Engine icing where you'd least expect
When the average traveler thinks about aircraft icing, they envision snow storms, harsh winters and grounded airplanes. But aircraft icing can also occur in tropical areas while flying at high altitudes through convective atmospheric conditions. The aviation industry has documented many engine events (such as power loss and damage) from commercial aircraft flying in these tropical convective environments.
The potential hazards and damage from tropical high altitude ice crystal icing conditions may be known, but the detailed dataset that can be used to characterize the icing environment and the physical processes that create these conditions are not yet well understood, making it difficult for aircraft manufacturers to design engines that can fly effectively in adverse weather. Looking for a breakthrough in understanding tropical high altitude ice crystal icing, the large multi-year, international High Altitude Ice Crystals-High Ice Water Content (HAIC-HIWC) project was created to collect and analyze deep convective cloud data to achieve scientific, industry and regulatory objectives.
Collaborating to address multinational concerns
Flight tests for Phase I of the HAIC-HIWC project took place in Darwin, Australia in 2014, using a French Falcon-20 aircraft equipped with specialized instruments including the Isokinetic Probe (IKP), specially designed for this project and jointly developed by the National Research Council of Canada (NRC), Environment Canada (EC) and Science Engineering Associates (SEA). Phase II of the project picked up in May 2015, when NRC and EC joined the international team to conduct further flight tests in Cayenne, French Guiana. The tests were needed to better understand the processes that form high altitude ice crystals and to characterize their microphysical composition—particle shape, size distributions, cloud structure and cloud dynamics.
Because collaboration is so critical to many research endeavors, NRC Senior Research Officer, Dr. Mengistu Wolde and EC Senior Scientist, Dr. Alexei Korolev worked together to develop the science plan and to secure the required approval and funding. Together, they led the Canadian team for instrument integration and flight testing. According to Dr. Korolev, the collaboration represents, "a continuation of NRC's long-standing relationship with Environment Canada of over more than 30 years. Our partnership has been very effective and has contributed to changing the regulations for certification of aircraft engines operating in super-cooled icing environments."
Recognizing the need to partner internationally as well, the Canadian team joined forces with the French research team. "Given the nature of these multinational issues, it is crucial for NRC to build and leverage collaborations with both national and international partners in order to be in a position where we can provide thoughtful solutions to these problems," said Dr. Wolde.
Convair-580: the perfect platform
For the flight test campaign in French Guiana, NRC provided its powerful Convair-580, a first-class airborne research laboratory. This highly capable aircraft can carry comprehensive in-situ and remote sensing systems needed for atmospheric research, as well as sensors that give pilots real-time warnings and guidance for adjusting their flight path to exit the high ice water content cloud segments if deemed not safe to operate. As the largest research aircraft of its kind in Canada, the Convair-580 supports a highly sophisticated array of instrumentation that can be configured for both civilian and military research. It has flown on research missions in the Arctic, Alaska, South America, and across North America, as well as through hurricanes on Canada's east coast. With NRC expertise and experience behind it, this versatile research facility can be instrumented to measure atmospheric conditions, cloud composition, air-quality or industrial emissions. With less than five comparable research aircraft in the world, it is little wonder the Convair-580 is in high demand for collaborative research campaigns.
The highs and lows of in-flight data gathering
The international teams (Europe, US, Canada and Australia), supported by other partners working in Cayenne, repeatedly flew into weather that produces the specific icing conditions being studied. They carried out flight tests in deep convective clouds to characterize the high altitude ice crystal icing environment that is known to cause engine events. While the Convair-580 sampled the atmosphere at lower altitudes (between 22000-24000 ft) in temperatures between -5 °C and -15 °C, a French Falcon-20 aircraft was positioned to take measurements at higher altitudes in temperatures of about -30 °C or colder.
Data gathered during these flights will contribute to new knowledge in the HAIC-HIWC project community that will encourage the design of new aircraft engines capable of withstanding ice crystal icing conditions. It will also be used to develop and validate detection of high altitude ice crystals regions from both ground-based and space-based remote sensing systems.
Establishing a safe and sustainable aerospace industry
NRC and the HAIC-HIWC project teams appreciate that their efforts will strongly support the aviation community in its ongoing quest to improve safety. "This research is very critical because the impacts of atmospheric conditions leading to engine icing are so widespread, and yet are still relatively unknown," explained Dr. Korolev.
Although this campaign provided significant insight into high altitude icing, there is still much more that remains unknown. Wolde explains that, "We are currently looking into another phase of this project. We want to add to our understanding of high altitude icing."
The team's immediate next steps involve analysis and quality control of the data, and making it available for other international working groups. The data will be used to develop and improve predictive models for high altitude icing, and to support applications such as NRC's miniaturized high altitude particle detection probes for commercial aircraft.
The French Guiana flight campaign was supported through NRC's Reducing Aviation Icing Risk program and Environment Canada.