"Significantly, this would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder," Houston said.
Still, Houston cautioned that it was too early to say the transmissions were coming from the missing jet.
"I would want more confirmation before we say this is it," he said. "Without wreckage, we can't say it's definitely here. We've got to go down and have a look."
The airliner's black boxes normally emit a frequency of 37.5 kilohertz, and the signals picked up by the Ocean Shield were both 33.3 kilohertz, said U.S. Navy Capt. Mark Matthews. But officials contacted the device's manufacturer and were told the frequency of black boxes can drift near the end of their shelf lives.
The Ocean Shield was slowly canvassing a small area trying to find the signal again, though that could take another day, Matthews said.
The ping locator is designed to detect signals at a range of 1.8 kilometers (1.12 miles), meaning it would need to be almost on top of the black boxes to detect them if they were on the ocean floor, which is about 4,500 meters (14,800 feet) deep.
"It's like playing hot and cold when you're searching for something and someone's telling you you're getting warmer and warmer and warmer," he said. "When you're right on top of it you get a good return."
If they pick up the signal again, the crew will launch an underwater vehicle to investigate, Matthews said. The Bluefin-21 autonomous sub can create a sonar map of the area to chart where the debris may lie on the sea floor. If it maps out a debris field, the crew will replace the sonar system with a camera unit to photograph any wreckage.