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Its screwy. It also pitches nose up at mach 1.75 and the speed drops to below mach 1 becauses there's a bug with the COG, TBH I think people & freware websites have given up on FSX because of MSFS 2020, (which is extremely over priced in my opinion).
I've tried rectifying it myself but couldn't I've stuck with the old Concorde pack (https://www.rikoooo.com/downloads/viewdownload/51/481) and made some ajustments to the passenger cabin view and imported the liveries I wanted from Concorde Historical Packs version 1 & 2.
If you would like to see what I've done let me know and i'd be happy to share.
I see this problem still hasn't been fixed in over 12 months whhich is a shame really this could be a good aircraft, why hasn't it been fixed you might ask well here's your answer, the absuredly over priced MSFS 2020 so no one gives a F about FSX anymore.