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this post was submitted on 01 Oct 2023
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I made a separate comment on the same topic, but AFAIK its not to protect the cockpit - engine communication, but rather to prevent radio polution from your phone attempting to connect to ground stations as it is passing by above.
Edit: ^C^V my edit from the other comment:
From my understanding, at worst, if enough interference from portable electronic devices is present, this could contribute to navigational issues, which could cause a crash. It will probably not cause the plane to nosedive or loose cabin pressure though.
Cell phones are on a completely different frequency band from any navigation systems on an aircraft. They do not cause interference. The only exception would be if you went all the way up into the flight deck and laid your cell phone right next to the magnetic standby compass (which they absolutely are not using).
The primary reason is a combination of safety during takeoff and landing (they don't want anyone distracted during these critical moments of flight); and years of federal regulation that will probably never be updated until the generational gap works its way through the FAA, or some sort of reform occurs.
I recently saw an article talking about Delta and how they’re finally updating the altimeters in their planes. They were apparently the last airline to do so and the main reason why carriers were not able to crank cell signals to full power around airports. Is that related?
Yes. The Rockwell-Collins radio altimeter system was lacking a low-pass filter in the transceiver, which was not a necessary item until cellular companies started rolling out 5G networks. Even still, with the highly directional nature and short range of SHF, it was assumed there wouldn't be interference at first.
During landing, if the right kind of object happened to pass by in the right location at the right time (such as a car driving down a road close to the runway, bouncing a 5G signal upwards as a plane passed over); the radio altimeter would suddenly get a signal that didn't make sense and kick off the Autoland system, warning the crew who is ready to take over immediately. It's very likely no passengers ever noticed the transition of controls.
As for the fix, Service Bulletins were issued to check antenna and transceiver models on all aircraft, and replace accordingly. It took my airline a few months to get through all of our planes. We have a very large fleet, and I was even servicing a few aircraft a night myself.
Cool insight. Thanks for sharing.
My edit was mainly based on a 2006 study, quote:
If I understand this correctly, there can be some interference, but it is likely not very significant. I assume that if enough devices are left with their GPS systems active, the pilots and auto pilot system could be fed data at a slower rate which is possibly less accurate. I don't interpret this as a direct cause for a aircraft to crash.
Also, again if I understand correctly, the FAA can do shit to allow people to have airplane mode disabled, due to the Prohibiting In-Flight Voice Communications on Mobile Wireless Devices Act or PIFVCoMWD Act for short. The act put responsibility to enforce this on the FCC, not FAA. It seems the FAA itself is pretty hands off, allowing the operator of the aircraft to allow any devices they deem to be safe.
Also also, the EU lifted its ban of PEDs not in airplane mode in 2014 (coincidentally the same year in which the act I mentioned above was passed and introduced), but in my experience airplane mode is still required on European airlines. Note that the EASA does require aircraft operators to "ensuring aircraft are not affected in any way by the transmission of signals from the PEDs" if they want to stop requiring airplane mode.
in other words ¯\(ツ)/¯
Regarding GPS interference, a GPS antenna is a receiver, not a transmitter. More GPS enabled devices around it will not affect performance, as they're all listening to the same frequencies. WAAS is also broadcast and received in a similar fashion and frequency, which is where you get down to Cat III levels of accuracy for Autoland.
As for bands, cell phones are sectioned to ~700-900 MHz and some small ranges above ~1700 MHz for VHF. VOR navigation operates between 108-118 MHz while GPS sits specifically at 1575.42 MHz (L1), 1227.6 MHz (L2) and 1176.45 MHz (L5) with WAAS and SBAS sticking close to those. From a VHF standpoint, a cell phone will not cause interference. I can also confirm this by goofing off with my phone while using an IFR4000 test set and watching the nav display indications in the flight deck.
Now, SHF is where things change a little bit. SHF is very directional and fairly short range. It will not make it inside or outside the metal tube of an aircraft very easily. Although the 5G cellular band is separated from the radio altimeter band, the Rockwell-Collins systems were receiving occasional interference from ground antennas during landing. Since the initial issue was discovered, they've patched the transceivers with better filtering (supposedly from just adding a LPF filter, which wasn't necessary before); and issued a service bulletin requiring the use of a newer model of antenna (which used to be optional. The 5 fleets I work on have all been updated or verified at this point.
Interesting!
The study I quoted stated that GPS is vulnerable to interference from PEDs as a fact, but it seems they only measured cell service frequencies. Since it seemed to be made by legitimate authors, I took its words.
From what I understand, neither the FAA (US) nor EASA (EU) require aircraft to be in no way affected by PEDs, though they do require a aircraft to be assessed as not affected to allow onboard WiFi or to allow devices with airplane mode turned off.
Thanks for your insight!
Also: out of curiosity: have any aircraft you've worked on been equipped with picocells?
I have not encountered any picocells on aircraft yet. Plenty of airborne wifi service equipment and some wireless mQAR's for uploading aircraft monitoring data once the aircraft parks at the gate, though.
I do specialize in avionics, though. Hence, the more in-depth experience with navigation systems and radios.