Flaps 10 would have not given them a takeoff warning.
Many differences with PanAmerican 747 aircraft, just as with their 707 airplanes, before.
Customer option, originally.
In the SFO case, a change of runway at the last minute.
Takeoff planned on the longer runway (flaps 10), but flaps 20 needed on the shorter runway, due to TOW.
A rather big wake-up call for PanAm, at the time, hence the
configuration check prior to departure, to be
sure that the correct flap selection was made.
I knew the Chief Pilot, Pacific at the time, nice guy.
Forgot the numbers for the Tristar...
160 knots, minimum, powers B system only.
If all three generators trip offline, RAT extends automatically...a nice safety feature.