American Airlines Group Inc. CEO Doug Parker will hand over the reins of the No. 1 U.S. airline to president Robert Isom on March 31, the company said on Tuesday, sending its shares up more than 3 percent before the bell. Parker will continue as chairman, while Isom will join the carrier’s board after he takes over as CEO. Isom, a longtime airline industry executive, took over as president in 2016 and has overseen operations, planning, marketing, and pricing. The leadership change comes as the industry recovers from the lows hit during the pandemic but faces operational challenges due to the threat posed by the Omicron coronavirus variant. In a letter to employees, Parker said the transition was the result of a “thoughtful and well-planned multi-year process,” dating back to Isom’s elevation to president in 2016. Parker said the transition would have happened sooner if it was not for the …