(Bloomberg) -- The U.S. Federal Aviation Administration is implementing recommendations it rejected six years ago that could have prevented pilots from nearly landing last month on a taxiway crowded with jetliners awaiting takeoff in San Francisco.
The National Transportation Safety Board in 2011 recommended a software upgrade to ground radar systems that would warn when a plane is landing in the wrong place. But the FAA dismissed the recommendation, declining to even study whether it was feasible, according to government records.
In an announcement issued since the San Francisco near-collision, the FAA says it has begun over the past year doing what the safety board recommended and testing could begin in a few months.
"We believe recent technological advances may now enable us to modify our ground surveillance systems to detect aircraft that are lined up to land on taxiways," the agency said Friday in an emailed statement.
Air Canada Flight 759 was approaching the San Francisco International Airport just before midnight on July 7. Instead of heading for the runway, pilots lined up about 500 feet to the right, aiming for a parallel stretch of pavement where four planes were preparing for takeoff, according to the NTSB. The tails of the first two planes on the ground were about 56 feet high, just three feet below the landing plane’s lowest altitude, according to the safety board.
"Where’s this guy going?" a pilot in a United Airlines plane that was at the head of the line said in a radio call to the airport tower. The air-traffic controller didn’t warn the Air Canada pilots until after the cockpit crew had already aborted the landing.
The potential risks of such a collision have been highlighted by several similar instances in the past, including when actor Harrison Ford landed a small plane on a taxiway in February at John Wayne Airport in California.
The NTSB examined the issue in 2009 after a Delta Air Lines Inc. plane touched down on a taxiway in Atlanta. No one was hurt because there were no other aircraft on the taxiway at the time. The safety board concluded the crew’s abilities were degraded by fatigue after an all-night flight.
As part of that investigation, the NTSB found that an existing radar system at major airports could be adapted to warn controllers if a landing plane was headed to a taxiway instead of a runway. This was critical, according to NTSB, because controllers stationed in airport towers often can’t tell whether an arriving plane is properly lined up for a runway.
Investigators contacted what is now Saab Sensis Corp., a division of Sweden-based Saab AB, to see if its system that tracks planes on the ground would help. Officials at Sensis concluded the technology, known as ASDE-X, could be programmed to detect a potential errant landing as far as 0.75 miles from the airport at Atlanta, according to a March 2, 2011, recommendation letter by NTSB.
"Such a warning would afford air traffic controllers the opportunity to assess the situation and provide instructions to a flight crew that would prevent a taxiway landing or potential collision with aircraft or vehicles that may be on the taxiway," NTSB wrote.
The safety board, which investigates accidents but has no regulatory authority, called on FAA to conduct a broader feasibility study and to upgrade the warning system where possible.
Randolph Babbitt, the FAA’s administrator at the time, responded later that year that the ASDE-X system wasn’t up to the task, according to NTSB records of correspondence in the case. ASDE-X’s primary job is to warn controllers when there’s a risk of a plane colliding with another aircraft or vehicle on a runway. Adding a taxiway warning would degrade the system’s primary mission of preventing runway collisions, Babbitt wrote.
"Simply concluding that the performance tradeoffs would outweigh the safety benefits of providing the recommended capabilities without performing the review ... does not constitute an acceptable response to these recommendations," the NTSB wrote in response.
As part of its formal system of tracking recommendations, the NTSB classified it as "closed -- unacceptable action."
A more recent taxiway landing, this one involving an Alaska Air plane in Seattle in 2015, helped prompt the agency to refocus on trying to develop a technological solution, according to the FAA. No other planes were on the taxiway and there were no injuries.
The upgrade was also made possible by recent software improvements in how the ASDE-X system tracked arrivals, the agency said.
"The FAA since last year has been working to modify the systems so they will also capture aircraft that are lined up for taxiways," the agency said in an emailed statement. "The agency expects to begin testing some modified systems in a few months."