Electronics in the Cockpit

This post was originally composed on Facebook to my old friend and colleague Ian Foster on the subject of whether there is a scientific reason for electronics must be turned off in the cabin on commercial airlines…

The safety issue is indeed overblown. Now that said, here’s why it’s more subtle than most people give it credit.

For starters, the FAA generally gives pilots the broad ability to allow any electronics they like. The language is something like the pilot in command must assure that there is no hazard posed by the electronic.

Now think about what that means. A pilot, or an airline, would have to do rigorous testing on every single device manufactured in order to assure that they don’t interfere with anything. Those tests would likely have to take place in a real airplane under flight conditions (because some electronics will behave differently at altitude than on the ground, think about devices with radio transceivers (wifi, cellular) that increase their transmission strength in a quest to find a far away receiver). The test would be time consuming as well as they would have to run them repeatedly in different parts of the plane in order to evaluate safety for the device being closer to various avionics. Finally, consider software defined radios and they would probably have to do an abbreviated version this test regiment for every version of the software that ships as the behavior of the radios could potentially change with patches to the radio libraries.

Realistically, devices with radios are the biggest threat vector, so we could just draw the line there and say that they must be turned off during critical phases of flight. That presents two problems. 1) Now the flight attendents have to be well enough trained in electronics to know which devices have radios and which don’t. 2) The electronics people want to use on airplanes are laptops, kindles, tablets and phones. All of which have radios. So the flying public doesn’t exactly get a big win with this sort of rule.

To make this more real, I’ll give you two real world examples of how iPads can interfere with flights. One involving a radio, one not.

1) I was flying a few months ago and noticed that my compass and my heading indicator (heading indicator is a gyroscopic instrument that also shows the direction of flight) kept getting out of sync. This is somewhat normal. The HI precesses (because the gyroscope isn’t perfect) and needs to be reset to the compas occasionally. What was weird was that instead of the typical 5 degrees left every 20 minutes kind of a precession, this time it was 20-25 degrees left, then 20-25 degrees right. It made holding a consistent path through the sky difficult. As I debugged the problem, I realized after a long while that the error was one direction when my ipad was on the top of the instrument panel and the other direction when it was on my lap. Finally I noticed that when it was on my lap there was no error, but when it was on top of the instrument panel there was an error. In the end, I figured out that it was the magnets that are embedded for the ipad cover that were tweaking the compass every time I put the ipad on the top of the instrument panel.

2) You know how sometimes you are on a conference call and you here a bunch of digital noise because someones mobile phone is too near the speaker phone while the phone sends out a ping to let the mobile network know it’s still alive or an incoming call causes a larger burst of noise? That happens in planes also. The odds that someone in the plane is going to get a call at the wrong moment and interrupt an emergency transmission from ATC telling the plane to abort a landing are pretty damn low, but it’s non-zero. Under ten thousand feet (when electronics are turned off) things happen very quickly and it can sometimes be a critical safety issue to get a message to a pilot that there is traffic five seconds from hitting him or a deer on the runway.

So, long story short, I think the risks are very, very small. But I think there is indeed scientific basis to the ban and that we should indeed be very careful about how it’s modified.

I’ll note that ipad use in the major airline cockpit is limited to ipads with their radios turned off. I trust pilots to do this. I don’t trust passengers.

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