| Descriptions of High-Temperature Aircraft Electrical Wire Types. |  |
| Descriptions of High-Temperature Aircraft Electrical Wire Types. | |
Only One, TKT MEETS FAA’s FAR 25 STANDARDS.
Sources; Industry Wire Experts. Contact jking1@mediaone.net
| Type | Properties | SOME Aircraft Used In |
| PVC/NYLON | *Heaviest and thickest at 6.8 lbs. per
1,000 ft. *Insulation burns readily creating copious smoke (e.g., ValuJet 592) *Insulation turns to hydraulic acid when exposed to water. |
Early DC-9s, 727s, 737s until 1979 |
| Poly-X (Aliphatic Polyimide) | *The first exotic blend of insulation
(due to Arab oil embargo) *Light weight, 4.7 lbs. per 1,000 ft. *Susceptible to solvents *Chafing resistant but cracks around Circumference *Copious smoke *Due to brittleness, 1" bare spots not uncommon * premature aging at just 4,000 hrs * Fails FAR 25 |
Early 747s and DC-10s (e.g., TWA 800) |
| XL Tefzel *(Spec 55) | *Copious smoke, density greater than
96% * Cracks easiest under vibration (ETEF Type) * Toxicity the worst (ETE Type) * Arc tracks * Soft as butter at rated 150 degrees C – not 200 C * Must not be mixed in bundles with harder insulations. * Explodes in oxygen-enriched areas * Fails FAR 25 |
747s, 767s, 777s
years?
(mixed bundles found in SR111 IFE system) |
| Stilan | *Light weight, 4.7 lbs. per 1,000 ft *Insulation breaks down in hydraulic and de-icing fluid *Microscopic crazing problem seen by microscope *Cracks under stress *Found to arc over * Spurious signal generation * Fails FAR 25 |
747s and DC-10s built in mid-to-late 1970s |
| Kapton (Aromatic Polyimide) | *Very light weight, 4.5 lbs per 1,000 ft *Insulation burns fiercely creating no smoke *Known to arc over * Burns fiercely with arc over * Fails FAR 25 |
727s, 737s, some 747s(400s) 767s, DC-10s MD-80, MD-11, and A300-600 (with teflon top coat) |
| TKT | *Light weight, 5.0 lbs. in per 1,000 ft. *Abrasion resistant *Superb insulation protection *High heat tolerance *Resists smoking when burning (less than 2% density) |
737s and 757s built late 1992 and
on *Used on some aircraft since 1992. |
FAR 25 states: that insulation material can not be used that is hazardous, unreliable, or contributes to smoke/fire. No particular uses of insulation were further specified so insulation material includes; seat insulation, insulation blankets, rug insulation, and wire insulation. They are all types of insulation materials. Unless they are tested with an electrical fire (2,000 degrees) igniter to prove flammability proof, the material can not meet FAR 25 requirements. By their own (Limited) standards, the FAA has said, in fact, that most types of wire can not be used !
Only TKT wire insulation meets FAR 25 Standards.
Wednesday, January 20, 1999
The Halifax Herald Limited
Food, games 'stress' on Flight 111 wiring
By Stephen Thorne / The Canadian Press
Ottawa - Food and entertainment played critical roles in the Flight 111 disaster off Nova Scotia, conclude experts who say the timing of the plane's cockpit smoke points to the cause of the crash.
An hour into the Swissair flight, attendants aboard the doomed jet would have just turned on the plane's microwave ovens as they prepared meals for their transatlantic passengers, say aviators
and industry experts.
Many passengers, in turn, would be switching on their inflight entertainment systems - watching movies, listening to music, playing video games and gambling.
"Your maximum power requirements were being utilized at that time," said Patrick Price, a retired Boeing technician.
"If any circuit is under-protected - if it's not designed properly or the wrong gauge of wiring is used - that would put a greater stress on it. If you have an injured wire ... this is when it's most vulnerable."
Further stress on already-damaged wires could have been caused by the rigours of takeoff - vibration and other system demands - or rough weather. It was stormy the night the plane went down Sept. 2, killing 229 people.
"You've probably got this wire hanging by a thread," said Armin Bruning, a PhD in insulation systems design and head of Lectrical Mechanical Design Co. outside Washington, D.C.
"Now you put a little more load on it ... so it gets hotter, plus you agitate it physically more in this first hour. It's the time when that thread is most probably going to be subjected to stress and break."
Ed Block, member of a U.S. federal committee on aircraft wiring, concurred.
"That's certainly when you're going to get the maximum draw and anything waiting to happen is going to have its ignition point at that time," Block said from his home in Pennsylvannia. "It's the most likely time frame."
Some experts believe excessive handling of the MD-11's sensitive Kapton-insulated wiring may have contributed to the jet's problems.
Kapton, or aromatic polyimide tape, was effectively banned by the U.S. military due to its propensity to crack, chafe or break down with age.
McDonnell-Douglas also found that with vibration from flight Kapton tended to sandpaper away softer insulations like the one used in a high-tech entertainment system that Swissair installed early last year.
Even microscopic insulation deficiencies can lead to electrical arcing and flashovers, or lightning-like jumps between wires and wire bundles.
Canadian investigators have discovered such damage among burnt wire insulation aboard Swissair Flight 111 and over a dozen other MD-11s they looked at. Their findings prompted their U.S.
counterparts to request regulators to demand an urgent inspection of all 174 MD-11s worldwide.
A retired pilot who used to fly transatlantic routes for a European-based airline agreed that microwaves and entertainment systems would be coming on between 45 and 90 minutes into such
a flight.
But he noted that most pilots "don't normally concern themselves" with what demands are placed on their aircrafts' electrical systems.
"We never thought about maximum points of electrical load or anything like that until this latest incident with Swissair," said the ex-pilot, who did not want to be identified.
"Our job was more to fly the aircraft and do the management from the cockpit," he said. "What went on in the cabin with regards to the ovens being turned on and the inflight entertainment was really not our business."
Block said that's just the problem with the airline industry and the Swissair crash in particular - the pilots don't know their own airplanes.
Had 111's pilots realized the gravity of their situation when they first smelled cockpit smoke at least 22 minutes before the crash, they might have saved 229 lives, he said.
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