Andrew B. Steinberg, a preeminent aviation lawyer who helped American Airlines prevail against charges of “predatory pricing” in the early 1990s and later, as a Transportation Department assistant secretary, helped negotiate a landmark “open skies” pact to expand U.S. commerce, died May 20 at his home in Chevy Chase. He was 53.

The cause of death was complications from uveal melanoma, a cancer of the eye, said his wife, Roxann Steinberg.

Mr. Steinberg, a Harvard Law graduate known for his soft-spoken but adroit diplomacy, spent more than two decades as a lawyer in the highly litigious aviation industry. Since 2008, he had been a partner of the Washington-based government regulation practice of the Jones Day law firm.

“Andy Steinberg was one of the greatest aviation lawyers of his generation,” said Jeffrey N. Shane, a partner at the Washington firm Hogan Lovells and a former undersecretary for policy at the Transportation Department. “He was in full command of the most complex and obscure laws and regulations — both domestic and international — and brought a level of creativity and intellectual rigor to his work that consistently impressed clients and colleagues alike.”

From 1990 to 1996, Mr. Steinberg was one of American Airlines’ senior attorneys, handling a range of employment and environmental matters for the carrier. In 1993, he was a member of the in-house legal team that helped American successfully defend against an antitrust lawsuit brought by rivals Continental and Northwest.

Andrew B. Steinberg. (Courtesy of Jones Day)

American, led by the hard-charging chief executive Robert L. Crandall, started a “value pricing” program in summer 1992. Much of the industry was reeling financially, and Continental had only recently emerged from Chapter 11 bankruptcy. Crandall’s plan, which he said was intended to simplify a complicated pricing structure, eliminated many discounts and reduced full-coach fares almost 40 percent in some cases.

Value pricing led competitors to slash rates, and American responded in kind. It was a quick race to the bottom (and a boon to travelers), and American ended its program by October 1992. Continental and Northwest sued in part to recoup enormous losses.

“The fact is that American has gotten to its place in the industry through hard work, skill and innovation, not through predatory conduct,” Mr. Steinberg said at the time. “For these plaintiffs, a couple of less-than-successful companies, to come into court and tell us we are barred from trying to innovate is ridiculous.”

The plaintiffs, represented by the legal powerhouses Joe Jamail and David Boies, charged that the pricing scheme was designed to “eliminate” the two financially weaker airlines. A federal jury in Galveston, Tex., ruled in American’s favor in 1993 after only four hours of deliberations. The plaintiffs did not appeal the verdict.

Winning the suit wasn’t enough to revive value pricing, said Aaron Gellman, a Northwestern University management professor who has studied airline regulation. “If the industry wasn’t going to go along with value pricing, it wasn’t going to work. It was clear all the other airlines opposed it, and American couldn’t get a tacit agreement” from its competitors.

After leaving American, Mr. Steinberg became chief legal officer with Sabre, a provider of computerized reservation and information technology services, and Travelocity, the online travel site. He helped take them both public.

Mr. Steinberg had a brief stopover with the consumer products manufacturer Church & Dwight before joining the FAA in 2003 as chief counsel. From 2006 to 2008, he was assistant secretary for aviation and international affairs at the Transportation Department, a presidential appointment.

Mr. Steinberg had supervisory responsibility for negotiation of the 2007 “open skies” accord between the United States and the European Union. The negotiations had begun before his arrival, but he was a pivotal driver in finalizing a new treaty that dramatically increased competition in the estimated $18 billion transatlantic market.

While the agreement failed to relax restrictions on foreign ownership of airlines — an objective of both sides that was vehemently opposed by Congress — the pact led to many breakthroughs on access to routes and the numbers of flights U.S. and European airlines were allowed to operate.

“The agreement changed the transatlantic air travel market immediately and became a template for similar arrangements in many other regions,” said Shane, who was the department’s undersecretary for policy at the time. “It was a transformational achievement.”

Andrew Bart Steinberg was born Oct. 12, 1958, in Perth Amboy, N.J., and raised in Scarsdale, N.Y. His father, a business executive, became chief executive of Mission Foods, the tortilla manufacturer, and founded the Tortilla Industry Association.

The younger Mr. Steinberg graduated magna cum laude from Princeton University in 1980 and cum laude from Harvard Law School in 1984. Before entering law school, he spent a year teaching English in Japan.

In the late 1980s, he practiced antitrust law and commercial litigation with the venerable Los Angeles-based law firm Gibson, Dunn and Crutcher.

Survivors include his wife of 20 years, Roxann Anderson Steinberg, and two children, Madeline Steinberg and Malcolm Steinberg, all of Chevy Chase; and a brother.

Mr. Steinberg was a past president of the International Aviation Club of Washington, a networking organization for lawyers, lobbyists and other industry representatives. He also volunteered for a Boy Scout troop in Chevy Chase and was a co-instructor for the aviation merit badge. The other teacher was Michael P. Huerta, now acting administrator of the Federal Aviation Administration.