VITA has initiated a committee, VITA-58, to produce an open standard that tightly defines the dimensions of line replaceable units (LRUs) and the appropriate connectors for power, data and cooling type. Technologically speaking, it doesn’t matter what processors, buses or serial connections are used inside the LRU, the sealed, protective metal "can" housing circuit boards. All that matters is what backbone data path and power bus are in the airframe, and how the electronics are cooled (liquid, air or conduction). These LRUs will be operational in the next few months, and the transition to two-level maintenance–and its huge life cycle cost savings–can start being recognized in military and commercial avionics.
The first of these LRUs will connect to the backbone ARINC wiring in avionics platforms, especially in military applications. Later versions will incorporate Mil-Std-1553 avionics bus, Ethernet, fibre distributed data interface (FDDI), and other new and existing networking technologies.
VITA-58 promises to ameliorate some of the maintenance, reliability, and life cycle cost problems with LRUs. In the past and even now technicians sometimes have to troubleshoot problems on the flight line and replace specific circuit boards, or line replaceable modules (LRMs), increasing the likelihood of malfunctions. When a military aircraft technician pulls a circuit board LRM from an avionics system on a carrier deck, for example, the electronics can be exposed to dust, dirt, jet exhaust, fumes, salt spray and sulfur smoke. That LRM would be sent to the maintenance department for repair, even though it may already have been contaminated.
When a VITA-58-compliant LRU is pulled and replaced on the flight line, or a flight deck, its contents are protected and taken to a depot maintenance operation for repair. The flight line technicians can easily see which LRU needs to be replaced via a red light indication, and aircraft can be mission-ready in minutes. Personnel can be trained in a minimum amount of time, rather than having to train as repair technicians. Flight line technicians would then become operational managers rather than technology repairmen.
This concept, two-level maintenance, comes from Dennis Carlson of Carlson Technology. He has shown how to completely replace all the electronics in an airframe or ground vehicle and have it mission-ready in less than 30 minutes, using no tools and with minimal technician training. According to Carlson, with LRUs, the life cycle cost savings for the electronics is tremendous and the mission readiness of the platform goes up dramatically.
Each LRU would have only three indicator lights: red, yellow and green. Red means the unit is faulty, yellow means it is starting up, and green means it is running properly. Any pilot or operational technician can see at a glance if all systems are green and the platform is mission-ready. If one of the units shows a red light, it can be replaced and restarted in minutes, and the defective unit can be sent off to a maintenance depot.
But how do you get the right software into the LRU? Again, solutions are found in everyday applications. For instance, a satellite TV receiver sends a message requesting program information and the satellite sends the data to a ground-based computer. The computer looks up a "smart card" number and identifies what channels the user is authorized to receive. Then that software is downloaded to the receiver. It is entirely possible for any LRU plugged into an avionics system to use a similar method: retrieving its code (encrypted, if necessary), and starting up just like the satellite receiver.
Now, think about one step ahead. What if the LRUs on aircraft and land-based systems had a high level of commonality. For instance, a communications LRU taken from a ground vehicle could be placed into a fighter jet and used to replace a faulty navigational computer. The LRU is simply a processing element, so what it does is purely a function of the software downloaded from a satellite. In this case, LRUs would not be unique units but operational units whose functions are defined by the appropriate software.
This concept of LRUs and two-level maintenance could vastly enhance aircraft operational readiness. With a high degree of commonality, LRUs from one vehicle could be readily used in another with minimum human intervention, technician training and operational delays. The VITA-58 standard seeks to accomplish these benefits.
Ray Alderman is executive director of VITA, an ANSI- and IEC-certified standards developer in Scottsdale, Ariz. VITA’s standards are used for helicopters, airborne refueling tankers, fighter aircraft and ground-based military vehicles.