The search for Malaysia Airlines flight 370 entered a new chapter early this morning, as retired Air Chief Marshal Angus Houston outlined during a press conference at 12 a.m. EST Monday morning.

With no pings for six days, officials involved in the search for Malaysia Airlines Flight 370 announced that the search will now move underwater. The Bluefin-21 autonomous underwater submarine will now be deployed, scouring a section of the ocean floor 8 meters by 5 meters.

"We haven't had a single detection in six days. It's time to go underwater," Houston said.

The section was determined due to four strong transmissions in the area, as well as an oil slick detected by the Australian search ship Ocean Shield.

“It’s a lead. This is what the business is all about,” said Houston. “You find something and then basically investigate it.”

He added, “We have an oil slick, and we’ll investigate. We have a position very close to where transmissions are coming from.”

Two liters of oil were collected by one of the ships involved in the ship, but Houston cautioned that analysis of the slick would take time.

“We’re in the middle of the Indian ocean. We can’t do analysis out at sea,” he said.

Houston indicated in the press conference that the air search will wind down in the next few days, with the underwater search of the Bluefin scouring the narrowed-down search area.

The Bluefin will operate in 24-hour cycles, in which it will go down to a depth of around 4,500 meters. And while the movement of the search from an air-based approach to a more fine-tuned underwater strategy may indicate the search area has been narrowed, Houston urged caution.

“Let’s hope this very strong signal we were receiving is from the black box,” Houston said. “But we won’t know that until we lay eyes on the vehicle.”