The date was 14 February 2014. An A320 aircraft was cruising at 36,000 feet on its flight from Perth to Soekarno-Hatta Airport in Java. Just before sunrise, the flight crew suddenly heard unusual faint noises. About 30 seconds later, the captain saw green sparks outside the cockpit. A faint sulphuric smell and light haze also began forming in the flight deck. Upon diagnosing that the plane had probably flown into volcanic ash, the flight crew immediately changed direction and donned oxygen masks. They later found out from the Jakarta Air Traffic Control Unit that the nearby Mount Kelud in Java had erupted.
Why Volcanic Ash Can Be Hazardous to Aircraft
Volcanic ash can have a serious impact on aircraft, in particular on the engines. Volcanic ash contains silica particles which have a melting point well below the core temperatures of jet engines. The silica particles would melt and fuse with parts of the engines, choking them and causing them to flame out. In this incident on 14 February 2014, the engine manufacturer recommended that both engines be removed from the aircraft as they were contaminated with volcanic ash.
Volcanic ash also poses other considerable threats. Ash, which consists of extremely fine powder of glass shards and pulverised rock, is very hard and extremely abrasive. It can erode airframe, flight surfaces, and engine parts. The abrasion of the cockpit windows can lead to reduction or loss of visibility for the pilot. As volcanic ash is generally too fine to be stopped by normal filtration systems, it can heavily contaminate an aircraft's electrical and avionic units, as well as cooling systems, rendering aircraft control difficult. Ash fall can also cause damage to aircraft on the ground and reduce visibility at aerodromes.
Large volcanic ash clouds are capable of travelling large distances when borne by the wind. When Mount Pinatubo in the Philippines erupted at least 16 times within five days in June 1991, the ash cloud circled for 22 days and damaged aircraft within a 1,800 km radius.
Risk Management for Volcanic Ash
As seen from the eruptions of the Icelandic Eyjafjallajökull in 2010 which lasted for about 39 days and disrupted at least 100,000 flights, it may not be feasible to halt air operations for extended periods merely because of the presence of volcanic ash. At that time, many air operators demanded to know how much ash is hazardous, and how much is safe enough, to fly into. This triggered the ICAO to set up an International Volcanic Ash Task Force (IVATF) immediately after the Eyjafjallajökull eruptions. The IVATF was tasked to develop a roadmap for establishing globally harmonised safe levels of operation in airspace contaminated with volcanic ash. It was also asked to provide options for improved volcanic ash detection systems, and recommendations to improve notification and warning systems.
The IVATF acknowledged that no matter how sophisticated observations and forecasts of volcanic ash may be, there is no assurance on how volcanic ash will behave in the atmosphere. Safety assessments need to be carried out by individual operators. The IVATF therefore developed guidance material (ICAO Doc 9974) on risk management of flight operations with known or forecast volcanic ash contamination. It encouraged operators to put in place an acceptable safety risk assessment process aswell as appropriate operating policy and procedures for the dispatch of flights into areas or aerodromes forecasted or known to be affected by volcanic ash contamination. In developing their policy and procedures, operators should also take into consideration guidance from the aircraft and engine manufacturers, and from local authorities.
The potential for more and greater volcanic ash disruption to civil aviation is high. The results of a volcanic ash study conducted by CAAS and the Earth Observatory Singapore, in partnership with the Meteorological Service Singapore indicate that in the next decade, there is a 60% chance that volcanic ash reaching potentially damaging concentrations will affect some areas of Singapore’s Flight Information Region. CAAS will continue to work with our stakeholders towards building a harmonised contingency plan in order to be more resilient when faced with volcanic ash disruptions.By Lim Lay Eng
Senior Inspector (Meteorology)
Article was first published in The Leading Edge issue 02/2014