National Airlines does not have federal authority to fly scheduled passenger flights between Long Island MacArthur Airport and Puerto Rico, according to the U.S. Department of Transportation.

At the time the Orlando-based airline announced it would be flying six weekly round-trips between Ronkonkoma and Puerto Rico, it had not applied to the DOT for permission, records show.

National announced its planned MacArthur service on Feb. 18, and the airline’s application to the DOT for authority to provide interstate scheduled flights is dated March 11 and is still pending.

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The airline last month announced it would have to delay its planned June 1 launch at MacArthur because it did not have an airplane to fly the routes to San Juan and Aguadilla. National is refunding passengers who bought tickets for those flights, it said.

National, which for years operated as a cargo airline and late last year began scheduled passenger service, has DOT authority to fly foreign passenger and foreign charter flights as well as interstate charters. The application and approval process is “an extended, complicated process,” according to an airline spokesman, who could not provide an estimate on when the application might be approved.

Town of Islip officials have sent a letter supporting National’s application.

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“The process appears to be cumbersome, requiring approvals from the FAA and the DOT. From the Town’s perspective, we have done all we can do to expedite National’s service to and from Long Island MacArthur Airport,” Islip Town Supervisor Angie Carpenter said in a statement. “We stand ready to welcome National Airlines and their additional flights.”

When the town recently announced National would have to delay the MacArthur launch because it didn’t have an airplane, an airline spokeswoman said the FAA’s permitting process, once a plane is acquired, could take three to six months.

National flies foreign scheduled passenger routes between Orlando Sanford International Airport and Canada. It also flies between Orlando and Puerto Rico, a U.S. territory, but those flights are designated as public charter, and must be booked at least a week in advance. The dates of those charter flights are also subject to change, according to the airline’s website.

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In its application to the DOT, National also floated plans to fly between MacArthur and a small airport in London three times a week.

Robert Mann, a former airline executive and president of R.W. Mann & Co., an aviation consulting group, said applying for this kind of authority is not like “flipping a switch.”

Mann said air carriers often make announcements of planned new service, but usually with the caveat that those routes are subject to government approval, if that’s the case.

In a news release announcing the MacArthur service, National did not say the routes were pending federal approval.

The National delay is another wrinkle for MacArthur, which has lost more than half its flights and almost half its annual passengers since 2007. New service that could potentially reinvigorate the airport is always seen as welcome news by Islip Town leaders.