How to Improve Credit Rating

I've given up on trying to find ways myself to improve my credit rating. It's stayed at CC for a year and half, and I cannot lease aircraft. Is there anyway to increase it?

Yes, ensure you pay your debts and keep up with lease payments, if your financial situation is stagnated, your credit rating will be as well.

Don't take out too much bonds as this will bring your credit rating down, and thus you can't lease more planes. Make sure you are making enough to keep up with the monthly payments and make a profit.