SAN FRANCISCO — It took at least 24 hours to report a near-disastrous collision at SFO, a delay that allowed a key piece of evidence — the cockpit voice recording from the jet that nearly landed on top of planes queuing to take off on a busy taxiway — to be erased.

The revelation is buried in the latest update from federal investigators looking into the near-catastrophic incident that aviation experts say could have triggered one of the worst disasters in aviation history.

So how did that happen? The delay in reporting the hair-raising event to the National Transportation Safety Board allowed the cockpit voice recorder to tape over itself multiple times before investigators came looking for it.

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Did brain phenomenon contribute to Air Canada pilot’s close-call at SFO? While federal officials have said there was no requirement to immediately report the incident, and the investigation can proceed without the cockpit dialogue, aviation experts hope this event will bring changes.

“They had an opportunity to make SFO safer and that’s gone now,” said aviation expert Mary Schiavo, former Inspector General of the U.S. Department of Transportation. “That cockpit voice recorder would’ve given a second-by-second account of what got (the flight crew) confused … You really don’t have anything comparable to it to explain what really was going on.”

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Cockpit voice recorders tape the dialogue among the flight crew that cannot be heard over the tower radio traffic and elsewhere. Newer planes must have a two-hour tape limit, while older models like this Air Canada Airbus 320 are only required to have 30 minutes of tape. The recorder runs as long as the plane is powered, but once the recording reaches the end, it begins taping over at the beginning.

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Many aviation investigations involve a crash where the cockpit recorder has stopped upon impact, so the data has no chance of being erased.

At 11:56 p.m. on July 7, Air Canada flight 759, with 140 people on board, flew about 50 feet over one of four fully-loaded passenger jets sitting on the taxiway, mistaking it for the runway. The pilot only climbed after a United Airlines pilot on the ground warned of the impending collision and an air traffic controller then ordered a “go around.”

The Air Canada plane circled around, landing safely on the correct runway and taxied to an airport gate about 21 minutes after the aborted landing. The cockpit recorder shuts off five minutes after gate arrival, according to an Airbus 320 expert. Even if the plane only had a 30-minute-long cockpit voice recorder, the final approach into SFO before the bungled landing would have been memorialized.

However, according to FlightAware, that Air Canada jet spent the night at SFO then flew three flights the next day on July 8, totaling more than 12 hours in the air, before NTSB officials were notified of the SFO close encounter at some point on July 9.

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Canadian officials were still able to recover the flight data recorder information from the botched landing at SFO, but the voice recorder had long been overwritten, NTSB spokesman Keith Holloway said.

“The information from the (flight data) recorder is what the NTSB is focusing on and has provided some good details on what the aircraft was doing at the time of the incident,” Holloway said in an email. “While it is an added bonus to have as much information as possible, NTSB investigates accidents and incidents often where a (flight data recorder) and (cockpit voice recorder) are not available. Investigators are still able to complete the investigation and determine cause.”

Holloway added that often in a crash investigation the flight crew does not survive, but in this case the pilot and co-pilot have been interviewed. SFO’s runway 28-Left was closed and darkened, with a large lighted “X” to warn pilots, and the jet was cleared to land on runway 28-Right.

The agency reported that the pilot and co-pilot told investigators they mistook the brightly lighted 28-Right for 28-Left, and thought the taxiway that runs parallel to 28-Right was their cleared runway.

“Also, just to make a point, the circumstances of this incident do not fall within the reportable requirements for NTSB, and therefore the operator was not required to make a report to the NTSB,” Holloway said.

Jim Hall, former NTSB chairman, said those reporting guidelines should be addressed in the SFO probe.

“I certainly hope the NTSB, as part of its investigation, will reevaluate what should get reported immediately,” Hall said. “This was probably the most significant near-miss we’ve had in this decade. I think splitting hairs on this issue on an incident of this significance is a disservice to safety.”

Schiavo agreed.

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“There are a lot of language loopholes you can use, but it should’ve been reported by both (the airline and air traffic controllers),” she said. “That kind of loss of separation (between airplanes) absolutely needs to be reported immediately.”

Both experts said the Air Canada flight crew should have immediately been tested for alcohol and drugs as well. A source familiar with the investigation told this news organization the flight crew spent the night in the Bay Area and flew out the next morning on their normally scheduled flight.

Air Canada has declined to comment on the pilots citing the ongoing investigation.

And while they have other evidence, Hall said, the cockpit voice dialogue is “critical” in this incident.

“It reflects the conversation in the cockpit of how this airplane might have ended up in this position,” he said.