Sometime it start with high fps (>50/60) sometimes with incredible low fps (5/10).
Same starting conditions (aircraft, airport, graphic configuration ecc), no other program running, bought it on steam 23 June.
Mac os Sierra 10.12.5 (16F73),
iMac 27 Retina 5K, 27-inch, Late 2014,
3,5 GHz Intel Core i5
32 GB 1600 MHz DDR3
AMD Radeon R9 M290X 2048 MB
1Tb Apple SSD