Swissair Flight 111 Tragedy
Wiring and Other Related Stories

News Briefs

July 27, 1998

Predicting wire insulation breakdowns.
When the FAA grounded 737s recently for wiring inspections, Administrator Jane Garvey offered this perspective in the May 14^th edition of USA Today newspaper: "Respected safety analysts say that failure of wiring - absent wear on the wire - is a random event (emphasis added)."

She went on to explain, "The variety or brand of wire in Boeing 737 fuel tanks is irrelevant to recent FAA actions because our concerns are about insulation wearing down and exposing the metal wire inside. When the wiring system was designed with insulation and a Teflon coating, it was thought it would remain intact for the plane's life span. Last week, it was shown wing vibration is wearing down the insulation."

However, the molecular structure of wire insulation degrades over time with exposure to heat, moisture, etc., and this breakdown, some experts point out, is not random. Indeed, it can be predicted with sufficient confidence to guide selective replacement of wiring in aging aircraft.

Wiring is not trivial.
Here's another perspective that came to our attention just recently. It is from remarks made by Air Marshal C.G. Terry, Chief Engineer of the Royal Air Force, at an RAF-hosted wire and cable symposium in the UK last September:

"...my main message this morning:

Firstly, wiring is not trivial. We have policies and standards...

We must acknowledge that wire is not without risks and we must understand the risks...Even small amounts of damage can result in the loss of an aircraft - we have painful experiences in this respect...

Make no mistake, as Chief Engineer (RAF), I view the integrity of an aircraft's wiring as of equal importance to that of the airframe components, engines and flight control systems."

Wire erosion over time.  Shown here, the effect of current leaking to the surface of the insulation and creeping along the surface, burning the insulation (about 1/2 inch of carbonized insulation in this case). In extreme instances, the creepage can run for many feet, burning up the wire insulation.     Source: U.S. Navy

The U.S. Navy's experience with wiring failures.
In a one-year period there were 143,000+ aircraft wiring failures. The repairs represented nearly 9% of all aircraft maintenance man-hours. The data are a bit dated (circa late 1980s) but relevant for two reasons: the number of airplanes in the U.S. Navy (3,000+) is roughly the same as the number of airliners in the U.S. fleet, and the average age is increasing in both the military and the civilian aircraft fleets.

A picture of aging.
A structural crack in the electrical insulation of a conductor can lead to electrical noise caused by current leakage, or worse. This photograph, taken of wiring on an in-service Navy aircraft, illustrates the effect of a current leaking to the surface of the insulation, and moving along that surface to a point where it touched structure (i.e., going to ground). The phenomenon is known as wet arc tracking (dry arcing is metal-to-metal contact). Over time, the degradation is seen as more noise. The photograph illustrates the kind of wear that can occur in an accelerated environment, in this case on a Navy aircraft exposed to salt-water humidity. Almost certainly it is occurring in the commercial fleet, where accumulated hours and cycles can be significantly greater than for military aircraft flying 20 hours or so a month (a typical jetliner will accumulate that many hours in 2-3 days of revenue service).

Electricity 101.
Dr. Armin Bruning, an expert on wire insulation, explains the difference between voltage and current, offered here for its succinct clarity: "Voltage is pressure. Current is flow." Hence:

Audit of success.
After a lapse of some years, the National Transportation Safety Board has just published the 2d edition of its report, "We Are All Safer; NTSB-Inspired Improvements in Transportation Safety." The 73-page report highlights the Board's success in improving aviation, railroad, maritime, highway and pipeline safety (the aviation section is the largest part). "This publication records some of the major lessons learned and the changes that have been made to prevent future accidents," Chairman Jim Hall explained in his introduction.

The improvements run the gamut from fire to ice. On fire: the Board pushed for the installation of automatic-discharge fire extinguishers in lavatory waste-paper containers in all airliners. On ice: 9 icing-related airline accidents have occurred since 1982. Among the worst, the 1994 crash of an ATR-72 in Roselawn, Indiana, prompting changes which the Board claims have made flying in icing conditions "considerably safer."

A reading between the lines of this report shows how it often has taken years for the Board to see its recommendations implemented. Copies are available through the NTSB's Public Inquiries Branch.

>> NTSB Public Inquiries, tel. 202/314-6551 <<

PRODUCTS

New product coming on the block.
The SnakeEye is not a flashlight, but a new hand-held remote video inspection tool. According to the manufacturer, the system delivers clear, full-color images under low-light conditions. It features an interchangeable camera head that can be attached to a rigid wand, a ring finger adapter or variable-length cables. For aircraft, the system can be used to inspect engines, fuel tanks, under instrument panels, and interstices of the fuselage. It weighs 2.5 lbs and operates on regular power (or 2 hrs on battery). A nice plus: the camera can be coupled to a video recorder. A borescope attachment is optional. Cost for the basic system: $1,750. William McCafferty, an official with the manufacturer, Aqua Communications Inc. of Cambridge, Mass., says the system is available for September delivery.

>> McCafferty, tel. 617/354-6353, ext. 3029;e-mail: billm@aquacomm.com; web site: http://www.aquacomm.com <<

SERVICES

Jet fuels' answer man.
A new web site has been created offering information to users about fuel quality and handling tips, technical support, and an area called "Ask The Expert," where users can ask fuel-related questions. The site was created by Hammonds Technical Services, Inc., of Houston, Texas. The company specializes in jet fuel additives. Featuring a built-in e-mail capability ("We understand that people need a quick response," said Hammond's Betsy Donnelly), the site is at http://www.hammondscos.com.

>>Donnelly, tel. 913/236-7757 <<

EVENTS

An impressive agenda.
The annual safety conference hosted by the Air Line Pilots Association (ALPA) last year was thankfully short on empty rhetoric and long on discussions packed with substance. The agenda for this year's conference looks even better, if we may suggest, with sessions such as "V1 and the Go/No Go Decision" and "Accident Survival - Crash Fire Rescue." The latter topic, by the way, was mentioned at last week's NTSB hearing as a continuing deficiency, where the track record is not good, and there seems to be little improvement in the capability to rapidly fight cabin fires.

This year's conference, with the theme "Schedule with Safety - Raising the Standards," is scheduled for August 18-20 at the Hyatt Regency Washington hotel on Capitol Hill, 400 New Jersey Ave., NW, Washington, D.C. For more information, contact ALPA's Engineering and Air Safety Department at its toll-free, 24-hour safety reporting line, tel. 1-800-424-2470.

Swissair Flight 111 Tragedy

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