The sentence fragment "they are failing at higher than expected rates" suggests that the turbines were designed with improper or incomplete or wrong understanding of (such) wind flows. But the word "without" in front of the blank necessitates a positive word. Clearly complete is the only option.

Since sudden gusts can both damage the turbines and lead to sudden transmission line overloads, the failure to anticipate them is problematic. If the failure to anticipate was elusive or intriguing it would not have had a well-defined consequence.

We are told that in the early days of aviation the atmosphere was poorly understood. And the current situation where the wind flows are poorly understood and gusts of wind are unanticipated is compared to the early days of aviation. This makes it clear that the aircraft designers were working not by sophisticated design or proven routine, but by trial and error.