How come airlines no longer require electronics to be powered down during takeoff, even though there are many more electronic devices in operation today than there were 20 years ago? Was there ever a legitimate reason to power down electronics? If so, what changed? (Question submitted on Reddit by ak2040)
There are a lot of misconceptions every time this subject is brought up. EMI, Electromagnetic Interference, is a serious consideration in aircraft design and operation, and has been for decades.
I highly recommend this NASA report from 1995, PDF here, which details several incidents, aviation and otherwise. Probably one of the most famous is the series of five UH-60 Blackhawk helicopters that crashed between 1981 to 1987. The accidents were a mystery for some time, but it was later confirmed that they were caused by signals from radio tower which caused the stabilator to go to a full down position, which put the helicopter in a dive. These accidents earned the UH-60 the nickname “lawn dart” at the time.
IIRC in the 1990s it was quite common for the crew to instruct passengers to turn off all electronic devices for take off and landing. This is because it was not uncommon for devices to cause things like radio static or in severe cases minor interference with navigation.
To be clear, I’m not sure that consumer grade electronics ever posed a deadly threat to commercial aircraft. However, EMI shielding and testing was not nearly as thorough back then as it is now. Part of the reason for that is small electronic devices were not ubiquitous back then. Asking people to simply turn off an electronic device during take off and landing (critical phases of flight for navigation and radio communication) was not a big deal to people back then. It was easier for the FAA to just require that they be turned off, than to require extensive (and expensive) testing.
Additionally, I’m not aware of any credible sources which say that the reasoning was that passengers would pay more attention in the event of an emergency. It was certainly my personal experience that back then passengers stuck their noses in magazines and books as much as they do their cell phones and laptops now. If that was ever an official reason it was almost certainly not very effective.
The FAA’s decision a few years ago to officially allow electronic devices at all phases of flight was, as far as I can tell, for two reasons: better understanding of the risks because of increased testing, and the fact that we all knew people were doing it anyway.
I’ve been involved with the testing and certification of aircraft at my airlinel to allow the use of onboard portable electronic devices, and in some cases onboard transmitting portable electronic devices. In the industry, these are known by the acronym PED or TPED.
The rules vary from country to country, but in Canada, before an airline can allow the use of PED or TPED during critical phases of flight, they have to demonstrate that they will not interfere with the onboard aircraft systems.
This is commonly accomplished by blasting large amounts of RF inside the aircraft, in various locations throughout the cabin, of varrying frequency and transmitting power. I’ll admit, I’m not an engineer, so the details of this test are a little lost on me. Anyway, while the RF storm is being conducted inside the aircraft, we need to test all of the aircraft systems and every possible combination of RF interference. This is done by actually powering up the aircraft, all electrical systems and all the engines. To test our aircraft took two 12 hour days of sitting in the airplane with the engines running and not going anywhere.
At the end of the day, I was quite surprised with the results. Our aircraft passed most of the tests, but failed a couple as well. The RF radiation was causing the door proximity (PROX) sensors to fail on the forward cargo door, causing warnings in the cockpit that the door was open, when in actuality it was not. As you can imagine, this wouldn’t be a good thing to happen in flight.
Long story short, after completion of this testing we can use non-transmitting PEDs in all phases of flight, and we can use Wi-Fi in non critical phases plof flight, but it’s the cellphone frequencies that caused our issues so we are not allowed to have cellphones active on cell networks during any phases of flight ( from cabin door close at the start to cabin door open at the end.)
Modern aircraft are built with this in mind, and all of this testing is normally completed by the manufacturer during the design and development phases. For older aircraft, this process that I outlined above needs to be completed.