American Airlines just broke up one of best management teams in modern airline history (AAL, UAL)

REUTERS/Yuri Gripas

Shortly after American Airlines announced the departure of company president Scott Kirby on Monday, United Airlines announced his arrival as its new president. 

Kirby's move over to American's major rival aside, the long-time executive's departure breaks up one of the most successful airline management teams in recent history.  

"American Airlines CEO Doug Parker and Kirby are perhaps the defining airline executive team (CEO + right-hand man) of the modern US Airline industry," Airways Magazine senior business analyst Vinay Bhaskara told Business Insider. 

The duo's ascent to airline industry rockstar-dom over the past decade is virtually unprecedented.

Parker and Kirby first teamed up more than two decades ago at Tempe-based America West Airlines. The highly respected duo helped engineer AWA's merger with US Airways in 2005 followed by US Airways' 2013 merger with American Airlines. 

In the period between the two mergers, the duo turned US Airways into a financially successful airline under less-than-ideal competitive conditions. 

"They built US Airways into a viable competitor in the US market when US Airways had by far the worst network conditions to build a viable business," Bhaskara said. 

Following the formation of the "new" American Airlines, Kirby and Parker worked their magic again with the airline reporting an adjusted profit of $6.3 billion in 2015. Although that figure was helped by a significant drop in oil prices.

Kirby's move from the largest airline in the world to a major domestic and international rival is uncommon, even in the topsy turvy world of the airline industry.

The exact series of events that led to Kirby's defection to United remains unclear.

REUTERS/Yuri GripasAlthough it is believed that his ambitions to one day assume the top job at American — currently filled by 54-year-old Doug Parker who is expected to be in that position for the foreseeable future — played a role in his decision. 

In a statement to Business Insider, American Airlines explained:

"The changes announced yesterday are the result of the Company’s Board of Directors’ ongoing succession planning process. 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."

Regardless of what happened during Kirby's final days at American, Parker remains (at least outwardly) highly complimentary of his former colleague.  

"On a personal note, Scott and I have worked together for over 20 years, beginning back at America West in 1995," Parker wrote in a letter to American Airlines employees on Monday. "He has been both a great colleague and a good friend and we are going to miss him. We will be forever grateful to him for his leadership and his influence in making American what it is today."

REUTERS/Yuri GripasIn addition, American also paid its former president a severance package valued at $13 million, the Wall Street Journal reported. 

At United, Kirby will be tasked with improving an airline that's lagged behind rivals American and Delta in terms of product and financial performance.

"Scott is a proven leader, whose deep airline experience and expertise will further accelerate our efforts to build the best airline in the industry," United Airlines CEO Oscar Munoz wrote in a press statement.

"Kirby brings a strong degree of credibility to United, which its current management team lacks," Bhaskara said. "He also brings a laser focus on revenue maximization and improvement, and I think he’s going to give United a more aggressive and growth oriented bent."

Upon his departure, American named former COO Robert Isom as Kirby's successor. 

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