"Theoretically" agile means that you have an easy access to the customer to help you with decision making and changing requirements. Unfortunately its VERY rar

"Theoretically" agile means that you have an easy access to the customer to help you with decision making and changing requirements. Unfortunately its VERY rare to meet that requirement for agile (multiple reasons). For mission critical projects like the one you mention, I think, company should pay good money even to few surgeons to be available for the devs. Problem often lies in management to understand that..