Originally Posted by FriendlyPilot

When an airline buys engines, they come with various ongoing service agreements. You can buy an engine with no coverage, or add on coverage, including repairs, replacement engines, etc.

Spirit chose to purchase none of these to keep costs down. The $150M in repair and inspection credits is a gift. Spirit also waived their rights to sue with this agreement.

Spirit bought the engines without ongoing coverage, and then agreed to settle for $150M in credits in lieu of a lawsuit which it might not win and would take a long time, which they don't have.