United Airlines(UAL) - Get Report President Scott Kirby's departure from American Airlines(AAL) - Get Report occurred after he was asked to leave American.

An airline industry source, who asked not to be named, said Kirby was asked to depart American due to executive suite tensions involving conflict with other top executives. He was provided with a separation package worth about $13 million.

American said on Aug. 29 that Kirby would leave immediately and that Robert Isom would succeed him as president.

"We have nothing new to add to our earlier announcement about Robert's new role as president and Scott's departure," American spokesman Josh Freed said late Friday. "These decisions were focused on succession planning and assembling the right team of executives for American Airlines."

Kirby's departure from American and arrival at United were both announced, "effective immediately," on Aug. 29. Sources said it had been made known to Kirby months earlier that United would be interested in him.

A United spokesman referred to the Aug. 29 letter in which CEO Oscar Munoz announced Kirby to airline employees. "While his credentials speak for themselves, what set Scott apart from the other impressive candidates I considered was his excitement at the passion and enthusiasm he is seeing from all of you over the past few months," Munoz wrote.

On Sept. 1, at an employee meeting in Charlotte, American CEO Doug Parker said that in Kirby's case, "We decided (that) as painful as it is, you should go transition out of the company."

Still, in its public statement, American was not entirely clear about the exact mechanics of Kirby's departure, referring to the move as the result of its board's consideration of succession planning.

"Today's management changes are the result of the company's board of directors' ongoing succession planning process," American said.

"As part of that process, and subsequent conversations regarding career expectations and the marketability of its executives, the company concluded it would not be able to retain its existing executive team in their current roles for an extended period," it said.

Additionally, John Cahill, the airline's lead independent director, emphasized in a prepared statement that Parker isn't going anywhere.

American "continues to be led by an exemplary individual who embodies the leadership qualities necessary to lead a large, complex service organization," Cahill said in the prepared statement. "We look forward to Doug's continued leadership for many years to come, welcome Robert to his expanded role, and are extremely excited about the future of American Airlines."

In an SEC filing, American said Kirby had entered into a "transition and separation agreement" under which he will receive a $3.9 million lump sum payment, continued health coverage for himself and dependents for up to two years and accelerated vesting of 258,958 shares of stock, worth about $9.4 million on Aug. 29.

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