SINGAPORE - A Singapore aircraft, which was intercepted by Indonesian jets on Tuesday, has been released. The plane and the three people on board returned to Seletar Airport at 7.18pm.

The C90GTi King Air plane owned by Singapore Technologies (ST) Aerospace and operated by its pilot training arm, Pacific Flight Services, was en route from Sibu, Sarawak, to Seletar Airport with a pilot instructor and two trainees on board when it was instructed by the Indonesian air force to land in Pontianak, West Kalimantan.

The Singaporean pilot and two foreign trainees are "in good condition" ST Aerospace told The Straits Times on Wednesday morning.

The Indonesian authorities say that the plane was flying over the country's airspace without the necessary flight permits.

ST Aerospace said that the required approvals had been duly sought before the flight.

"We would like to clarify that we filed the flight plan in accordance with airspace regulations through the Civil Aviation Authority of Singapore and have been operating this route for a number of years without prior notification from the authorities of any issue for using this route," she said.

Plans for the return flight which was intercepted were filed through the Malaysian authorities.

According to industry experts, the norm is that the aircraft operators will file their flight plans through the civil aviation regulator of the country from which they depart.

The information is then conveyed to the authorities overseeing the skies along the path.