This security camera footage shows the moment the blades of two Pasadena Police Department helicopters collided at a heliport in Altadena, California, on November 17, 2012, leaving both damaged and injuring six people, according to reports.The video was released by the National Transportation Safety Board (NTSB) in August, 2016, but only came to light in early March, 2018, when it was published by US news media.The footage shows one helicopter attempting to land at the heliport next to another that was preparing for a flight. NTSB said blamed the collision on rainy weather and a lack of communication between pilots – the landing pilot’s failed to seek clearance from the departing pilot, who should have parked the chopper inside a marked pad but did not do so due to drainage issues.“At the time of the accident, there was no established monitored UNICOM frequency at the heliport, and there were no procedures to alert ground personnel that a helicopter was arriving to the heliport other than by ground personnel ‘hearing’ it approach,” NTSB said. Authorities have since had monitored universal communications radio procedures in place for helicopter arrival and departure. Credit: National Transportation Safety Board via Storyful