Flight Details
Golden West Flight 261 departed Ontario, California at 15:56 PST for a visual flight rules (VFR) flight to Los Angeles. At 16:04, the crew contacted LAX arrival and reported their position over Rose Hills. They were cleared for the Terminal Control Area (TCA) and assigned the number 2 arrival to runway 24L. The Cessna 150, registered as N11421 and operated by CessnAir Aviation, had departed from Long Beach on a local training flight at 15:46.
Collision
At 16:05, the arrival controller advised the Twin Otter crew of traffic 5.5 nautical miles ahead, climbing from 1,500 to 3,000 feet. This traffic was a police helicopter on a VFR flight. A further advisory was transmitted at 16:06, but no response was received. The two aircraft collided in flight at an altitude of 2,200 feet. The Twin Otter was on a heading of 250 degrees, descending at 300 feet per minute with an airspeed of 146 knots. The Cessna was flying at 94 knots. The closing speed between the two aircraft was 174 knots.
Aftermath
Both aircraft crashed following the collision. Debris from the crash caused damage to houses and lawns near the impact site.
Probable Cause
The official probable cause, as determined by the investigation, was the failure of both flight crews to see the other aircraft in sufficient time to initiate evasive action. The board was unable to determine why each crew failed to see and avoid the other aircraft. However, it was believed that the ability of both crews to detect the other aircraft was reduced due to the position of the sun, the closure angle of the aircraft, and the necessity for the Twin Otter's flight crew to acquire visual contact with radar-reported traffic directly in front of them.