A proposed revision of FAA Advisory Circular AC 20-136 was developed by EUROCAE Working Group 31 and SAE Committee AE4L to address requests by some users of this FAA advisory circular for more specific guidance for selection of equipment transient design levels (ETDL’s) applicable to electrical and avionic systems performing essential or critical functions, and for selection of verification methods for these systems. The proposed revision also makes use of the expanded data base of measured induced transient levels in aircraft since publication of the original draft advisory circular in the United States in 1987 (the original “Orange Book”), to enable descriptions of aircraft interconnecting wiring installations corresponding to each of the standard transient levels. Overall, this proposed revision would offer routes to certification of systems and installations performing critical display or essential functions by reference to level selection guidelines instead of expensive full vehicle tests. If adopted by the certifying agencies, this proposed revision would become (in the U.S.) FAA Advisory Circular 20-136A, and a new advisory circular - joint in Europe. Its implementation would facilitate cockpit avionics upgrades (i.e. modifications) for existing airplanes, in some cases, without full vehicle tests to verify the transient control levels.