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View Full Version : E.M.I. what are the industries feelings?


JayBird
13th Aug 2004, 13:09
The History Channel had a show last night that showed a possible cause of the TWA, SwissAir, and Egypt Air crashes to be Electro Magnetic Interference from land and air based radars. I was just wondering what effects have you guys witnessed, and do you think it is possible for EMI to fry the electronics to a state that there could be a departure from normal aircraft flight.

avioniker
13th Aug 2004, 16:12
I wish I'd seen that show.
Sounds like someone has found some drugs I missed in the 60's.
EMI of sufficient power to fry the planes to a degree causing the fires and explosiions that brought them down would require the power of the sun at today's technology level.
I'd say the producers were watching a Battlestar Galactica rerun when the idea hit them.
Just one avionics instructor's opinion mind you:p

lomapaseo
13th Aug 2004, 17:04
Saw it also, their interviewed experts know nothing about evidence vs deductive reasoning in accident investigation. One of them was Scary :)

If there was any viable concern about EMI most planes would never make it beyond the taxi-out beyond the ground radar shack.

JayBird
13th Aug 2004, 18:38
The only thing that was brought up that kind of made me wonder was the fact that both the Swissair and TWA left JFK at 819pm on the same departure on a wednesday. They also said that the Swissair lost coms with ATC in very close proximity to where the TWA flight terminated. Is it posible that there was bad shielding on a wire in the TWA flight and when a burst of EMI radiated it shorted and caused the spark, igniting the hot fuel tank. With that theory the same could be said about the coms on the Swiss fight going out due to poor shielding. This is just all wild speculation and something to ponder. I did find it very interesting that NASA did a study that said that, like you said, there is more EMI at the airport before you leave than on the flight.

avioniker
13th Aug 2004, 20:49
Okay, back to basic natural science;
To initiate visible oxydizing combustion (flame or explosion) in an atmosphere you must have 18 to 20 per cent oxygen.
In any fuel tank with any liquid fuel there will be virtually no oxygen.
TWA had 1000lbs in the tank.
Sparks and arcs in a fuel rich atmosphere without enough oxygen don't cause flame or explosion.
That's the single biggest reason why engineers in the 40's and 50's knew they didn't have to enclose the wiring in fuel tanks in conduit or any other sealed vessel.
Engineers today are learning from instructors and teachers in their third and fourth (and if you count my niece, fifth) generation of instructors and teachers who learned what they know from instructors and teachers who haven't practiced what they're teaching.
When I got my credentials in the state of Florida, two years post graduate experience was required before you could be certified in any of the aeronautical or electronic disciplines.
Now we have 22 year old kids with four year degrees trying to tell technicians with 30+ years of airline experience how to put things together and they have to invent new words to explain their machinations because they don't know the vocabulary that's been in place for the last 60+ years.
I don't like flying any more and I'm liking teaching even less.:mad:

JayBird
13th Aug 2004, 21:13
The NTSB report says that there was an ignition source in the CWT but the cause of the spark was not determined.
The National Transportation Safety Board determines that the probable cause of the TWA flight 800 accident was an explosion of the center wing fuel tank (CWT), resulting from ignition of the flammable fuel/air mixture in the tank. The source of ignition energy for the explosion could not be determined with certainty, but, of the sources evaluated by the investigation, the most likely was a short circuit outside of the CWT that allowed excessive voltage to enter it through electrical wiring associated with the fuel quantity indication system.

avioniker
13th Aug 2004, 21:26
The ignition source was most likely the generator output cables arcing in the hole caused by the first explosion at the forward upper right corner of the center wing tank. As the plane flew on, descending from 13,200ft to 10,400 ft the air/fuel mixture in the tank is believed to have reached a combustable level and the second explosion blew the nose off the aircraft.
The only question is: "what caused the first explosion and put the hole in the plane at the wing root?" The first explosion did not originate in the center tank. I'm not talking from someone else's experience.
And before this gets crazy again let's not start the NTSB/FAA/FBI arguments all over again.
Fact: two explosions
Fact: aircraft descended after the first explosion and flew for approx 2 miles straight and level before the second explosion
Conjecture: 1. It was a missle
2. It was a bomb under the R2 F/A seat
3. It was a bomb above or on the halon bottles in the back of the front pit
4. It was overheating of the tank caused by the A/C pack
5. It was a power surge in the Fuel Quantity wiring caused by a short outside the tank
Fact: Nobody in the government teams had relavant experience to make the conclusions they made and please don't bring up the ex-IAM NTSB guy.
Fact: Nobody on any of the government teams wanted to hear from any of the TWA people on scene even though they had all had direct recent experience in an overhaul capacity with that very aircraft.
Are you getting the idea that I'm less than thrilled with any of the official conclusions?
Don't believe everything you read and exercise judicious doubt regarding most everything you think you do.:suspect:

lomapaseo
14th Aug 2004, 00:17
avioniker

You need to get your facts right.

There is no support for your facts.

A fact that you missed was :

That there were a lot more expertise on that investigation supporting the findings than just those paid by the government.

I don't understand what you are saying about TWA support. There was plenty of valuable support from TWA.

Lu Zuckerman
14th Aug 2004, 00:26
Yes Virginia there is a/an EMI. The FAA and the US Navy have been sued in South Carolina Federal Court after High-energy radio frequency transmissions allegedly interfered with on-board electronic equipment and caused a fatal crash of a small plane.

:E :E

ICT_SLB
14th Aug 2004, 03:56
According to CASB, the Swissair flight was due to plain overloading of wiring - even if your Pax entertainment only uses quarter of an amp at 28V per seat get 200 using it (plus the PA muzak) and you've got welding current looking for somewhere to go.

There is no comparison between light and commercial aircraft as far as wiring and shielding practises are concerned. Most modern transports have survived HIRF testing with fields of 50V/m or even 100V/m - much higher than any radar field.

All our aircraft are test vehicles with lots of extra instrumentation wiring but the only effect we've had when getting too near the "1 million watts" weather radar on the field is a jump in the Radio Altimeter which happens to be on the same frequency. This happened so regularly during storm season that my nickname was "NEXRAD".