if you want job security then i guess yeah take it but 7 years is a terribly long time to sign a contract.
The company will always have the upper hand and could treat you like a dog knowing full well that you have signed a contract for 7years and you are unlikely to be able to leave.
2 years "bond" for training is as far as one should really go anything else and the price in my opinion is too high.
Especially for somethong like the dornier 228!
Your choice after all this is just my opinion!
best of luck