Sentence:  At 3 : 58 a. m. , with the plane about twenty minutes out of El Paso , passenger Robert Berry , a San Antonio advertising man , glanced up and saw the man and boy , accompanied by a stewardess , <WSD>walking</WSD> up the aisle toward the cockpit . 
Meaning of the word marked with <WSD> tags:  use one's feet to advance; advance by steps