Originally Published: 08 JAN 24 12:30 ET

By Gregory Wallace, CNN

(CNN) — Investigators will never know exactly what the Alaska Airlines pilots were saying last week in the chaotic, loud first moments after a door plug blew off a Boeing 737 MAX 9, leaving a hole in the side of its fuselage shortly after takeoff.

That’s because the cockpit voice recorder – one of the virtually indestructible so-called black boxes onboard every airliner – has a critical weakness: a short memory span.

Under US standards, cockpit voice recorders, or CVRs, are set up to record on a two-hour loop. As each cycle repeats, the previous audio is overwritten with new sound – a factor that has impacted 10 investigations in the last five years, including several probes into near-collisions on US runways in 2023, according to National Transportation Safety Board Chairperson Jennifer Homendy.

“Cockpit voice recorders aren’t just convenient … they are critical to helping us accurately pinpoint what was going on,” she said in a news conference Sunday night. “And it’s key to safety.”

It is an anomaly in the era of inexpensive and expansive digital storage, when the phone of each passenger onboard a flight could easily have more capacity than the plane’s voice recorder.

Now, Homendy wants the recording standard to change.

She is calling on the Federal Aviation Administration to require a 25-hour recording window for the cockpit voice recorder in all aircraft – a duration that is already a standard requirement under European airline regulations.

The FAA last year proposed requiring 25 hours of recording for cockpit voice recorders. But it would only apply to newly-manufactured planes, Homendy noted, adding she wants the FAA to change its proposal and require aircraft currently flying to be retrofitted.

“You can easily install a different cockpit voice recorder and increase the time from two hours to 25 hours,” she said Sunday night.

CVRs are a crucial tool in investigators’ efforts to shed light on an incident like the one that unfolded Friday above Portland, Oregon.

“When we have the CVR, we kind of match up the timeline with everything that was occurring in the cockpit,” Homendy told CNN’s Pete Muntean, adding investigators are “able to isolate the smallest sounds” to help shed light on an incident.

“It’s not just about communication – it’s about everything else. You can hear what’s happening with the engines. Often you can hear what’s happening with the door that blew open, headsets that might have flown off,” she said. “It’s really key.”

Lost recordings are ‘a loss for safety’

There is a process for freezing the recording and preventing further overwriting. A mechanic or pilot can cut off power to the recorder, preserving it as a time capsule that later can be downloaded at a specialized laboratory, such as at the NTSB’s Washington lab or the French Bureau d’Enquêtes et d’Analyses.

Alaska Airlines tried to do that in this case, Homendy suggested in the news conference. After the plane landed in Portland, airline officials were busy setting up their emergency operations center. They eventually sent a mechanic to look into the voice recorder.

“There was a lot going on, on the flight deck and on the plane. It’s a very chaotic event,” she said. “The circuit breaker for the CVR was not pulled. The maintenance team went out to get it, but it was right at about the two-hour mark.”

“That is unfortunately a loss for us, and a loss for FAA and a loss for safety,” Homendy said. “That information is key not just for our investigation, but for improving aviation safety.”

Asked for comment about the overwritten CVR and other aspects of the incident, Alaska Airlines told CNN it was unable to comment, saying it would need permission from the NTSB.

“We have asked for permission from the NTSB to address these questions – they will not permit us to comment at this time,” the airline said. “We will provide information as soon as the NTSB gives us permission to do so.”

In some cases, two hours is sufficient: A plane lands shortly after the incident, and the plug is pulled to save the recording. But in other cases, the planes keep flying. In the case of a dramatic runway incursion last year at New York’s John. F. Kennedy International Airport, the pilots took off for the multihour trip to London after nearly hitting another loaded passenger jet.

While CVRs used to only record the prior 30 minutes of a plane’s audio, the two-hour recording capacity is still “a pet peeve” of CNN Aviation Analyst Miles O’Brien, he said.

“To me, in this day and age, it’s kind of scandalous that we only capture the last two hours,” he said Monday. “With digital data and hard drives, and we don’t have looped tapes anymore, we can capture in excess of 24 hours,” he said.

O’Brien also wants to go further than Homendy’s recommendation: He would like to see video recordings captured in the cockpit in addition to audio, something he suggested pilots bristle at because they consider it an invasion of privacy.

“If what you’re doing can involve the consequences that leads to the deaths of others, I think you might have to give up a little bit of your so-called privacy,” he said. “It’s high time that we improved the amount of data we got out of these cockpit voice recorders, including video.”

CNN’s Dakin Andone contributed to this report.

The-CNN-Wire