i finally find a old easter egg in simpleplanes is the "Brown Pearl" (or black pearl in POTC)
a screenshots to see:


here's how I find it
spawn at wright airport
go to south west bearing at 247*
wait until a text says "Ye made a grave mistake"
restart here and pause quick look around switch air-to-ground mode then click the target it should be brown pearl
Then go to north west (middle)
and hunt it down