Getting a Primary Fly-by-Light Control System into Flight

A new redundant 4-axes 100% authority fly-by-light (FBL) control system with dissimilar hard- and software in an EC135 helicopter asks for adequate methods for the development, verification and testing of such a complex system. The constraints on meeting the requirements, the tight cost and time schedule and getting the system successfully into flight are mastered by the following methods: high requirements traceability, early design prototyping, transparent change management, early development of test procedures and prototype testing, effective problem tracking and resolving mechanism, complete ground and robustness testing with full test coverage before the first flight. The ground integration testing was complicated by the high number of possible multiple failures to be analysed. A failure mode effect analysis (FMEA) with probability numbers of multiple failures screened out test cases for obligatory (Q >~10-9/fh) and random (Q <10-9 /fh) execution. A global worst case failure condition set could be identified which included all multiple failures with regard to their failure effect. Flight testing has been successfully performed with 22 flights within a short time period of 3 weeks. The FBL control system worked trouble-free and the flight characteristics are equal to a standard series helicopter.