State-owned Indonesian Flight Navigation Service, also known as AirNav Indonesia, said six planes were flying at the same time and a similar height as AirAsia flight QZ8501, which was flying from Surabaya to Singapore and lost contact with air traffic control at 6:17am local time on Sunday.
"At the same time, six planes were around the missing AirAsia flight," AirNav president director Bambang Cahyono said, as quoted by Antara news agency during a press conference at Soekarno-Hatta International Airport in Jakarta on Monday.
Among the six were planes belonging to Garuda Indonesia, Lion Air and Emirates, he added.
"At that time, the AirAsia flight was at 34,000 feet and asked for permission [from air traffic control] to fly higher, to 38,000 feet," said Bambang.
At 38,000 feet, however, there was a Garuda Indonesia flight, so the AirAsia flight turned left before it lost contact.
"So because there was a Garuda Indonesia flight there, the AirAsia flight could not climb to the height it had requested," said Ahmad.
He said a string of measures in line with procedures had been conducted to communicate with the AirAsia pilot but all failed, then the Airbus 320-200, which took off from Surabaya at 5:36am local time, lost contact with air traffic control and could not be monitored anymore.
Separately, Transportation Minister Ignasius Jonan said up until now, the missing AirAsia flight had not been detected.
"A joint search and rescue team led by the National Search and Rescue Agency [Basarnas] has not yet found the location of the AirAsia flight, which is thought to have crashed," he said.
The Transportation Ministry has dispatched various vessels, including navigation vessels, on the search and activated coast guards and is monitoring radios. It has also requested local fishermen take part in the rescue operation.
"All facilities have been activated to help search for the AirAsia plane and to get information on possible crash sites," said Jonan.