Complex sentence: Aircraft components are often expensive to purchase, and access to real aircraft cockpits is likely to be restricted due to security concerns, especially in the wake of the 9/11 attacks or if the builder has chosen a current military aircraft.
Split into simpler sentences: Aircraft components are often expensive to purchase, and access to real aircraft cockpits is likely to be restricted due to security concerns. Especially in the wake of the 9/11 attacks or if the builder has chosen a current military aircraft.