Flight missions: fairplay or hijacke!

[NWA Air]

I have been playing the game for a considerable time now and currently completing flight missions level 21-30 and have noticed upon achieving the next skill level, my efforts to progress further are hampered! The flights I have accumulated are either erased entirely or partially, so that I'm forced to keep flying the missions to reach the next flight skill level. Also the drop rate on some flight missions is pathetically low! I presume this is a cunning ploy from Game-Insight to force their higher level gamers to fork more cash to keep playing a game that is -in my opinion -over-priced on its in-game credits! Game developers really need either to put a more effort in making the in-game experience more rewarding to justify the extortionate cost of in-game purchases or lower the cost!!