Guidelines for Time-Limited-Dispatch (TLD) Analysis for Electronic Engine Control Systems
This SAE Aerospace Recommended Practice (ARP) provides methodologies and approaches which have been used for conducting and documenting the analyses associated with the application of Time Limited Dispatch (TLD) to the thrust control reliability of Full Authority Digital Electronic Control (FADEC) systems. The TLD concept is one wherein a redundant system is allowed to operate for a predetermined length of time with faults present in the redundant elements of the system, before repairs are required. This document includes the background of the development of TLD, the structure of TLD that was developed and implemented on present generation commercial transports, and the analysis methods used to validate the application of TLD on present day FADEC equipped aircraft. Although this document is specific to TLD analyses (for FADEC systems) of the loss of thrust control, the techniques and processes discussed in this document are considered applicable to other FADEC system failure effects or other redundant systems, such as, thrust reverser, and propeller control systems, and overspeed protection systems.