Hong Kong government pilots fly into eye of typhoons to better understand their secrets

When Super Typhoon Saola hit Hong Kong on September 1, government pilot Elaine Chan Yee-ling was flying into the eye of the storm, trying to steer her aircraft as turbulence made it violently shake.

Her mission was to deliver dropsondes, a cylindrical weather device packed with sensors, into the heart of Saola so key data about the storm could be collected for the Hong Kong Observatory.

“It was my first time in the eye of a typhoon,” the pilot recalled. “It was mesmerising, as I wasn’t able to see anything during my flight, but then the next second, it was all sunny and calm with a circular cloud surrounding me.”

Pilot Elaine Chan in the cockpit of her Government Flying Service Bombardier Challenger 605. Photo: Jonathan Wong

Pilots with the Government Flying Service have been braving the city’s roughest storms to collect meteorological data for the forecaster since 2011, racking up 81 trips as of last month.

According to Chan, pilots were often forced to make detours before reaching drop points inside the typhoon, flying to avoid the worst pockets of turbulence and hail while flying at 31,000 to 35,000 feet.

Visitors walk along the Tsim Sha Tsui waterfront as Super Typhoon Saola hits on September 1. Photo: Yik Yeung-man

The dropsonde, which is attached to a parachute, records data on temperature, humidity, air pressure and wind speed, along with other storm conditions, at various altitudes as it drifts down towards the sea. The information allows the Observatory to improve its computer predictions on typhoon paths and intensity, according to Cheung Ping, senior scientific officer in aviation meteorological data analytics.

“A sensor on the wing of the plane can provide good data, but when used for tropical storm detection missions, it is limited to the same height as the plane is flying,” Cheung said.

But the dropsonde could collect data at different heights, which could be very helpful in analysing a storm’s strength and how other weather systems affect it, he added.

The Government Flying Service only switched from plane wing sensors to dropsondes in 2016 after spending HK$9 million on revamping its weather data collection equipment, which included obtaining the proper accreditation to use the new system.

Air crewman Alfred Tsang Chi-ho explained dropsondes required installing a control block and a launcher with two release valves on the government’s Challenger-605 fixed-wing aircraft.

“The control block is used to connect with dropsondes,” Tsang said. “We have also retrofitted luggage space in our aircraft to hold our launcher, which is used to release dropsondes.”

The two-valve system used to deploy dropsondes so the plane’s cabin does not lose pressure. Photo: Jonathan Wong

The device is dropped using a two-valve arrangement, where one is closed while the other opens to prevent the cabin from depressurising.

The Government Flying Service carried out its first nighttime typhoon survey mission during Koinu’s pillage last month. The typhoon hit the city worse than expected, with the No 9 storm warning issued with only 15 minutes’ advance notice, leaving many residents stuck at MTR stations as open-air rail services ground to a halt.

Pilot Mavis Tsang Ka-yee, who flew into the storm, said the operation went smoothly, but she had to fly in pitch black surroundings.

“During daytime, you can see your surroundings,” Tsang recalled. “If there’s a particularly dark cloud nearby, you know it’s going to be turbulent. However, we had to rely entirely on our radar at night.”

Government Flying Service pilots have been braving the city’s roughest storms to collect meteorological data for the forecaster since 2011, racking up 81 trips as of last month. Photo: Jonathan Wong

Senior Scientific Officer Cheung said the city’s weather forecaster had been sharing its typhoon data with neighbouring meteorological organisations and hoped to boost collaboration with its national counterpart by monitoring typhoons together.

“The Government Flying Service’s mission range is only within the city’s air space,” Cheung said. “If we could collaborate with [the mainland], when the typhoon goes to their side, they could observe. This would improve continuity of analysis.”