Crews trying to find Malaysia Airlines Flight 370, or MH370, were working this week not only to recover debris from the missing plane but also to find to find a key piece of equipment lost during the search.

The Australian Joint Agency Coordination Centre, which is leading the hunt for the vanished Boeing 777, announced in an operational update Wednesday it lost a towfish and depressor last month. A towfish is a high-tech sonar device that can be used to scan the ocean floor for items like aircraft debris, while the depressor helps keeps the equipment in place.

"On 21 March, the failure of a tow cable connector resulted in the loss of the SLH-ProSAS-60 towfish and the attached depressor," the center wrote Wednesday.

The investigative team called in an American remotely operated vehicle, called the Remora III, and hooked it up to the Dong Hai Jiu 101, a Chinese vessel that joined the search this year. The newly outfitted boat started traveling to the search area April 11, and once it arrives the Remora III will begin trying to detect the lost equipment. 

"Recovery operations will then be undertaken," the center said, adding that the Remora III was also used to help recover debris from Air France Flight 447, which crashed into the Indian Ocean in 2009 after a mechanical malfunction and pilot error. 


The MH370 searchers are no strangers to losing equipment, or even towfish. In January, the Fugro Discovery's $1 million towfish was knocked off when it ran into an underwater mud volcano. It was recovered in February.

A center spokesman told NBC News Wednesday the investigators were using three towfishes in total. He said didn't know whether the towfish lost in January was the same lost last month.

The search for MH370, which disappeared in March 2014, has covered about 100,000 square kilometers of sea floor so far. If it reaches 120,000 square kilometers without finding anything, the search will be called off. The only confirmed MH370 debris so far was not discovered by the vessels but instead washed up on the shore of Réunion Island last summer.