Alerting pilots and drivers to dangerous ice

Scientists from the University of Michigan have developed a pair of sensors that could help planes and cars avoid potentially fatal accidents.

Ice on roads causes about 20% of weather-related car crashes in the US each year, while ice build-up on planes causes roughly 10% of all fatal air carrier crashes by interfering with aerodynamics and controls. This was the case with a flight from Brazilian airliner Voepass Linhas Aéreas, which crashed near São Paulo on 9 August 2024 after the plane’s de-icing systems failed, according to a report in the Aviation Safety Network. In another example, an Air France flight crashed in the Atlantic Ocean on 1 June 2009, after ice blocked the probes that measure the plane’s speed. In both cases, all occupants died.

“More people are travelling by plane each year, and there’s more pressure to fly in all weather conditions,” said Nilton Renno, the U-M professor of climate and space sciences and engineering who led the development of the technology, with support from the National Science Foundation.

“Our technology can help airplanes, drones, cars and trucks be as safe and efficient as possible.”

The two complementary sensors were tested in a single engine aeroplane, as well as a light business jet equipped with scientific instruments for taking reference measurements.

Image caption: Rohan Madathil (left), a Master’s graduate in climate and space sciences and engineering and co-author of the study, helps Nilton Renno (right). Image credit: Brenda Ahearn, Michigan Engineering.

The set-up involves one sensor lying flush against the plane, using microwaves to detect when ice forms on its surface. Meanwhile, another sensor uses lasers to detect freezing rain and large water drops in clouds, alerting pilots to danger in advance. This sensor could also work in cars and trucks, detecting ice on roads.

The results of the experiments are described in the journal Nature Scientific Reports.

Renno began development of the microwave sensor after NASA’s Phoenix lander mission, which found evidence for liquid water on Mars. The professor wanted future missions to be able to measure the amount of moisture in soils and differentiate water from ice. But after he found his personal aeroplane covered in ice one winter, he started thinking about how the technology could be applied to aircraft as well.

“Icing of airplanes is a worldwide problem that can happen any time of the year with aircraft of all sizes, depending on the flight altitude,” Renno said. “I realised that that was a problem that I could do something about because of my background as both a pilot and an atmospheric scientist.”

Currently, aeroplanes detect ice with two styles of probes that protrude from the plane, but because they extend above the surface, they don’t provide information about what’s actually on the plane. The microwave sensor directly detects ice build-up because it’s embedded in the plane’s surface, with the frequency of the sensor’s microwave signal changing when the sensor is covered by water or ice.

The complementary (second) sensor detects freezing rain within seconds of entering a cloud by firing three infrared lasers with different wavelengths.

The first two laser beams are absorbed by water and ice differently, so the ratio of the return signals tells pilots whether a cloud contains ice particles, water droplets or a mix. Planes freeze when they hit water drops chilled below the freezing point, but ice particles just bounce off, so the sensor could help pilots identify a hazardous cloud and fly away before the plane ices over.

The third laser helps determine the size of the water droplets and the amount of droplets in the cloud by comparing its return signal with those of the other two lasers. Larger droplets are more hazardous because they are more likely to hit the plane, while smaller droplets ride the flow of air around the plane.

The lasers could also warn drivers of black ice before they start sliding, or perhaps trigger the car’s automatic safety systems. As slowing by 4–9 miles (≈6.4 x 14.5 km) per hour can reduce the risk of serious injury during car accidents by half, according to research from the University of Adelaide, this could have a real impact.

“You can save a lot of lives by just slowing down when you detect a slippery road ahead,” Renno said.

The device was built and developed in part at the U-M Space Physics Research Laboratory. Intelligent Vision Systems, a U-M startup, developed the optical sensor and licensed the technology with the assistance of Innovation Partnerships, which also has patented the sensors. Renno and the University of Michigan have a financial interest in Intelligent Vision Systems.

The study, ‘A new type of aircraft icing detection system’ can be read at DOI: 10.1038/s41598-025-30681-3-.

Top image caption: Rohan Madathil (left), a Master’s graduate in climate and space sciences and engineering and co-author of the study, and Nilton Renno (right), a professor of climate and space sciences and engineering, prepare the infrared sensor for a test flight on Renno’s personal plane. Image credit: Brenda Ahearn, Michigan Engineering.