The hunt for evidence of missing Malaysia Airlines Flight 370, also known as MH370, resumed this week after both vessels sweeping the Indian Ocean floor for debris had to return to port. The Fugro Discovery and Fugro Equator returned to the search area last weekend, and the latter officially relaunched its deep tow survey system Tuesday, according to an operational search update from Australia's Joint Agency Coordination Center.

The two vessels sailed separately this month to Fremantle, near Perth. The Equator had been scheduled for a Nov. 8 visit for resupply while the Discovery continued operating, but a Discovery crew member fell ill Nov. 4. The ship went back to port so the crew member, diagnosed with likely appendicitis, could get treated at an Australian hospital.

"The remoteness of the search area has been an ongoing challenge in the search for MH370," the agency wrote in its Nov. 11 operational update. "At the time the crew member became unwell, Fugro Discovery was more than 2,000 kilometers (1,200 miles) from Fremantle — well beyond the range of any land-based helicopter. The only viable option was to return to port ... this incident is a timely reminder of the difficult conditions in which crew members work."

The weather in the search region is forecast to improve, according to the update. The safety of the crews remains the most important consideration.

The Discovery and Equator have led the underwater search for MH370 for most of this year. The plane, with 239 people on board, disappeared without a trace on March 8, 2014. The only debris confirmed to be linked to the missing Boeing 777 was found this July: a flaperon wing part on Réunion Island in the western Indian Ocean.

The search now covers 120,000 square kilometers, or about 46,300 square miles, of ocean floor. About 70,000 square kilometers have been swept so far.