Control systems cited in unmanned aerial vehicle crashes
A series of drone malfunctions poses a unique challenge to the Air Force and Army
- By Sean Gallagher
- Oct 09, 2009
The hazards of operating unmanned aerial systems were magnified in September by a number of UAS mishaps for the Air Force and Army. On Sept. 27, an Army RQ-7B Shadow UAS crashed into the Mosul, Iraq, office of the Iraqi Islamist Party, just a few weeks after an Air Force MQ-1 Predator crashed in central Iraq.
And in Afghanistan, on Sept. 13, the Air Force was forced to shoot down one of its own MQ-9 Reaper aircraft that did not go into failsafe mode after the service lost remote control of the aircraft.
Although mishaps with UASs have happened before as the military services push them to the edge of their operational capabilities, one major difference in how the Army and Air Force operate their systems has been identified as the cause for many of the Air Force’s mishaps with Predators.
Earlier this year, John Young, departing undersecretary of Defense for acquisition, technology and logistics, openly criticized the Air Force for failing to follow the Army’s approach of installing technology on UAS systems that lets software handle their landings, rather than pilots.
According to numbers released by the Office of the Secretary of Defense in March, 65 of the 195 Predators the Air Force had acquired since 1994 had been lost because of “Class A mishaps.” Of those aircraft lost in accidents, 36 percent were attributed to human error. And 15 percent of the accidents occurred during landing.
“The very straightforward difference [between flying combat aircraft and UASs] is, when you go in as the pilot of the Predator, No. 1 – you’re making strokes on a keyboard,” said Brig. Gen. Guy Walsh, commander of the 451st Air Expeditionary Wing at Kandahar Air Field, Afghanistan. "No. 2 is that you’re sort of looking through a soda straw. To me, it’s a lot easier when you have a stick and rudder in our hand as opposed to the keyboard.”
Walsh said one of the biggest challenges pilots were facing when he arrived at Kandahar in July was dealing with the handling characteristics of a Predator at the end of a mission, when it was extremely light, in high crosswinds.
“This airplane is a bit lighter, and it becomes much more difficult to handle, almost like trying to fly a paper airplane, when it gets very, very light,” Walsh said. “So as we try to stretch the capabilities of the airplane out here, and you run into crosswind landing problems, it’s not like back in Baltimore where you can go 20 miles down the road and find a runway that’s directly into the wind. I know that has been one of the issues we’ve had — that the pilots have had some challenges with some of the strong winds we’ve had here and up in Jalalabad where we also fly the Predator missions.”
The 451st Air Expeditionary Wing’s Predator responsibilities are focused on maintaining and preparing Predators and Reapers and handling takeoffs and landings. After the UAVs are in the air, they’re handed off to pilots at Creech Air Force Base in Nevada via a satellite link and flown on their missions — and then handed back to the Launch and Recovery Element at Kandahar to be brought back down to earth via a local radio circuit.
Automated takeoff and landing
The Army flies its version of the Predator, the MQ-1C Sky Warrior, and the Shadow UAV a bit differently. The Army maintains control using AAI’s One System Ground Control Station from within the operating theater — though over-the-horizon control for the Sky Warrior is maintained with a Ku-band satellite connection, just as the Air Force’s Predators are controlled. And both the Sky Warrior and Shadow are launched and recovered automatically, without human control.
Like the Predator, the Sky Warrior is flown over the horizon via a Ku-band satellite connection; the Shadow is flown only within electronic line-of-site, meaning it must stay within UHF radio range of its control station. But like the Air Force’s Global Hawk UAS, both the Sky Warrior and Shadow use an automated landing system that hands over control to a computer networked to ground-based radar sensors.
The system used with Shadow and Sky Warrior is called the Tactical Automatic Landing System (TALS) and is manufactured by Sierra Nevada. “It's a small monopulse radar tracking system,” said Russ Walker, division vice president of tactical UAS programs at AAI. "There's a ground component — an antenna — and there's an air component that's a transponder and an antenna. The transponder that's on the aircraft gives position data to the antenna on the ground, and the antenna on the ground tracks the transponder and monitors the azimuth and elevation of the aircraft. And what the system does is to put the aircraft on a glideslope that will successfully land it.”
The software element of the TALS system sends speed, pitch and roll commands to the aircraft to keep it within the glide slope, Walker said. If it gets pushed outside of the lines set by the system to keep the aircraft on track for a safe landing — by a sudden crosswind or other disturbance — it performs a wave-off and automatically brings the aircraft back out and around to try again.
“We’ve found the system is pretty robust. We do operate in unpredictable wind conditions,” Walker said, “and typically we’re able to land [the Shadow UAS], even with a wave-off, using the TALS system. We’ve done over 100,000 missions now, all using TALS. And there have been very few landing incidents in my memory that were caused by the TALS system.”
Sean Gallagher is senior contributing editor for Defense Systems.