Alan Mulally, head of The Boeing Co.’s commercial airplanes division, sold $3.8 million in company stock last week, about half of his total outright stock holdings.

Mulally, a graduate of Lawrence High School and Kansas University, had been a top internal candidate to become Boeing chief executive after ex-CEO Harry Stonecipher left in March. The job instead went to former 3M chief James McNerney; Mulally has said he intends to stay on.

Mulally opted to sell the substantial chunk of his holdings because, as a company insider, he is allowed to sell shares only during certain narrow windows, Boeing spokesman Peter Conte said.

“His recent sale is due to a desire to rebalance his investment portfolio,” Conte said.

Mulally continues to hold more than enough shares to meet the guidelines set by Boeing directors. Top executives must hold four times their base salary; Mulally now owns 58,670 shares outright, and his 2004 salary was $819,692.