The helicopters were nine miles inside Israel, well inside the Israeli- controlled area which extends into southern Lebanon. The weather was bad, and experts believe a combination of darkness and rain may have obscured the pilots' ability to see through their night vision equipment. They added, however, that Israeli pilots are among the best in the world.
The US built Sikorsky CH-53 D Sea Stallions - Hebrew name Yasur ("Petrel") - 2000 - were among 42 modified since 1993 by the Bedek company, which is part of Israel Aircraft Industries.
When helicopters themselves are at fault they tend to drop vertically, rather than smash into other helicopters horizontally. "In this case it does not appear to be a fault of the aircraft", said Paul Jackson, editor of Jane's All the World's Aircraft.