Could the Titan be on the ocean surface — and other questions about the missing submersible

It's been more than 72 hours since contact was lost with OceanGate's Titan submersible during its dive to the bottom of the North Atlantic Ocean to see the wreck site of the Titanic. 

There was hope Wednesday that it could be located, after a Canadian military aircraft with underwater sonar capabilities picked up underwater sounds, described as banging, in the search area, though no other signs of the Titan were detected. 

There are many questions about how the search is unfolding and the challenges faced in trying to find the Titan before its oxygen supply runs out. CBC News can provide some of the answers. 

The Titan was about one hour and 45 minutes into its dive off the coast of Newfoundland when contact was lost around 8 a.m. local time on Sunday. 

It takes about two and a half hours to reach the Titanic wreckage at a depth of 3,800 metres, said Mike Reiss, a television writer and producer who travelled on the Titan last year. 

But it's not necessarily a direct voyage to the wreck, he said. 

"It's just a giant tube that they drop in the water and it sinks all the way down," he told CBC News Wednesday morning, explaining that on his trip the Titan drifted as it descended due to underwater currents. 

He said the Titan was about 450 metres from the wreck when it finally reached that depth but they had to spend "about two and a half hours of our three hours down there just kinda groping in the dark trying to find the Titanic." 

The Titan has "seven different return-to–the surface backup systems" that allow it to float back up to the surface, according to David Pogue, a CBS News correspondent who also travelled on the Titan last year, so there is a chance the submersible is bobbing somewhere on the remote Atlantic Ocean. 

He said those include sandbags and lead pipes that can drop off, thrusters and an air balloon. 

But he said there is also a "time release" system that sends the submersible back to the surface after a certain number of hours "even if everybody on board is unconscious."

Air crews have searched an area spanning about 26,000 square kilometres so far, looking for a white submersible that is 6.7 metres long and 2.8 metres wide.

If the Titan is on the surface, the crew and passengers would not be able to escape the capsule because it is bolted shut from the outside, Pogue explained, meaning the oxygen supply remains limited, just as it would in the depths of the ocean.

A U.S. Coast Guard official told BBC News Wednesday there is likely less than 20 hours left in the Titan's estimated 96-hour oxygen supply, which includes oxygen tanks and equipment known as carbon dioxide scrubbers to absorb the CO2 exhaled by the passengers inside the confined space.