A quick answer to your direct question is by. But:
1. I tend to think of extending inspection to mean it is taking more time. If more things are being inspected, then I would say 'expanded'.
2. By your use of two, I guess there are more than 2 rudder blades/stocks. Is that the case?
3. Why were the rudder blades/stocks removed? Were they removed for repair(s) and an inspection of the rest of the system is being inspected as a preventative measure?
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