Integrated Systems Health Management emerging as critical new aircraft technology

  • Published
  • By Holly Jordan
  • AFRL Air Vehicles Directorate
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  It's happened to almost all of us. We board an aircraft, get settled in, and await the pushback from the gate and the beginning of our journey. Suddenly, a voice over the loudspeaker announces that the flight will be delayed, or worse, canceled, because of an unexpected maintenance issue.

Delays such as these not only frustrate the traveler, but result in costly schedule changes for the airlines themselves. And for military aircraft, the consequences can be far more serious.

The military aircraft fleet must be safe, reliable, and ready at a moment's notice. Unexpected maintenance, and even scheduled maintenance checks, can keep an aircraft out of service when needed most.

That's where Integrated Systems Health Management or ISHM comes in.

ISHM is a term applied to a system that collects data from various areas of an aircraft and transmits real-time information about the condition of the vehicle back to the maintenance depot. This instant information helps flight support personnel know if a problem arises with the aircraft and helps them predict when it will need maintenance or repair.

Air Force Research Laboratory ISHM Lead Mark Derriso compares the typical aircraft to people with congenital insensitivity to pain. People suffering from this condition cannot feel pain and, therefore, cannot inform doctors of their symptoms. Aircraft, of course, also cannot inform maintenance crews of their "health."

"What we are doing with ISHM is trying to determine the condition of the entire vehicle," Derriso said. "We want the vehicle to tell us how it feels. Then we can decide whether it is safe to perform the next mission, send it to be repaired, or perform real-time mission or trajectory replanning."

One needs only to examine the Missouri Air National Guard Mishap that occurred in November 2007 to understand the safety benefits of ISHM. During a training exercise, the forward fuselage of an F-15 broke apart from the rest of the vehicle, forcing the pilot to eject and causing the loss of the aircraft. Fortunately, the pilot survived with only minor injuries, but the entire fleet of F-15 A-D aircraft was subsequently grounded until emergency inspections could be completed.

The cause of the F-15 incident was deemed to be fatigue cracks in the upper cockpit region. According to Derriso, this is the type of structural damage AFRL engineers believe can be detected through ISHM.

While mission safety is the most critical element of ISHM, it also provides benefits in terms of cost and aircraft availability. Continuous real-time monitoring of the aircraft prevents the vehicle from having to undergo unnecessary pre-scheduled maintenance, which can be costly and cause the aircraft to be out of service for long periods of time.

Derriso said ISHM also helps maintenance crews continuously monitor the status of aircraft components, allowing them to have parts in stock beforehand, ready for installation when the aircraft is scheduled for maintenance.

ISHM can be of tremendous benefit for current and future military aircraft. The next generation of space vehicles must be able to fulfill a mission and quickly be ready for another if needed. The elimination of routine pre-flight inspections through ISHM will assist in making this goal a reality.

ISHM can be beneficial not only for military vehicles, but for commercial aircraft as well. According to Derriso, commercial airframe manufacturers are already employing elements of ISHM to aircraft such as the Boeing 777 and the new 787 Dreamliner. Recent groundings of commercial aircraft such as American Airlines' MD-80 fleet and Southwest Airlines' Boeing 737s to inspect for possible wiring and structural problems emphasize the need for ISHM on commercial applications.

AFRL researchers are currently examining ISHM systems at the subsystems level to try to examine and improve ways the components can work together to more effectively gather data. Researchers are currently monitoring data from piezoelectric sensors installed on an F-16 test vehicle at Luke Air Force Base. Derriso says that by monitoring this data, researchers are not only able to determine the quality of the damage detection techniques, but also the durability of the sensors themselves.

According to Derriso, the next ISHM test will be on a Global Hawk wing. The wing will be equipped with a sensor array and subjected to two lifetimes worth of structural fatigue. Researchers will then assess how well the health monitoring system detects fatigue damage and how well the sensors themselves withstand the test.

After the structural testing is complete, AFRL researchers plan to move toward an integrated ISHM test. The test will use a recently-designed ISHM architecture--combining components from aircraft structure, flight control, and propulsion--that performs real-time diagnosis and prognosis at the platform level. The testing will serve as another step toward eventually maturing a system that can be incorporated onto military vehicles. Derriso says his hope is that the ISHM architecture used in this test will become the standard for the ISHM community.

Current and future ISHM developments from AFRL and other organizations will be the focus of the upcoming 2008 Integrated Systems Health Management Conference (www.usasymposium.com/ishm), to be held August 11-14 at the Northern Kentucky Convention Center in Covington, Ky. During this event, experts from throughout the aerospace community will gather to discuss new breakthroughs in the area of air vehicle health management, with topics to include ISHM in current and future aircraft, various approaches to fatigue diagnosis and prognosis, and emerging space vehicle technologies and their associated ISHM requirements.

"It's important to get the ISHM community together to discuss problems, developments, and current state of the technology," Derriso said. "These systems can not only save countless hours of aircraft downtime, they can save lives as well. ISHM is not just a convenience; it is emerging as a critical element of aircraft design."

ISHM is a combined effort of the AFRL Air Vehicles, Propulsion, Sensors, and Materials and Manufacturing Directorates, as well as numerous airframe designers and contractors.