WASHINGTON (AP) — As the Justice Department launches an investigation into possible collusion in the airline industry, experts say the government faces the burden of proving that carriers were deliberately signaling business decisions to each other. [...] in recent years, airline executives and Wall Street analysts have been much more open in discussing how the airlines have kept their passenger capacity — the number of seats they put into given markets — in check. "Matching supply to demand is not a novel idea and running a company for profit is not a crime," Raymond James analyst Savanthi Syth told investors in a note Thursday. [...] if the government does find evidence of improper collusion, it could attempt to negotiate a consent decree with the airlines to stop them from certain behavior, such as issuing public statements about their intentions about capacity. Ever since the government stopped regulating routes and prices in 1978, airlines have struggled to avoid nasty and unprofitable fare wars. In 1982, Robert Crandall, then a senior executive who would become CEO of American Airlines, expressed his anger about these fare wars in a phone call with Howard Putnam, CEO of Braniff Airways. After a brief industry increase in seats in the spring, American Airlines CEO Doug Parker spoke about the need for capacity discipline to a Reuters reporter at the International Air Transport Association's annual conference in Miami. Jonathan Baker, an antitrust law professor at American University, said investigations like this one generally need more than just circumstantial evidence.