Production delays by state run Hindustan Aeronautics Ltd ( HAL ) have seriously impacted air combat strength, particularly when it comes to its Mirage 2000 and Jaguar fighter fleets that are currently undergoing upgrades, the air force has informed the government.Pointing to delays ranging from two to six years, the air force has brought out that HAL has not been able to meet delivery schedules, resulting in both fleets being in a sub optimal state, besides raising questions on the trainer aircraft being developed by the agency.The Mirage 2000 is India ’s cutting edge fighter, tasked with a nuclear weapon delivery role as well. The Jaguar fleet was purchased in the late 1970s but is still a potent ground attack fighter designed for surgical, deep penetration missions.However, in a review of the aeronautic company late last year, the air force has said that the series upgrade of 47 Mirage 2000 fighters that was signed in July 2011 has seen three production schedule delays already. It has informed the government that as per schedule, HAL should have delivered 21 upgraded jets but has actually been able to send only six.Sources informed ET that since the review, one more jet has been delivered. HAL has blamed the delay on the non-availability of kits from France but the air force is not impressed by the argument, given that the contract was signed over seven years ago. Officials say this delay has seriously impacted operational preparedness as well as availability rate for the ‘very competent fighter’.Besides the 47 Mirage fighters, the air force has also red flagged a six year delay in the upgrade of the Jaguar fleet to DARIN III standard. The contract to upgrade 61of these fighters was signed in December 2009, with the understanding that all of them would be ready by December 2017.However, not a single aircraft has yet been delivered to the air force with HAL struggling to integrate a new radar on the jets. IAF has informed the government that it now expects the upgraded fighters to join service only by 2024.Sources said the delay has again come at the cost of combat strength as it has pushed down availability of fighters. At present, an entire squadron strength of 20 fighters is not operational, awaiting the upgrade.HAL’s record on the delivery of Su 30 MKI fighters has also been questioned, with the government being informed that there is an overall delay of three years in the production schedule. While all aircraft were to be delivered by 2017, HAL still has at least 23 of the fighters to deliver to the air force.On trainer aircraft, the air force has raised questions on the development schedule of the HTT 40 basic trainer. While the timeline for certification of the trainer was February 2015, the air force says the project is running behind time and it is not expected that HAL will manage even to certify the aircraft as fit for service before 2021.