An Israeli pilot was killed and his co-pilot seriously injured in an Apache helicopter crash in southern Israel.

Before the crash at the conclusion of a training exercise Monday, the pilot alerted the tower at Ramon Airbase that the helicopter was experiencing a technical malfunction.

The Apache is manufactured by the American Boeing Co. The entire fleet of Apache helicopters has been grounded until the investigation is completed.

The fleet had been grounded in June after a crack was discovered in the rotor blade of one helicopter. The investigation into that damage ended in July, and the helicopters were gradually being returned to service.

An initial investigation into Monday’s crash found that the accident was not connected to the earlier problem.

At the time of the crash, Israel had 44 Apaches in service, according to HIS Jane’s Defence Weekly. The helicopters provide close air support for ground troops.

The dead pilot was identified as reservist Maj. David Zohar, 43, of Haifa. His co-pilot, a lieutenant on active duty, was in critical condition following  surgery Monday night, according to reports.

The crash initially was under a gag order by the military censor until the families of the victims could be notified. During that time, rumours circulated on social media that IDF Chief of Staff Gadi Eisenkot was aboard the downed helicopter.