Summer of '87
I've heard this story from a number of viewpoints and can summarize (if memory serves me well) as follows:
The Delta TriStar was equipped with triple INS and went off-course as a consequence of an error in waypoint lat/long entry.
As the Delta procedures of the day did not include
- customary pre-flight checks of "PF enters / PNF checks" waypoint data;
- no prescribed 'crosschecks' of next lat / long, distance to next waypoint, or desired track when passing a waypoint;
- and no plotting chart (or procedures for its use) by which a 2 degree / 10 minute plot might have been accomplished
the turn off track to the erroneously entered waypoint was not noticed by the crew.
The hero of the day might have been the Delta second officer who was required to load his INS independently from the PF / PNF and display 'XTE' on his #3 INS whilst in the track; supposedly, a food tray on the center console obscured the vital data which may have prevented the near miss.
As the aircraft windscreen had been 'papered over' for sun block purposes (sun screens were not provided in those days) the first 'clue' the Delta crew had that something was amiss was the 'thump' of the DC-10s wake turtbulence as the TriStar passed some 50' beneath it.
Subsequent radio comments encouraging the Continental crew to not report the near miss apparently did fall on deaf ears - understandable given the 'scab' rhetoric of the day as well as the fact the passengers were more than a little agitated after the 'thump' of the near miss and the sight of the Delta aircraft out the window.
As a Continental passenger in posession of a video camera noticed the approaching Delta aircraft and filmed the entire incident (that is, until the TriStar disappeared from view beneath the DC-10 and shook the aircraft so badly that the poor man dropped the camera) any attempt at a cover-up would have been short-lived.
The tape of the subsequent radio chatter actually came courtesy of the aircraft commander of a USAF flight from the 89th Military Airlift Wing at Andrews AFB (the 'VIP' transport wing which includes Air Force One).
Disgusted by the subsequent entreaties to cover up the incident, the man directed his crew to use the communications gear on board his aircraft (can't recall, but I think it was a VC-135) to record the chatter and later forwarded the tape to the authorities.
Happily, luck smiled on all that day as a tragedy was averted by the 'soft' altitude hold feature of the TriStar that allowed the aircraft to wander as much as 200' from the MCP altitude.
In the post-incident investigation, I understand an FAA inspector audited the next DAL transoceanic procedures ground school; when he asked the instructor at the conclusion of the course why he was not teaching procedures contained in the then-current FAA Advisory Circular on Long Range Navigation Procedures, supposedly the man replied "I've never heard it."
To their credit, the Delta people were quick to get their house in order with the appropriate procedures and hundreds of line checks to ensure that the crews fell in line.
The effort to 'raise standards' at the airline was motivated as well by the other incidents in that 'Summer of '87' - including an inadvertant dual engine shutdown at low altitude on a 767 departing LAX and a 'wrong airport' landing by a 737 in Frankfort, Kentucky - to say nothing of the relentless black humor of Johnny Carson who 'had his way' with the airline on late-night television.
The footnote to the story was the less than good fortune of the USAF skipper who suffered both fame and notoriety for his part and - after retiring some years later - had little luck with his application for a job at Delta.