A version of this article appears in the September 8 issue of Aviation Week & Space Technology.
Europe’s aviation regulator is holding off on setting turbine engine volcanic ash ingestion certification standards, bowing to industry calls for deeper research and continued collaboration on developing best practices for keeping aircraft away from ash clouds.
The European Aviation Safety Agency (EASA) decision, issued July 30, followed input from more than 100 industry representatives that responded to a February 2013 proposal asking for input on whether rules were needed. The consensus: Efforts led by the International Civil Aviation Organization (ICAO) and supplemented by both long-standing recommendations and guidelines developed after the highly disruptive 2010 eruption of Iceland’s Eyjafjallajokull volcano are enough to keep airliners safe while research continues.
“Opinions expressed were unanimous in that there is no rationale to depart from the current ICAO operator-centric approach, whereby it is the responsibility of the operator, based on a safety risk assessment and supported by existing data streams, to decide whether to fly or not,” EASA explained.
Certification requirements do not mandate testing for volcanic ash’s effects on engines. Instead, operators have long been advised to avoid flying through visible ash. The efforts have proven effective, figures show. Since 1976, when ash cloud reporting became commonplace, “damaging” airliner encounters with ash have averaged about two per year. Seven “severe” incidents involving engine failures have been reported, but there has never been a fatality or hull loss.
While see-and-avoid creates adequate safety margins, it can cripple operations. During the Eyjafjallajokull event, forecasting models projected that most of Europe’s airspace contained ash. As operators and air traffic management providers reacted based on ICAO guidance that included more conservative aircraft spacing, air traffic flow slowed, rendering normally congested airspace all but unavailable. Some 100,000 flights were canceled in a six-day span.
Subsequent work by engine makers has refined guidance to include more specific criteria tied to levels of ash concentration in the air. But linking specific standards to engine types and then determining when they are exceeded during real-time operations remains elusive.
“[T]he diversity of ash characteristics, engine designs, flight plans and volcanic ash contamination forecasts’ precisions make it quite difficult to set precise concentration limits usable in a certification process,” said France’s DGAC safety agency.
EASA also noted that setting limitations based only on engine tolerances ignores potential hazards with other aircraft systems and occupants. “Furthermore, the current state-of-the-art in volcanic cloud monitoring or forecasting, while improving, has not yet reached the stage where it can be used for an inflight assessment against an airworthiness limitation.”