Electronic devices in planes: 3 questions.
Discussion
Is not a large part of the reason for turning devices off the distraction factor? Most people using devices will be using them with headphones- iPods, iPads to watch movies, etc. if anything were to happen, getting 100+ people's attention is easier if they were just reading a book/ mag, rather than if 50 of them were plugged in and oblivious?
Sponge01 said:
Is not a large part of the reason for turning devices off the distraction factor? Most people using devices will be using them with headphones- iPods, iPads to watch movies, etc. if anything were to happen, getting 100+ people's attention is easier if they were just reading a book/ mag, rather than if 50 of them were plugged in and oblivious?
That's also a factor. It's why we ask people to remove headsets. If you've got something like proper noise cancelling headsets on, then you generally can't hear a thing. Your attention might be required, so that's why people are asked to take them off, even if the device is switched off. It's also a visual check for the crew, as they haven't got time to ask each person on board if the thing is off or on.If you're reading a book, and someone comes on the PA and makes an announcement, then you hear it, so there's no problem there at all.
Whether or not your electronic device will have any effect on the on board avionics is a question of RF immunity. A measure of how much electric field can be induced into the victim circuit before a malfunction occurs.
RF immunity is a phenomenon that can be likened to a sort of resonance. You need to hit just the right frequency for the maximum effect. All avionics will be tested for RF immunity under RTCA DO-160f section 20.
A basic immunity test will be to subject the equipment to a high RF field and then check there is no malfunction (or degradation below a critical level) of all applicable modes of operation.
Thats the theory but what happens in practice is different. For a complex piece of avionics it may take 10-20 minutes to check all modes. Now repeat that for all frequencies from 80 MHz to 18 GHz. You will still be testing the system long after the aircraft is obsolete. So the test frequency is stepped.
Now how big is your aircraft? How big is the RF test chamber? So most avionic units are tested in isolation. There is the statistical principle that connecting compliant units together will result in a compliant installation but thats just statistics.
Next not all avionics perform the same function. The immunity level required depends on how safety critical the unit is. An Airbus ADIRU will be tested far beyond the level for something like a remote sensor.
The net result of all this testing is the statistical probability that nothing will happen, not the guarantee.
The problem was worse in the past as mobile phones used higher powers. Also the type of modulation used will exacerbate the problem. TDMA (ie GSM) being the worst. Modern 3G+ devices operate with lower powers with a more immunity friendly emission classes.
Cases noted with mobile interference include:
- Autopilot disconnects on 737NG aircraft
- Nav display mode switching on 737NG
- Hold smoke/fire detectors triggered.
The first two can be classified as “inconvenient” whereas the third might cause the flight crew to make decisions about landing the aircraft asap in less than optimal conditions. Nothing that will bring down an airliner but still ‘another hole in the cheese’.
RF immunity is a phenomenon that can be likened to a sort of resonance. You need to hit just the right frequency for the maximum effect. All avionics will be tested for RF immunity under RTCA DO-160f section 20.
A basic immunity test will be to subject the equipment to a high RF field and then check there is no malfunction (or degradation below a critical level) of all applicable modes of operation.
Thats the theory but what happens in practice is different. For a complex piece of avionics it may take 10-20 minutes to check all modes. Now repeat that for all frequencies from 80 MHz to 18 GHz. You will still be testing the system long after the aircraft is obsolete. So the test frequency is stepped.
Now how big is your aircraft? How big is the RF test chamber? So most avionic units are tested in isolation. There is the statistical principle that connecting compliant units together will result in a compliant installation but thats just statistics.
Next not all avionics perform the same function. The immunity level required depends on how safety critical the unit is. An Airbus ADIRU will be tested far beyond the level for something like a remote sensor.
The net result of all this testing is the statistical probability that nothing will happen, not the guarantee.
The problem was worse in the past as mobile phones used higher powers. Also the type of modulation used will exacerbate the problem. TDMA (ie GSM) being the worst. Modern 3G+ devices operate with lower powers with a more immunity friendly emission classes.
Cases noted with mobile interference include:
- Autopilot disconnects on 737NG aircraft
- Nav display mode switching on 737NG
- Hold smoke/fire detectors triggered.
The first two can be classified as “inconvenient” whereas the third might cause the flight crew to make decisions about landing the aircraft asap in less than optimal conditions. Nothing that will bring down an airliner but still ‘another hole in the cheese’.
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