As an aircraft moves from the freezing temperatures of high altitudes through wet clouds, moisture on the metal skin turns to ice, which can change how air flows over and around the leading edge surfaces. The changes can cut lift forces, which keep aircraft in the air, by a factor of two or three. The aviation history books are filled with sad stories about what can happen then.
The problem is not that commercial aircraft do not have systems to remove or prevent ice buildups during flight. Rather, these systems rely heavily on pilots' knowledge and experience for operation. Pilots must make critical decisions without specific information about how conditions are affecting their aircraft's handling and performance.
A team led by Michael Bragg, an aeronautical engineer at the University of Illinois in Champaign-Urbana, is looking to take that kind of data out of the black box and put it into the cockpit.
"Ice becomes a hazard when the aircraft is flying in conditions that it has not been certified to fly in, or if it is flying in severe icing conditions that may overwhelm its protection systems," Thomas Bond, who manages NASA's icing research program at the John Glenn Research Center in Cleveland, told United Press International.
That is what happened when a commuter plane with 68 people aboard went down near Roselawn, Ind., on Oct. 31, 1994. The American Eagle flight, which had taken off from Indianapolis, spent more than an hour circling O'Hare International Airport in Chicago waiting to land. Ice built up on the plane's wings until it become uncontrollable and crashed to the ground.
Accident investigators later determined the automatic pilot had shut itself down when the icing became too extreme and returned control of the craft to the pilots. They, however, had no information about the conditions or the level of danger.
"If you can use the smart icing system as part of your onboard capabilities, you can increase the opportunity to have a successful flight from departure to end," Bond explained.
The standard procedure for preventing icing is to first, avoid flying in icy conditions. Second, pilots can operate ice protection systems to mitigate the affects of buildups. These systems include heaters on vital control surfaces, such as the wings' leading edges and horizontal stabilizer; inflatable tubes or bladders, called boots, which expand when air is pumped through, causing the ice to break; and antifreeze, which is released through tiny pores in the wings.
The third step is for the pilot, based on his or her knowledge or experience, to understand the circumstances of icing and exercise good judgment. The smart icing system aims to put another layer of safety between the hardware and the human operator to prevent or remove ice during flight.
The Roselawn crash provided the impetus for the program's start. Bond, who was working with a team from the National Transportation Safety Board, said he and Bragg came to realize there had to be a better way to identify and use information onboard to improve safety.
The philosophy behind the smart icing system is to collect information real-time from onboard flight data recorders and sensor packages and present that data on the flight deck for operation and management of the ice protection system.
In addition to measuring the amount of ice buildup, for example, the system would tell pilots the exact location of the ice, issue alerts to activate the ice removal system, restrict the aircraft from potentially dangerous maneuvers and report aircraft performance changes in terms of lift, drag and other flight characteristics.
"We see this as a routine system that can be added to revenue-generating aircraft," Bond said.
A six-year research effort culminated last year in a computerized demonstration simulation. Work is underway for a follow-on program for a test flight.
To create the simulator, the team gathered data to validate their computational models by flying a specially outfitted Twin Otter aircraft through icing environments and measuring performance changes. Additional work was conducted in an icing wind tunnel at Glenn Research Center to obtain data about clean and contaminated wing configurations.
"We (created) ice shapes on the aircraft and flew it," said Bond. "It's the shape that affects everything."
Irene Mona Klotz covers space and aviation for UPI Science News. E-mail email@example.com
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