Missing Titanic Sub Update as Time Running Out in Frantic Search

Despite the sounds heard on Tuesday during the search for the submersible that went missing on Sunday while on an expedition to the Titanic's wreck site, U.S. authorities said they haven't yet found the vessel.

The Titan, owned by OceanGate, went missing after leaving Cape Cod, Massachusetts, on Sunday morning, half-way through its descent to the wreckage of the Titanic, which lies around 370 miles off the coast of Newfoundland, Canada.

Aboard the sub were five people: Stockton Rush, CEO of OceanGate, a private company organizing deep-sea expeditions, French submersible pilot Paul-Henry Nargeolet, billionaire British explorer Hamish Harding and Pakistani businessman Shahzada Dawood and his son Suleman Dawood.

Rescuers have been racing against time to find the missing submersible, as the crew has only a limited amount of oxygen. As of Tuesday afternoon, the crew had about 40 hours left of breathable air.

The sonar of a Canadian aircraft picked up banging sounds from underneath the water in the North Atlantic on Tuesday, according to an internal U.S. government memo on the search for the missing vessel.

The banging sounds were detected every 30 minutes, according to the memo first obtained by Rolling Stone, and the aircraft's crew could detect the sounds four hours after first picking it up. It's unclear exactly when the crew picked up the sounds, or what their origin was.

An internal email sent by the Department of Homeland Security's National Operations Center and obtained by the magazine reads: "RCC Halifax launched a P8, Poseidon, which has underwater detection capabilities from the air. The P8 deployed sonobuoys, which reported a contact in a position close to the distress position."

It adds: "The P8 heard banging sounds in the area every 30 minutes. Four hours later additional sonar was deployed and banging was still heard."

But the U.S. Coast Guard wrote on Twitter that the banging sounds heard by the Canadian aircraft, which it identified as a P3, didn't lead them to the missing sub.

"Canadian P-3 aircraft detected underwater noises in the search area. As a result, ROV operations were relocated in an attempt to explore the origin of the noises," the Coast Guard wrote. "Those ROV searches have yielded negative results but continue."

At a press briefing on Tuesday, Capt. Jamie Frederick, First Coast Guard District, said that crews "are working around the clock to ensure that we're doing everything possible to locate the Titan and the five crew members."

A unified command has been set up on Tuesday including experts from the U.S. Coast Guard, U.S. Navy, Canadian armed forces and Coast Guard, and OceanGate, the Titan's parent company, to find the missing submersible.