Boeing 727-214 accident at San Diego, California, 25 Sept 1978 (N7711G)

Accident narrative

About 0901:47 P.s.t. on September 25, 1978, Pacific Southwest Airlines Flight 182, a Boeing 727-214, and a Gibbs Flite Center Cessna 172 collided in midair about 3 nautical miles northeast of Lindbergh Field in San Diego, California. Both aircraft fell into a residential area. The collision and crashes killed all 135 persons aboard the Boeing 727, both occupants of the Cessna, and seven people on the ground. Nine people on the ground were injured, and 22 dwellings were damaged or destroyed. At the time of the accident, the weather was clear with 10 miles of visibility.

### The Flights

The Cessna 172, registration N7711G, departed Montgomery Field about 0816 for an instrument training flight. A flight instructor occupied the right seat, and a certificated pilot receiving instrument training occupied the left seat. Operating under visual flight rules (VFR) without a flight plan, the Cessna completed two practice approaches at Lindbergh Field before beginning a climbout to the northeast at 0857.

Pacific Southwest Airlines (PSA) Flight 182, registration N533PS, was a scheduled passenger flight from Sacramento to San Diego, with an intermediate stop in Los Angeles. It departed Los Angeles at 0834 on an instrument flight rules (IFR) flight plan with 128 passengers and a crew of seven. The first officer was flying the aircraft, while the captain handled radio communications. A deadheading company pilot occupied the forward observer seat in the cockpit.

### Sequence of Events

At 0857, Flight 182 reported leaving 9,500 feet for 7,000 feet with the airport in sight. San Diego approach control cleared the flight for a visual approach to runway 27.

At 0859:50, the Cessna pilot contacted approach control, reporting that he was at 1,500 feet and northeastbound. The approach controller instructed the Cessna to maintain VFR conditions at or below 3,500 feet and to fly a heading of 070 degrees. The Cessna pilot acknowledged the instruction.

Meanwhile, the approach controller issued a series of traffic advisories to Flight 182. At 0859:39, the controller advised of a Cessna 172 climbing out of 1,400 feet at twelve o'clock, three miles, northeastbound. The PSA copilot responded, "Okay, we've got that other twelve." At 0900:15, the controller again advised Flight 182 of traffic at twelve o'clock, three miles, out of 1,700 feet. The first officer said, "Got em," and the captain radioed, "Traffic in sight."

At 0900:23, the approach controller cleared Flight 182 to "maintain visual separation" and to contact Lindbergh tower. Shortly after, the approach controller advised the Cessna pilot that an eastbound PSA jet descending for Lindbergh had him in sight.

Flight 182 contacted Lindbergh tower at 0900:34, reporting on the downwind leg. The tower local controller advised them of a Cessna at twelve o'clock, one mile. Inside the cockpit, the first officer asked, "Is that the one (we're) looking at?" then added, "Yeah, but I don't see him now." At 0900:44, the captain radioed the tower, "Okay, we had it there a minute ago," and six seconds later added, "I think he's pass(ed) off to our right."

Cockpit voice recorder transcripts showed the PSA crew continued to discuss the traffic. At 0901:11, the first officer asked, "Are we clear of that Cessna?" The flight engineer replied, "Suppose to be," the captain said, "I guess," and the jumpseat occupant added, "I hope." At 0901:21, the captain stated he had seen the aircraft about one o'clock before turning downwind and that it was "probably behind us now."

At 0901:28, an automated conflict alert warning began sounding in the San Diego Approach Control facility, indicating the predicted flightpaths of Flight 182 and the Cessna would intersect. The approach controller did not inform the tower or the aircraft because he believed the PSA flightcrew had the Cessna in sight.

Witnesses observed both aircraft proceeding easterly. Flight 182 was descending and overtaking the climbing Cessna. Just before impact, Flight 182 banked slightly right, and the Cessna pitched noseup, striking the Boeing 727's right wing at 0901:47 near 2,600 feet. The Cessna broke up immediately and exploded. Flight 182 began a shallow right descending turn, trailing vapor and then a bright orange fire from the right wing, with its bank and pitch angles increasing to about 50 degrees at impact.

### What the Investigation Found

The collision destroyed both aircraft. Wreckage examination revealed that a piece of the Cessna's propeller blade was lodged in the Boeing 727's right wing leading edge flap actuator. The Boeing's three engines had separated from the aircraft; damage to their fan blades indicated they were rotating at impact, with no evidence of foreign object ingestion.

A cockpit visibility study determined that the Cessna would have been almost centered on the PSA pilots' windshields from 170 seconds to 90 seconds before the collision. Afterward, it would have been positioned on the lower portion of the windshield. Conversely, the Boeing 727 would have been hidden behind the Cessna's ceiling structure for most of the time preceding the collision.

The Board analyzed the air traffic control handling of the flights. The approach controller had not instructed Flight 182 to maintain 4,000 feet until clear of the Montgomery Field airport traffic area, which was contrary to a facility order. Furthermore, ground track plots showed the Cessna pilot did not maintain the assigned 070-degree heading, turning instead to about 090 degrees.

The Board noted that both aircraft were receiving Stage II terminal radar services. While this service did not require lateral or vertical separation between IFR and participating VFR aircraft, the San Diego approach control had the capability to provide it.

The approach controller's conflict alert system activated 19 seconds before the collision. Procedures required the controller to take appropriate action to resolve the conflict. However, the controller took no action because he believed Flight 182 was visually separating itself from the Cessna. The procedures in effect did not require the controller to warn the pilots of the conflict alert.

The investigation also evaluated witness reports of a third aircraft in the vicinity, which might have been mistakenly identified by the PSA crew as the Cessna. After reviewing radar data and witness locations, the Board concluded the weight of the evidence indicated there was no third aircraft that could have been mistaken for the Cessna.

The Board concluded that by accepting the "maintain-visual-separation" clearance, the PSA flightcrew became responsible for seeing and avoiding the Cessna. The crew lost sight of the Cessna but did not clearly inform controller personnel of that fact. Following the collision, due to structural damage and fire, the Board concluded the Boeing 727 was probably uncontrollable.

### Probable Cause

The National Transportation Safety Board determined that the probable cause of the accident was the failure of the flightcrew of Flight 182 to comply with the provisions of a maintain-visual-separation clearance, including the requirement to inform the controller when visual contact was lost; and the air traffic control procedures in effect which authorized the controllers to use visual separation procedures in a terminal area environment when the capability was available to provide either lateral or vertical separation to either aircraft.

Contributing to the accident were the failure of the controller to advise Flight 182 of the direction of movement of the Cessna; the failure of the pilot of the Cessna to maintain his assigned heading; and the improper resolution by the controller of the conflict alert.