HAL-built trainer aircraft HTT-40 clears crucial flight test successfully

Clearing the HTT-40's six-turn spin tests removes a monkey from our backs, said design chief Arup Chatterjee

Hindustan Aeronautics (HAL) has underlined its growing capability to design and develop fixed-wing aircraft by steering its home grown Hindustan Turbo Trainer-40 (HTT-40) basic trainer to the brink of final flight clearance.

In flight-testing on Saturday in Bengaluru, HAL’s test pilots threw the HTT-40 into multiple spins and, each time, the trainer returned to level flight smoothly. In so doing, the HTT-40 cleared the so-called “six-turn spin test”, regarded as the ultimate and most difficult test for a trainer aircraft.

The HTT-40 has already met and, in many aspects of flight performance, surpassed the so-called “Air Staff Qualitative Requirements” (ASQRs), which lists out the flight performance — speed, turn, ceiling, etc. — that the IAF demands from an aircraft.

Since 2012, the Indian Air Force (IAF) has consistently opposed the HTT-40, first pressuring the Ministry of Defence (MoD) into importing 75 Pilatus PC-7 Mark II basic trainers from Switzerland, and then demanding more imports because HAL would allegedly never be able to steer the HTT-40 through all its tests.

“There is no need for [the HTT-40 trainer]”, then IAF boss, Air Chief Marshal NAK Browne, had dismissively stated at the Aero India show in 2013. “We have the Pilatus PC-7. It’s a proven aircraft. The project HAL plans is from scratch. Our indications are that the cost will be too high. There is no need for all this.” Each successive IAF chief followed the same line, criticizing the HTT-40, while demanding more Pilatus imports.

As Business Standard reported (June 10, 2019, “IAF block on indigenous HTT-40 trainer aircraft keeps door open for Swiss trainers”) the current IAF chief refused to even issue a tender for the HTT-40, which was needed to procure engines for the production aircraft. The IAF stated it would only do so after the HTT-40 cleared the six-turn spin tests. HAL has responded to IAF opposition with defiance. Successive HAL chiefs backed the HTT-40, committing Rs 350 crore of internal HAL funds to the project. A team of young, talented HAL designers have worked without IAF assistance or funding, backed to the hilt by former defence ministers, A K Antony and Manohar Parrikar.

For the Pilatus PC-7 Mark II trainer, the procurement of which is already under the scanner of the Central Bureau of Investigation, this most likely spells the end of further imports. The HTT-40 falls under the category of “Indian designed, developed and manufactured” (IDDM) equipment, and the MoD cannot import more Pilatus without a detailed explanation of why the HTT-40 is being ignored.

“For HAL, clearing the HTT-40’s six-turn spin tests removes a monkey from our backs. Our intermediate jet trainer (IJT) aircraft had failed its spin tests and we were determined this would not be the fate of the HTT-40. In fact, not just has the HTT-40 cleared its spin and stall tests, we have revived the IJT project as well,” said HAL’s design chief, Arup Chatterjee.

HAL has manufactured the IAF’s fleet of Hawk advanced jet trainers (AJT), with technology from BAE Systems. With the HTT-40 poised for final clearance, a breakthrough on the IJT could mean that the IAF’s entire training aircraft fleet comprises of HAL-built aircraft.