India's Comptroller and Auditor General watchdog has taken the country's air force to task over irregularities in a contract to upgrade 40 RSK MiG-27 fighters, and also criticised the service over its purchase of three Boeing Business Jets for VVIP transport duties.

State-owned Hindustan Aeronautics is continuing work to equip the MiG-27s with new navigation equipment to enable them to operate at night, and to upgrade their attack and electronic warfare systems, despite the project having slipped four years behind schedule.

Spending has also more than doubled from an original budget of 4.5 billion rupees ($111 million), according to the CAG, which says the air force "severely understated" the project costs.

The upgrade may also have "limited viability", it says, as inherent airframe and engine problems have not been resolved. "Upgraded aircraft will have a very short residual life," it adds.

The 9.97 billion rupee purchase of three BBJs also "deviated from laid-down procedures and well recognised norms of propriety", says the CAG.

Supplies worth $50 million were contracted without competition, an "inordinate delay" of eight years in selecting the aircraft and its self-protection suite increased costs by $19.7 million, and the purchase of the third aircraft was an unnecessary expense, it concludes.

Pre-requisite conditions such as an ability to fly non-stop to cities like London were also not adhered to during the procurement, it adds, forcing some VVIP transport to be conducted using commercial Air India flights.