I took woojink's use of the phrase "milk run" to be derived from the term WWII Allied bomber pilots used to describe any flight that was uneventful and relatively free of hazards. So while bombing Schweinfurt in broad daylight without fighter cover was tough, flying VIPs around England or some other, easier mission was a "milk run" by comparison.

I also hear it from former Navy fighter pilots now working for the commercial airlines, that compared to landing a supersonic jet on a heaving carrier deck (all 300 yards of it) at night with no lights, flying an airliner is usually a "milk run".

So I think woojink describing the LAX-ORD flight as a milk run would be accurate in an aviation context while bawm's understanding of the term may be more literal and perhaps outdated.