Which Aircraft Have PVC Wiring, and What's the Problem? - NewsChannel5.com | Nashville News, Weather & Sports

Which Aircraft Have PVC Wiring, and What's the Problem?

PVC/Nylon Flammability Test (Source: FAA) PVC/Nylon Flammability Test (Source: FAA)

Polyvinyl chloride wiring (with a nylon topcoat) - also known as PVC/nylon - was used on commercial aircraft beginning in 1960 and continuing until 1979, according to a spokesperson for Boeing Aircraft. 

Among the aircraft on which Boeing says it was used were:

  • Douglas DC-9s
  • Boeing 707s, 727s and early 737s

Northwest Airlines is the only major carrier that still flies aircraft wired with PVC/Nylon.  Foreign carriers and charters also may use such aircraft.

Its advantage is that it provides good resistance to chafing because of its thicker insulation, according to wiring experts at Lectromechanical Design Co. in Dulles, Virginia.  

But it also suffers from serious disadvantages.  PVC/nylon is flammable and "gases from burning are extremely harmful if inhaled."

In fact, PVC wiring never passed the first - and only -- flammability standard for aircraft wiring imposed by the Federal Aviation Administration.  That standard was established in 1972.  As FAA researchers discussed at a 2002 meeting about aging aircraft, new aircraft designs had to meet the new standard, but manufacturers were allowed to continue using the flammable wiring if they kept with a pre-1972 aircraft design.

A 1991 FAA report notes that "PVC/nylon wire insulation will not pass the current flammability test for aircraft wiring.  Also, "PVC/nylon insulated wire involved in a fire contributes significantly more smoke, heat and hydrogen chloride to the cabin" than other commonly-used aircraft wires.

More extensive testing, published in a 2004 report, notes that PVC/nylon was used to re-evaluate the flammability standard because that type of wiring represents  a "worst-case scenario." 

When subjected to a "more realistic" test, PVC/nylon was "a poor performer with flame spread that practically consumed the entire sample....  The amount of flaming and flame propagation was very extensive for PVC/nylon, and the bundles were almost completely consumed....  The PVC/nylon test was also very smoky."

And there are real-world examples of the dangers on those aircraft.

In 1983, the pilot of an Air Canada DC-9 managed to land it with what was believed to be an electrical fire. Still, 23 people died of smoke or fire.  According to the National Transportation Safety Board (NTSB), the rest of the passengers survived by breathing through wet towels and clothing.

Then, in 2000, an AirTran DC-9 was forced to make an emergency landing with heavy smoke in the cabin after an electrical arc "ignited the surrounding wire insulation and other combustible materials within the electrical power center panel," the NTSB concluded. Three crew members and five passengers had to be treated for smoke inhalation.

But it may not just be an issue for older aircraft.  At the 2002 aging-aircraft meeting, a Canadian transportation official suggested that:

"... there are post-1972 aircraft that are less than 20 years old that have PVC wiring. Also, it appears that PVC wiring is being used in some of the commuter-type aircraft that is about 10 years old. Therefore, it is safe to say that PVC wiring is not just an aging-aircraft issue, so a review of airplanes under 20 years old should be considered in the flammability issue. When asked for an example of a newer aircraft with PVC wiring, Mr.Goyaniuk indicated ‘ATR-42.'"

A spokesman for Transport Canada tells NewsChannel 5 Investigates:

"In some cases the wiring was installed as part of repairs or modifications in the field. The manufacturer was not specifically identified as being the source of the PVC material as it may have been installed after manufacture.  There are 20 of this aircraft type (ATR-42) on the Canadian Aviation Register. Operators of these aircraft are aware of the issues with PVC wiring and, should PVC be identified as still being on any of their aircraft, it would be removed according to manufacturer's instructions. Transport Canada is not aware of other post-1972 aircraft that have been identified as having PVC wiring."

Boeing issued the following statement:

"While there are still some DC9s, 727s or the early 737s still in service with PVC wiring, older aircraft are overseen by an industry Aging Fleet Program. That program requires specific, ongoing inspections to systems (including wiring) and structures to detect and repair or remove parts in order to maintain airplane integrity. Since PVC was banned and is no longer in commercial aviation use, modifications or changes to the aircraft (like maintenance) that involve a wire change require an upgrade to approved wire. So, either the airplanes have had the wire changed out, or they are under the rigid inspection requirements laid out in the Aging Fleet program."

Still, some of the nation's top wiring experts suggested, as part of a January 2008 study published by the FAA, that PVC "should not be used in airborne applications." (Click here for the quoted excerpt.  Click here for the full report.)

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