5000 feet calls
The 5000 feet calls were standard when the Voice recorder was on a 30 minute loop tape and the flight recorder was an independent "box" ( usually a silver tape +/- 200 hours if my memory serves me right )
The 5000' calls gave investigators a point to line the flight and voice recorder up for any investigation after an incident / accident.
Alt. setting, also to do with old generation vibrators in the capsules blah blah blah....
Bottom line, "that's how we did it in the Tri Star and B707 is correct".