An Indian air force Su-30 MKI twin-seat fighter, the mainstay of the nation’s combat fleet, crashed on 19 May, with both pilots ejecting safely.

A statement issued by the ministry of defence says the aircraft was on a “routine sortie” and crashed approximately “36km south of Tezpur in Assam.”

The fighter took off from Tezpur air base, located in India’s North-Eastern region at 1230 local time and crashed a short while later. The air force has ordered a Court of Inquiry.

It is not yet known if the air force will ground the entire Su-30 MKI fleet, as was done following the loss of another SU-30 MKI on 21 October 2014.

There appears to be some confusion about the cause of last October’s crash. At the time it was attribued to an uncommanded seat ejection. Unsourced reports have since emerged that the loss was actually the result of pilot error. The air force, however, insists that crash investigations had “not indicated human error or technical defect as the cause,” and it will not reopen investigations on “any of these accidents.”

Indian Su-30 MKI’s have also seen recurring problems with the NPO Saturn AL-31FP thrust-vectored engines.

In March, defence minister Manohar Parrikar told parliament that from January 2013 to December 2014, “a total of 35 incidents of either engine failure in air or engine related problems have occurred.” “As advised by the OEM, the precautions / predictive maintenance during exploitation of aero engines have been implemented by the Indian air force.”