The cockpit voice recording from Air Canada flight 759 that in July nearly landed on other planes on a busy San Francisco International Airport taxiway has been erased, according to the latest in a string of startling revelations about the near-disaster.
A National Transportation Safety Board document indicates that a delay in reporting the incident allowed the recorder to tape over itself multiple times, the Mercury News reported. This information was buried in the latest NTSB update.
Cockpit voice recorders tape conversations among the flight crew, which cannot be heard over the radio and elsewhere. Newer planes have a two-hour tape limit, while the Air Canada Airbus 320 is older and so only required to have 30 minutes of tape. The Mercury News says that recorders work as long as the plane is running. It starts over at the beginning when a recording has concluded.
The ongoing investigation won’t be hampered because the cockpit dialogue is not essential.
Information is still available from the flight data recorder.
Data and photos from July 7 show how shockingly low the Air Canada jet was when it pulled up to avoid crashing into planes at SFO.
The Air Canada jet pilots mistook the taxiway for the runway next to it and dipped to just 59 feet above ground before pulling up to attempt another landing, according to the NTSB.
That's barely taller than the four planes that were on that taxiway when the incident occurred late at night.
Pilots in a United Airlines plane alerted air traffic controllers about the off-course jet, while the crew of a Philippine Airlines jet behind it switched on their plane's landing lights in an apparent last-ditch danger signal to Air Canada.
NTSB investigators said they have not determined probable cause for the incident that came within a few feet of becoming one of the worst disasters in aviation history.
Aviation expert Mike McCarron reviewed the NTSB report and shared his take on the findings.
"Right now, everything is pointing to human factor, a pilot error," he said. "The back-ups to the back-ups eventually kicked in, but you shouldn’t have to go that far down the checklist to get to that point."
The investigators said that as the Air Canada jet approached the taxiway just before midnight after a flight from Toronto, it was so far off course that it did not appear on a radar system used to prevent runway collisions.
Those systems were not designed to spot planes that are lined up to land on a taxiway — a rare occurrence, especially for airline pilots. But the Federal Aviation Administration is working on modifications so they can, agency spokesman Ian Gregor said. The modified system could begin testing in a couple of months, officials told NBC Bay Area.
Both pilots of the Air Canada Airbus A320 jet were very experienced. The captain, who was flying the plane, had more than 20,000 hours of flying time, and the co-pilot had about 10,000 hours.
The pilots told investigators "that they did not recall seeing aircraft on taxiway but that something did not look right to them," the NTSB said.
Investigators could not hear what the pilots said to each other during the aborted landing because that tape was recorded over.
SFO and Air Canada officials declined to comment, citing the ongoing investigation.
NBC Bay Area's Michelle Roberts contributed to this report.