A “ping” sound believed to be emitted by the black box of an Indonesian jet that crashed into the sea this week with 189 aboard is getting clearer, the deputy of a national transport safety committee said on Thursday.

Ground staff lost touch with flight JT610 of budget airline Lion Air 13 minutes after the Boeing 737 MAX 8 took off early on Monday from Jakarta, on its way to the tin-mining town of Pangkal Pinang. There were no survivors.

“The ping sound is clearer,” Haryo Satmiko, deputy chairman of the National Transportation Safety Committee (KNKT), told Reuters.

“We’ve deployed a remote operating vehicle and detected a large chunk on the bottom of the sea. We suspect that is a part of the plane’s body.”

A team of divers had gone down since 5 a.m. to map the area where the black box is thought to be, he added, describing sea conditions as normal.