September 29th 1992 - on Tuesday at 12:19 p.m., four persons were killed as two sightseeing helicopters collided in mid-air.
The collision took place in Canadian air space approximately 100 meters (330 feet) west of the Horseshoe falls in front of the Minolta Tower and Incline Railway. The weather was crisp and clear. Wind wasn't a factor
link to full story
http://www.iaw.com/~falls/accident.html
and here
http://www.ntsb.gov/ntsb/GenPDF.asp?...92WA186A&rpt=p
reminds me of this incident .