The ubiquitous black boxes on airliners — designed to capture the sometimes gruesome words and sounds leading up to crashes — need an upgrade, U.S. accident investigators say.


In too many cases, the current two hours of sound on the cockpit voice recorders hasn’t been enough to aid investigations, the National Transportation Safety Board said in a recommendation posted to its website Thursday. The board cited several dozen instances in which the recorders were overwritten before they could be brought into the lab.Investigators want the requirement to be increased to 25 hours of sound, and are seeking retrofits for current aircraft by 2024.


The 2017 case of an Air Canada flight that came within feet of striking other planes on the ground in San Francisco illustrates the issue. In that case, the plane’s black box recorders weren’t pulled immediately, so the potentially critical recording of the incident was lost, hampering the NTSB’s probe.


In a 2009 case, after pilots on a flight to Minneapolis from San Diego went silent for more than an hour and flew past their destination, the recording device provided little help because the relevant portion was recorded over later in the flight, NTSB said. The crew said they became distracted, but the recording would have shed more light on what happened.


Investigators cited 34 cases from 2002 to the present in which longer recordings might have helped investigators. “Data continue to be overwritten and are unavailable for safety investigations,” NTSB said in a letter to the Federal Aviation Administration.


The NTSB recommendations follow a similar effort in Europe, where the European Aviation Safety Agency will require larger airliner models to have 25-hour recorders by 2021.