The design issue in India's ALH Dhruv has been fixed, with helicopters being fitted with an upgraded control system to improve airworthiness

A design issue in the military’s advanced light helicopter (ALH) Dhruv has been fixed and the locally made helicopters are being fitted with an upgraded control system to improve airworthiness after a series of accidents led to the grounding of the fleet and called into question their flight safety record, two senior officials aware of the matter said.

A top government regulatory body responsible for the certification of the airworthiness of military aircraft ordered the design review in April.

Aircraft maker Hindustan Aeronautics Limited (HAL) has begun supplying new booster control rods made of steel instead of aluminium to ALH squadrons across the country, and the “tested and proven” design improvement will ensure flight safety, said HAL helicopter complex CEO S Anbuvelan.

These rods allow pilots to control the helicopter’s motion, and any failure can severely affect power input to the rotor blades and cause accidents.

“Control rods for 120 helicopters have been dispatched to different squadrons. The remaining helicopters will get these rods by November. Incidents linked to control rod failure will not recur,” Anbuvelan said. The design improvement is critical as the armed forces operate around 330 twin-engine ALHs, designed and developed by HAL. It began delivering these helicopters in the early 2000s.

This is the first upgrade in the ALH’s control assembly, which consists of the collective, pitch and roll control rods. “What is being replaced right now is the collective control rod. The other two rods will be similarly replaced between November 2023 and June 2024,” he said.

The ALH fleet was grounded for weeks following three incidents in less than two months earlier this year. The multi-mission helicopter has been involved in 12 accidents during the last five years.

The design improvement was much needed as the armed forces use the ALH extensively and India is also looking at tapping its export potential, said another official.

The Bangalore-based Centre for Military Airworthiness and Certification (CEMILAC) ordered the design review of the booster control rods to improve the ALH’s airworthiness. CEMILAC, which functions under the Defence Research and Development Organisation, reached the conclusion that the design review was mandatory after an expert committee, formed in the backdrop of a navy ALH ditching (emergency landing in water) into the Arabian Sea on March 8, explored the possible failures that led to the incident.

A coast guard and an army ALH were involved in accidents after the navy incident.

The panel found that the most probable cause of the navy ALH incident was a technical failure --- an error in the assembly of serrated washers in the booster control rods.

The design, development and qualification of the steel booster control rods that are tolerant to assembly errors shall be expedited, and the compliance of the new design shall be aimed for implementation in six months to one year, CEMILAC wrote in a letter dated April 23 to HAL, the three services, and the coast guard.

“Though the helicopters are matured from the design point of view, having been exploited for more than 3 lakh hours, still there is scope to review the design/lifting aspects of the safety-critical system by an expert committee as a long-term measure,” said the letter, written by CEMILAC director (helicopters and missiles) DM Isack.

The regulatory body red flagged the drastic reduction in the fatigue life of the control rods.

The Indian Air Force’s latest light combat helicopters (LCH), which inherit several features of ALH, were also grounded earlier this year. LCH is capable of targeting enemy air defences, slow moving aircraft, high-altitude bunkers as well as carrying out counter-insurgency operations.

CEMILAC had earlier prescribed measures for the resumption of ALH and LCH operations.

Clearance for both platforms, limited to 100 flight hours each, will be given after mandatory inspections, it said. Further clearance for up to 500 flight hours or one year, whichever is earlier, will be based on the successful completion of two critical tests by HAL, it added.

These tests involved the flight testing of two helicopters with instrumented control rod assembly for verifying the multi-axis loads on the control rods, and the fatigue testing of the rods with correctly assembled serrated washers to confirm their original capability.