It actually matters more than you might think.
We're sure when traveling by plane you've wondered why airlines ask that all cell phones and devices be turned off during your flight...and does it actually affect the plane? Well one pilot has told the truth about the peculiar request, revealing "a cell phone could potentially cause a minor deflection on navigational equipment. Where this becomes most relevant is in the landing phase, especially in bad weather. What I think most people don't understand is exactly how precise the instruments are."
"Here are some examples of how close the instruments bring an airplane in to landing:
What's called category 1: a layer of clouds 200 feet above the airport and 1/2 mile forward visibility. This is able to be flown manually by the pilot.
What's called category 2: a layer of clouds 100 feet above the airport and 1/4 mile forward visibility. The approach is typically flown by autopilot now but manually landed.
What's called category 3: For all intents and purposes this is no visibility. This is fully automated."
"Now, to give you an idea, these systems are putting an airplane travelling at nearly 175 MPH onto a piece of pavement that is generally 150 feet wide. The localizer, which is a component of the Instrument Landing System (the ILS some others have mentioned) shoots a beam which does this laterally. At the runway's end, this beam is 750 feet wide.
That means that in the cockpit, if the indicator is even a little off, you're going to land in the grass. And if you land in the grass, you're gonna have a bad day."
"As others mentioned, there is radio interference. Hearing the cell phone clicks over the headphones could cause the pilots to miss valuable instructions from air traffic control, which could lead to you flying into a mountain or another airplane. And if you fly into a mountain, you're gonna have a bad time.
But the most important thing that people ignore here is SCALE. Sure, one person may leave their cell phone on for a flight in good weather conditions, but if you had 150 cell phones on during a flight, the navigational error may be larger. It may not matter on most days, when the weather is not an obstacle and approaches are done "visually" with the pilot navigating to the runway by just using his eyes, but it will matter when you get into the bad weather that you see in the videos above."
"And to all of those who said "Well I leave my cell phone on and I have never crashed" you should really rethink your strategy. If I eat raw chicken and don't get salmonella, does it mean that you can't get salmonella from eating raw chicken? NO IT MEANS YOU GOT LUCKY. And so if you want to gamble on your plane not crashing so that you can get that extra three minutes of text messages in (because as others have noted, signal is garbage at altitude because of tower switching), then keep in mind there are hundreds of other passengers on the airplane who would prefer to probably live their life. The idea of text messages vs a 1/10000000 chance of dying being an acceptable trade off is an embarrassing state of our society."