With regard to fuel tank inerting, the FAA letter stated that its research on ground-based inerting indicated that the costs associated with the needed ground equipment are significantly less than what was estimated by the FTHWG and, further, that analysis indicated that ground-based inerting would reduce the fleetwide average flammability exposure for affected CWTs to about 2 percent. The FAA indicated that it planned to conduct ground and flight tests to determine how long ground-based inerting would remain effective during flight and whether vent system modifications would be required to ensure its effectiveness. The FAA stated that it is also establishing an ARAC working group to gather additional data on the practicality of both ground-based and on-board inerting methods.