Operators of turbine-powered aircraft must avoid flying through volcanic ash clouds, according to engine and airframe manufacturers, but if ash is encountered in flight, there are specific techniques that pilots should use as well as post-flight maintenance procedures. According to the U.S. Geological Survey, there were 100 documented encounters of aircraft with airborne volcanic ash from 1973 through 2000, but the Survey doesn't believe that aircraft operators have reported all such encounters. “Severity of the encounters has ranged from minor (acrid odor in the cabin and electrostatic discharge on the windshield) to very grave (engine failure requiring in-flight restart of engines). Engine failures have occurred 150 to 600 miles from the volcanic sources. Fortunately, engine failure leading to crash has not occurred,” according to the Survey.
Pratt & Whitney Canada says it “does not recommend operation in conditions where volcanic ash is present. Volcanic ash may clog air filters of turbine engines, block cooling-air passages, erode the gas path components and erode the protective paint on casings. Volcanic ash entering the engine can also melt in the combustor and then re-solidify on the static turbine vanes, potentially choking the turbine airflow and leading to surging and an inflight shutdown. It is also noted that there is a high level of acidity associated with volcanic ash, and this may also lead to deterioration of engine components.”
Honeywell issued a recommendation to operators on April 20, warning that “volcanic ash consists of particulate matter that ranges from powder-like dust to grit [and is] highly abrasive.” Damage can occur because of “erosion of flow path components, blockage of pneumatic system components with mechanical linkages, blockage of cooling passages [and ash material can] collect on turbine components [and] cause long-term detrimental effects such as corrosion.”
Cessna issued advice on how to protect parked airplanes-especially those parked outside-during volcanic ash fallout events. The advice includes sealing openings with vinyl tape and installing engine, pitot and windshield covers.
Maintenance cost-per-hour provider Jet Support Services (JSSI) pointed out that its engine care program does not cover damage caused by volcanic ash. Customers should contact the engine and airframe OEM for any questions regarding ash encounters as well as JSSI.
Pilots may want to review information on the Aviation Troubleshooting blog, which includes photos of damage caused to turbine engines and a list of steps pilots should take during an airborne encounter with volcanic ash.