On Sunday mount Hunga Tonga Hunga Ha’apai Exploded underwater.
This eruption is the largest volcanic eruption in the last thirty years.
Let’s consider the risks that volcanic ash causes to the engines, fuselage, and windows of a jetliner.
“Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get them going again. I trust you are not in too much distress.”
This public announcement to the passengers of BA flight 9 on June 24th, 1982, was made by Captain Eric H Moody. As the huge 747 on a flight from Kuala-Lompur Malaysia to Perth Australia as they flew into a volcanic ash cloud near Java Indonesia.
Following the bug 2010 Iceland volcano eruption aviation shutdown over Europe an ICAO task force International Volcanic Ash Task Force (IVATF) and their recommended practices can be found in ICAO doc 9974
In the simplest sense Volcanic ash cloud is made of Silica dust. That is a fancy name for glass. The problem is that the particles are small enough to be sucked into the engines. The silica which is a solid form in the atmosphere melts in the engine but resolidifies on the turbine. Deforming the blades. This can lead to engine flameout.
The same effect goes to pitot tubes. And may cause blockage.
A third threat is abrasion of the cockpit windows limiting visibility.
Volcanic ash sometimes is accompanied by Sulphur Dioxide – This substance in the presence of water vapor produces Sulphuric acid.
Another element often found in volcanic ash is Chlorine That combined with water produces Hydrochloric acid.
These acids are corrosive and toxic.
The main mitigation for volcanic ash risks is avoidance. Volcanic Ash Advisory Centers VAACs were established worldwide to provide information and warnings for ash clouds.
CAAs and operators are called to establish risk-management processes based on the information provided in the manual and real time information provided by the VAACs.
This should be based on the density of particles in the ash cloud PPM.
A better more robust checklist guidelines for Ash-cloud encounter was developed.
Pilots and dispatchers are required to be trained in these procedures.
We are better prepared for a volcanic ash cloud presence than ever before. Still a big eruption like the 2010 Iceland event has the potential to take a heavy toll on aviation