NEW DELHI, June 27 -- Plane maker Hindustan Aeronautics Limited (HAL) is struggling to pinpoint and fix a lingering flaw in the Dhruv advanced light helicopters operated by the navy and coast guard, and a question mark hangs over when will the locally produced choppers --- grounded for almost six months now --- return to service, officials aware of the matter said on Wednesday. The military's advanced light helicopter (ALH) fleet was grounded following a fatal coast guard crash at Porbandar in Gujarat on January 5, but the army and air force choppers were declared airworthy after comprehensive safety checks on May 1. P4...