6 ms·

The article describes numerous crashes associated with Kapton, beginning with a story about a passenger plane where hundreds perished. It also mentioned a short

by dfee 6y ago

The article describes numerous crashes associated with Kapton, beginning with a story about a passenger plane where hundreds perished. It also mentioned a short circuit on the launch of the Columbia Space Shuttle, and military planes. When used as an insulator where it can rub or be exposed to moisture: you’re going to have a failure at some point. What’s alarming then, was the conclusion: > Still, hundreds of planes take off and land every day with Kapton insulated wires routed through every nook and cranny, some almost impossible to reach for inspection. And even when wire bundles are accessible, inspection comes down to a flashlight and a Mark I eyeball, looking for that cracks that might be lurking.

x3haloed 6y ago
> inspection comes down to a flashlight and a Mark I eyeball, looking for that cracks that might be lurking. Where is our reassurance that everything is OK now??
- nitrogen 6y ago
  I don't know if such things are used on passenger aircraft, but I've heard that fighter jets use time domain reflectometry to detect potential faults in wires, and how far along the wire the fault lies. Even a small nick in the insulation is supposed to change the impedance enough to create a detectable reflection. At least some gigabit ethernet interfaces have built in weaker TDR that measures the length of each twisted pair, but I've only ever had one computer that showed that info in the BIOS/UEFI. So, maybe if TDR is used for inspection, we can rest assured.
  - toast0 6y ago
    > At least some gigabit ethernet interfaces have built in weaker TDR that measures the length of each twisted pair, but I've only ever had one computer that showed that info in the BIOS/UEFI. I've seen this info in the Realtek NIC diagnostic tool for windows (on one machine, anyway), and I've got a couple of semi-managed switches that show a line length estimate which I assume is based on similar measurements.
  - wiremaus 6y ago
    Unfortunately I don't think TDR would help here: the issue isn't gross damage to the metal of the wires, it's subtle damage to the insulation.
    - nitrogen 6y ago
      From my prior comment: "Even a small nick in the insulation is supposed to change the impedance enough to create a detectable reflection." This is what I was told by the person who saw the demo. I believe them, because it'd just be a matter of sending an impulse (or sweeping a tone) and looking at all of the spikes in the impulse response.
  - jcrawfordor 6y ago
    Sort of unrelated, but a very interesting application of TDR on cables: in military, infrastructure, and certain other installations, a common security measure is a fiber optic cable woven into the chain-link fence or shallowly buried. Any deflection of the cable (e.g. due to a person climbing the fence) results in a subtle reflection in the cable. By knowing the layout of the embedded cable, not only can the event be detected, but it can be localized and used to e.g. trigger automatic pan of PTZ cameras. A major brand-name for this system is FiberPatrol but there are several vendors. Unfortunately it is rather false-positive prone when applied to fences, significant wind loading can cause the chain-link to lash back and forth and repeatedly deflect the cable. The resulting alarm fatigue was implicated in the somewhat (in)famous case of the nuns as site Y-12. Nonetheless this application is very common at federal installations and also certain non-federal infrastructure installations, e.g. the legacy iron fences around Portland, Oregon's surface water reservoirs (where remote-controlled PTZ cameras appear to be used for rapid remote confirmation of FiberPatrol detections... you can give the fence a shake and watch a camera pan to you almost immediately).
- DanBC 6y ago
  This is a nice article that touches on the complexity of specifications for wiring harnesses used in aerospace. https://www.assemblymag.com/articles/94857-designing-aircraft-wire-harnesses-101 https://www.assemblymag.com/articles/94857-designing-aircraf... > In the 1970s, the most common wire for aircraft was Kapton-insulated wire. Kapton is a DuPont trade name. Today, aircraft wiring is typically insulated with Teflon, Tefzel, Cross Link Tefzel or TKT (Teflon-Kapton-Teflon). Typically, the AVS for an aircraft lists the type of wire insulation that will be used throughout the aircraft. For example, the OEM might decide that TKT will be used, with some exceptions such as radio cables and Teflon-insulated wire in boxed assemblies. I've worked with kapton tape (but never kapton insulted wire) and I can't imagine it being much good as insulation for wires. I've also worked with lots of PTFE insulated wire and it was nice to work with, but only once you'd got used to its low friction.
- throwaw4y-plate 6y ago
  Did this sort of inspection in a nuclear plant before. It sucks.
- jdietrich 6y ago
  No part of an aircraft is 100% reliable. Manual inspections are a fundamental part of keeping an aircraft safe. How do you know that the tires haven't perished? How do you know that a bulkhead isn't developing severe stress cracks? How do you know that the bearings on a control surface aren't just about ready to seize? Because the aircraft operator is required by law to systematically check every part of the aircraft according to a strict schedule. Your reassurance is the fact that flying is the safest form of travel thanks to decades of diligent work by engineers, mechanics and accident investigators.
  - mirimir 6y ago
    Right, we know that it's not a huge problem because not that many planes are crashing. Also, I suspect that circuit checks could detect at least some shorts in wiring that can't be physically inspected.

by dfee 6y ago

x3haloed 6y ago

> inspection comes down to a flashlight and a Mark I eyeball, looking for that cracks that might be lurking. Where is our reassurance that everything is OK now??

nitrogen 6y ago
I don't know if such things are used on passenger aircraft, but I've heard that fighter jets use time domain reflectometry to detect potential faults in wires, and how far along the wire the fault lies. Even a small nick in the insulation is supposed to change the impedance enough to create a detectable reflection. At least some gigabit ethernet interfaces have built in weaker TDR that measures the length of each twisted pair, but I've only ever had one computer that showed that info in the BIOS/UEFI. So, maybe if TDR is used for inspection, we can rest assured.
- toast0 6y ago
  > At least some gigabit ethernet interfaces have built in weaker TDR that measures the length of each twisted pair, but I've only ever had one computer that showed that info in the BIOS/UEFI. I've seen this info in the Realtek NIC diagnostic tool for windows (on one machine, anyway), and I've got a couple of semi-managed switches that show a line length estimate which I assume is based on similar measurements.
- wiremaus 6y ago
  Unfortunately I don't think TDR would help here: the issue isn't gross damage to the metal of the wires, it's subtle damage to the insulation.
  - nitrogen 6y ago
    From my prior comment: "Even a small nick in the insulation is supposed to change the impedance enough to create a detectable reflection." This is what I was told by the person who saw the demo. I believe them, because it'd just be a matter of sending an impulse (or sweeping a tone) and looking at all of the spikes in the impulse response.
- jcrawfordor 6y ago
  Sort of unrelated, but a very interesting application of TDR on cables: in military, infrastructure, and certain other installations, a common security measure is a fiber optic cable woven into the chain-link fence or shallowly buried. Any deflection of the cable (e.g. due to a person climbing the fence) results in a subtle reflection in the cable. By knowing the layout of the embedded cable, not only can the event be detected, but it can be localized and used to e.g. trigger automatic pan of PTZ cameras. A major brand-name for this system is FiberPatrol but there are several vendors. Unfortunately it is rather false-positive prone when applied to fences, significant wind loading can cause the chain-link to lash back and forth and repeatedly deflect the cable. The resulting alarm fatigue was implicated in the somewhat (in)famous case of the nuns as site Y-12. Nonetheless this application is very common at federal installations and also certain non-federal infrastructure installations, e.g. the legacy iron fences around Portland, Oregon's surface water reservoirs (where remote-controlled PTZ cameras appear to be used for rapid remote confirmation of FiberPatrol detections... you can give the fence a shake and watch a camera pan to you almost immediately).
DanBC 6y ago
This is a nice article that touches on the complexity of specifications for wiring harnesses used in aerospace. https://www.assemblymag.com/articles/94857-designing-aircraft-wire-harnesses-101 https://www.assemblymag.com/articles/94857-designing-aircraf... > In the 1970s, the most common wire for aircraft was Kapton-insulated wire. Kapton is a DuPont trade name. Today, aircraft wiring is typically insulated with Teflon, Tefzel, Cross Link Tefzel or TKT (Teflon-Kapton-Teflon). Typically, the AVS for an aircraft lists the type of wire insulation that will be used throughout the aircraft. For example, the OEM might decide that TKT will be used, with some exceptions such as radio cables and Teflon-insulated wire in boxed assemblies. I've worked with kapton tape (but never kapton insulted wire) and I can't imagine it being much good as insulation for wires. I've also worked with lots of PTFE insulated wire and it was nice to work with, but only once you'd got used to its low friction.
throwaw4y-plate 6y ago
Did this sort of inspection in a nuclear plant before. It sucks.
jdietrich 6y ago
No part of an aircraft is 100% reliable. Manual inspections are a fundamental part of keeping an aircraft safe. How do you know that the tires haven't perished? How do you know that a bulkhead isn't developing severe stress cracks? How do you know that the bearings on a control surface aren't just about ready to seize? Because the aircraft operator is required by law to systematically check every part of the aircraft according to a strict schedule. Your reassurance is the fact that flying is the safest form of travel thanks to decades of diligent work by engineers, mechanics and accident investigators.
- mirimir 6y ago
  Right, we know that it's not a huge problem because not that many planes are crashing. Also, I suspect that circuit checks could detect at least some shorts in wiring that can't be physically inspected.