American Airlines is moving forward with plans to close its St. Louis pilot base this September, notifying the state of Missouri this week that 153 pilots will be affected by the closure.

Those pilots won't lose their jobs; instead they'll have the opportunity to relocate or begin commuting to work out of one of the carrier's other 10 pilot bases -- including Dallas-Fort Worth, Miami, Charlotte and Chicago -- subject to the airline's seniority rules. Two administrative staffers also affected by the closure will be able to apply for other jobs with the carrier or take a severance package.

The closure will begin in early September and should be complete by the end of the month, American said in a letter to the Missouri Department of Economic Development as required by state's the Worker Adjustment and Retraining Notification Act.

The closure, first announced last October, comes as American's network and fleet shift. Most notably, the carrier is retiring McDonnell Douglas MD-80 aircraft operated out of St. Louis at a rapid rate as it phases the older generation of aircraft out of its fleet.

"Taking these factors into consideration, a difficult decision has been made to close the [St. Louis] base in September 2018," American's vice president of flight operations Kimball Stone said last year.

The affected pilots previously worked for Trans World Airlines, which operated a major hub at St. Louis Lambert International Airport and was acquired by American in 2001. American closed TWA's St. Louis hub in 2003 and the carrier's daily flights at Lambert Airport have since fallen from a peak of more than 400 to less than 50 as of last year.

American said the closure of the pilot base won't impact its flight schedule in St. Louis.

Other American employees working in flight service, maintenance, customer service and other jobs in St. Louis will not be affected by the closure.