A communication error preceded the deaths of two fighter pilots in the Scottish Highlands, according to US air crash investigators.
Both pilots were killed in the crash
The F15 pilots were flying in variable cloud on a low altitude training mission and were lost from radar during an air traffic control handover on 26 March, 2001.
Lieutenant Colonel Kenneth Hyvonen, 40, and Captain Kirk Jones, 27, were killed instantly when their aircraft crashed into Ben MacDui in the Cairngorms.
In February, air traffic controller Malcolm Williams was cleared of causing the deaths by an RAF court martial.
The pilot made the first error as he should not have relinquished that responsibility unless he could see the ground
The jets, which were flying under the call sign BITE 21, crashed during a snowstorm in March 2001, while on a low flying exercise, from RAF Lakenheath in Suffolk.
The results of the US Air Force inquiry had been withheld while the British controller, from RAF Leuchars in Fife, faced charges.
The court martial, the longest in RAF history, acquitted Flight Lieutenant Williams.
The US Air Force Accident Investigation Board has now found the crash was caused by a "breakdown in terrain avoidance responsibilities between the pilot(s) and air traffic controller(s) on the ground".
The planes were lost as they descended to 4,000 feet and were still within Leuchars airspace.
The report said: "As the flight approached the limits of Leuchars airspace, the controller attempted a handoff to Lossiemouth radar service.
"During this time, BITE 21 dropped off the radar screen and did not reply to radar calls.
"Breakdown in terrain avoidance responsibilities between the pilot (s) and air traffic controller (s) on the ground led to a descent below safety altitudes without having positive visual contact with the ground."
Lieutenant Colonel Scott Vadnais, who is based at Ramstein Air Base in Germany, said he did not wish to attribute blame for the tragedy and stressed many factors were involved in the accident.
But on the issue of avoiding collision, he said: "In the UK the pilot has responsibility for terrain avoidance but the pilot relinquished that responsibility to air traffic control.
"The pilot made the first error as he should not have relinquished that responsibility unless he could see the ground."
The US Air Force investigation was separate from the RAF court martial, which focused on the role of air traffic control.
The American pilots were 50 minutes into a low-flying exercise from RAF Lakenheath when they disappeared.
It was alleged Flt Lt Williams of RAF Leuchars, Fife, told the Americans to fly below 6,500ft when they requested the "minimum vectoring altitude" - a US term unfamiliar to the RAF at the time.
Malcolm Williams was found not guilty
In February a jury of six senior RAF officers took just over six-and-a-half hours to acquit the 47-year-old.
After the 22-day case in Helensburgh, Argyll and Bute, the Guild of Air Traffic Control Officers (Gatco) called for an inquiry into the case, claiming Flt Lt Williams would never have face a court martial if crucial evidence had not been overlooked by the prosecution.
He was also found not guilty of an alternative charge of professional negligence.
Flt Lt Williams is believed to have been the first UK military controller in living memory to face a court martial in connection with a fatal air crash.