ARTICLE

May 2003

Pentagon Unhappy About Drone Aircraft Reliability

Rising mishap rates of unmanned vehicles attributed to rushed deployments

by Michael Peck

Crashes and component failures are driving up the cost of unmanned air vehicles and limiting their availability for military operations, said a Pentagon report. Of particular concern are those UAVs that have become useful tools of war—such as the Predator and the Global Hawk.

The reliability issue has sparked disagreements among military and civilian experts, amid congressional criticism that UAVs are becoming too expensive. Heating the controversy were comments by Air Combat Command chief Gen. Hal Hornburg at an Air Force Association conference in February. Hornburg dismissed the notion that UAVs are simple expendable vehicles. “Number one, we can’t treat these things like disposable diapers and just throw them out,” Hornburg said. “These things cost money, and it comes out of your treasury, just like it comes out of ours.”

Hornburg put Predator’s crash rate last year at 32.8 per 100,000 flight hours, and this year’s at 49.6. “If you want to talk about Global Hawk, which we are measuring, the accident rate for the Global Hawk right now is 167.7. That is unsatisfactory.”

The Defense Department’s 2002 UAV Roadmap confirms a mixed history of Class A mishaps—those causing loss or severe damage to an aircraft—especially compared to manned aircraft. Officials noted, however, that comparing UAV mishap rates against manned aircraft may not be entirely fair, because commanders take risks with UAVs that typically they would not with piloted airplanes.

While the F-16 was recently assessed at a mishap rate of 3.5 per 100,000 flight hours,

• The RQ-2A Pioneer has a mishap rate of 363 per 100,000 hours, though the figure for the RQ-2B declined to 139.
• The RQ-5 Hunter racked up a mishap rate of 255 for pre-1996 aircraft, but it has plunged to 16 since.
• The Predator RQ-1A had a mishap rate of 43, and the RQ-1B 31, according to Defense Department figures.

“The mishap rate for large UAVs should be reduced to less than 25 per 100,000 hours by 2009 and less than 15 by 2015,” recommended the report, which did not set specific goals for smaller UAVs, citing a need for further research into factors affecting their aerodynamics. It did suggest examining a retrofit of Predator B components on the more crash-prone Predator A, standardizing reliability measurements between all services and incorporating all-weather capability into future designs.

However, some Air Force officials question the validity of the Defense Department’s statistics, particularly the 100,000-hour statistical benchmark, which was derived by combining the flight hours of Predator, Pioneer and Hunter, rather than focusing on each individually. “Predator has only reached about 65,000 hours. Global Hawk is only at about 2,500 hours. You are nowhere near where you can statistically try to project what your mishap rate is for 100,000 hours,” said Lt. Col. Douglas Boone, deputy chief of the Air Force’s Airborne Reconnaissance Division.

Although 27 out of 80 Predators have been lost due to combat and non-combat causes, Boone told National Defense the program is almost where it should be, with a crash rate of one every 1,900 hours, compared to an initial program goal of one crash no more than every 2,000 flight hours. He believes the mishap rate is skewed because Predators were sent to Bosnia lacking spare parts, maintainers and adequately trained operators.

Similarly, Boone blames the Global Hawk’s crashes, which have claimed four of six prototypes, on hasty deployment to theaters such as Afghanistan. Accolades earned during Operation Enduring Freedom have obscured the fact that the Global Hawk is still in the development stage. “In normal times, it would never have been deployed,” added Boone.

Even determining why a UAV is lost on a mission is difficult. “If it doesn’t return, did we get shot down, or did we have a normal mechanical failure?” Boone asked.

Brad Brown, president of the Association for Unmanned Aerial Aircrafts International, said that reliability will determine further acceptance of UAVs. “According to several senior officers, who wouldn’t admit it publicly, the reason they were against the use of some of these platforms, including Global Hawk, was reliability. It isn’t just a matter of cost. It boils down to a matter of capability. If you only have two, and you lose one, there goes 50 percent of your capability.”

Agreeing that UAV reliability should improve is easy, but how this will be accomplished is another matter. Cost is a concern. More redundancy of flight control systems boosts reliability, but beyond a certain threshold, they negate the UAV cost advantage over manned aircraft, the Pentagon report noted. Similarly, the absence of components needed for manned aircraft make UAVs cheaper, but also affect reliability. And if reliability is overly compromised, then high attrition will require more UAVs to be acquired, thus negating the cost savings. The report recommends focusing improvement efforts on UAV flight control systems, propulsion and operator training, which account for 80 percent of mishaps. It suggests possible remedies such as decreasing maintenance requirements by substituting electrical for hydraulic systems, and digital for analog sensors.

Redundancy is difficult to add to smaller UAVs, but larger aircraft, such as the Global Hawk, have dual redundancy flight control systems and communications, which add reliability but also cost and weight. Triple redundancy is an even more expensive option. “If you make UAVs too expensive or too capable, now you’re going to say that you can’t afford to lose them. You have a Hobson’s choice,” said Timothy Beard, a retired admiral and aviator who is now Northrop Grumman’s director of business development for unmanned vehicles.

Boone foresees UAVs with more sophisticated guidance systems that will enable them to do more than return to their launch point if there is a problem. “With more power in the computer, you can give it more complex instructions like, ‘in an emergency, fly to emergency landing field A.’”

Brown points to Athena Technologies’ “fault tolerant” approach that equips a UAV with an autonomous capability to respond to failures. Frequently operators on the ground cannot determine if or where a UAV has experienced a failure, said David Vos, chief technology officer. Athena’s control system uses onboard sensors to detect malfunctions such as in the rudder, which the aircraft’s computer then compensates for by adjusting other flight controls.

UAV reliability affects more than military use of unmanned vehicles. It is also key to convincing both the Federal Aviation Administration to relax its restrictions on UAVs flying in civilian airspace, and foreign governments to allow overflight and landing rights.

Brown warned that FAA approval will not be forthcoming unless unmanned vehicles approach the reliability of manned aircraft. Boone expects that in the wake of last year’s collision between a Russian passenger jet and a DHL cargo 757 over Switzerland, international agreements governing international flights will require aircraft to carry both radar and optical collision avoidance systems. “Our UAVs are going to have to be compliant with that, too. If you have a Global Hawk flying over Switzerland and it encounters another aircraft, it must deconflict automatically.”

Though it has no jurisdiction over military UAVs and their operators, the FAA does require Certificates of Authorization for flying in controlled airspace. Even though UAV supporters point out that Global Hawk operates at 60,000 feet, well above the altitude of commercial flights, FAA spokesman William Shumann replied that the UAV may ascend or descend through passenger jet altitudes during its missions.

Filing a flight plan can take up to 60 days, and there are currently about 30 of these certificates, with about three-quarters awarded to military UAVs such as Global Hawk, according to Shumann. Military users wants to file and fly on the same day, and the Air Force’s Boone predicts that Global Hawk will be permitted to do this within two years.

Back To Top