Controllers lost contact on May 1 because a temporary control tower antenna had not been set up at the correct location, Brig. Gen. Matthew Braman told AP.
The ADSB safety system has become a flashpoint as some have pointed to its likely lack of use by the helicopter as a potential cause of the Jan. 29 crash.
U.K. police have opened a criminal investigation into a collision between two ships in the North Sea and have arrested a man on suspicion of manslaughter.