Fire and Ice: Software Fix Tackles Rare and Poorly Understood Icing Inside the Hot Core of a Jet Engine
November 27, 2013
In 2006, a group of researchers that included senior engineers from Boeing and Honeywell published a scientific paper on the threat of microscopic ice particles to jet engines in flight. The rare and poorly understood phenomenon has been drawing the attention of investigators since the 1990s, when the aviation industry started reporting a growing number of engine icing events, frequently near large and complex storms in the tropics.
The incidents involved passenger and large transport aircraft that temporarily lost power at altitudes higher than 22,000 feet, the extreme upper limit recognized for the existence of super-cooled liquid water. “Often the event report mentioned being in cloud, but when interviewed, the pilot reported no significant airframe icing, nor any remarkable weather encounter,” the researchers said. “Some pilots were even surprised that the investigators suspected icing as the cause of the engine powerloss.”
GEnx engines at GE’s testing facility in Winnipeg, Canada, must power through tests in sub-zero weather, while ingesting thousands of pounds of water, ice and wind per second.
While engine icing never resulted in an accident, it has not gone away. A small number of GEnx jet engines powering Boeing’s large 747-8 and Dreamliner aircraft have recently battled through such extreme weather conditions. GE engineers are now working on an engine software fix that will open and close “bleed valve doors” behind the engine’s front fan and booster, prevent ice build-up behind the front fan and eject the ice crystals before they enter the core section of the engine.
NASA, the Federal Aviation Administration, as well as air safety and regulatory organizations in Europe and Australia have been studying the phenomenon. This spring, NASA scientists were able to re-create the high-altitude ice crystal cloud environment in the Propulsion Jet Laboratory during a full scale engine test, which resulted in a loss of engine power. “For the first time ever, scientists calibrated to a very fine degree ice crystal clouds found at the high altitude and pressure conditions typical in flight,” NASA said in a news release. The agency will share the test information with manufacturers “to establish test methods and techniques for the study of engine ice crystal icing in new and existing commercial engines.”
The ice crystals, which can be the size of a grain of flour, often occur near massive convective thunderstorms can be as large as 400 miles in diameter. The complex thermodynamic flows inside these systems suck up warm and moist air and then circulate it with descending cold air to form tiny ice particles as small as 40 microns in diameter. NASA said that the ice crystals can travel up to 30 nautical miles away from the main storm. Airlines have started telling pilots to fly around them.
GE said that earlier this year, there were six events involving GEnx-powered aircraft where the engines experienced momentary reductions in thrust in rare high-altitude icing conditions. All of the aircraft landed at their planned destinations and there were no engine in-flight shutdowns. In nearly every case, the engines quickly resumed their thrust levels.
The engines affected were the GEnx-2B engine for Boeing 747-8 planes, and also the GEnx-1B engine for the Boeing 787 Dreamliner. There are about 500 GEnx engines in operation powering some 150 planes, out of a total of 26,000 GE jet engines in service.
GE said that crews can install its icing software fix in an hour while the engine is on the wing. “We have done initial flight testing with the new control software on a Boeing 747-8,” said Chuck Nugent, general manager for the GEnx program at GE Aviation. “This testing provided initial validation and results to refine and finalize the control logic for the new software. We expect it to be available to aircraft operators in the first quarter of 2014, once certified.”