New Delhi/Bangalore, Jan. 6: The armed forces have been forced to delay the reinforcement of aviation wings after the grounding of the indigenously-manufactured Dhruv advanced light helicopter.

The aircraft were grounded after the manufacturer, Hindustan Aeronautics Limited (HAL), a defence public sector undertaking, decided to inspect each of the flying machines that it had supplied to the services following repeated complaints of a technical snag.

An air force source said two additional squadrons of the helicopters that were being created in addition to the two existing ones would now be delayed till the choppers were inspected and certified for airworthiness. This means a delay of at least two months.

Likewise, the army aviation corps, which was operating 30 Dhruv helicopters, will also have to delay the raising of two more units. The army is the largest user of the helicopters among the armed forces.

The grounding of the aircraft and an advisory by the head of the air force, Air Chief Marshal S.P. Tyagi, not to fly them till each machine and component has been cleared means a setback to efforts to export the helicopter.

HAL had received repeated complaints of a technical snag involving the helicopter’s tail rotor.

The immediate reason to ground the machine was an accident in November in Andhra Pradesh when a Dhruv came down while being flown from Bangalore to Ranchi to be delivered to the Jharkhand government.

The Dhruv uses a four-blade bearingless cross-beam tail rotor fitted on the starboard side of pylon.

The rotor is made from material that was imported from a European country in the mid-1990s and is now understood to have outlived its utility. This means HAL was using material declared expired by its European supplier.

HAL, however, has defended the aircraft, saying it had been grounded only as a precaution. It said Dhruv’s tail rotor blade was of very sound design and has been extensively tested.

“The tail rotor blades of the helicopter involved in the mishap belong to a particular batch of blades, which are not in service with customers as yet,” a company release said.

Defence minister Pranab Mukherjee said that a board of inquiry has been set up to probe the accident in Andhra Pradesh.