SINGAPORE — Indonesia has accepted a Singapore Armed Forces’ offer of a submarine support-and-rescue vessel in the search for the missing AirAsia plane that entered its second day yesterday.

Apart from the vessel, MV Swift Rescue, Singapore offered personnel from the Maritime and Port Authority of Singapore (MPA) and additional equipment, including a sidescan sonar system and a robotic remotely-operated vehicle.

The MPA equipment will support the operation by Singapore Ministry of Transport’s Air Accident Investigation Bureau, whose offer of two teams of specialists and two sets of underwater locator beacon (ULB) detectors — to assist in locating the plane’s flight data recorder — has been accepted by Indonesia.

The detectors come with hydrophones, akin to underwater microphones, which can detect acoustic signals that are emitted from the ULB attached to the missing plane’s flight data recorder.

“An operator will submerge the hydrophone underwater and rotate it 360°. Another operator will use headsets to listen for the signal. The theory is that, as the hydrophone rotates towards the black box directly, the sound will get louder. If it starts to get softer, we know we have passed it,” Mr Steven Teo, senior investigator at the Air Accident Investigation Bureau, told a media briefing at Changi Airport yesterday.

The operator will then try to determine the probable location of the plane’s ULB and the information will be forwarded to the Indonesian authorities, he added.

Earlier in the day, two Republic of Singapore Navy ships — RSS Supreme, a Formidable-class frigate, and missile corvette RSS Valour — arrived in the search area and began a search-and-locate operation.

A landing ship tank, RSS Persistence, also sailed from Singapore yesterday evening to join the efforts.

The vessels joined two C-130 aircraft from the Republic of Singapore Air Force, which were sent to comb the Java Sea for objects linked to the missing plane, which had 162 people on board when it went missing on Sunday morning.

Second Minister for Defence Chan Chun Sing, who sent off the RSS Supreme and RSS Valour from the Changi Naval Base at 11.55pm on Sunday, said the close relationship shared between Singapore and Indonesia would facilitate the operation.

“I believe with the strong relationship Indonesia and Singapore have built over many years, which transcends all levels — from the highest political level to the military commanders — we will be able to work closely and execute the search-and-locate operation effectively.”

ADDITIONAL REPORTING BY ELGIN CHONG