The co-founder and former CEO of OceanGate, the company that operated the submersible that went missing on an expedition to the Titanic, says this "a critical day" in the efforts to recover the craft and the five people aboard.

But a short time after he posted a statement urging people to "remain hopeful" about the chances of a successful rescue, the U.S. Coast Guard announced that a "debris field" had been found in the underwater search area.

Guillermo Sohnlein said in a personal statement posted on Facebook that he was a friend of Stockton Rush, the CEO of OceanGate who was piloting the submersible. Rush and the four passengers aboard the craft have been missing since Sunday, when the submersible lost contact with its support ship. Sohnlein said he and Stockton last spoke just weeks before the expedition. 

It's been estimated that the sub started out with about 96 hours of emergency oxygen, but Sohnlein said he believed a longer survival was possible. 

"Today will be a critical day in this search and rescue mission, as the sub's life support supplies are starting to run low," Sohnlein wrote. "I'm certain that Stockton and the rest of the crew realized days ago that the best thing they can do to ensure their rescue is to extend the limits of those supplies by relaxing as much as possible. I firmly believe that the time window available for their rescue is longer than what most people think." 

Sohnlein did not elaborate on other life support supplies that might be available on the ship, like food and water, but urged people to "remain hopeful." 

"I continue to hold out hope for my friend and the rest of the crew," Sohnlein wrote. 

He cited a dramatic 1972 rescue as an example of what was possible. In that case, the two pilots, Roger Mallinson and Roger Chapman, were in a submersible trapped on a seabed about 480 meters underwater. The rescue took about 76 hours and was the deepest sub rescue in history, the BBC reported. However, the two were at a much lower depth than where the OceanGate submersible was heading. The Titanic wreckage is about 12,500 feet deep — nearly two and a half miles below the surface.  

Sohnlein said he and Stockton co-founded OceanGate in 2009, and that he served as a CEO, expedition leader and sub pilot in the early stages of the venture before Stockton took sole control in 2013. Since then, he said Stockton has served as a lead designer of two subs, including the Titan, the one that went missing. He also served as the company's chief test pilot, Sohnlein said. 

"Our annual science expeditions to the Titanic are his brainchild, and he is passionate about helping scientists collect data on the wreck and preserve its memory," Sohnlein said. 

Sohnlein noted that his comments were personal and "in no way an official statement" from OceanGate. The company has faced criticism, including a lawsuit, over safety concerns.

The race to find and rescue the missing submersible and its crew has captured the country's attention for days. There has been no contact with craft since Sunday, though on Tuesday and Wednesday, search planes reported hearing banging noises at roughly half-hour intervals. The source of the noises was unclear.

"If I were a family member, I would remain hopeful," Capt. David Marquet, who commanded the U.S. Navy submarine USS Santa Fe, told CBS News. "But people generally do not come back from the bottom of the ocean."

In:
• Oceans
• RMS Titanic

Kerry Breen

Kerry Breen is a news editor and reporter for CBS News. Her reporting focuses on current events, breaking news and substance use.