Summary
The FAA proposes to adopt a new airworthiness directive (AD). The new AD is for Sandel Avionics Incorporated Model ST3400 terrain awareness warning systems/radio magnetic indicator (TAWS/RMI) units as described above. This proposed AD would require installing a warning placard on the TAWS/RMI, installing upgraded software in the TAWS/RMI, revising the limitations section of the Airplane Flight Manual (AFM), and removing the placard and AFM revision after installing the software. This proposed AD results from a report that an in-flight bearing error occurred in a Model ST3400 TAWS/RMI, due to a combination of input signal fault and software error. We are proposing this AD to prevent a bearing error, which could lead to an airplane departing from its scheduled flight path, which could result in a reduction in separation from, and a possible collision with, other aircraft or terrain.