Aircraft and spacecraft are complex vehicles whose maintenance requires time-consuming and expensive manual inspections. But a suite of new technologies, such as sensor-actuator networks, can enable Structural Health Monitoring (SHM), a revolutionary method for automatically assessing the integrity of aerospace and other complex structures. As these technologies are gaining significant attention from industry, a new international aerospace group has been launched to promote industry-wide cooperation on the use and development of SHM.

"We're talking about building a nervous system for aircraft," says Fu-Kuo Chang, a professor of aeronautics and astronautics at Stanford University and chair of the Structural Health Monitoring - Aerospace Industry Steering Committee (SHM-AISC). "SHM technologies can give maintenance professionals the information about what is going on in an airplane's structure whenever is needed, just like we have in our own bodies."

SHM has the potential to replace manual inspections, thereby reducing manpower and airplane downtime for maintenance.

"SHM has been identified as one of the key drivers for Airbus to enable the 'Intelligent Structure' philosophy," says Holger Speckmann, the focal point person for SHM Technology at European airplane manufacturer Airbus. "SHM will lead to a reduction of direct maintenance costs, increased availability and innovative design approaches, which will have a huge benefit for our customers in according to their fleet performance"

Adds John C. Coles, 787 support and services manager for Boeing Commercial Airplanes: "We see SHM as one of the emerging technologies that may provide significant improvements in operational efficiencies for the airlines. These improvements would be largely in the capability to immediately scope the extent of visible damage with on-board equipment, eliminating the time to locate and employ non-destructive inspection equipment, and shortening the time required to plan a repair."

The SHM-AISC
The SHM-AISC held its first meeting at Stanford on November 7, 2006, during which members agreed on a charter and confirmed a management board. Chang was elected to serve as the first chair.

The international management board comprises representatives from major aerospace industries from across the globe (Airbus, Boeing, EADS, Embraer, Honeywell, BAE Systems), regulatory agencies from the United States and Europe (FAA/EASA), the government agencies (U.S. Air Force, U.S. Army, and NASA), and research and development institutions (Sandia National Labs, Stanford University).

The aim of the SHM-AISC is to formulate a collective view of the way forward for the practice of Structural Health Monitoring (SHM) and its impact on the management of structural health. The group will plot a course to efficiently and effectively implement the technology in a wide variety of commercial and military aerospace applications. This will be achieved by the development of standards, procedures, processes and guidelines for implementation and certification. The mission of the SHM-AISC is to provide an approach for standardizing integration and certification requirements for SHM of aerospace structures, which will include system maturation, maintenance, supportability, upgrades, and expansion.

Over the coming weeks, the committee will be establishing working groups to focus on the detailed tasks needed to fulfill this vision. More pertinent private and government organizations will be invited to serve on the working groups. The first working group – Commercial Aviation – is to be established by early 2007 and expects to produce draft standards within the next two years.

About SHM technology
SHM is a new technology in aerospace that is increasingly being evaluated by industry and government as a potential method to reduce operational costs and possibly improve the safety and reliability of aerospace vehicle structures. The core of SHM technology is the development of self-sufficient systems using built-in, distributed sensor-actuator networks as part of overall vehicle health management strategies. The SHM approach can provide continuous monitoring, inspection and detection of damage in structures with minimal human involvement.

The purpose of SHM is not only to detect the presence and extent of structural defects, but to also determine the effects of structural usage and provide an early indication of physical damage. The early warnings provided by an SHM system can then support remedial strategies before emerging structural damage can impact flight safety. The same technology could also be used to enhance the design of future aircraft structures.

NASA began to implement SHM in the Space Shuttle program after the loss of the Shuttle Columbia in 2002, says William Prosser, a senior scientist with NASA.

"The impact damage to the thermal protection system highlighted the need for onboard SHM systems," Prosser says. "In response, a Wing Leading Edge Impact Detection System has been installed on all Shuttles and is monitored on every flight. Similar systems are under consideration for the International Space Station and future space vehicles."

The Air Force is also looking at adopting SHM in a reusable launch vehicle known as the Space Operations Vehicle. "An automated system could assess the health of the entire structure within hours of a completed mission, and re-certify the structure for flight," says Mark M. Derriso, structural health assessment team leader for the Air Force Research Laboratory Air Vehicles Directorate. This optimized turnaround time would, in turn, reduce the vehicle's launch costs.

During the third European Workshop on Structural Health Monitoring (held in Granada, Spain, in July 2006), government and industry representatives expressed the need for creating industry-wide policies and procedures for the standardization and implementation of SHM technologies. In response to this consensus, workshop participants asked Chang to create the SHM-AISC.

"SHM is a timely development because the costs associated with the increasing maintenance and surveillance of aging infrastructure are rising at an unexpected rate," says Dennis Roach, a distinguished member of the technical staff at the Airworthiness Assurance NDI Validation Center established for the FAA by Sandia National Labs in Albuquerque, N.M. "Aircraft maintenance and repairs now represent about a quarter of a commercial fleet's operating costs.”