Complex sentence: These crashes prompted a review of the maintenance and usage of the entire U.S. large airtanker fleet, and ultimately the grounding of the whole fleet, 33 aircraft in all, resulting in a major impact on the resources available to fight major wildfires.
Split into simpler sentences: These crashes prompted a review of the maintenance and use of the entire U.S. large airtanker fleet. Ultimately, the whole fleet, 33 aircraft in all, was grounded, dramatically reducing the resources available to fight major wildfires.