If you're still curious about NW 188, the flight whose pilots "missed" Minneapolis and realized their error halfway across the next state (background here and here), via AVweb here is the NTSB's extensive full docket of info on the case, including interview summaries with the two pilots, the airline's dispatchers, and others.
Chronicles of aviation mishaps can be very gripping, as my former Atlantic colleague William Langewiesche has demonstrated many times. In this case (as with the "miracle on the Hudson, subject of Langewiesche's latest book) the fascination is guilt-free, since there were no fatal consequences. Sample detail from this new info: whatever the root of the problem here, it certainly wasn't lack of experience. The Captain had 20,000 hours of flight time (a lot), and the First Officer began flying at age 14 and had been an F-111 pilot in the Air Force. Reading the comments of these very, very experienced people who realize they have done something .... inexplicable is surprisingly absorbing.*
Also several graphics, including the one below plotting info from the Flight Data Recorder ("black box"). The original, as a PDF, is here, and you can click on the image below for a larger version. What's we're seeing here: the two vertical, magenta-purplish text boxes mark the last radio transmission before the roughly 80-minute period of being out of touch with controllers, and the first radio transmission afterwards. In between that time, we see: autopilot turned on (steady red line at top); unchanging horizontal and vertical guidance from the autopilot (steady black line at the top and steady green line); stable altitude (steady blue line); slight variations in aircraft heading (lower black line), because of wind or other factors; and apparently no attempts for 80+ minutes to make outbound radio contact (orange "Key VHF" line at bottom of screen). You could write a real-life aviation drama based on this chart.
After the jump: Since a previous colloquy, here and here, about the legal implications of the terms "frolic" and "detour" also arose from NW 188, two final reader dispatches on the legal semantics of the question.
* Speaking of gripping and inexplicable: this story, by Gene Weingarten in the Washington Post magazine, recounts the horror and living hell of parents who... somehow... forgot that they had left an infant in the back seat of the car on a broiling hot day. I read it when it came out early this year and can't get it out of my mind. By comparison, the NW 188 story is light comedy.