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

SAN FRANCISCO — Federal aviation officials investigating the Air Canada near-disaster at SFO determined the wayward plane dropped off radar displays for 12 seconds in the moments before it nearly landed on four fully-loaded passenger jets on the taxiway, according to new information released by federal investigators Wednesday.

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

The Airport Surface Surveillance Capability (ASSC) system — which monitors incoming aircraft to ensure they are safely landing at SFO and 34 other airports across the country — is designed to sound a warning from a loudspeaker in the tower if an airplane plans to land on an occupied runway. The system, which picks up planes on final approach and provides a computerized visual to air traffic controllers, does not warn for wayward planes — yet.

Since last year, the Federal Aviation Administration has worked to modify the system to also alert towers to planes lined up to taxiways.

“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 an approved runway, nearly triggering one of the worst aviation disasters ever, the radar system would offer 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.

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

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