In-flight break-up of high-altitude pseudo-satellite UAS – Drones Information
An Airbus Zephyr Heights UAS. broke up in flight after encountering unstable atmospheric conditions that resulted in a series of unconditional rolls and an uncontrolled spiral descent over remote northwestern Australia.
The unmanned Zephyr flight system (UAS), which was designed as an ultra-light pseudo-satellite at high altitude, was launched from Wyndham Airport on September 28, 2019 for a high-altitude flight.
Ascending through an altitude of 5,200 feet and about an hour after takeoff, the UAS encountered unstable atmospheric conditions that resulted in an unauthorized roll to the right and a lane change of about 180 degrees before self-recovering. The flight crew at the ground control station, consisting of a remote pilot, a commanding remote pilot, a mission planner and a flight test engineer, decided to continue the ascent and pointed the UAS north in anticipation of calmer conditions.
However, atmospheric conditions became increasingly unstable and the UAS experienced a second unauthorized throw while traversing 8,700 feet but was again able to correct itself, with the crew increasing power and steering the aircraft to quieter conditions. Wind conditions reduced ground speed to about 1 knot, reducing the ability to get out of the unstable conditions in time, and the Zephyr descended about 1,000 feet over the next 7 minutes.
The UAS then experienced a third unauthorized throw to the right. Failing to recover on its own, the UAS entered an uncontrolled spiral descent that exceeded its maximum airspeed and increased the roll angle beyond its structural limits, causing both wings to break at about mid-span.
Derek Hoffmeister, Acting Director of Traffic Safety at ATSB, noted that the solar-electric Zephyr is designed to operate in the stratosphere above weather and conventional air traffic and is extremely sensitive to atmospheric instability during the climb and descent phases.
“When the Zephyr entered an area of unstable atmospheric conditions that exceeded the aircraft’s ability to remain in flight, it became disconnected in-flight,” Hoffmeister said.
A separate Zephyr UAS was involved in an accident following Wyndham launch in March 2019. The September 2019 accident was only Wyndham’s second launch for the Zephyr program.
“At the time of this occurrence, the Zephyr program was in the early operational phase. Therefore, the information on the structural limitations of the UAS and the methods for predicting turbulence continued to develop, ”said Hoffmeister.
“However, operational and post-crash management procedures have been effective in minimizing risk to the public and the environment.”
In response to this accident, Airbus conducted an investigation into the incident, which resulted in several safety recommendations being made to the design and operations departments of the Zephyr program.
“The number of UAS and remote controlled aircraft in Australia and around the world is growing rapidly,” said Hoffmeister.
“By reporting and investigating UAS and remotely controlled aircraft accidents and incidents, the ATSB can monitor trends and identify areas for safety improvement.
“This information will help improve the safety of all aircraft and the public in general, and will enable this sector of the aviation industry to continue to grow and develop.”
Read report AO-2019-056: Terrain collision with unmanned Airbus Zephyr aircraft near Wyndham Airport, Western Australia on September 28, 2019