double tolérance de pannes

CONT: For ascent and descent vehicles, the time constraints of the dynamic flight modes preclude the opportunity to utilize in-flight maintenance and system reconfiguration to recover from failures. Therefore, two-fault tolerance is a critical element in ensuring adequate vehicle reliability and should be incorporated whenever possible. When two-fault tolerance is either impractical or may have a negative impact on overall vehicle reliability, single fault tolerance will be provided wherein no single-failure will result in the loss of the crew.