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NASA's DC-8 Flight Laboratory undergoes a flight safety inspection at Cecil Airport in Jacksonville, Florida. NASA's High Ice Crystal Water Content (HIWC) project traveled through thunderstorms in July 2022 to study the formation of ice crystals and how they affect the performance of aircraft engines.

Source: NASA/John Gould

A team of NASA researchers is again using NASA's DC-8 Flight Laboratory to study ice crystals and more at the center of large thunderstorms, a study aimed at optimizing jet engine design and improving flight safety.

The research work is part of NASA's High Ice Crystal Water Content program, which has flown two previous missions: the first in Florida in 2015, and the second in 2018 in Florida, U.S. California and Hawaii.

In July 2022, the research team conducted a mission over the southeastern coast of the United States and the Gulf of Mexico. This time, the research team, which includes the FAA and Japanese partners, is using Cecil Airport in Jacksonville, Florida, as their base of operations.

"In this mission, we're trying to do something a little different," said Thomas Ratvasky, principal investigator for the High Ice Crystal Water Content program at NASA's Glenn Research Center in Cleveland, Ohio. The mission is to fly in areas where anthropogenic source aerosols are present to better understand the effects of these aerosols on the formation of high concentrations of ice crystals."

These tubular instruments on the DC-8 wingtip are used to collect ice crystal data in NASA's High Ice Crystal Water Content program. The isokinetic probe (left) is used to measure the total water content in the cloud. Another device is a cloud droplet probe, which measures smaller cloud particles.

Source: NASA/John Gould

Aerosol 101

Aerosols are tiny particles suspended in the air, caused by both natural processes and human activities. Anthropogenic sources include the burning of fossil fuels, industrial emissions, and emissions from agricultural activities.

Once released into the air, these aerosol pollutants can be transported through the atmosphere and eventually even reach the oceans.

According to one theory, the interaction of aerosols with convective systems increases the concentration of ice crystals in thunderstorms, but scientists do not yet understand exactly how this complex interaction works.

During storms, especially mesoscale convective systems, high concentrations of ice crystals form. As the plane travels through it, the power and performance of the jet engine is reduced.

So researchers at the High Ice Crystal Water Content project have been collecting data on ice crystals and their effects on jet engines.

With this additional mission to study aerosols, the high ice crystal water content project will bridge the existing data gap. The data will inform the development of new safety standards by relevant regulators to mitigate the effects of ice crystals.

Thomas Ratvasky said: “We wanted to make sure that the high aerosol environment was represented in this data set. Most engines today do not have to demonstrate the ability to fly in this ice crystal environment, but future engines will need to demonstrate the ability to fly in this ice crystal environment. Safe flight in an ice crystal environment."

Power loss / engine damage

Over the past 30 years, there have been more than 170 incidents involving loss of power and engine damage on commercial transport aircraft, such as airliners, while flying over convection systems.

These accidents happen because when a jet is flying over an area with a high concentration of ice crystals, some of the ice crystal particles enter the core of the engine, the part that generates power.

In some cases, ice crystals can form a layer of meltwater inside critical components such as compressors. Heat transfer from the engine to the meltwater containing ice crystals can cause ice to form in the compressor. When ice cubes fall off, it can cause loss of engine power or damage.

Instruments located elsewhere on the plane that collect vital information for the pilot, such as the plane's speed, can also be obscured by ice crystals, resulting in erroneous and inaccurate readings in the cockpit.

To understand the role aerosols play in the formation of high concentrations of ice crystals that affect aircraft performance, the High Ice Crystal Water Content project will utilize a DC-8 aircraft at NASA's Armstrong Flight Research Center in California, and Fly missions in storm areas with high concentrations of ice crystals and aerosols.

An intake duct sticks out of a modified window at NASA's DC-8 Flight Laboratory. During flight, air enters the tubes and is directed into the interior of the aircraft, where instruments will detect the amount of aerosols in the atmosphere. This research work is part of NASA's High Ice Crystal Water Content program.

Source: NASA/John Gould

flying laboratory

The High Ice Crystal Water Project team upgraded NASA's DC-8 aircraft with data-gathering instruments and other technologies that allow crew researchers to take real-time observations of the environment.

The DC-8's left wing and nose were equipped with devices to measure the total water content of the clouds the aircraft traversed, as well as cloud drop detectors. The right wing, meanwhile, houses instruments capable of measuring the size and shape of larger ice crystal particles.

Inside the nose is a modified weather radar to detect storm conditions in the DC-8's forward flight path. The project team used the radar unit in collaboration with researchers at NASA's Langley Research Center in Virginia.

For this mission, the researchers installed a new passive cavity aerosol spectrometer probe on the plane to measure the number of aerosol particles in the atmosphere. The passive cavity aerosol spectrometer probe and other aerosol measurement instruments, owned by Nagoya University in Japan, were used in joint research in the high ice crystal water content project.

The plane has an air intake on the starboard side that directs air into the plane itself, where it flows through a series of instruments before exiting downstream of the plane.

Inside the DC-8 are racks of monitors, displays and other sites where researchers can sit and view flight data.

Each mission lasts approximately seven hours and travels thousands of miles at a variety of speeds and altitudes.

In a typical flight profile, the project team flew at the same high altitude as the airliner to fly over the ice crystals. Then descend to a very low altitude (even below 1,000 feet) to catch the aerosol before it rises into the storm and interacts with clouds and ice crystals.

Rest assured: safety comes first. The experts operating the plane knew what to expect and how to deal with ice crystals.

Thomas Ratvasky said: "We don't fly outside of the airliner's flight area, so we can obtain data suitable for normal flight operations. The pilots and the entire team on our project are aware of the impact of high ice crystal water content on the engine and air data systems. performance and have procedures to minimize these hazards.”

A view of the interior of the NASA DC-8 aircraft (facing forward). The researchers of the high ice crystal water content project sit in front of these consoles to operate the equipment and collect relevant data about the external conditions of the flight. The cockpit of the plane can be seen in the background.

Source: NASA/John Gould

high altitude partnership

The research work on the high ice crystal water content project has been carried out smoothly thanks to the close cooperation between several institutions providing expertise and project funding.

"We wouldn't be able to do this project without these collaborations both inside and outside NASA," Ratvasky said. "We have the science team from Langley Research, the icing team from Glenn and the aircraft from the Armstrong Flight Research Center. The FAA provides support for instrumentation, and Nagoya University and the Japan Meteorological Agency provide their expertise and aerosol instrumentation."

After the flight activity, the next step is to process the data before handing it over to relevant agencies such as the FAA and the Ice Crystal Icing Advisory Committee on Aviation Rulemaking.

Once the study is complete, the certification criteria for the relatively new jet engine will be assessed and power loss events due to ice crystals in the convective system will all but be eliminated.