Background
On October 14, a four-engine aircraft departed Frankfurt-Main Airport at 0936 local time on a flight bound for Lajes. The aircraft landed at Lajes at 1603 local time. After refueling, it departed Lajes at 1851 local time heading for Westover Air Force Base in Massachusetts.
Technical Issues and Return
Approximately one hour into the flight, the crew informed ground personnel about technical problems with the radio compass and radio altimeters. The crew decided to return to Lajes, where the aircraft landed safely at 2019 local time. Based on duty and rest time regulations, the crew decided to stay overnight in Lajes.
Final Departure and Disappearance
On October 15, the aircraft departed Lajes at 0843 local time, again bound for the United States. The aircraft failed to arrive at its destination.
Search Operations
Search and rescue (SAR) operations were conducted after the aircraft failed to arrive. However, these operations were eventually suspended a few days later, as no trace of the aircraft or the crew was found.
Probable Cause
The official investigation determined that in the absence of evidence, the exact cause of the accident remains unknown.