In the dynamic world of aviation, few aircraft have achieved the widespread recognition and operational versatility of the Eurocopter EC135. This twin-engine, light utility helicopter, now known as the Airbus Helicopters H135, has carved out an indispensable niche across a multitude of sectors, from critical air medical transport to demanding law enforcement operations and specialized corporate travel. Its journey began with a vision for a highly adaptable and efficient rotorcraft, a vision that has been meticulously refined over decades, culminating in an aircraft celebrated for its reliability, advanced technology, and remarkably quiet operation. This article delves into the fascinating history, innovative design, diverse applications, and enduring impact of the EC135, exploring what makes it a true workhorse of the modern sky.

From Concept to Icon: The EC135's Evolutionary Journey

The story of the EC135 begins even before the formation of Eurocopter, tracing its roots back to the Messerschmitt-Bölkow-Blohm (MBB) Bo-108 project in the 1970s. Initially conceived as a technology demonstrator, the Bo-108 aimed to integrate the proven attributes of the successful MBB Bo-105 with groundbreaking advancements. This included the pioneering implementation of full-authority digital engine controls (FADEC) on a helicopter, a revolutionary hingeless main rotor, and an innovative transmission system. The first prototype took to the skies on October 17, 1988, powered by Allison 250-C20R/1 engines, followed by a second prototype in June 1991, featuring Turbomeca TM319-1B Arrius engines. These early demonstrators, while utilizing conventional tail rotors, laid the foundational groundwork for what would become a hallmark of the EC135.

The late 1990s marked a pivotal period in the EC135's evolution. The design underwent significant refinement with the introduction of the distinctive Fenestron tail rotor system, an advanced rigid main rotor, and the extensive use of composite materials, complemented by sophisticated resonance isolation systems. This comprehensive overhaul led to a full certification program, and the Bo-108 was officially rebranded as the EC135, aligning with the newly established Eurocopter company. A strategic decision was made to offer the EC135 with a choice of two powerful and reliable engines: the Turbomeca Arrius 2B and the Pratt & Whitney Canada PW206B. Both powerplants proved highly successful and have been integral to subsequent production aircraft.

The EC135 made its public debut at the Heli-Expo convention in Las Vegas in January 1995, where its impressive appearance and performance figures garnered significant attention from prospective buyers. A key characteristic that quickly became apparent upon its entry into service was its remarkably low noise signature, largely attributable to its Fenestron tail. For over 15 years, the EC135 held the distinction of being the quietest aircraft in its class, a testament to its innovative design. While initially conceived with emergency medical operators in mind, the helicopter's inherent versatility quickly broadened its appeal across a wide spectrum of operators. European JAA certification was secured in June 1996, with FAA approval following swiftly in July. Further cementing its operational capabilities, the EC135 received single-pilot IFR (SPIFR) certification from Germany's Luftfahrt-Bundesamt (LBA) in December 1999, a certification echoed by the United Kingdom's Civil Aviation Authority in December 2000.

Continuous Innovation: The EC135's Ongoing Evolution

Eurocopter, and subsequently Airbus Helicopters, has consistently invested in the EC135's development, ensuring its continued relevance and enhanced performance. In 2000, the EC135P2 was introduced, featuring the Pratt & Whitney Canada PW206B2 engines, which offered improved single-engine performance and a crucial 30-second emergency power capability. This variant received LBA certification in July 2001, with the first delivery to the Swedish Police Authority in August of the same year. The EC135T2, equipped with the upgraded Turbomeca Arrius 2B2, followed in September 2002, further boosting single-engine performance.

Innovation extended beyond engine upgrades. In 2002, the EC135 active control technology demonstrator/flying helicopter simulator (ACT/FHS) took its maiden flight, serving as a research platform for fibre optic-based flight control systems. By 2014, Airbus Helicopters launched the Bluecopter demonstrator, a project aimed at exploring more efficient design elements. This included optimizing single-engine operations, incorporating Blue Edge swept rotor blades for noise reduction and increased efficiency, and relocating the horizontal stabilizer to minimize main rotor downwash. These advancements, alongside an active rudder and new water-based external paint, were designed to achieve a remarkable 40% reduction in fuel consumption.

The EC135 has also seen bespoke luxury adaptations. In March 2007, Eurocopter unveiled the 'L'Hélicoptère par Hermès' at the NBAA in Atlanta. This special-edition VIP model, designed by Hermès International, S.A., featured a lavish four-place main cabin, a sliding glass partition, and redesigned external elements, catering to the discerning tastes of corporate clients. Further personalization options for this exclusive variant were made available in July 2014.

Global collaboration has also played a significant role in the EC135's production. In 2011, Eurocopter formalized a license manufacturing agreement with Zhong-Ou International Group for the production of the EC135 luxury helicopter in Zhejiang Province, China. This was followed by a letter of intent in October 2015 between Airbus Helicopters and Ecopark to establish a final assembly line (FAL) in Qingdao Province, China, accompanied by a substantial $1.1 billion order for 100 Chinese-assembled H135s. While the majority of assembly work remains at Airbus Helicopter's Donauwörth facility, the Qingdao FAL commenced production in April 2019. Similarly, in January 2016, the Ural Works of Civil Aviation (UWCA), a division of Rostec, signed an agreement to license-build the H135 at its facility in Yekaterinburg, Russia, with production anticipated to begin in 2017.

Further performance enhancements arrived with the EC135 T3 and EC135 P3 variants, designed for improved high-altitude and hover performance. These modifications included repositioned engine air intakes, wider main rotor blades, and refinements to the Fenestron anti-torque tail device. The EC135 T3 entered service in December 2014. In a significant development in December 2020, the H135 helicopter family received EASA certification for a new Alternate Gross Weight (AGW), increasing the maximum takeoff weight by up to 265 lbs (120 kg) and extending its range by up to 75 nautical miles or endurance by up to 40 minutes under standard conditions. This AGW upgrade is available as an option and can be retroactively applied to all Helionix-equipped H135s. Additionally, December 2020 saw Airbus certify a new single-pilot IFR Helionix cockpit for the H135, offering customers the flexibility to optimize the cockpit layout for enhanced field of view or specific STC equipment installation.

Engineering Excellence: The EC135's Core Design

The H135, a testament to sophisticated engineering, is a twin-engine rotorcraft offering power choices between the Turbomeca Arrius 2B and Pratt & Whitney Canada PW206B engines, influencing its variant designation as 'T' or 'P' respectively. Its main rotor is a four-bladed, hingeless fiber-composite design, continuously refined since its introduction to boost performance and reduce maintenance. A key factor in the EC135's reputation as the quietest helicopter in its class is its anti-resonance isolation system, which effectively dampens main rotor vibrations. The advanced Fenestron anti-torque device, actively regulated by a HI NR rotor optimization mode, further enhances controllability, particularly during high-weight take-off and landing operations. The EC135 is fully capable of Category A operations throughout its flight envelope, underscoring its robust design and safety features.

Pilots of the EC135 benefit from a choice between a conventional flight deck and the advanced Avionique Novelle glass cockpit, the latter enabling single-pilot instrument flight rules (IFR) operation. This modern glass cockpit features multiple liquid-crystal displays, including two Sextant SMD45 displays and a central panel, with the main avionics suite supplied by Thales Group. Operators also have the option to integrate various avionics suites from manufacturers such as Russian firm Transas Aviation and British firm Britannia 2000. Newer H135 models come equipped with a four-axis autopilot, sharing commonality with other Airbus Helicopters rotorcraft like the H160 and H175. Earlier EC135 versions featured a three-axis autopilot with integrated stability augmentation and a First Limit Indicator (FLI) for simplified engine and torque monitoring. Optional cockpit touch screens further enhance the pilot's interface.

Beyond its technical prowess, the EC135 excels in adaptability, offering diverse cabin and cockpit configurations tailored to specific operational roles and operator preferences. It can comfortably accommodate a pilot and up to five passengers in a standard executive layout, or up to seven passengers in a high-density corporate configuration. The helicopter features modular multi-role interiors, allowing for rapid reconfiguration of the main cabin. Access to the main cabin is facilitated by large doors on either side, complemented by clamshell doors at the rear, directly beneath the tail boom. These clamshell doors are particularly advantageous for emergency medical services (EMS) and cargo operations, streamlining loading and unloading processes.

For medical missions, the EC135 can be outfitted with comprehensive in-flight intensive care stations, including resuscitation capabilities, incubators, and hygiene-friendly flooring. In challenging mountain rescue scenarios, the cabin is designed to simultaneously accommodate two stretchers, along with the pilot, an anaesthetist, winch operator, mechanic, and a mountain rescue specialist, highlighting its exceptional utility in demanding environments.

A Global Presence: The EC135 in Operation

The operational history of the EC135 is a testament to its global appeal and robust performance across diverse environments and missions. Deliveries commenced in August 1996, with the first two helicopters, serial numbers 0005 and 0006, being handed over to the German emergency aero medical service provider, Deutsche Rettungsflugwacht. By June 1999, when the 100th EC135 was delivered to the Bavarian police force, the worldwide fleet had already accumulated approximately 30,000 flight hours, underscoring its rapid adoption and high utilization. The 300th EC135 was delivered to UK-based McAlpine Helicopters in September 2003, solidifying the EC135's position as the best-selling new light twin-engine helicopter in the UK market.

Its popularity continued to soar, with Eurocopter announcing in 2011 that the 1,000th EC135 had been delivered to the German operator ADAC, roughly 15 years after its initial production. In 2012, Flying magazine lauded the EC135 as "the industry's best-selling twin-engine helicopter." A notable milestone was achieved by G-NESV (cn 0067), operated by the Cleveland Police Air Operations Unit based at Durham Tees Valley Airport, UK, which became the world fleet leader in flight hours for the type, having accumulated over 10,000 flying hours since its original delivery to the North East Air Support Unit in April 1999.

The EC135 has also played a pioneering role in the offshore wind industry. In 2009, it was the first aircraft selected for offshore wind support in the UK, following approval from the Civil Aviation Authority for helicopter operations to the Greater Gabbard offshore wind farm. Its utility in this sector extended to Denmark, where it supported the Horns Rev offshore wind farm. By 2013, the EC135 had facilitated over 10,000 successful personnel transfers in this demanding environment. In Mexico, operators like Transportes Aéreos Pegaso, Servicios Aéreos Estrella, Transportes Aéreos del Golfo, and AeroLogística Aéreo have deployed fleets of EC135s to service extensive oil and gas offshore platforms in the Gulf of Mexico.

Its primary role in air medical services remains significant. In 2013, it was reported that the EC135 accounted for approximately 25% of the world's total emergency medical services flights. By late 2013, despite a brief grounding due to fuel gauge concerns, the EC135 comprised half of the UK's operational air ambulance fleet. The first EC135 air ambulance was delivered to the Chinese market in October 2014, further expanding its global reach in critical care.

Beyond civilian applications, the EC135 serves as a vital training platform. The German Army operates 19 H135s as basic trainers at the School of Army Aviation in Bückeburg, maintaining an impressive operational availability exceeding 95%. In 2014, the German Army identified a potential for vibration-induced rotor cracking during autorotation training, which could shorten the main rotor's lifespan. The Japanese Maritime Self-Defense Force has also procured 13 EC135 trainers, designated as the TH-135.

Recent developments continue to enhance the EC135's capabilities. In December 2014, the first production EC135 T3 entered service with Aiut Alpin Dolomites, a mountain rescue operator in Italy. In June 2015, Airbus Helicopters delivered the first retrofitted H135 from the earlier EC135 standard, incorporating an enlarged main rotor, relocated engine air intakes, elevated engine performance, and redesigned horizontal stabilizer endplates for increased span. In October 2015, Waypoint Leasing and Airbus Helicopters signed an agreement for the acquisition of up to 20 H135s for public leasing purposes.

The EC135 also plays a crucial role in military training. In 2017, the Royal Air Force received the first two of 29 H135s, designated as Juno HT.1s, for the UK Military Flying Training System, with training provided by Ascent Flight Training. In 2018, the Australian Defense Force established the Joint Helicopter School, operating 15 EC135T2+ helicopters procured under Project Air 9000 Phase 7, to train both Australian Army and Royal Australian Navy pilots. This school is based at Navy's 723 Squadron at HMAS Albatross. Looking ahead, in 2024, following the retirement of the MRH-90 Taipan helicopter, the Australian government announced a five-year lease of five H135T3 (Juno) helicopters from the United Kingdom Ministry of Defense to meet essential training requirements for Australian Army pilots. These helicopters will be based at the Oakey Army Aviation Centre.

Variants: Tailored for Every Mission

The EC135 family boasts a range of variants, each meticulously designed to meet specific operational demands and performance requirements:

• EC135 P1: Powered by two Pratt & Whitney Canada PW206B engines, each producing 463 kW (621 shp). Initial maximum take-off weight (M.T.O.W.) was 2,630 kg (5,798 lbs), later increased to 2,720 kg (5,997 lbs) and then 2,835 kg (6,250 lbs). Later versions included the Centre Panel Display System (CPDS).

• EC135 T1: Equipped with two Turbomeca Arrius 2B1/2B1A/2B1A1 engines, each delivering 435 kW (583 shp). Similar M.T.O.W. progression and CPDS integration as the P1.

• EC135 P2: Replaced the EC135 P1 in production in August 2001, featuring increased thermodynamic and mechanic OEI (One Engine Inoperative) ratings (128% OEI torque).

• EC135 T2: Replaced the EC135 T1 in production in September 2002, powered by two Turbomeca Arrius 2B2 engines, each providing 452 kW (606 shp), with increased thermodynamic and mechanic OEI ratings (128% OEI torque).

• EC135 P2+: Introduced in 2006, replacing the EC135 P2. It is powered by two Pratt & Whitney Canada PW206B3 engines, each producing 498 kW (668 shp), with further increased thermodynamic and mechanic OEI ratings (128% OEI torque).

• EC135 T2+: Also introduced in 2006, replacing the EC135 T2. It features two Turbomeca Arrius 2B2Plus engines, each delivering 498 kW (668 shp), with increased thermodynamic and mechanic OEI ratings (128% OEI torque).

• EC135 P3: Powered by two Pratt & Whitney Canada PW206B3 engines, this variant boasts an increased maximum take-off weight of 2,980 kg (6,570 lb).

• EC135 T3: Equipped with two Turbomeca Arrius 2B2Plus engines, this variant also features an increased maximum take-off weight of 2,980 kg (6,570 lb).

• H135: This is the current designation for the EC135 after Airbus Helicopters' rebranding, signifying the continued evolution and integration of the type within the Airbus family.

A Legacy of Excellence

The Eurocopter EC135, now the Airbus Helicopters H135, stands as a remarkable achievement in rotorcraft engineering. From its humble beginnings as a technology demonstrator to its current status as a globally recognized workhorse, its journey has been marked by continuous innovation, adaptability, and an unwavering commitment to performance and safety. Its quiet operation, advanced avionics, and versatile configurations have made it the preferred choice for a wide array of missions, from life-saving air medical transport to demanding law enforcement and critical military training. The enduring legacy of the EC135 is not just in its impressive technical specifications or its widespread adoption, but in its consistent ability to meet and exceed the evolving demands of modern aviation, truly earning its place as a versatile workhorse of the skies.

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