynamics tactical processor (derived from the Wildcat), five 10 x 8inch (254 x 200mm) General Electric integrated display units, three BARCO touchscreen units for controlling the aircraft’s systems and mission equipment, two devices for cursor control of the tactical displays, a new communication suite (derived from Merlin HM2 communication control and intercom system) with a specific radio fit for the HC4/HC4A requirement, and an I-band transponder system navigational equipment (again, similar to the HM2, but integrated into the aircraft avionics)

Integrated defensive aids suite with additional chaff dispensers mounted in the roof of the aircraft

Additional systems for civil airspace operational requirements include a civil twin global positioning system, dual VHF omnidirectional range/instrument landing system

Folding main rotor head and tail pylon, cockpit controlled as per HM2

Fast roping and abseiling beam

The first HC4 made its initial flight on October 24, 2016. The first HC4A is expected to fly in early 2019. The HC4 initial release to service is scheduled for Quarter 1 2018 with the first aircraft delivered to the Royal Navy and the CHF at Yeovilton immediately post issue of the release to service as mentioned above. All 25 helicopters are scheduled to be delivered by December 2020, with full operational capability also set for the end of 2020. As operational frontline aircraft, LH confirmed they will not be deemed as out of service when they arrive at their Yeovil facility for upgrade; the airframe and HC3/3A legacy equipment are still classed as being in service and they will therefore have to be maintained in accordance with each aircraft’s specific maintenance schedule. In theory, some aircraft will go to Yeovil to receive depth maintenance before entering the HC4/HC4A upgrade programme.

Ship optimisation

It was imperative the HC4/HC4A incorporated a tail fold system like that installed on the HM2 to enable embarked operations. As a consequence, the HC4/HC4A will have an automatic main rotor and tail folding system with BERP III blades that is identical to the HM2. Whilst the iHC3 blade fold was completed by the ground crew who connected an external controller into the aircraft to fold the blades, the HC4/HC4A main rotor and tail fold can be completed automatically by the aircrew from the cockpit. To complete the tail fold, LH confirmed it has replaced the rear fuselage module between the cabin module and tail pylon module with a new module incorporating the tail fold hinges and modified tail rotor drive shaft. The existing tail pylon is modified with the other half of the tail fold mechanism. The gearbox and transmission within the existing HC3/ HC3A and upgraded HC4/HC4A are the same, but LH confirmed that an index motor is installed to the front of the main gear box, which rotates the rotor head to the correct position to allow the main rotor blades to fold. The system is already proven on the HM2 and export utility aircraft including the Italian Navy’s Amphibious Support Helicopter variant of the AW101.

In addition, the HC4/HC4A will receive the revised undercarriage introduced on the iHC3, but further uprated with higher gas pressures to permit maritime operations above 14,600kg (32,187lb). The HC4/HC4A will retain the twin-wheel configuration of the HC3/3A, unlike the HM2, which has a single-wheel undercarriage). Also unlike the HM2, the HC4/ HC4A will not have a harpoon deck securing system.

Four Merlin HC4 aircraft are in flight test programme, one of which was delivered to the Royal Navy on April 25. At the end of February, a further six aircraft had entered the modification programme.
Ian Harding


As mentioned earlier, LH confirmed that phase 2 will eliminate most of the differences that currently exist between the HC4 and HC4A (originally HC3 and HC3A), including the nose cone that is currently such a distinctive feature of the HC3A. In this respect, the engine and transmission rating structures and the nose mounted electro-optical/infrared device will be common for both types. Elsewhere, the HC4A will receive a hydraulic rescue hoist to replace the present electric hoist, the cabin port door will now slide rather than push open and the cabin egress windows will be standardised across the fleet to the HC3 configuration to improve emergency egress. Inside the cabin, LH confirmed that although the new HC4/HC4A cockpit is very similar to the HM2 cockpit, it is not exactly the same. The differences are those associated with the different bespoke roles undertaken by each aircraft, which is reflected in the respective cockpit functionality. In essence, a HM2 pilot would instantly be familiar with the HC4/HC4A cockpit stepping into it, but it is different in respect of mission and tactical system information. (The Commando Merlin mission system is very similar to the Wildcat BRH (Battle Reconnaissance Helicopter in this respect.) The HC4 retains the HC3 heavy-duty cabin floor and four-tank fuel system whereas the HC4A will retain the HC3A standard floor and five-tank system. From an external view point, the HC4/HC4A fleet will be painted grey in common with the Navy’s HM2 Fleet. LH confirmed that in excess of 95% of the HC4/HC4A internal wiring is new.

Trials programme

Four aircraft will participate in the trials programme. The core element of flight trials covering the HC4 is scheduled to last approximately 13 months, ending in November 2017, and will be conducted utilising three HC4 aircraft. Over 100 hours of flight testing has been completed across the trials fleet since the first aircraft conducted its initial flight on October 24, 2016, with the second trials aircraft joining the flight trials programme on March 9, 2017. The third aircraft entered the trials programme in May 2017 primarily focussing on electromagnetic compatibility trials. As part of the test programme, embarked trials for shiphelicopter operating limits were conducted in summer 2017.

The fourth trials aircraft will be the only HC4A trials aircraft and will cover specific deltas between the HC4 and the HC4A. This aircraft is scheduled to make its first flight in January 2019. LH confirmed that all trials aircraft will be brought up to final variant configuration before their delivery to the fleet. It should be noted that the flight test programme is not a ‘traditional’ flight test programme in the sense that test pilots have to test the capability and envelope of the aircraft and its systems. Although the UK Military Aviation Authority (MAA) considers the HC4/HC4A as a new aircraft, LH confirmed that almost every element of the aircraft has been previously tested and flown during almost 30 years of the Merlin’s development. LH is not seeking to expand the aircraft’s flight envelope; it is already proven and therefore its flight testing is more a flight-and-check programme. Despite the aircraft’s extensive history and longevity, it should be noted that the Merlin was designed before the latest MAA rules and regulations came into being. LH has therefore certified the HC4/HC4A against these latest requirements.

Flight training

LH signed a separate MLSP training contract with the MoD in March 2015 to deliver two flight training devices, a flight navigation and procedures trainer and a rear crew trainer. LH will ‘train the trainers’ so the Royal Navy can train its own aircrew and maintenance personnel. Unlike the Wildcat training contract, LH is contracted to deliver the training system, but will not operate the training facility. This responsibility rests with the Royal Navy and CHF at Yeovilton.

Colonel Lenny Brown, Commanding Officer, CHF, provided his view of the Commando Merlin: “The first flight of the Commando Merlin at Leonardo Helicopters facility was the culmination of years of hard work by both industry and military subject matter experts to design and build an aircraft that would meet the exacting requirements for the Commando Helicopter Force, tasked to operate from land or sea, in austere environments and the harshest conditions imaginable. CHF operates wherever and whenever Royal Marines are – and they get around. CHF now has in its inventory a strategic aircraft. By that, I mean it can independently deploy strategic ranges to conduct the full spectrum of military tasks. We have been hand-picked by the Royal Navy to support the Queen Elizabeth’s first deployment next year and in doing so will offer defence choice to deliver soft or hard military output. The Sea King HC4 provided CHF with an operational legacy, the Commando Merlin will continue that proud tradition.”