The recently issued FAA Notice JO 7110.616 “adds the detection of sulfur gases (H2S and SO2) in the aircraft cabin,” to questions briefers might ask pilots when soliciting for Pireps. H2S, also known as sewer gas, has the odor of rotten eggs, while SO2 is identifiable as the sharp, acrid odor of a freshly struck match. The FAA plans to report volcanic activity when pilots do not see an ash cloud but do smell sulfur gases within the aircraft. The agency warns that the odor of sulfur gases without an ash cloud may indicate that the aircraft is about to penetrate a region of unreported volcanic activity.

If a pilot reports only the smell of H2S or SO2 in the cabin and confirms no volcanic ash clouds are present, the FAA will classify the report as a routine Pirep and include “VA” in weather and “H2S NO ASH,” “SO2 NO ASH,” or “SULFUR SMELL NO ASH” in remarks. Volcanic eruption and/or ash clouds are urgent Pireps, according to the FAA.