PXI speeds aircraft maintenance

As a safety feature in commercial aircraft, proximity sensors monitor the status of mechanical elements such as forward wing flaps, landing gear, and access doors. But when the sensors give false error readings, the need to find the problem can keep an aircraft grounded for hours, annoying travelers and cutting airline revenue.

Now, aviation consulting firm R.H. Caldwell & Associates uses a PXI-based aircraft sensor test system that speeds problem solving and supports preventative maintenance. I spoke with project consultant Roger Caldwell to learn more about the system.

Q: What does the test system do?

A : This system runs real-time tests on a variety of safety sensors in Boeing aircraft to determine if they are operating properly. Sensor issues have plagued airliners during the last seven or eight years, with erroneous messages indicating wing flaps and slat position, landing gear, and access doors and hatches being open, and the like. These false errors may account for over half of aircraft flight delays and are very expensive to diagnose and repair, notwithstanding the obvious passenger inconvenience. The standard method for testing, however, uses a manual LCR meter and simple breakout box that looks like something right out of the 1950s.

This new system automates the testing, provides a graphical indication of a failed sensor's location, and gathers data for long-term, fleet-wide performance analysis and predictive failure models. In essence, the entire aircraft is viewed as a flying circuit board, and multiple onboard electrical networks with passive and active components may be ATE test subjects.

Q: What made you choose PXI?

A : We fell into it by accident. When we first set out, we contacted Tektronix to see if there was anything suitable off-the-shelf. There wasn't, but Tektronix put us in touch with Geotest, which built us a system using its portable PXI box.

Our job was to define the aircraft interface, specify how the system would operate, and generate maintenance manuals with related aircraft technician training. Geotest configured the chassis and created the software, while the Seattle-based engineering firm Aero Northwest helped design and fabricate the aircraft interfaces.

Q: What do you think of PXI?

A : It has been great. It is so readily configurable that we can write a statement of work, and in a week Geotest will come back with an implementation plan. The software is also configurable, so we can tweak it ourselves as we gain field experience with the system.

PXI instrument cards offer capabilities that we want to tap in new applications. For instance, aircraft maintenance has a need for updated time-domain reflectometry testing to identify the location of failures in cabling without crawling all through the airframe. In fact, any maintenance procedure that has an electrical interface with the aircraft is a candidate for a PXI test system. The only real concern has been mechanical. The equipment operates in a heavy aircraft maintenance environment and must be mechanically secure and protected from the environment.

Q: Any recommendations for other system designers considering PXI?

A : Spend extra time ensuring the user interface is correct. Our users are not engineers looking at data; they are technicians and mechanics looking to resolve problems quickly. Engineers can analyze the data later, but the mechanics need something that simplifies the job at hand. So, making sure the system is easy to transport and attach and has informative display screens have been key elements in this system's success.