NTSB finds ‘blind spot’ in SFO radar after Air Canada event

SAN FRANCISCO –The wayward Air Canada plane that nearly caused an aviation disaster at San Francisco International Airport last month dropped off radar displays for 12 seconds in the moments before it approached four fully loaded passenger jets on the taxiway, according to new information released Wednesday from federal aviation officials investigating the incident.

The National Transportation Safety Board also released stills of a harrowing airport video showing the Airbus 320 nearly landing on the four planes awaiting departure on Taxiway C.

The Airport Surface Surveillance Capability (ASSC) system monitors incoming aircraft to ensure they are safely landing at SFO and 34 other airports across the country. The system, which provides a computerized visual to air traffic controllers, is designed to sound a warning from a loudspeaker in the tower if an airplane on final approach is heading for an occupied runway. But it does not warn for planes that may be incorrectly aligned to land on a taxiway, as was the case for the Air Canada plane.

Since last year, the Federal Aviation Administration has worked to upgrade the system to also alert towers to planes lined up to taxiways, where planes awaiting takeoff queue up.

“The agency expects to begin testing some modified systems in a few months,” a FAA spokesman said.

However, on July 7, when Air Canada Flight 759 mistook a crowded taxiway for its approved runway, nearly triggering one of the worst aviation disasters ever, the radar system offered no help.

Shortly before midnight that night, “the airplane flew too far right off course to be observed by the local controller’s ASDE-X/ASSC and was not visible on the ASDE-X/ASSC display for about 12 seconds,” the NTSB reported Wednesday.

By the time it reappeared on the air traffic controller’s radar display system, “it passed over the first airplane positioned on taxiway C,” federal investigators found.