NTSB recomendations are clear...
From the NTSB:
Therefore, the Safety Board believes that the FAA should require, for all aircraft required to have TCAS installed and for existing and future system designs,14 that the airborne loss of collision avoidance system functionality, for any reason, provide an enhanced aural and visual warning requiring pilot acknowledgment. This is an important consideration for the development of runway incursion collision avoidance systems, as well. Without aural and visual warning requiring pilot acknowledgement, there would be a loss of runway incursion avoidance system functionality if a system on an individual aircraft were to fail or be inadvertently turned off. Therefore, the Board believes that the FAA should evaluate the feasibility of providing enhanced aural and visual warnings for future systems that may provide ground collision avoidance functionality. If feasible, require that future design criteria include such warning functionality