U.S. Transportation Secretary Ray LaHood on Friday tempered his criticism of ExpressJet Holdings Inc. (XJT) for a high-profile passenger "stranding" and laid the blame at a unit of Delta Air Lines Inc. (DAL).

A weather delay that saw passengers stuck for six hours on an ExpressJet plane in Rochester, Minn. earlier this month saw LaHood ask officials to check whether the airline had "violated" any laws.

LaHood said on a blog entry Friday that a preliminary review revealed that the ExpressJet crew was not in fact at fault. He said they had "repeatedly" sought permission to allow passengers to leave the plane and enter the airport.

ExpressJet shares jumped after the announcement, and were recently up 15.7% at $1.84.

The probe instead blamed an official at Mesaba Airlines, who had "improperly refused" requests to allow passengers into the airport.

"The Aviation Enforcement Office is considering appropriate action to take against Mesaba as it completes the investigation, which it expects to conclude within a few weeks," LaHood said in his blog, noting that he remained angry at the incident.

Delta, which owns Mesaba, did not offer immediate comment.

ExpressJet operated the flight for the Continental Express arm of Continental Airlines Inc. (CAL), and LaHood did say that more senior staff from both companies should have become involved in efforts to allow passengers off the Hosuton-Minneapolis service. ExpressJet and Continental were preparing comment when contacted by Dow Jones Newswires.

LaHood's intervention reawakened the debate over a long-mooted "passenger bill of rights" in the U.S. While there are no mandatory requirements for airlines in handling flight delays, LaHood reiterated Friday that his department may introduce some as part of a proposed rule-making. Some lawmakers are pushing for a three-hour limit before passengers must be allowed off a delayed aircraft.

-By Doug Cameron, Dow Jones Newswires; 312-750-4135; doug.cameron@dowjones.com