U.S. airlines shares were falling Friday due to the perceived impact of Great Britain's exit from the European Union, with American Airlines (AAL) showing the biggest decline.

Fears relate to the devaluation of the British pound, although that could make Great Britain a more desirable travel destination. Investors are also worried about weakness in the British and European economies. Additionally, aviation agreements with Great Britain will have to be renegotiated, although little reason exists to assume they will be altered.

In Friday trading, American shares were listed at $28.26, down $2.07 or 7%. United  (UAL - Get Report) shares were trading at $42.88, down $2.30 or 5%. Delta (DAL - Get Report) shares traded at $36.71, down $1.60 or 4%.

Of the three global carriers, American has the biggest presence in the United Kingdom. American and British Airways are founding partners of the Oneworld alliance and have antitrust immunity for their trans-Atlantic partnership.

American operates an average of 25 daily summer departures to the United Kingdom. It serves London Heathrow from eight U.S. airports; as well as Manchester, England, from Chicago; Birmingham, England, from New York Kennedy and Philadelphia; and two Scottish airports.

No immediate changes are planned.

"Like the rest of the world, we will learn more as the exit process unfolds and as the effects of that exit become more clear," said American spokesman Matt Miller.

In a recent report, Buckingham Research analyst Dan McKenzie said 6.2% of American capacity touches the U.K., compared with 5.3% of United capacity and 2.7% of Delta capacity. Delta also has an ownership stake in British airline Virgin Atlantic.

Aviation consultant Bob Mann said he doubts that Brexit's impact on U.S.-U.K. commercial aviation will be as broad as some people imagine.

"There will be some currency effect, and some rearrangement of demand," Mann said. "The U.K. just got cheaper as a destination, and I think there's going to have to be a reset of the air services arrangements between the U.S. and the U.K. But it's just a matter of mirroring those arrangements -- I can't imagine we would want something that looks different."

Among the individual airlines, American "has the greatest exposure of the three U.S. carriers by dollar exposure and by capacity exposure, but they have British Airways on the other end of the arrangement," he said. "That should give them immunity from some of the effects."

Like American, Delta issued a statement early Friday saying it is too soon to judge the impact of Brexit.

Calling the U.K. "one of the world's leading air markets," Delta said, "It's business as usual for the foreseeable future for Delta's flights between the U.S. and Britain. Delta remains committed to the U.K. market."

Delta offers 13 flights a day to the United Kingdom, including flights to London Heathrow from eight U.S. cities; a flight to Edinburgh from JFK; and a flight to Manchester from JFK. The busiest route, JFK-Heathrow, has three daily flights.

United offers 26 flights a day to the United Kingdom from five U.S. airports. The busiest route, Newark-Heathrow, has five flights a day.

In a report issued Friday morning, Raymond James analyst Savanthi Syth said she expected initial pressure on airline stocks in a "shoot first, ask questions later," market move.

Syth said that the near-term Brexit impact on airline earnings would be diminished because tickets are sold in advance and because fuel prices may decline. However, a fuel price decline would mean that fare growth would likely slow, which would delay an expected recovery in the airlines' passenger revenue per available seat mile. In trading airline shares, investors tend to prioritize PRASM growth over profits.

"The greatest near-term risk to earnings is from a stronger [dollar], primarily against sterling (GBP) and the euro (EUR)," Syth wrote. "In addition to translation risk, and similar to last summer, transatlantic demand to the U.S. is likely to suffer (partially offset by increased demand from the U.S.) and domestic European travel is likely to be boosted."

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.