During last weekend, I found how to eliminate sudden drops of fps on a second flight especially in Melbourne downtown area. In the past, last year, I experienced similar experience at the airport of Miami. At that time I resolved the issue by resetting the rolling cache by turning off and then on. And now I did the same thing but turning off permanently. Surprisingly all that fps drop disappeared like magic. And also I have found the similar post. Stutters when Rolling Cache file is fully filled and start to get rolled w/ new data - Bug Reports & Wishlist / Install, Performance & Graphics - Microsoft Flight Simulator Forums