Hi, I've been lurking around FT for nearly a year, and finally have become bored/moved enough to post.

The regulation is that electronics must be powered down when below an altitude of 10,000' mean sea level. The flight deck crew gives the two or four bells signifying this altitude usually right when they're at that altitude on the climb or descent. It definitely will vary depending on the flight and the airport, because we aren't always instructed to descend below 10,000' at the same place. For instance, NY approach may instruct us to descend below 10,000' quite a distance from the airport. In the back of the aircraft, it may seem as if the "put your laptops away" call is premature on those flights because the descent happens some time before landing. On the other hand, some airports are notorious for leaving aircraft high and "slam-dunking" them in at the last minute. These aren't always the high altitude ones, either. ATL often leaves aircraft high when the weather is good, then asks them to do a steep descent into the airport. MCO does this, too. In those cases, the below 10,000' notification may come with barely enough time to put your laptop away before landing.

Why is it important? 10,000' is seen in many different FAA regulations. Passenger jet aircraft typically don't descend below that until the final stages of an approach. Below 10,000' is always a relatively critical phase of flight. There is more traffic down there, there are speed restrictions on all aircraft, and the flight deck crew is supposed to be sterile (the pilots can't talk about anything except the flying). Hence, the reason that electronics are supposed to be turned off below that altitude. If a device is going to affect an ILS needle or cause a burst of static in a headset at cruise altitude, it's not a big deal. At 4,000' in busy airspace, it is a big deal. We all know that there's only a slight chance of that happening, but it's an easily avoidable chance.