Might be all BS but I think if one of the check valves that are at the low point didn't close, as one pump was stronger than the other, fuel would circulate back through the open check valve rather than operate the ejector function.
I think the regular test was to have a fuel quantity lower than the exit height to the main tank from the ejector outlet and run the aircraft up to 100% on the ground with the boost pumps off and if the check valve wasn't working it would draw air back the through the ejector exit which was above the fuel level and it would flame out! If so, time to clean the check valves!
Seem to remember it being done pretty regularly back in the day in a land far away with questionable fuel and was more than 30 years ago!
Last edited by RVDT; 12th Jan 2024 at 02:49.