Warning Messages — Page 526, Lesson 496

I want to walk you through the aviation warning system for volcanic ash, starting with a real example of a Volcanic Ash Advisory message. Here we have the body of an actual advisory. It begins with ERUPTION DETAILS, which tells us the eruption exploded at a specific time: 20120801/0035Z — that's the 1st of August 2012 at 00:35 Zulu time. The ash cloud was observed at FL070, flight level 70, which is 7,000 feet, and it was moving to the southwest. The next line is OBS VA DTG, which stands for "observed volcanic ash date-time group" — that's 01/0015Z, the time the observation was actually made. Then we have OBS VA CLD: the observed volcanic ash cloud. In this case, it says VA NOT IDENTIFIABLE FM SATELLITE DATA — the ash could not be seen on satellite imagery. The wind at FL070 is given as 070/55KT, meaning the wind is from 070 degrees at 55 knots. The forecast sections follow: FCST VA CLD +6 HR, +12 HR, and +18 HR. Each one reads NO VA EXP — no volcanic ash expected at those times. The RMK or "remark" says they will issue a further advisory if ash is detected in satellite imagery. Finally, NXT ADVISORY: NO FURTHER ADVISORIES — that's the end of this particular advisory chain. Now, alongside these advisories, the International Civil Aviation Organization, ICAO, recommends a colour-coding system for volcanic activity. There are four levels: Green, Yellow, Orange, and Red. Green means the volcano is in a normal, non-eruptive state. It can also mean that after a change from a higher level, volcanic activity is considered to have ceased and the volcano has reverted to its normal, non-eruptive state. Yellow means the volcano is experiencing signs of elevated unrest above known background levels. Or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for a possible renewed increase. Orange means the volcano is exhibiting heightened unrest with an increased likelihood of eruption. Alternatively, a volcanic eruption is underway with no or minor ash emission. If possible, the ash-plume height should be specified. Red is the highest level. It means an eruption is forecast to be imminent with significant emission of ash into the atmosphere likely. Or, an eruption is underway with significant emission of ash into the atmosphere. Again, specify ash-plume height if possible. Now, why does all this matter? Volcanic ash is a form of silica with a relatively low melting point. The hazards it presents to aviation are serious: engine flameout, reduced visibility, scoring of windscreens, pitot blockage, and a sandblast effect on the airframe and antennae. Also, volcanic ash is a very fine powder that, if inhaled, can cause severe respiratory problems. So this colour code and these advisory messages are how the aviation world keeps pilots informed about the status of volcanic activity and the presence of ash in the atmosphere.