Comments by "vk2ig" (@vk2ig) on "Mentour Pilot"
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During my career I've had people try the "nothing bad has happened therefore there's no reason to change what we're doing" excuse for not doing anything. My response is "Have you conducted a hazard analysis followed by a risk assessment, and identified if the existing controls mitigate the risk So Far As Reasonably Practicable (SFARP)?", which is the law in my country.
One particular case comes to mind, where the response was "We have 1,000 of these out in the field for five years and no-one's dead yet", to which I asked "OK, how many were actually operating for the full five years, as opposed to sitting in storage or powered down, being rotated through the maintenance pipeline, etc?" They couldn't answer that, which immediately blew a hole in their "no accidents in 5,000 operating years" statistic underpinning their safety argument.
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@vanstry I agree with you regarding the potential for interference by a mobile phone transmitter.
As a professional radiocommunications engineer with a few decades of experience, it used to surprise me that people don't recognise the potential interference issues of mobile phones in aircraft. Nowadays, noting the lack of experience most people in the electronics industry have with anything related to radio (for example, look at how much radio frequency interference pours out of a typical solar panel inverter or a switch-mode power supply), it doesn't surprise me at all. I've seen plenty of engineers come unstuck, and companies and governments lose lots of money, because people didn't understand the mechanisms by which interference from radio transmitters occurs.
Anyway, to further to the points you made:
- Just because a receiver is designed to operate at 117, 330, 1500 MHz or some other frequency doesn't mean a nearby transmitter operating at 800 or 1900 MHz won't cause problems. It depends on how susceptible the receiver is to strong out-of-band signals - there are a number of mechanisms by which receivers can suffer interference from non-co-frequency interferers, e.g. poor front-end bandpass filtering, poor IF image rejection, etc. It also depends on how spectrally "dirty" the mobile phone transmitter is - poor output stage filtering can allow appreciable energy on other frequencies to be "unintentionally" emitted by the phone, and increasing the number of phones in the cabin increases the radio frequency noise on a given frequency.
- Signals emitted by a mobile phone transmitter can couple into cables within an aircraft. Whether the circuits at each end of the cable can operate properly in the presence of such signals is another issue. That depends on whether EMI/EMC principles were employed when designing the circuit - the designers may have operated on the assumption that there would be no strong radio signals inside the aircraft - put one or more mobile phones in the cabin and that assumption doesn't hold. MIL-STD-461 (in whatever revision it currently is - I used "E" last) is a suitable standard.
- Radiation of signals internal to the mobile phone receiver (e.g. heterodyne oscillator, etc) is "a thing". One of the terms for it is "backwave", which comes from the earlier days of radiocommunications. This too can cause problems with radio receivers and other equipment, although arguably often it's not as impactful as the transmitter signal. (This is the principle underlying how the radiofrequency regulator in the UK can track down people who are using TV sets without a licence ... they can even tell whether it's colour or monochrome receiver due to unintentional radiation of the colour-burst signal.)
With regard to aircraft accidents, it may be that there have been none due to mobile phones. But airline pilots have reported navigation issues when mobile phones have been used by passengers. I guess those who think mobile phones aren't a problem are willing to tolerate that sort of event ... an event which might just be one of the Swiss cheese holes needing to line up one fateful day.
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