Mark E. Gale, CEO of the Philadelphia International Airport for seven of his nearly 28 years working at the airport, will retire early in 2016.

For more than 20 of those years, Gale worked a variety of jobs overseeing airport operations and facilities.

Mayor Nutter, who appointed Gale to the CEO post in 2009, made the retirement announcement Monday and called him "an outstanding leader."

"As the city has grown into a world-class destination, Mark has kept Philadelphia International on pace to address the needs of today's air travelers," Nutter said.

Gale, 53, told his senior staff on Monday morning that he would be stepping down.

"He has been talking about retiring and doing something different," Philadelphia airport spokeswoman Mary Flannery said. Before becoming CEO, Gale served as the airport's acting aviation director for 11 months, succeeding Charles J. Isdell who retired.

"I have thoroughly enjoyed my years at the airport, especially the last seven," Gale said in a statement. "I thank Mayor Nutter for the opportunity he gave me to lead this great organization and I thank all our employees dedicated to serving the airport's customers. Now, I'm looking forward to the next phase of my life, both personally and professionally."

It was unknown Monday who Mayor-elect Jim Kenney, who takes office in January, has in mind to run the airport.

Gale's No. 2 at the city-owned airport, Chellie Cameron, is the chief operating officer who had served as deputy director of aviation, finance, and administration at Philadelphia airport since 2011.

Gale, who grew up in Levittown and lives in the city's Fox Chase section, graduated from Embry-Riddle Aeronautical University. In 1985, he worked as an intern in the Philadelphia Aviation Division, and joined the airport full-time in 1989.

From 1996 to 2000, Gale was airport operations manager. In 2001, as deputy director of aviation for operations and facilities, he supervised managers in security, safety, maintenance, information technology, engineering design, construction, emergency plans, grounds, and snow removal. Gale also managed daily operations at Northeast Philadelphia Airport.