The preliminary report on the Philadelphia jet crash found the cockpit voice recorder likely hadn't recorded audio for several years.

The National Transportation Safety Board has released a preliminary investigation into the Philadelphia medevac jet crash that killed seven people last month, just days after the country’s deadliest aviation disaster in over 20 years.

The cockpit voice recorder recovered from the deadly Northeast Philadelphia plane crash was not operational and “had likely not been recording audio for several years,” federal investigators said last week.