Cessna 150 accident at Whittier, California, 9 Jan 1975

Accident narrative

On January 9, 1975, at approximately 1607 Pacific standard time, Golden West Airlines Flight 261, a De Havilland Twin Otter, and a CessnAir Aviation Cessna 150 collided in flight near Whittier, California. Both aircraft were destroyed by the collision and subsequent ground impact. The 10 passengers and two crewmembers aboard the Twin Otter, and the instructor pilot and student pilot aboard the Cessna, were killed. Falling wreckage inflicted substantial damage to houses and lawns in the area, but there were no reported injuries to persons on the ground.

### The flight

Golden West Airlines Flight 261 was a regularly scheduled passenger flight between Ontario, California, and Los Angeles International Airport (LAX). The flight departed Ontario at 1556 on a visual flight rules (VFR) flight plan. The captain had 9,366 total flight hours, including 2,774 hours in the Twin Otter. The first officer had 2,555 total flight hours, with 2,065 hours in the Twin Otter.

The Cessna 150 departed Long Beach Airport at 1556 on a local training flight. The instructor pilot had 22,010 flight hours, and the student pilot had 42.8 hours. The crew did not file a flight plan with air traffic control, nor was one required. Following takeoff, the Cessna was cleared to maintain runway heading with a left turn after passing the Los Angeles River. There were no further radio contacts with the Cessna crew.

### The sequence of events

At 1604:45, Flight 261 contacted the LAX arrival radar controller and reported over Rose Hills, a local landmark. The controller acknowledged, stated the flight was in radar contact 23 nautical miles east of the airport, and cleared Flight 261 for a terminal control area arrival to runway 24 left. Twenty-one seconds later, the flight was acquired automatically by the air traffic control computer. The aircraft's transponder showed an altitude of 2,800 feet.

At 1605:45, the controller verified that Flight 261 was leaving 2,600 feet. The controller then advised the crew of traffic in front of them, climbing from 1,500 to 3,000 feet. The reported traffic was a police helicopter on a VFR flight. The controller stated he would point the helicopter out again when it was closer and asked the crew to let him know when they had it in sight. At 1605:55, Flight 261 replied, "Two sixty one, we'll do it." This was the last known transmission from the flight.

At 1607:35, the controller transmitted another advisory, stating the helicopter was at their 11:30 position, three miles northbound. He repeated the advisory 20 seconds later. There was no response to either transmission. About that time, the controller noted the loss of the flight's radar data block and track data. Repeated attempts to contact the flight were unsuccessful.

### What the investigation found

The wreckage of both aircraft was scattered over an 8- to 10-city block area. The Twin Otter's fuselage fell into a schoolyard, and its wings fell two blocks away. The Cessna's fuselage fell into the front yard of a residence about a block and a half from the Twin Otter's fuselage.

Examination of the wreckage revealed that the major in-flight impact forces were on the Twin Otter's left side. The left wing leading edge sustained crushing damage and contained green paint matching the Cessna. A tire print matching the Cessna's right main wheel was found on the Twin Otter's left wing strut. The Twin Otter's left engine and nacelle were driven inboard, and portions of the Cessna's right side door frame were lodged between the propeller and spinner. The Cessna's right wing showed propeller slash marks at an 88-degree angle to the leading edge, and its instrument panel was found embedded within the left side of the Twin Otter's fuselage.

Based on the physical evidence and witness statements, the Board concluded the Cessna was on a northerly track at and just prior to impact, crossing almost 90 degrees to the Twin Otter's 250-degree magnetic course. The collision occurred at approximately 2,200 feet. One witness stated that neither aircraft made any abrupt evasive maneuvers prior to the collision, leading the Board to conclude neither flightcrew saw the other's aircraft in sufficient time to attempt an evasive maneuver.

The investigation noted that the Cessna was not equipped with a transponder. The LAX arrival controller stated he did not observe any primary radar returns for the Cessna on his display. Flight tests conducted the night of the accident indicated that an aircraft on the Cessna's presumed track did not produce a primary return. The Board concluded this was likely due to the "tangential effect," an inherent limitation of the radar's moving target indicator circuitry, which can cancel out returns from aircraft flying a course tangential to the radar antenna.

Because the controller could not advise Flight 261 of the Cessna, both aircraft were operating under the see-and-avoid concept. Weather was not a factor; visibility was 40 miles. A collision geometry study indicated that the aircraft were closing at a speed of about 174 knots. The Twin Otter was 57 degrees to the right of the Cessna, a position where it would have been masked by the Cessna's right wing and outside the pilots' normal scan pattern.

The Board noted two factors that lessened the Twin Otter crew's ability to see and avoid the Cessna. First, considering the elevation and azimuth of the sun, the Cessna would have been positioned between Flight 261 and the setting sun, making it difficult to see against the sun's backdrop. Second, the controller had advised Flight 261 of helicopter traffic directly in front of them. The Board believed the pilots of Flight 261 had limited their visual search to an area straight ahead in an effort to acquire a known target that constituted a definite threat.

### Probable cause

The National Transportation Safety Board determined that the probable cause of the accident was "the failure of both flightcrews 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, the Board believed that "the ability of both crews to detect the other aircraft in time to avoid a collision was reduced because of the position of the sun, the closure angle of the aircraft, and the necessity for the Twin Otter's flightcrew to acquire visual contact with radar-reported traffic directly in front of them."