Investigators have found the Army helicopter involved in a deadly mid-air collision over Washington DC was receiving faulty altitude data, causing it to fly higher than intended.
The findings, revealed during National Transportation Safety Board (NTSB) hearing, indicate that the helicopter's altimeters - devices that tell pilots how high off the ground they are - showed discrepancies ranging from 80ft (24.4m) to 130ft.
All 64 passengers onboard an American Airlines flight, along with three crew members on the helicopter, were killed in the 29 January crash.
Investigators are not expected to identify the cause of the crash at the hearing but will present insights into what led to the tragedy.
The first day of the three-day hearing has focused on the military helicopter's altimeter, performance and navigation systems.
