IAF’s Training Aircraft Requirements and Indigenous Development Status – A Comprehensive Picture

anil chopra, air power asia, Trainer Aircraft

With a renewed emphasis on “Atmnirbharta” (Indigenisation) it is nice to see that the two trainers under development by Hindustan Aeronautics Lt (HAL), the HTT-40 and the IJT have taken centre stage again. A country that has successfully built the modern Light Combat Aircraft ‘Tejas’ and is now flying in Indian air Force’s (IAF) combat squadrons, should have been flying its own trainers for decades.

HAL HT-2 Basic Trainer. Picture Source: doc8643.comaircraftHT2


          The Hindustan Trainer HT-2 was an Indian two-seat primary trainer designed and built by HAL which entered production in 1953. It replaced Havilland Tiger Moth as trainer for the IAF and Indian Navy. This low-wing cantilever monoplane with a fixed tail-wheel landing gear was powered by a 155 hp (116 kW) Cirrus Major III piston engine. The tandem cockpits had dual controls. The aircraft looked quite similar to, and was perhaps influenced by the design of  de Havilland Canada DHC-1 Chipmunk. Apart from military use, the aircraft was also used by some Indian flying schools. A total of 172 were built. 12 HT-2s were delivered to the Ghana Air Force and used between 1959 and 1974.The aircraft retired in 1990. Many of had learnt our powered-aircraft flying on this aircraft. Some of us including myself had instructed on this aircraft at basic flying training stage. Though a little under powered, and the long nose did restrict forward visibility, the aircraft proved a good “eliminator” to decide who must continue to become a pilot. Overall it served the purpose it was built for.

HAL HPT 32 Deepak. Picture Source: Wikipedia

HPT 32 Deepak

          The HAL HPT-32 “Deepak” was an HAL manufactured prop-driven primary trainer with the student and the instructor sitting side-by-side. The aircraft, with speeds of 280-kmph and a range of 1,400-km, was also meant to be used for observation, liaison and target towing. The aircraft did its first flight on 06 January 1977. Aircraft also had four hard points to carry 255-kg war load, machine gun pods, bombs and rockets, and could have been used as fighter plane. It however was not used in these roles. It was used as a Basic Trainer for the IAF and Indian Navy till grounded for good in 2009 after a fatal accident in which two ace pilots were killed. The single 195kW (260hp) Textron Lycoming EIO-540-D4B5 flat six piston engine with a two-blade constant speed propeller, was known to be a reliable engine flying worldwide. However, there was some serious mismatch between the aircraft and engine fuel systems that could not be resolved. The 125 aircraft fleet had seen the IAF through 25 years of basic flying training.  There were frequent cases of engine cuts in flight and in many cases the engine could not be restarted. A total of 19 pilots had lost their lives in HPT-32 crashes, not all necessarily due engine cuts. HAL did make an attempt to install a parachute assisted recovery system for safe landing in case of emergency, but the project was considered unviable and called off. In any case the service life of HPT-32 was virtually over. If the HAL’s attempt at enabling safe landing of the aircraft with parachute recovery system succeeded, the aircraft may be in service for a few more years. IAF deciding to get rid of the fleet due to flight safety considerations.

IAF Harvard T 6G aircraft. Picture Source: warbirdinformationexchange.org/

Harvard T-6G

          The North American Aviation T-6 Texan was an American single-engine advanced trainer aircraft used to train pilots of the United States Army Air Forces (USAAF), United States Navy, Royal Air Force (RAF), and other air forces of the British Commonwealth during World War II and into the 1970s. The aircraft had first flight on 01 April 1935. Designed by north American aviation, the T-6 was known by a variety of designations depending on the model and operating air force. in India it was called the Harvard, the name by which it was best known outside the US. It was a very safe aircraft to fly and a total of 15,495 T-6s of all variants were built. India and Pakistan had inherited these from the RAF and added more for training requirements.    The aircraft had seen combat actions in many countries including Middle-East, Africa and Vietnam. The Pakistan Air Force used T-6Gs in the Indo-Pakistani War of 1971 as a night ground-support aircraft, hitting soft transport vehicles of the Indian army. The IAF used the Harvard for Stage-2 training and was flown over the years at IAF flying training establishments/academies at Ambala, Begumpet, Jodhpur, and Air Force Academy at Dundigal, Hyderabad. It was also flown at the Flying Instructors School at Tambaram. The Harvards were phased out in 1973.

IAF Vampire T-55. Picture Source: bharat-rakshak.com

Vampire T-55 and Type 52

          The de Havilland Vampire was a British jet fighter. It was the second jet fighter to be operated by the RAF, after the Gloster Meteor, and the first to be powered by a single jet engine. The aircraft and done its first flight on 20 September 1943 and entered service in 1946.  During its early service, it was recognised for accomplishing several aviation firsts and various records, such as being the first jet aircraft to traverse the Atlantic Ocean. The Vampire remained in front-line service with the RAF up until 1953. It was thereafter progressively reassigned to secondary roles, such as ground attack missions and pilot training. During 1966, the Vampire was officially retired by the RAF. 3,268 Vampires were built in 15 versions, including twin-seat night fighters, trainers and carrier-based aircraft designated Sea Vampire. The Vampire was used by 31 air forces.

The No.7 Squadron, IAF received Vampires in January 1949. No.17 and No.37 Squadrons also operated flew a number of Vampire NF54 night reconnaissance missions over Goa during the 1961 Annexation of Goa. On 1 September 1965, during the indo-Pakistani War, No.45 squadron used the aircraft for strikes against Pakistan army. T.55 was export version of the DH.115 trainer. 216 built. IAF used De Havilland Vampire T55, PR55 and NF54 (Twin Seaters) and T-52 night fighter for stage III training till early 1970s. The Two Seater Vampire was a completely different aircraft from the single seater fighter. The aircraft featured ejection seats, larger wings, larger fuselage and came in different variants. 

PZL-Mielec TS-11 Iskra – India Air Force. Picture Source: airliners.net

Polish Iskra

The PZL TS-11 Iskra was a Polish jet trainer, developed and manufactured by aircraft company PZL-Mielec. It has been used by the air forces of Poland and India. Poland’s ability to independently develop aircraft in an era of political and economic subservience to the neighbouring Soviet Union was in question during the 1950s. Following the death of Joseph Stalin, more liberty could be taken. It made its first flight in 05 February 1960 powered by an imported British Armstrong Siddley Viper turbojet engine. During 1975, an initial batch of 50 Iskra bis D trainer aircraft were acquired by IAF for stage III training, the type’s sole export customer. During the 1990s, a further 26 aircraft were procured. By 1987, a total of 424 aircraft had reportedly been constructed, after which point production of the type was terminated due to a lack of demand. However the type remained in service with the Polish Air Force and the Indian Air Force into the 21st century. In December 2004, the Indian Air Force officially withdrew the last of its Iskra trainers.

HTT-34. Picture Source: flickr.com

HTT- 34

          The Hindustan Turbo Trainer, the turboprop powered HTT-34 was developed as an internal venture by HAL. The 313kW (420shp) Allison 250-B17D powered HTT-34 flew for the first time, in a converted HPT-32 prototype form, on 17 June 1984. The new engine significantly boasted performance on the basic aircraft, but was cancelled as official interest was not forthcoming.

Pilatus PC-7 Mk II Turbo Trainer. Picture Source: economictimes.indiatimes.com

Pilatus PC-7 Mk II Turbo Trainer 

          The Pilatus PC-7 Turbo Trainer is a low-wing tandem-seat training aircraft designed and manufactured by Pilatus Aircraft Switzerland. The aircraft is capable of all basic training functions including aerobatics, instrument, tactical and night flying. The PC-7 was introduced during the 1970s, it has since developed a sizable presence of the global trainer market, adopted by in over 20 air forces as ab initio trainer. Over one million hours have reportedly been flown by PC-7s worldwide. In addition to training operations, some aircraft are armed and have been used for combat missions by several customers. PC-7 Mk II is an improved model developed in the 1990s by combining the newer PC-9s airframe and avionics with the PC-7’s smaller turbine engine. Reportedly, in over 500 PC-7s have been sold to various operators, the majority of which still being in service. IAF has procured 75 aircraft, and received the last aircraft in July 2018. The plan to acquire additional 38 has been shelved. In 2017, the maintenance agreement with Pilatus lapsed, resulting in the IAF becoming solely responsible for performing these activities. In July 2019, the Indian government had terminated business dealings with Swiss company Pilatus Aircraft Ltd. for one year following allegations of monetary kickbacks in 2012 in the 75 aircraft deal.

HAL HTT-40. Picture Source: economictimes.indiatimes.com

HTT – 40

            The HAL HTT-40 is a training aircraft, which was meant to replace the IAF’s HPT-32 basic stage trainer.  The all-metal tandem seat aircraft powered by a 1,100 hp (820 kW) turboprop engine. In early 2012, HAL forecast building 106 examples. The sudden grounding of the HPT 32 had brought a crisis situation to IAF training. A fast track competition and selection process short listed Pilatus PC-7 Mk II as the winner. By the middle of 2012 the HTT-40s future was in doubt as the IAF ordered 75 Pilatus PC-7 Mk IIs to fill its urgent trainer aircraft requirements, the role envisioned for the HTT-40. In September 2012 the IAF also indicated that it had formally rejected the HTT-40 for service based on its cost per aircraft being double that of the PC-7 Mk II, a proven aircraft already in service worldwide. More recently when the HTT-40 started flying, the Indian Air Force Chief publicly stated that IAF would be buying HTT-40 in large numbers. On 28 February 2015, it was reported that Indian defence ministry was considering to procure 68 HTT-40 trainers. On 21 June 2015, HAL chose the Honeywell Garrett TPE331-12B turboprop with four-bladed propeller to power the trainer. HAL rolled out the first prototype on 2 February 2016. The HTT-40 had its first flight on 31 May 2016. The flight lasted for about 30 minutes. The pilot carried out circuits and the aircraft performance was reported satisfactory. The HTT-40 in its new avatar made its first public introduction flight on 17 June 2016. On 19 May 2017, the second prototype completed its maiden flight. On 10 November 2018, HTT-40 started its spin test by successfully entering into two-turn spin and subsequently recovering with the appropriate controls. The spin testing is the most crucial and challenging aspect of flight testing of any trainer aircraft development program. On 6 September 2019 HTT-40 completed a five turn spin trial successfully and on 7 September 2019 it successfully completed a six turn spin trial. HAL had planned IOC (Initial operational clearance) by end of 2019 and after placement of order 1st aircraft will be handed over to IAF within 1 year. HAL is looking for LSP (limited series production) by 2020. IAF is likely to order 106 aircraft. In a major endorsement, last November, the IAF chief Air Chief Marshal Rakesh Bhaduria flew the HTT-40.

HTT-40 and Pilatus PC-7 Mk II Basic Characteristics

          HTT-40 aircraft powered by a 1,100 hp (820 kW) turboprop engine and has a gross weight of 2,800 kg and fuel capacity of 450 Kg.  Its Maximum speed is 400 km/h. The service ceiling is 6,000 m (19,680 ft) and the g limits are +6/-3. PC-7 Mk II is powered by Pratt & Whitney Canada PT6A-25C of 410 kW (550shp) with three bladed propellers. Its  Max takeoff weight is 2,700 kg. It has a Fuel capacity of 474 Liters. The Maximum speed is 412 km/h. The Service ceiling is 10,000 m (33,000 ft). It can be seen that in most counts the aircraft are comparable.

HAL HJT-16 Kiran. Picture Image: defpost.com

HJT-16 Kiran

          The HAL HJT-16 Kiran is a two-seat intermediate jet trainer that performed its maiden flight on 4 September 1964. The mass production commenced shortly thereafter. Furthermore, during the 1980s, the IAF procured a number of Kirans that were furnished with a more powerful engine and a higher number of hard points, and the variant designated Kiran MK II. It has also been adopted by the Indian Naval Air Arm. The last Kiran was completed during 1989, after which the assembly line was closed. The Kiran has been in operational use for over 50 years. IAF has been awaiting its successor HJT-36 Sitara since the late 1990s. By the 2010s, use of the type was gradually declining as increasing numbers of newer BAE Systems Hawks, built under license by HAL, have been introduced to IAF service. The Kiran was being used in the Surya Kiran aerobatic team  of the IAF up until February 2011. A total of 190 Kirans were built and have been great service for IAF training.

Intermediate Jet Trainer HJT-36 Sitara Then (Top) and Now. Image Source: defencenewsofindia.com

Intermediate Jet Trainer HJT-36 Sitara

          The HAL HJT-36 is a subsonic intermediate jet trainer (IJT) aircraft developed for IAF and Indian Navy. The HJT-36 will replace the HAL HJT-16 Kiran as the Stage-2 trainer. The Sitara is a conventional jet trainer with low swept wings, tandem cockpit and small air intakes for the engine on either side of its fuselage. It entered limited series production by 2010 but according to the IAF it remained “unfit” for service due to technological issues related to spin test. In April 2019, Sitara flew for the first time in three years with a modified air frame to correct its spin characteristics.

          HAL started design work on an IJT in 1997. In 1999, following reviews by the IAF, the Indian Government (GoI) awarded HAL a contract for development, testing and certification of two prototype IJT aircraft. The first and second prototypes flew on 7 March 2003 and in March 2004, respectively. The program was then delayed with the Air Force assessing the SNECMA Turbomeca Larsac engine, with 14.1 kN of thrust, as under-powered. In response, in August 2005, HAL reached a deal to replace the SNECMA engine with the NPO Saturn AL-55I with 16.9 kN of thrust. The deal also provided for license-production of the engine in India by HAL. Further delays were caused by delays in delivery of the NPO Saturn engine by 2 years, as well as due to two accidents in February 2007 and in February 2009 involving each of the prototypes, which grounded the aircraft for repairs and investigations. The first AL-55I engine was received from Russia only in December 2008, 2 years later than committed, and was installed on PT-1. Flight tests with the new engine started on 9 May 2009.

          After further development and extensive testing, the IAF placed an order for 73 aircraft. After over 280 test flights, the aircraft entered limited series production in 2009 for the first 12 aircraft to be delivered to the IAF. The first flight test for the limited series aircraft occurred in January 2010, and initial operational clearance (IOC) was expected by July 2011. The IAF order was expected to grow to over 200 aircraft. The third Prototype did its first engine ground run on 27 July 2012. In December 2013, HAL declared that Sitara was ‘weeks’ from certification.

On 19 February 2014 the Indian MoD made a statement that the development of IJT was in the advanced stages of certification, with more than 800 test flights completed so far. The activities were progressing well with completion of sea level trials, night flying trials, high altitude trials as well as weapon and drop tank trials. The activities left for obtaining Final Operational Clearance (FOC) are the refinement of stall characteristics, and spin testing which will be commenced as soon as stall characteristics were refined. All efforts were being made to achieve FOC by December 2014. Production of aircraft was to commence immediately thereafter. However, it was realised that the stall cannot be tested until HAL redesigns the entire aircraft to correct its “inherent asymmetry”. BAE was consulted on certain design changes, specifically the tail. Afterwards the design was put to mathematical and wind tunnel tests. The modified aircraft was expected to complete the spin tests by September 2015, and the production of 85 aircraft for the IAF to begin.

          In March 2017, Jane’s reported that due to the HJT-36’s “unresolvable” issues associated with critical stall and spin characteristics the aircraft was not yet  ready to serve as an intermediate jet trainer for IAF. HAL took advice from U.S. aviation technology and testing firm Bihrle Applied Research Inc. to redesign major parts of the aircraft’s tail end, resulting in significant airframe changes, first visible when the redesigned jet flew in April 2019. The air frame was modified to move the tailfin and tailplane further down which was expected to make spin recovery easier.

          HJT-36 uses a quarter of the aircraft’s line replaceable units (LRU) which are common with HAL Tejas trainer variant. The prototype aircraft used Russian Zvezda K-26LT lightweight zero-zero ejection seats. However, these may be replaced with Martin-Baker Mk.16 IN16S seats, due to a price escalation of the former. The pilots have both conventional and manual flight controls. The trainer has a full glass cockpit with a layout similar to current generation combat aircraft. It uses an integrated digital avionics and Head-up display and repeater. The aircraft has five external hard-points for weapons-training. The maximum external payload is 1,000 kg. All production models will use the NPO Saturn AL-55I engine with about 16.9 kN of thrust, as stipulated by the 2005 air staff requirements from the IAF.

          In an interview with the HAL Chairman, of 08 July 2020, LiveFist’s Shiv Aroor writes that, four years after failed spin trials brought the aircraft program to a halt, HAL’s HJT-36 Sitara intermediate jet trainer (IJT) will restart a crucial set of spin trials this month. With a significantly altered airframe that returned to flight last April, and with a vitally awaited spin recovery chute just delivered, test crews will shortly commence spin trials that must be successfully completed if the aircraft is to have a chance to continue. “We have not given up on the IJT, in fact we have restarted the program,” HAL chairman & managing director R. Madhavan told Livefist. HAL was hoping that spin trials mirror successes achieved with the HTT-40 trainer. Delays in the Sitara program had compelled the IAF to reconfigure its flying training stages, to basic and intermediate training stage on PC-7 Mk.II trainers and advanced/lead-in training on HAL-built Hawk Mk.132 jets. Ageing HJT-16 Kiran jets continue to be used in training much that IAF would like to phase them out. Seventeen years after the Sitara first flew, the flight tests that take place this month will determine if the aircraft has a career in the Indian military.

IAF’s BAE Systems Hawk 132. Picture Source: defpost.com

BAE Systems Hawk 132

          The BAE Systems Hawk is a British single-engine, jet-powered advanced trainer aircraft. It was first flown in 1974 as the Hawker Siddeley Hawk, and subsequently produced by its successor companies, British Aerospace and BAE Systems. It has been used in a training capacity and as a low-cost combat aircraft. Operators of the Hawk include the RAF and many foreign military operators. The Hawk is still in production in the UK and produced under license in India by HAL. Over 1000  Hawks have been built and sold to 18 operators around the world.

          On 23 February 2008, the Hawk Mk. 132 formally entered service with the IAF, after one a very protracted procurements in India’s history, two decades having elapsed between the initial interest and the contract signing on 26 March 2004. The IAF received 24 aircraft directly from BAE Systems with deliveries beginning in November 2007, and further 42 Hawks assembled by HAL between 2008 and 2011. In February 2008, India planned to order 57 more Hawks, 40 for IAF and 17 for the Indian Navy. The additional aircraft were to be all built in India by HAL. On 10 February 2011, HAL and GE Aviation signed a contract under which GE Aviation will conduct the next 30 years of maintenance on the Hawk fleet. In 2011, the IAF was reportedly unhappy with the provision of spare components, so in December 2011, BAE received a contract to provide India with spares and ground support. The Hawk fleet is based at IAF’s Bidar Air Force Station in Karnataka. As of 2015, a total of 123 aircraft were on order by the Indian Air Force and 17 by the Indian Navy. An additional order of 20 aircraft were ordered or the Surya Kiran Aerobatic Team. The second Hawk Training base is at Air Force Station Kalaikunda in West Bengal. The Hawk is being used like a lead-in-fighter-trainer (LIFT), just before the fighter pilots can move to their respective operational squadrons on different front-line fighters. Though the Hawk-132 is basically an Advanced Jet Trainer (AJT) and not an LIFT. It is also used to train the fighter Weapons Systems Officer (WSO)

          In May 2015, HAL revealed that it was examining the prospects of performing its own Hawk upgrades, including armed light attack variants. The IAF, which were in the process of receiving trainer Hawks built under license by HAL, were reportedly interested in the upgrade proposals, which would also include avionics and cockpit modifications; HAL has stated that it also aims to export combat Hawks to other countries in partnership with BAE. Missile developer and manufacturer MBDA may provide their ASRAAM and Brimstone missiles to arm the new attack type called Hawk i.

HAL Hawk i. Picture Source: indiandefencereview.com


          The HAL HJT 39, or CAT (Combat Air Trainer), was an Advanced Jet Trainer (AJT) project proposal by HAL for the IAF. HAL HJT 39 CAT Program was announced first at Aero India, February 2005, with mockup of front fuselage and cockpit shown. It was projected to fly within three and a half years of go-ahead with airframe and engine commonality with HJT-36 Sitara, avionics comparable with those of HJT-36 and LCA Tejas. CAT was planned as a twin engine transonic LIFT with a very substantial ground attack capability with a maximum speed of 1,000 km/hr. HAL has alos been talking of Supersonic Omni Role Trainer Aircraft (SPORT).

          CAT was to feature Multi Function Displays (MFD) for tactical navigation, Radar Warning Receiver (RWR) and indigenous CSIO/BEL-developed Head Up Display (HUD) and Up Front Control Panel (UFCP), used on the LCA. The HUD would display both navigation and weapon aiming. CAT also features redundancy features like stand by instrumentation system, Fly-by-Wire (FBW), hands-on-throttle-and-stick HOTAS), INS along with GPS receiver, flight control computer and display processor. It were to have Full Authority Digital Engine Control (FADEC). It was to have an airborne radar or simulator. The HJT-39 was to be an all-composite aircraft. In view of the ground attack requirements, it was to be powered by two NPO Saturn AL-55 turbofans of 2,200 kg thrust each, compared to the 1,800 kg thrust of the variant for the single-engined HJT-36 intermediate jet trainer. CAT was to feature 5 hard points. The external stores with practice bombs, rockets, missiles and a gun in central fuselage. The maximum takeoff weight with external stores was projected as 9,500kg. The HJT-39 will also have a virtual training capability, with radar simulation, computerised training aids and the like. An item of optional equipment for the HJT-39 was the On-Board Oxygen Generation System (OBOGS). HAL had planned to deliver a prototype in 39 months after the clearance from the government with the project cost of Rs 750 Crore (2005). Would have been a tall order considering that the IJT has still to induct. There is no further news of the project after Hawk-132 was bought. Unless Hawk i is meant for such a role.

Two Stage Vs Three Stage Training

          World over there has been debate about two/three stage flying training. Most air forces believe in three stage training. The stage-I is usually the stage for basic training to get the trainee to learn basic flying. Also it is a stage to eliminate those who either don’t have piloting skills or are rather slow learners and can’t cope with military flying. In countries where there are many flying schools, such skills are established and basic training is completed before the individual joins the Air Force. In countries like India we prefer such training in service and also utilise that time for other service training. Normally the aircraft used for this stage are relatively slower piston engine aircraft. Pilatus PC-7 and HTT-40 make good contenders. Stage-II training is normally on medium speed jets like the Kiran, HJT-36 etc. The pilot gets exposure of more tactical flying in this stage. The Stage-III training is on even more advanced jet trainer (AJT) where the pilot gets to do all types of combat exercises and also weapon firing. IAF will thus require the HTT-40 to augment the numbers of Pilatus and later replace them all together. There will be requirement of IJT to replace the Kiran aircraft. This is way behind schedule and IAF cannot afford to wait endlessly. IAF needs an AJT of the Hawk-132 class. It also needs an LIFT. We presume that all concerned are talking.

Way Ahead India       

          Last over a decade has been tough for IAF in terms of indigenous training aircraft. Such was not the case earlier. India had to resort to a fast track procurement approach for Pilatus PC-7 Mk II. That was unfortunate. HAL must quickly resolve all pending issues on HTT-40 and HJT-36 and start series production. Currently IAF is down to 30 fighter squadrons. Once the numbers start building towards 42, pilot and WSO requirements will go up. IAF will need many more trainers. India is working on the fifth generation aircraft such as the Advanced Medium Combat Aircrfat (AMCA). We therefore should first succeed in trainers. “Atmanirbharta’ is the slogan. Time to act is now.     

Picture Source: commons.wikimedia.org

Published by Anil Chopra

I am the founder of Air Power Asia and a retired Air Marshal from the Indian Air Force.

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