The proceeds from a land sale tied to Boeing Co.'s expansion plans at Charleston International have plenty of strings attached.

The $13.8 million must be used for aeronautical purposes. It must spent in five years. And it can't be used to help build a parking deck or pay for a new public bus route, as some airport officials had hoped.

The reason: The Federal Aviation Administration controls how the money from the sale of 267 acres will be spent, said Judi Olmstead finance director for the Charleston County Aviation Authority.

A state agency purchased the land from the airport last month and is leasing it to Boeing. The airplane manufacturer has an option to buy the property outright in 2027.

Some authority members thought the cash infusion could be used to double the size of the existing 1,200-space parking deck at Charleston International.

"At some point, we have to put in a new parking garage," said Paul Campbell, airports director. "That's a good problem to have."

But Olmstead said the money can be used for air-side ventures only, meaning those having to do with aviation-related purposes as determined by the FAA.

Aviation Authority attorney Arnold Goodstein said even the interest earned on the proceeds comes with restrictions. For example, it can't be tapped to pay for a proposed CARTA bus route between the airport and Tanger Outlet Center.

A couple of years ago, the Aviation Authority agreed to contribute about $300,000 to fund that project, but it has hit at least two dead ends.

Its other idea was to use airport fines. When Charleston International set up its police department more than two decades ago, Charleston County chipped in. The authority decided to repay the money from its police fines, which are processed and collected by the county, Goodstein said.

The debt was repaid in 2005. Since then, the county has accumulated an additional $292,000 from airport police fines. The authority has asked for that money to pay for the bus route, but the county has declined, officials said.

Campbell said the issue is now between CARTA and the county.

As for spending the Boeing land sale profits, that question will be revisited in the spring, when the airport board puts together its spending plan for its next fiscal year.

Reach Warren L. Wise at 937-5524 or twitter.com/warrenlancewise.