I've flown Delta and United at times where the pilot would run a feed through the entertainment system. Check with the "allowed electronic devices" to see if they have a policy against it. Delta used to allow scanners, but it's been a while since I looked. Some airlines won't even allow laptops, such as Singapore Airlines. If they don't allow FM radios (which most if not all don't), then scanners usually are not either.
The simplified technical reason for this (if you're interested), is that most FM radios use a 10.7 MHz I.F. (intermediate frequency), and most scanners use 10.7 or 10.8 MHz. Remembering that the air band is from 108-118 Mhz (navaids) and 118-136 MHz (voice/other), if you have a cheep FM radio and your listening to 107.7, to receive that frequency, the radio uses an internal L.O. (local oscillator) to generate a signal at 118.4 MHz, then mixes it at the 10.7 MHz IF to get 107.7 (118.4 - 10.7 = 107.7). As you can see, a carrier at 118.4 MHz could pose a real problem in-flight. Cheep FM radios are the worst, because they don't spend a lot money and trouble to shield and suppress the LO. Another example is if you were listening to 99.3, then the radio would be generating a carrier at 110.0, smack dab in the Navaids band. If you're interfering with the ILS receiver on landing, that could lead to a real bad day.
Scanners are not near as bad, because most of the voice comms that you would listen to are in the 118-136 MHz band, which could potentially generate a signal above 125 MHz. The main difference is that most scanners are designed to be significantly better for IF and LO carrier suppression. I have several older Bearcat scanners, and non of them generate any appreciable level of IF/LO carrier, even when its directly connected to another radio by a coax connection.
Of course, you could try to convince the flight attendant or captain that your scanner clean, but you'd probably loose the argument.