Preempting aircraft wiring failures will have a direct impact in making commercial and military aircraft safer.

AFRL's Information Directorate, Information Technology Division, Dynamic Command and Control Branch, Rome NY

Wire cable chafing and connector corrosion are well understood and age-related problems, which contribute greatly to aircraft wiring failure. They are also suspect in several military and commercial aircraft incidents and accidents. The Information Directorate developed several innovative techniques to detect these problems before they cause system failures. ^1,2,3 Both techniques discussed in this article received patents in the summer of 2001 (Patent Nos. 6,265,880 and 6,275,050).

Directorate engineers developed a simple technique to detect the event of cable chafing well before the chafing can cause damage to the internal structures of the cable. This technique is lightweight, non-intrusive, and easily retrofitted on existing systems. It can detect chafing in both a continuous or periodic testing mode, against grounded or non-grounded structures, and in many cases, does not require the use of electric current at any time, even for testing. This is advantageous for use in and around fuel tanks. The technique can also detect chafing on other types of conduits such as hydraulic and pneumatic hoses and fuel lines.

Continuous monitoring is not the preferred mode of detection since chafing usually develops slowly over a period of weeks or months. Rather, periodic testing for chafing can be performed during regularly scheduled inspections or depot rework.

Figure 1 shows a sample embodiment of the chafing detector. An optical fiber, spirally wrapped around the conduit from end to end or doubled back on itself so both ends are in close proximity, is held in place by an additional tape wrap on the outside of the conduit. Significant chafing of the conduit will cause the optical fiber to break. An optical time domain reflectometry test determines the distance along the fiber to the break, locating the chafed area. Operators can use this technique for periodic manual testing or for continuous monitoring.

Other methods of this invention involve the use of an electrically conductive sense element, which is accessed at any point along its length to verify the continuity of its entire length. The sense element identifies whether the chafed area is electrically grounded, floating, or electrically energized. Kildeer Mountain Manufacturing Company of Kildeer, North Dakota, licensed this invention in 2000. The company is currently teaming with United Airlines on an FAA-funded program to prototype the invention on high-risk aircraft cables. (See TechLink Press Release 2/26/2001 NORTH DAKOTA COMPANY AND AIR FORCE DEVELOP AIRCRAFT SAFETY DEVICE)

One of the most frequent causes of intermittent failures and other abnormal electrical and electronic system behavior is corrosion in the junctions of the signal-carrying connectors. This is an especially insidious problem because inspection of these connectors can temporarily wipe away corrosion during the process of unmating and remating the connectors.

The directorate contracted with Semtas Corporation of Annandale, Virginia, to develop prognostics techniques that detect connector corrosion. The result was an elegant technique that detects significant levels of corrosion on the connector junctions without unmating the connectors. Semtas based its approach on experience with electromagnetic interference problems such as the Navy's rusty bolt problem. A rusty bolt or other corroded structure onboard a ship will receive a radio transmission and reradiate the signal at a different frequency than the received frequency. Experimentation determined that this known effect of corrosion also applies to the corrosion in the junctions of electrical connectors.

Semtas developed an advanced development model (ADM) that is very sensitive to corrosion in the connector junctions. Figure 2 shows one method of connecting this instrument to test a connector pair. ADM experiments demonstrated the ease of identifying a single corroded connector pin/sleeve junction in a multi-conductor cable bundle. Semtas developed the ADM without the use of any custom-built hardware components. It incorporates a transmitter and receiver, a microprocessor, and signal conditioning components. This connector corrosion testing technique could easily fit into an existing portable maintenance aid with minor modification.

Cable chafing and connector corrosion are possibly the two biggest causes of aircraft system failures. Detecting these conditions prior to system failures directly results in safer commercial and military aircraft. The Information Directorate no longer performs diagnostics research and seeks to transition this technology to private enterprises for commercialization opportunities.

Mr. Frank Born of the Air Force Research Laboratory's Information Directorate wrote this article. For more information, access the Technical Support Package (TSP) free on-line at http://www.afrlhorizons.com, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn/index.htm. Reference document IF-00-11.

References

¹ Boenning, R. A. and Colbaugh, M. "Electronic Equipment Readiness Testing - Marginal Checking." US Air Force Technical Report RL-TR-91-121, July 1991.

² Duff, W. G., et al. "Detecting Corroded Connectors." US Air Force Technical Report AFRL-IF-RS-TR-1998-165, August 1998.

³ Koford, S. "Improved Aircraft Wiring and Connector Performance." Final Report of US Air Force Contract No. F33657-84-2222, August 1987.

Back to Top