The AirTight protocol supports mixed criticality wireless traffic and temporal guarantees based on defined fault models. In some systems, following a catastrophic failure, it is necessary to communicate crucial data away from the site of the failure in order to better understand (post-hoc) the reasons why it occurred. To support this action it is necessary for a mode change request to be propagated to all the non-failed nodes in the system, and for these nodes to switch their behaviour so that the crucial data is given high priority in its use of the wireless network. This paper explains how Airtight can support such a critical mode change. A uni-cast protocol is utilised to flood the system with mode change messages, each node then locally prioritizes its use of the available bandwidth to support the defined UC (Ultra-Criticality) packet flows. An aircraft engine control scenario is used to motivate the requirements for the mode change protocol. Protocol-accurate simulations are then used to illustrate and evaluate the approach
