A cockpit (also called flight deck) is an interactive environment of an aircraft which enables both pilot and first officer to monitor the aircraft systems and to control them. Allowing the crew to control aircraft systems through display unit by using keyboard and cursor control unit is one of the main novelties in the new generation cockpits based on ARINC 661 standard. Currently only secondary aircraft systems are managed using such interactive cockpits. Generalisation to other aircraft systems would require introducing mechanisms aiming at ensuring the fault-tolerance of such interaction in cockpits. Such mechanisms would allow designers to take into account the new functions' safety requirement. However, it is possible that such mechanisms may have consequences (positive and/or negative ones) on the crew activities. This paper reports studies that have been performed on fault-tolerance mechanisms in the domain of ARINC 661 interactive cockpits. More precisely this paper focuses on interactive systems, showing how these fault-tolerance mechanisms (mainly redundancy as segregation and diversity are not exemplified here) could affect the usability of the interactive system, making both the tasks of the crew members and their training more complex. We propose a generic approach to analyse the trade-offs between dependability and usability in a software interactive cockpit environment.