PSA Airlines, the carrier involved in the mid-air accident over Washington, ironically preserves the name of another airline whose involvement in two mid-air collisions – one of which remains the worst in US history – contributed to airspace safety reforms, and helped spur the advancement of collision-avoidance systems.
Among the earliest US discount carriers, Pacific Southwest Airlines was based in San Diego and had primarily operated as a Californian intrastate service.
While climbing out of San Francisco, bound for Ontario, in January 1969 a Pacifc Southwest Boeing 727 hit a Cessna 182 light aircraft in controlled airspace. The aircraft were operating on the same radio frequency.
“Both pilots had equal opportunity to see each other,” stated the National Transportation Safety Board, adding that they had “failed to see and avoid”.
Despite sustaining damage, both aircraft landed safely.
But almost a decade later, in September 1978, another Pacific Southwest 727 – conducting a visual approach, in clear weather and good visibility, to San Diego’s Lindbergh Field – collided with a Cessna 172 which had been climbing out of the airport ahead of the jet.
While the 727 pilots had made visual contact with the Cessna, they subsequently lost sight of the aircraft, and believed it had moved clear, when it was actually beneath them.
The crew did not inform Lindbergh tower that they could no longer see the Cessna, and – despite receiving an automated conflict alert – the tower controllers did not issue a warning.
Conflict procedures at the time, says the National Transportation Safety Board’s inquiry into the accident, “did not require” controllers to warn either aircraft.
As the 727 overtook the climbing Cessna, the jet’s right wing struck and destroyed the light aircraft, the impact inflicting sufficient damage to cause a fire in the 727’s wing and a loss of control. The 727 crashed with no survivors among its 135 occupants; the accident also resulted in seven fatalities on the ground.
The inquiry attributed the accident to the 727 crew’s failure to keep sight of the Cessna despite the requirement to maintain visual separation, as well as air traffic control’s authorising visual separation procedures in the terminal airspace when separation capabilities were available.
As a result of the collision, the US FAA established terminal radar services or terminal control areas at several airports, although it maintained that visual separation remained a viable concept.
But the FAA says the crash “served to increase” the regulator’s efforts to develop independent airborne anti-collision equipment, and it initiated a programme three years later, in 1981, to develop the traffic collision-avoidance system, TCAS, using previously-tested beacon interrogation as the basis.
Pacific Southwest performed weakly in the post-1978 US airline deregulation environment and was eventually taken over by USAir which sought to acquire the carrier in 1986.
The occurrence of another fatal mid-air collision over California in the same year – involving an Aeromexico McDonnell Douglas DC-9 and a Piper PA-28 near Cerritos – drew comparisons with the Pacific Southwest accident.
The FAA says both collisions were “instrumental” to the development and implementation of on-board collision-avoidance technology, with the Cerritos accident prompting the NTSB to reiterate an earlier recommendation to expedite development, and mandate carriage, of such systems.
Rulemaking to this effect was initiated by the FAA in 1987.
USAir continued its consolidation in the same year, taking over Piedmont Airlines and its subsidiary Jetstream International Airlines.
After the acquisition USAir preserved the ‘PSA’ brand of Pacific Southwest, by renaming Jetstream as PSA Airlines. Following USAir’s merger with American Airlines, PSA Airlines operates as a regional feeder for American – flying routes in the eastern USA, despite the origins of its brand name.
