Several companies have taken a hard look at aircraft electrical systems. They focused on the area of wire harness inspection and testing processes and the wire harness as it ages during its service life. Honeywell's Nova wire integrity program was one result of this scrutiny,

 according to Rob Fioto, technical sales leader of the Nova Program, who gave a demonstration of this unique tool developed by Honeywell in conjunction with DIT-MCO International, GRC International, Qualtech Systems, and Lectromec Design.

Diagnostic equipment available today can perform more detailed nondestructive examinations of wire harnesses and their connected electrical components more efficiently and cost effectively than ever before. The Nova wire program is built on these ideas:

• Vehicle modeling: Vehicle modeling is an understanding of the wiring architecture in a system. This includes enough information to determine criticality to safe flight and impact to other functions when a failure occurs.

   

• Test planning and monitoring: Tools for planning, tracking and managing the testing of each wire in a system and vehicle over its useful lifetime. Existing maintenance programs would be examined to see when wires could be available for inspection and what the best test equipment would be to test them.

   

• Testing: A comprehensive suite of test equipment, adapted to the different stages of maintenance (bench, hanger, line) that can detect anomalies in wiring and the degradation of wiring and insulation caused by contamination, physical abuse, and aging.

   

• Data management: The collection and archiving of information, such as vehicle architectures, test plans, schedules, testing programs and test data.

   

• Low cost: The program must be affordable to operators at any level of aircraft maintenance activity. Users must be trained to use this program based on the abilities of the technician, and the equipment must be lightweight and portable, with a high degree of reliability.

Honeywell's Nova wire program started with these points and developed into a product that can be used easily and cost effectively by most operators. In reality, many aircraft will undergo some electrical or avionics upgrade through their service lives as they get sold or leased from owner to owner.

Who keeps track of all these changes? Certainly there will always be a logbook sign-off. However, is there a wiring diagram stapled to the maintenance logbook or filed in the maintenance records for small or larger aircraft that have been delivered or returned as part of a lease? The documentation might consist of microfiche of the blueprints that the designers drew up. How up to date is that drawing? What if there isn't any technical documentation available and nobody's picking up the phone at the maintenance support customer service number, or your Internet connection is down and you cannot connect to your technical data at the maintenance base?

Fioto believes the Nova program can increase operational safety and reduce electrical maintenance costs. Honeywell, working in cooperation with Northrop Grumman, researched and developed a process to apply the principle of time domain reflectometry (TDR) to enhance the inspection and analysis of wire harnesses. To do this, engineers began with a piece of equipment commonly found in electronic manufacturing and repair shops called a circuit analyzer. Knowing just what the circuit analyzer does, they built capabilities into the unit that surpassed the original designer's intent and went to work testing out new theories. TDR is similar to radar, in that a signal or multiple signals are transmitted in a conductor, and the return signal contains information. Analysis of the return data can reveal defects within the conductor, the insulation surrounding that conductor, and the condition of the shielding on the wires being examined. Poor grounds, interference, or sympathetic influence from nearby electrical subsystems can also be identified as they operate simultaneously.

This test process can be configured to test anywhere from 1 to 1,000+ wires in a bundle with a few mouse clicks. The FLB-1000 can be used in smaller shops, or the HIT-1000 for larger operators and this best can be done in microseconds. No matter how many wires are in a particular wire harness, this equipment can inspect and test faster and more accurately than the technician ever could with ordinary test equipment.

In the setup process, first, a specific connector harness is fabricated to connect the TDR equipment to the aircraft wire harness or electrical

 component line replaceable unit (LRU). Next, a little time needs to be spent configuring the equipment to the aircraft. Data such as the tail number, aircraft type, and name and part number of the wire harness being tested are entered as well as what zones the wire harness is installed.

As the technician conducts tests with the program, the equipment builds its own database. The software will compare an aircraft-specific baseline database preinstalled in the operator's TDR equipment to the live data being gathered. That gathered data will generate a new database that will grow past a certain point and then take over to produce accurate warnings of impending wire failure, failed wires, and LRUs with impending failure indications. Not only can the techician tell what electrical component failed, this technology can identify the location of the fault within the airframe or narrow it down to the correct zone.

As this database continues to grow, it identifies within the fleet all aircraft that have had failures by part number, location, and frequency and it can even record other environmental conditions such as humidity level and temperature. This information is incorporated directly from the database into the operator's engineering, then maintenance publications department in the form of accurate printed wire diagrams and schematics. This translates into the ability to generate detailed work cards in a short time with less human data manipulation.

According to Fioto, Honeywell's Nova wiring program helps operators maintain a high level of wiring and electronic component test consistency. The system also indicates what has changed within any particular electrical system as the aircraft ages. All aircraft electrical equipment is designed to last a specific life span. At each interval of that unit's life span, it will use a little more current because of the increased resistance of that component. These little pieces of evidence add up to aid understanding of the characteristics of items that fail.

Honeywell's Nova wire program is able to monitor, locate, and detect faults far beyond the human scope of ability. The program incorporates a software design feature called open architecture. This allows the equipment and software to talk to an operator's existing computer systems, databases, engineering and publications departments, and enables a transfer of this intricate data for a particular aircraft to the next owner or operator.

The Nova Wire program is capable of producing a tremendous amount of specific life cycle data that is not easily gathered and maintained by human hands. This technology could be incorporated into the aircraft's on-board diagnostics systems in the future.

-- By Paul A. Bass