Senior authorities with knowledge of the situation said on Wednesday that flaws on the Dhruv advanced light helicopter, whose safety record came under scrutiny after a succession of mishaps earlier this year, have been found and are being corrected on a priority basis to address flight safety issues.

One of the individuals listed above, who requested anonymity, claimed that while looking into the recent occurrences involving the India-made helicopter, some design and metallurgy flaws came to light.

More than 330 DHRUVs are in use with the army, navy, air force, and coast guard. The helicopter was suspended from March through May after safety concerns became acutely apparent in the wake of three mishaps during this time. The helicopter was subsequently cleared to fly again.

After thorough inspections, the state-owned Hindustan Aeronautics Limited-designed and developed helicopters are being approved to fly in batches for urgent missions, according to the second person listed above who also sought to remain anonymous.

The DHRUV was engaged in 12 mishaps during the previous five years, including the army helicopter crash-landing in Kishtwar, Jammu & Kashmir, on May 4 that resulted in the death of one soldier and the injuries of two pilots. Prior to it, a naval DHRUV ditched (made an emergency landing in water) into the Arabian Sea on March 8 and a coast guard DHRUV made a forced landing in Kochi on March 26.

Resuming urgent flights required the required “satisfactory conduct of independent maintenance flight safety audit” of critical components and systems, as well as adherence to safety-related “special technical instructions and alert notices” issued by technical authorities, according to a government letter dated May 22.

A design assessment of a “safety-critical system” on the DHRUV may be necessary, according to a key government regulatory authority in charge of certifying the airworthiness of military aircraft, HT reported on May 10. The three military and the coast guard were informed of this in a letter from the Centre for Military Airworthiness and Certification (CEMILAC), which has its headquarters in Bengaluru. To increase the airworthiness of the DHRUV, it mandated a design study of the booster control rods.

After an expert committee established in the wake of the navy DHRUV incident on March 8 looked into potential failures that may have contributed to the incident, CEMILAC, which is part of the Defence Research and Development Organisation (DRDO), came to the conclusion that the design review of the booster control rods is required. The motion of the helicopter is controlled by these rods, and any failure can significantly reduce the amount of power applied to the rotor blades and result in mishaps.

The committee, which was created by the chief executive (airworthiness) of CEMILAC, determined that a technical failure – a mistake in the installation of serrated washers in the booster control rods – was the most likely cause of the event on March 8. It suggested both immediate and long-term actions to improve the DHRUV’s safety.

In a letter dated April 23 to HAL, the three services, and the coast guard, CEMILAC instructed them to speed up the design, development, and qualification of the steel booster control rods that are forgiving of assembly errors and to aim for implementation of the new design within six months to a year.

For the restart of the DHRUV, Rudra (the armed version of the DHRUV), and the Light Combat Helicopter (LCH) operations, CEMILAC specified steps. The most recent LCHs of the Indian Air Force were also grounded early because they incorporate some DHRUV characteristics.

After required inspections, clearance for these platforms—each with a cap of 100 flying hours—would be granted. Additional approval for up to 500 flying hours or one year, whichever comes first, will be contingent on HAL passing two crucial tests, it was stated.

In order to check the multi-axis loads on the control rods, these tests include the flight testing of two helicopters with instrumented control rod assemblies as well as the fatigue testing of the rods with properly assembled serrated washers to verify their original functionality.