The Tejas Success Story In One Picture

A picture taken from an amateur video just moments before the crash of India's homegrown Tejas fighter jet's first-ever accident sums up its entire story.

It may be perplexing how this crash, an expensive one at that (each Tejas costs $43 million), which breaks Tejas' almost perfect safety run of over decades, (23 years to be precise), can define the hard work, sweat and dedication of its developers.

The amateur video of the crash, which can be watched here, captures the final moments before the Tejas crashes into a small home in Jaisalmer. It shows the pilot successfully ejecting and safely descending with his parachute open, while the Tejas appears to glide smoothly, a scene that abruptly ends as the video cuts off.

Initial reports claim that the crash happened due to engine failure, but the entire picture will only get clear after a detailed inquiry is completed.

Surprisingly, even after the pilot had ejected, the jet can be seen smoothly gliding down with its landing gear down, without showing any signs of sudden jerks and movements, before crashing to the ground.

This is even more significant since the jet is designed to be inherently unstable (in the pitch axis).

If its all-digital fly-by-wire (FBW) flight control system (FCS) — which the designers went to extreme pains to develop — is not working properly, the jet will simply fall to the ground like a rock dropping from the sky.

The fact that the jet's FCS was working flawlessly even after engine power was lost (as far as we know) shows the resilience of the FBW FCS and its control laws (CLAW) designed by the developers.

When India set out to develop the Tejas in 1986, the all-digital fly-by-FBW FCS with quadruple-redundant channels controlled by a microprocessor-based all Digital Flight Control Computer (DFCC) was one of the four main next-generation systems, and also the single most sophisticated and complex tech, to be incorporated in the jet.

The other three technologies were a glass cockpit (replacing the old analogue rounded dials), composite wings and airframe, and finally, microprocessor-controlled general systems.

The FBW FCS technology was so advanced that only the Americans and British had successfully developed and operated such advanced control systems.

Even the Europeans (the French) were behind.

The French offered India a hybrid-FCS that had three digital channels and one analog. The designers rejected this offer and went alone with designing the FCS (with some consultancies like Wright Brothers of the USA, and BAE Systems of Britain).

This decision caused some heartburn in the Indian Air Force (IAF) since this could delay the whole programme — which it did — with the first flight taking place only in 2001, five years after the expected maiden flight in 1996.

In traditional control systems, there is a physical connection between the pilot control column and the jet's control surfaces, viz, the ailerons, elevons and rudders.

In comparison, the all-digital FBW FCS has no physical connection between the pilot control column and jet’s control surfaces.

When the pilot moves the control column, the DFCC interprets the inputs into electrical signals, using a control law, and transmits it to the electro-hydraulic actuators connected to the control surfaces, which moves the control surfaces as determined by the control law.

Writing the control law and testing it before going into the actual aircraft is the most crucial component in the development of the FCS — more so since nobody in India had ever worked on designing an FCS, let alone testing it.

To that regard, the Indian government selected the erstwhile Martin Marietta Control Systems (MMCS), now known as Lockheed Martin, from the US for consultancy in designing and testing the FCS, as well as developing the DFCC, while the British BAE Systems was chosen to assist with the integration of the FCS into the Tejas prototype.

A national-level team to write the control law was formed in 1992, with personnel drawn from ADA, HAL, IAF and NAL. A National Flying Test Centre (NFTC) was established (in 1992) for the exclusive testing of the FCS.

Writing the CLAWs is one thing, testing it is a whole another level.

Even a single anomaly can cause the prototype to crash, potentially setting back the already delayed programme several years, or worse, the cancellation of the programme.

The Swedes suffered this when they were developing the FBW FCS of their Gripen fighter jet, and that too, twice.

India went to extreme lengths to ensure that the FCS was as safe as possible. There were five testing checks before the FCS and its DFCC was integrated with the airframe.

Before the code of the CLAW even went to testing at the real-time simulator at the NFTC, a test pilot with the control engineers tested the code in a simulator called the Engineer-in-Loop Simulator (ELS).

The software was independently verified by a team called Independent Verification and Validation (IV&V) to validate whether the software was written according to industry standard and verify whether the code does what it is meant to do. Following which the code would be taken to an In-Flight Simulator (IFS) at Calspan in the US where the code was installed on real planes (a commercial Learjet, T-33 trainer and an F-16) to test how the FCS works in real-world conditions.

In one of the IFS testing, the CLAW worked better than even the F-16’s own FCS.

The code was then tested on another test rig, called the Iron Bird, which verifies whether the software and hardware are ready for actual flight or not.

Moreover, three committees, the FCS review committee, a Performance Verification Committee (PVC), and a Flight Readiness Review Board (FRRB) were formed to keep oversight on the development of the FCS, apart from the independent verification conducted by the Centre for Military Airworthiness and Certification (CEMILAC).

Finally, when the first prototype — TD-1 — took to the air, the test airframe flew without any hiccup.

And all this while simultaneously battling budget crunch, lack of infrastructure, which India had to develop on the fly, sanctions, and various intra-organisational battles.

Fast forward to now, all pilots who have flown the jet unanimously praise the jet for its flying characteristics and its intuitive man-machine interface, talking about the multifunction display, which was another pioneering tech that the designers took upon themselves to develop.

Group Captain Dinesh ‘Danny’ Dhankar, the Commanding Officer (CO) of No. 18 Squadron ‘Flying Bullets', praises the aircraft's capabilities. He appreciates the nimbleness of the jet, apart from its carefree handling, high rate of turn, and its climb performance.

The Group Captain credits its relaxed static stability and the indigenously designed fly-by-wire (FBW) controls for making the aircraft highly maneuverable and agile.

He says that "the type's g onset is 'very comfortable,'" adding that, “It responds to your inputs in the entire envelope very well.”

“It's not as if you need to be at certain speeds to get the maximum out of it. At any speed, it gives you whatever you demand,” he explains, detailing the capabilities of the FBW flight control system (FCS).

Dhankar states that the FCS also increases the jet's safety factor, saying, "It is impossible to depart from the approved flight envelope limits," which can be evidenced by the fact that by 2021 the plane had undertaken more than 5000 sorties without a single crash — until now.

Tejas test pilot Group Captain Rajeev Joshi describes its FCS as "throw it around as much as you can — when she says ‘no’, she will take over and recover the situation for you. The control and handling in high gain tasks like aerial refueling is superb. It will beat contemporaries or older birds in this area. It really makes you feel like a great pilot!”

Sure, such world-class advanced technologies caused delays in the programme, but the hard work done then has now paved the way for the development of even more advanced and cutting-edge systems for the future fighter jet projects, viz, the Tejas Mk-2 and 5th generation Advanced Medium Combat Aircraft.

The Indian Air Force has constituted a court of inquiry to identify the cause.

Whatever delays the jet saw in its development, whatever may be the cause of the crash and whether the assertion that the FCS was working perfectly till the jet crashed is true or not, the fact remains that Tejas is one of the safest fighters in IAF’s inventory. It is a success story for Defence Research and Development Organisation and for the entire Indian scientific community.