WASHINGTON (AP) — A federal safety agency is recommending that air tours and other commercial aircraft operators be required to have certificated dispatchers to help pilots plan their flights.

The National Transportation Safety Board said Tuesday that and other recommendations are based on a study of more than 500 accidents, some of them fatal.

The NTSB said it began the study after seeing a “cluster of safety issues” from investigations of crashes between 2010 and 2022.

The recommendations would not apply to major airlines, which operate under the most stringent U.S. rules. The NTSB noted that historically airlines have had lower accident rates than charter operations.

The board said the Federal Aviation Administration should require air tours, commuter services, air ambulances and business jet charters to employ certificated flight dispatchers. The board said it found 12 accidents with a total of 45 deaths where flight dispatch was “deficient” because current regulations don’t require people performing the work to meet particular standards.

The NTSB said it found four accidents and 11 deaths involving small planes that were not loaded in a safe manner. It recommended expanding a current rule on weight and balance documentation to single-engine planes.

The board also repeated a previous recommendation that planes used in non-scheduled commercial operation be outfitted to collect data that indicates when pilots fail to follow proper procedures.

The FAA said it takes NTSB recommendations seriously and will respond “within an appropriate timeframe.”