Graham Warwick / Washington DC

Prognosis systems under development will be able to find microstructural changes before a detectable crack forms

Technology to assess the health of individual aircraft and engines, rather than the statistical methods now used to determine remaining fleet life, is to be developed under the US Defense Advanced Research Projects Agency's (DARPA) Prognosis programme.

General Electric and Pratt & Whitney have been awarded $7.1 million each to develop a prognosis system for predicting near-term engine capability as well as providing the pilot with early warning of pending failure. Northrop Grumman earlier received $14.1 million to develop an airframe structural integrity prognosis system.

Today fleet management is based on safe lives and predetermined inspections to detect damage before it becomes critical. Prognosis systems will combine physics-based failure models and state awareness sensors to predict individual aircraft capability, reducing the need for fleet-wide inspections.

"Prognosis will develop technology to manage the fleet based on individual and actual capability, and not on a statistical basis," says programme manager Dr Leo Christodoulou. "The system will make predictions in the near term - 10, 100 or 1,000 cycles, not hundreds of thousands."

While failure models will predict damage evolution with usage, sensors will "interrogate" structures and materials to determine their state. "At any point in the life, the system can make a prediction based on the models, but the models are imperfect so we modulate prediction with interrogation to provide us with state awareness," Christodoulou says.

The sensors will detect the significant microstructural changes that occur in materials well before a detectable crack forms, he says. In an engine, where damage evolution models are driven by throttle setting, ultrasonic sensors could detect the crystalisation of directionally solidified turbine blades, he says. Under the Prognosis programme, Southwest Research Institute has received $1.7 million to demonstrate a wireless sensor system for crack detection and monitoring in engine components.

Instead of a "fly/not-fly" decision, a prognosis system will provide information on the conditions, such as speed and altitude, under which an individual aircraft can be operated safely. "This will enable the local commander to decide which aircraft are most capable for the mission," says Christodoulou.

Under the 24-month first phase, contractors will demonstrate critical technologies, such as feature extraction from complex signals. The 24-month second phase will demonstrate prognosis systems integrated into an airframe and engine and will culminate in a blind "can they find the flaw?" test.

Source: Flight International