The HAL Dhruv is a twin-engine, intermediate-weight, tandem-seat Indian utility helicopter typically powered by two Turbomeca (now Safran) TM 333-2B2 turboshaft engines, or, in later variants, two Hindustan Aeronautics Limited (HAL)/Turbomeca Shakti turboshaft engines, an evolution of the TM 333. The Dhruv is almost exclusively in Indian service, although it is also operated by the Maldives, and was previously operated by Ecuador and Nepal.
India’s quest to develop an indigenous light helicopter began in 1969, when it signed a 10-year contract with France’s Aerospatiale to design a single-engine helicopter. This became the Advanced Light Helicopter (ALH) program. In 1977, however, the Indian Air Force (IAF) recommended that the program shift to developing a dual-engine helicopter. The government canceled the contract with Aerospatiale in 1981, and in 1984 signed a contract with Messerschmitt-Bölkow-Blohm (MBB) to consult for the design of the helicopter that would eventually become the Dhruv. This contract was to last seven years, was later extended by three years, and was allowed to expire in 1995. This would cause substantial developmental delays and cost escalations for the program.
The Dhruv was developed by the Rotary Wing Research and Design Center at HAL and produced by its Helicopter Division. It was intended to meet the requirements of the Indian Navy, Army, and Air Force, which imposed contradictory pressures on the design.
The first Dhruv prototype flew in August 1992. HAL originally intended to fit the Dhruv with the LHTEC T800 powerplant, but after India’s 1998 nuclear tests U.S. sanctions negated this option. Instead, HAL opted for the Turbomeca TM333-2B2. The hingeless rotor system used by the Dhruv is essentially an implementation of the rigid rotor system used by MBB on the Bo-105 and the MBB/Kawasaki BK-117. Without MBB support after 1994, HAL struggled with the rotor system. The end result was a system with significantly poorer reliability than its equivalent on the Bo-105 and BK-117. Compounding these problems, MBB’s withdrawal came just as integration and testing of the Dhruv’s anti-resonance vibration isolation system (ARIS) began, which HAL subsequently redeveloped independently. This would prove insufficient to meet the demands of the Indian military, so HAL contracted Lord Corporation to develop an active vibration control system (AVCS) for the aircraft in mid-2002. The AVCS supplemented the basic pylon-isolation ARIS system built by Lord for the aircraft. It also became apparent that the TM333-2B2 was underpowered for the “hot and high” requirements of the Indian Army, and in 2000 HAL contracted Turbomeca (now Safran Helicopter Engines) to develop a follow-on engine, the Shakti.
The failure to renew the MBB contract also caused immediate disruption to the certification process, and the five prototype aircraft, which were initially to be certified in 1994, were not certified until 2002 for the military version and 2003 for the civil version. In 1999, before certification was achieved or the design was frozen, a decision was made to begin limited series production. The year prior the Cabinet Committee on Security (CCS) also authorized the development of an armed variant of the Dhruv, the ALH-WSI (weapons systems integrated). This would later become the Mk. IV Rudra. While the weapons integration project was envisioned in 2005 as a 36-month development program, it did not achieve initial operating capability (IOC) until February 2013.
The Dhruv formally entered service with the Indian Air Force, Navy and Coast Guard in March 2002. The next year it appeared at the Paris Air Show, where potential export customers were invited to participate in flight demonstrations. It appeared again internationally at Le Bourget in 2005 alongside the Intermediate Jet Trainer. In 2006 the tail rotor was redesigned due to excessive vibrations, incorporating new materials and other design changes.
Since 2008, the Dhruv has been the subject of 33 airworthiness directives issued by India's civil aviation regulator, the Directorate General for Civil Aviation (DGCA). Problems with the aircraft include issues with the tail rotor drive, cracking in main rotor blade bolts, cracking in the tail and intermediate gearboxes, flight control problems, separation of GPS antennas from Dhruvs in flight, leaks in the hydraulic system and power loss in the engines . Deficiencies addressed by these airworthiness directives necessitated inspections and represented serious problems with the production of the aircraft, many of which were likely caused by quality control deficiencies at HAL.
The aircraft has also suffered from lateral cyclic control separation, in which the aircraft no longer responds to cyclic input while it is in “a very high degree of bank to the left combined with high rate of roll” and “excessive collective input,” according to a 2011 Human Factors Analysis and Classification system (HFACS) assessment of the October 2009 crash of a Dhruv during an Ecuadorean military parade. This was found to be the cause of at least two Dhruv crashes, and eventually led to Ecuador’s grounding and retirement of the remainder of its Dhruv fleet. While the problem had been known since at least 2002, HAL failed to implement remedial measures until 2010, when it disseminated an RFP for a Control Saturation Warning System (CSWS) for Dhruv aircraft. The Indian Ministry of Defense (MoD) announced in 2015 that the system was being fitted to Dhruv helicopters. The statement did not give details on when the upgrades were to be completed, whether civil aircraft were also receiving the upgrade, or what measures HAL and the MoD had taken in the interim to prevent further crashes.
The Dhruv airframe is built primarily with composites, which make up 60% of the surface area of the aircraft and 29% of the structural weight. This includes glass fiber, carbon and Kevlar composites. The airframe is optimized for crew survivability, with safety seats and controlled deformation of fuselage crumple zones in the event of a crash. Vertical impacts of up to 30 ft. per second are survivable for the crew.
To further enhance survivability, the Dhruv features FPT Industries (now GKN Aerospace Portsmouth) self-sealing crashworthy fuel tanks, damage-tolerant drive shafts and control rods, FPT Industries inflatable emergency flotation equipment and redundant load paths.
The aircraft also features a Safran four-axis automatic flight control system (AFCS) consisting of two redundant computers and a single center-console-mounted Pilot Control Unit (PCU). Sensors serving the AFCS include two altitude and heading reference systems (including two magnetometers and one panel-mounted attitude indicator), two Air Data Units (ADUs) supplying barometric altitude, indicated airspeed, and true airspeed, one radio altimeter, a heading selector equipped with two radio magnetic indicators and the aircraft’s FADEC. The AFCS operates through seven Stability Augmentation System (SAS) series actuators and four trim parallel actuators. All major components of the AFCS are made in India.
To accommodate cargo, the aircraft features large real clamshell doors. In addition to the aircraft’s two crew, it can seat 12 passengers in its normal configuration or up to 14 in a more crowded configuration if required. The underslung load capacity of the Dhruv is 3,307 lb. (1,500 kg), and the aircraft can automatically release a sling load when it touches the ground. Provisions exist for mounting a rescue hoist on the starboard side of the aircraft.
Rotor and Drive System
The Dhruv features a four-blade hingeless main rotor fitted with radial elastomeric bearings and a bearingless tail rotor mounted on a high tail boom. A skid is mounted under the tail boom to protect the tail rotor. The rotor blades are made of carbon fiber composite, feature swept tips for noise reduction and are resistant to impacts from up to 12.7mm projectiles. The rotor blades lack an automatic blade-folding system, but can be folded manually. The rotor hub is constructed of carbon composite with a titanium alloy centerpiece. Rotor brakes and main and tail rotor servos are supplied be Elettronica Aster S.p.A., an Italian company.
To transfer power from the engines to the rotors, the Dhruv features what HAL calls the Integrated Dynamic System (IDS), comprised of four gearboxes and the tail rotor driveshaft. The main gearbox (MGB) for the Dhruv was subcontracted by MBB to Zahnradfabrik Friedrichshafen (ZF), the German firm that developed the gearboxes for the Bo-15 and BK-117. It was designed to be compact to maximize cabin volume and is a two-stage reduction system. Flight can continue for at least 30 min. if the MGB loses lubrication. The MGB drives the intermediate gearbox (IGB) via the tail rotor driveshaft, and the IGB in turn drives the tail gearbox. Between the MGB and IGB sits the auxiliary gearbox (AGB), which is used to cool the lubricating oil from the MGB and circulate it back to the MGB. The MGB is fitted with a LORD Corporation active vibration control system, with four Frahm dampers.
In 2010 it emerged that the IDS was experiencing significant reliability issues that restricted the aircraft’s cruising speed to 250 km/hr. against the 270 km/hr. specified by the MoD. HAL opted to hire Italian aerospace firm Avio to consult on the problem. HAL claimed in 2011 to have resolved the issues with changes to the design and production process. Later in 2011, it emerged that in 2010 the DGCA had considered grounding civil variant Dhruvs over cracks in the IGB.
The original Dhruv variant (the Mk. I) features two Turbomeca TM333-2B2 turboshaft engines supplying 1,106 shp each at takeoff. The TM333-2B2 is a twin spool modular engine design with a two-stage axial compressor, a single stage centrifugal compressor driven by a single-stage turbine, and a single stage axial power turbine that drives a forward mounted reduction gearbox. Each engine is fitted with full-authority digital engine control (FADEC), and is started by a 10 shp generator. Due to the limitations of the TM333, the early Dhruvs could not exceed 16,400 ft. (5,000 m).
In 2016, HAL signed an agreement with Safran Helicopter Engines to conduct maintenance, repair, and overhaul of TM333-2B2 and Shakti engines at a facility in Goa.
Both wheeled and skid-based variants of the Dhruv exist, independently of their broader variant designations. The wheeled variants–with retractable wheels–are used by the Coast Guard and the Navy, and the skid variants are used by the Army and Air Force.
The Mk. I is the original variant of the Dhruv and features a conventional analog cockpit. The Mk. I is no longer in production.
The Mk. II features the Integrated Architecture Display System glass cockpit developed by Israel Aerospace Industries. This suite features NVG compatibility, high modularity (utilizing the MIL-STD-1553B data bus), multifunctional displays, and a modern navigation suite. The navigation system includes a digital moving map, mission planning, integrated display of weather data, support for VOR/DME systems and support for instrument landing system (ILS) stations. Like the Mk. I, this variant is no longer in production.
The Mk. III is the first Dhruv variant to be fitted with the Shakti engine, giving it improved performance at high altitude. The new engine permits the Mk. III to operate at the maximum altitude originally specified by the Indian military–20,000 ft. (6,000 m). This allows the Dhruv to support military operations in India’s mountainous border regions. In October 2007, a Mk. III in the Siachen Glacier flew up to 27,500 ft. (8,400 m). Despite this apparent success, the engine had earlier in 2007 been judged operationally deficient, and it was redesigned. It finally achieved certification in 2010 after a 46-month delay. The Shakti, a HAL-assembled derivative of the Safran Ardiden 1H1, features monocrystalline turbine blades and supplies 1,383 hp (1,031 kW) at takeoff.
The aircraft also has a variety of new avionics, countermeasures and sensors fitted, including an Elbit Systems Compass EO/IR pod and a solid-state digital video recorder. In Indian service, the Mk. III has been equipped with the Saab Integrated Defensive Aid Suite (IDAS), which includes radar warning receivers (RWRs) and a missile-approach warning system (MAWS). The system also includes the Saab BOP-L countermeasures dispenser system, and is integrated with the aircraft’s flare and chaff dispensers. Saab agreed in March 2017 to transfer IDAS technology to HAL to enable in-country maintenance of the system aboard the Dhruv.
Mk. IV (HAL Rudra)
The Mk. IV (also known as the HAL Rudra) is an armed variant of the Dhruv. It can carry a variety of armaments, including a nose-mounted Nexter M621 20mm cannon mounted in a THL 20 turret, 70mm rocket pods (in Indian service the Thales FZ231 12-rd pod), air-to-air missiles (the MBDA Mistral) and anti-tank guided missiles (ATGMs). To accommodate the cannon, the EO/IR pod is mounted on the upper side of the nose, instead of the usual underside. The Rudra is also fitted with a helmet-mounted weapons cueing system. The external rocket and missile stores are mounted on wing hardpoints on either side of the fuselage. Based on the configuration of the ammunition feed system, which runs into the cabin, the troop-carrying ability of the Rudra is reduced substantially compared to the base Dhruv.
Efforts to select and deploy an ATGM have floundered in India’s procurement system, but final tests are ongoing with DRDO’s indigenous Helina (the helicopter-launched variant of the Nag missile system) ATGM. Helina is a lock-on before launch (LOBL) system with an integrated infrared seeker. After exploring the procurement of foreign ATGMs such as Spike, India has elected to wait for the completion of Helina to arm the Rudra. Testing of the Nag system was reportedly completed in July 2019. Like the Mk. III, the Mk. IV is equipped with the Saab IDAS self-protection system.
Light Combat Helicopter
The Light Combat Helicopter (LCH) is an attack helicopter derivative of the Dhruv that dispenses entirely with the passenger compartment and streamlines the airframe into a tandem-seat layout. The aircraft has crashworthy tricycle wheeled landing gear and additional armor. It shares the Dhruv IDS drive system, rotor system and carries the Shakti engines used on the Dhruv Mk. III and Rudra. The avionics and mission systems and EO/IR pod are the same, though HAL is working to deploy an indigenous display system and AFCS aboard the LCH after the initial batch is completed. The LCH can carry a maximum of 1,543 lb. (700 kg) of ordinance across four pylons. The LCH carries the M621 gun system (in a Nexter THL 20 mount), and other weapons will include the Helina, MBDA Mistral and 70mm rocket pods (the same pods used on the Rudra).
For self-protection the LCH carries the same Saab IDAS system as the Dhruv Mk. III and Mk. IV. Later variants of the LCH are expected to carry active laser missile spoofing measures. IR suppressors have been fitted to the engines to reduce the thermal signature, and the streamlined airframe necessarily reduces the aircraft’s radar cross-section relative to the Dhruv. No contract for the LCH has been awarded as of May 2021, but three limited series production aircraft destined for the IAF have been built. These complement the four LCH prototypes, which are expected to remain with HAL indefinitely.
The limited series production contract is expected to cover 15 LCH airframes. 10 of these will go to the IAF with the balance for the Indian Army. Over the life of the program, the Army intends to acquire 97 LCHs and the Air Force at least 63.
A variant fitted with an Indian LRDE SuperVision-2000 sea-search radar was contemplated in the early 2000s but ultimately rejected by the Indian Navy in 2008. This variant could also carry two lightweight antisubmarine torpedoes, depth charges or anti-ship missiles, and was fitted with a dipping sonar. The Navy opted to adopt wheeled Dhruv Mk. I and Mk. III helicopters instead, in a generalized shore-based utility role, and has pursued the Sikorsky MH-60R to fulfill antisubmarine warfare requirements. This is largely because the Navy did not believe the Dhruv to be a useful shipboard capability without an automatic blade folding system, a strengthened undercarriage, or greater payload capacity.
Naval Utility Helicopter Contender
HAL is offering a variant of the Dhruv Mk. III for the Indian Navy’s Naval Utility Helicopter (NUH) program. Under NUH, the Navy intends to procure 111 shipborne helicopters for search and rescue (SAR), medevac, counterpiracy, communications and humanitarian assistance and disaster relief (HADR) purposes to replace the HAL Chetak (a license-built Alouette III). This variant is to be equipped with a folding tail boom and an automatic rotor blade folding system. Other contenders in the NUH competition include the Sikorsky S-76, the Bell 429, and the Airbus AS656.
Following a deadly June 3, 2019 crash of an Indian Air Force An-32 transport aircraft, India has elected to fit a wide variety of aircraft, including the Dhruv, with Elbit Systems emergency locator transmitters and airborne locator systems. An oxygen life-support system was also developed by DRDO for the Dhruv.
Production and Delivery History
Serial production for the Mk. I began in 2001, which was followed by the Mk. II in 2007 and the Mk. III in 2012. HAL produces all of its ALHs from its helicopter division’s factory in Bangalore at a rate of 24 ALHs per year. Dhruv production is expected to continue into the early to mid-2020s, with production for the LCH extending beyond that.
Seven Mk. I Dhruvs were delivered to the Ecuadorean Air Force. Four aircraft crashed between 2009 and 2015. Following the last accident, the remaining three Ecuadorean Dhruvs were grounded and eventually withdrawn from service outright. They remain in storage as Ecuador looks for opportunities to divest itself of them.
Ecuador’s Military Accident Investigation Board (JIAM) determined in 2015 that one of the Ecuadorian military’s four Dhruv crashes was due to a tail rotor problem similar to those disclosed in the 2011 airworthiness directive. Of the other three crashes, Ecuador determined that the first two were due to human error while the last was also due to technical problems with the helicopter. In October 2015, Ecuador unilaterally terminated its contract with HAL.
The primary operator of the Dhruv, the Indian Armed Forces, possesses 287 aircraft across all four armed services as of October 2021. This figure excludes the LCH. The Indian Coast Guard (ICG) began receiving Dhruvs in late 2003. 60 Dhruv Mk IVs were contracted for the Army in December 2007 for ₹62.96 billion in then-year rupees ($2.03 billion in 2019 USD).
159 Dhruv Mk. I, Mk. II and Mk. III aircraft were originally ordered for the Indian Air Force and Army. Six Dhruv Mk. Is were ordered for the Border Security Force by 2008. The BSF opted to procure the wheeled variant of the Dhruv, as opposed to the skid variant in service with the Air Force and Army. In July 2014, the Coast Guard and Navy agreed to purchase 32 Dhruv Mk. III aircraft (16 for each service) under a performance-based logistics contract worth about ₹80 billion rupees ($1.4 billion in 2019 USD). Deliveries began in 2020 and are expected to conclude in 2023. In September 2017, a contract for 41 Dhruv Mk. IIIs was awarded–40 for the Army and one for the Navy.
24 Mk. I Dhruvs are in service with the Indian Air Force (IAF). 38 Mk. IIIs and 16 Mk. IVs were also delivered by the end of 2017. In 2021, the IAF received a 17th Rudra, and will receive two more by the end of the year. It is unlikely this marks the end of the IAF's Rudra commitment.
IAF Dhruvs have fulfilled primarily general transport and attack roles but can also perform search-and-rescue (SAR) and observation missions. The IAF is now focusing on procuring the Light Combat Helicopter (LCH), which is rooted in the Dhruv design. The LCH will fill a gap between the Rudra and the AH-64E as the IAF’s dedicated intermediate-weight attack helicopter. At least four Dhruvs in Air Force service have been written off following accidents. The IAF has a requirement for 63 LCHs which are expected to be delivered throughout the 2020s.
The Indian Army possesses 32 Dhruv Mk. Is, 20 Dhruv Mk. IIs, 72 Dhruv Mk. IIIs and 58 Dhruv Mk. IVs. Ten Mk. IIIs remain on order, with deliveries anticipated to conclude in 2021. Army Dhruvs are used primarily for general transport and attack duties. Three Dhruvs and one Rudra in Army service have been written off following accidents. The Army has also contracted for five Light Combat Helicopters, with deliveries scheduled to begin in 2019. The Army has a total requirement of 114 LCHs.
Border Security Force
Six Mk. I Dhruvs are in service with the Border Security Force. No additional Dhruvs are on order, and the six in service are used for observation purposes. Two more Mk. I aircraft were operated by BSF but crashed in 2011 and 2012 and were written off.
Three Mk. I Dhruv helicopters are in service with the Coast Guard, though four were delivered; one was transferred to the Maldives. Two of the 16 Mk. IIIs on order have been in service since March 2021. A third was handed over midway through the year. Under current plans the balance should arrive by the end of 2023. These aircraft are used primarily for SAR operations. The Dhruv has been deployed in support of disaster relief in Nepal in 2015 and used by the Indian Coast Guard for medical evacuation in the Maldives.
The Indian Navy received eight early-build Dhruv Mk. Is before deciding the helicopter was generally unsuitable for naval operations. In July 2014, the Navy reluctantly agreed to purchase 16 Dhruv Mk. III helicopters. Six were delivered in 2021.
While the Mk. IIIs will not be used in a shipboard role, they will provide the Navy with an enhanced shore-based SAR capability. The first three were delivered in February 2021. In November 2013, the Indian Navy stood up its first Dhruv squadron, INAS 322, at INS Garuda, Kochi. The Navy is investigating the modifications HAL recently unveiled permitting the folding of the tail boom and accelerating folding of the rotor blades.
Three Dhruv Mk. I helicopters were delivered to the Maldives National Defense Forces. One of them was returned to India, but the other two were not and remain in service. The Maldives uses the Dhruv for SAR.
Two Dhruv Mk I aircraft were delivered to Nepal in 2004, and an additional Mk. I was delivered in November 2014. One was damaged in 2004 and by mid-2016 all three were withdrawn from service.
An offering for three Dhruvs to Suriname was reportedly contemplated but never taken up. Suriname did receive three HAL Chetaks in 2015, however. The Chetak is a domestically-produced Alouette III derivative.
While HAL has long intended to break into the civil helicopter market with the Dhruv, it has been largely unsuccessful. HAL has so far failed to obtain an European Aviation Safety Agency (EASA) type certification for the aircraft, and there are no confirmed civil operators outside India. The civil operators that do exist in India are either affiliated with the national government or the state government of Jharkhand.