Commuter Ops

An exterior loading door of a 7300 coach randomly opened while train 49 was at track speed between Wheaton and Winfield. At Wheaton a detraining passenger alerted me that one of the two exterior loading doors of a 7300 type coach had not opened. I positioned myself in the vestibule of that coach after departing Wheaton. I noticed a small gap of less than an inch between the door panels but the train had a door light and was moving west toward Winfield. While at track speed, the west exterior door of this coach opened 3/4 of its travel and closed tightly. I wrote up this defect on an exception report and contacted commuter control verbally reporting this incident.