A Pentagon report on the incident leaked to the New York Times says that some controllers on the AWACS radar plane circling over northern Iraq were aware that two US Blackhawk military helicopters were taking a group of allied military officers to see Kurdish leaders.
For reasons still not explained, they failed to tell other controllers on the plane who were in touch with the pilots of the F-15s, and allowed them to misidentify the helicopters as Iraqi. Since 1991 the US and its allies have overflown northern Iraq and forbidden all Iraqi air activities in the region.
The report blames the attack on multiple human error and holds eight people, including the F-15 pilots, responsible. One of the helicopters did have its electronic system operating, which should have allowed other allied aircraft to identify it as friendly, but it was emitting the wrong signal.
The pilot of one of the F-15s visually identified the Blackhawks as Russian- made, though he was flying at 500 miles an hour at the time. The helicopters had large stars and stripes painted on their fuselages, but they were underneath to prevent Kurds shooting at them from the ground.
The F-15 pilots are said not to have been told that there would be allied helicopters flying in the area they were patrolling.