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patcat88

join:2002-04-05
Jamaica, NY
kudos:1
reply to ptbarnett

Re: All electronics are "transmitters"

said by ptbarnett:

The problem is not shielding of circuit boards. It's whether an errant transmission blocks reception by a navigation radio.
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You can design the device to shield RF emissions. But, it is difficult to completely seal it unless it is a metal box with no buttons, plugs, etc. The best you can do is reduce it as low as possible. That what FCC class B certification is about: it has to be below a certain level, but that level is not zero.
...............................
However, that's only the transmission side of the issue. The next inevitable question is: why don't the aircraft receivers reject these unwanted signals? Aircraft navigation and communications use several different frequency bands. On any given flight, the pilots will be switching frequencies many times. And depending on the phase of the flight, the signals being received may be relatively weak, and more susceptible to interference.

All it takes is for an electronic device to inadvertently transmit on the same frequency an aircraft receiver is receiving, and you'll have interference. Some of the navigation radios work by measuring the phase of a received signal, so it doesn't take much to mess them up. Once again, it is the laws of physics. A very low power transmitter on the plane can block receipt of a signal from a much more powerful transmitter far away.

Ever heard of a solar storm? Planes dont fall out of the sky.

(b) Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized radio station, by another intentional or unintentional radiator, by industrial, scientific and medical (ISM) equipment, or by an incidental radiator.

»www.law.cornell.edu/cfr/text/47/15.5

So the circuit boards on planes are not FCC certified?

said by ptbarnett:

r
Fortunately, the instruments usually indicate when there is interference, and pilots are trained to switch to alternate means of navigation.

The radio instruments do not fly the plane, nor will they make it go into a steep dive to the ground like in a cartoon. Inertia gyroscope doesn't use radio waves. Loosing radio instruments is like the street name on the road being covered, but you can still see the curve up ahead. You are right the instruments detect interference and lock themselves out.

said by ptbarnett:

So, one outage is not going to cause an accident. But, accidents are rarely caused by a single event -- it's a chain of events. A communication or radio outage caused by interference can be a distraction, and become the first or subsequent event in a chain that leads to an accident.

That is a sign of bad training or social problems at the airline.

ptbarnett

join:2002-09-30
Lewisville, TX
said by patcat88:

Ever heard of a solar storm? Planes dont fall out of the sky.

A solar storm can cause interference with the radio communication and navigation, especially in the high-frequency bands. The VHF bands used by aircraft are not immune, but less so than HF. Satellites are more vulnerable than anything, because they aren't protected by the Earth's magnetic field. But, the nice thing about radio interference from solar storms is that it can be forecasted. Airplanes can, and have modified procedures in advance to compensate for the expected interference.

However, did I ever write that planes would fall out of the sky? Rather than building a strawman argument, maybe you should read what I wrote, rather than what you think you can argue against?

said by patcat88:

So the circuit boards on planes are not FCC certified?

The US code that you cited says that the device must accept interference without damage. It doesn't say that it must function properly during the interference. An example would be your Wi-Fi connection or Bluetooth headset: Have you ever lost a connection or heard a crackling noise when the microwave oven was running in your kitchen? That's interference. But, unless you put the device IN your microwave, it resumed functioning after the microwave shut off.

The electronic devices on civil planes (other than experimentals) in the US are TSO certified, which is far more stringent than any FCC certification. The TSO standard relevant to this situation is rejection of interference from an ADJACENT frequency. That is specified in terms of both frequency deviation and power level, as a very strong signal on an adjacent frequency can also "blank" a receiver. Again, it's laws of physics.

said by patcat88:

The radio instruments do not fly the plane, nor will they make it go into a steep dive to the ground like in a cartoon.

Actually, in a Cat III approach, the autopilot is coupled to the navigation radios, and does fly the plane. However, the pilots monitor the landing and will command a missed approach if anything appears amiss.

said by patcat88:

That is a sign of bad training or social problems at the airline.

No, it's the conclusion of many accident investigations. Pilot training, air traffic control procedures, and equipment design all have layers of redundancy to prevent a single failure from leading to an accident. Removing or circumventing a single layer doesn't necessarily cause a crash, but may increase the probability of one in the event all other layers fail.