An aircraft equipped with underwater search technology has detected periodic banging sounds in the area where rescuers are searching for the lost Titanic submersible with five people on board.

The tourist sub went missing on Sunday on what was meant to be an eight-hour trip to view the Titanic shipwreck 12,500 feet (3,800 meters) below the ocean, about 435 miles (700 kilometers) off the coast of Newfoundland. The underwater vehicle only has enough oxygen for about 96 hours, so time is running out for those on board.

Sharing news of what appears to be a significant breakthrough in the search for the submersible, the U.S. Coast Guard tweeted on Tuesday night: “Canadian P-3 aircraft detected underwater noises in the search area. As a result, ROV [remotely operated vehicle] operations were relocated in an attempt to explore the origin of the noises. Those ROV searches have yielded negative results but continue.”

Another tweet issued a short while later said: “Additionally, the data from the P-3 aircraft has been shared with our U.S. Navy experts for further analysis which will be considered in future search plans.”

At around the same time, Rolling Stone shared similar information from what it said were internal email updates sent to officials at the U.S. Department of Homeland Security.

“RCC Halifax launched a P8, Poseidon, which has underwater detection capabilities from the air,” one of the emails said. “The P8 deployed sonobuoys, which reported a contact in a position close to the distress position. The P8 heard banging sounds in the area every 30 minutes. Four hours later additional sonar was deployed and banging was still heard.”

Rolling Stone noted that the email didn’t say what time the noises were heard.

While locating the stricken submersible would be a major breakthrough, rescue teams will then have limited time to bring it to the surface to rescue the occupants, who include American Stockton Rush, CEO of OceanGate Expeditions which operates the tourist trips to the famous shipwreck, British billionaire and adventurer Hamish Harding, Pakistani businessman Shahzada Dawood and his son Suleman, and French explorer Paul-Henry Nargeolet.

Speaking in a BBC documentary last year, Rush described the vehicle as an “experimental sub,” adding, “People are informed that it’s very dangerous down there.”

In November last year, CBS reporter David Pogue took a trip on it, and at the time voiced concerns about elements of its design.