(Bloomberg) -- The Transportation Security Administration is joining a broader federal review of regulations governing public charter flight operations, a move that could imperil the less onerous airport security measures that have boosted their popularity.

This development comes on top of a move by the Federal Aviation Administration in August to consider sweeping updates to existing safety standards for charter and “hop-on” flight companies, which now operate under less stringent standards than larger carriers. 

TSA is taking a closer look at the operations from a security threat risk perspective, according to a person with knowledge of the matter who wasn’t authorized to speak publicly. 

Any mandate to have stronger security could drive up costs for a growing sector that includes closely held JSX and a proposed charter unit at SkyWest Inc., the largest regional airline in the US. The rapid growth of such carriers poses “an increased risk to safety if left unchecked,” the FAA has said.

JSX and peers are popular with travelers because they avoid airport crowds and the hassle of lengthy security lines. They operate from private airports and cater to people who want a better experience than those that commercial airlines offer, but can’t afford the normally high price tag of flying private. 

JSX’s security program is accepted by TSA and “is every bit as thorough” as procedures at commercial airport terminals, Ben Kaufman, a spokesman for JSX, has said. The regimen includes swabbing bags for explosives and vetting passengers against no-fly lists, he said. 

TSA and others declined to discuss the specifics of security rules governing the charter companies, but they don’t involve passing through a TSA-operated checkpoint.

There are more than 1,800 charter air companies in the US, according to the US Private Aviation Association. Fifty-three of those offer public charter service, according to the National Air Transportation Association, or NATA. 

Such carriers can use pilots who are older than 65, the required retirement age at larger airlines. The charter companies also don’t require the minimum 1,500 flying hours needed for a commercial pilot and don’t have to follow the same rules for required pilot rest as larger airlines. 

The “size, scope, frequency and complexity” of charters conducted as on-demand operations “has grown significantly over the past 10 years,” the FAA said in its August announcement and some appear “essentially indistinguishable” from domestic flights at larger scheduled carriers. A TSA spokesperson said these charters “have fixed routes and are selling boarding passes to individuals.”

The FAA is now gathering public comments ahead of a decision on what changes it may propose. In a filing Monday, Southwest Airlines Co. urged the agency to “take all steps necessary” to return to one level of safety standards for all passenger carriers.

“Whether flying on an aircraft with 10 seats or 250 seats, the flying public deserves nothing less than to be assured of a consistent and rigorous level of aviation safety,” Southwest said. 

NATA welcomes the debate over current policies “especially when it comes to trying to ensure that operations are conducted safely,” said Alan Stephens, vice president of regulatory affairs at the association. “We also want that debate to be done in precise ways.”

Passengers can book some JSX flights on the websites of United Airlines Holdings and JetBlue Airways, which was an early investor in JSX’s parent company and maintains a seat on its board. Both also allow members of their loyalty programs to earn credit for flights with JSX. 

SkyWest Charter would cater to different travelers by flying to airports generally in smaller cities and ferrying consumers to larger airports. The company is awaiting US Transportation Department approval to begin flights. Many of the planned destinations have lost some or all of their air service since major airlines trimmed back such flying after the pandemic. 

Any change in federal regulations governing such models could include SkyWest Charter, which earlier said it “exceeds current safety requirements and will transition to any additional requirements that may be adopted by the FAA.”

(Updates with Southwest comments, other details throughout)

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