No. Even using solid state electronics and the most efficient batteries that exist you cannot generate enough power to incapacitate the on-board avionics. Further, even if you did affect the avionics, there is no guarantee that the result would a) give you control of the airliner, or b) incapacitate the airliner.

Whether or not the TSA could detect it is not the issue.

The problem is that you can't get enough EMI power generated from a portable device with a battery power supply over a long enough period of time to get the results you're talking about. You can get a couple of moderately high power pulses, but generating high power levels requires large components, lots of energy, and lots of heat dissipation. AND you need to generate enough energy across a wide band of frequencies to jam everything on a plane. Total power required can be figured by doing an integral calculus across bandwidth and instantaneous power on a given frequency. You can't generate more energy than the batteries can provide.

Here are a couple of examples: On the river approach into DCA, from the north, you pass within relatively close proximity to several TV towers. A couple of those transmitters have effective radiated power in the megawatts at UHF frequencies. There are also several of the FM stations close by to the approach path - generating kilowatts of power each. Planes don't fall out of the sky there....

There are a number of other places in the world where aircraft regularly land adjacent to very high power transmitting stations, including the Meadowlands (NJ), near Newark and Teterboro, or planes landing at SFO and Oakland.

Now, it is possible to affect specific frequencies navigation electronics or communications electronics. But even if you affect certain frequencies, there are alternative frequencies available, and there are alternative landing locations that may not require the affected frequencies. And there are still some PAR approaches available around the country (PAR = ground controller issues left-right-descend instructions to the pilot via radio) that could be used if no other nav gear were working on the plane.

Now, I'm not saying it would be completely impossible to incapacitate an airliner, but the equipment required to do so would be large, bulky, and require more energy than can be carried on an airliner, even as cargo. Ergo, it is highly unlikely that you can cause a crash in that fashion. And even then, it would not be predictable.... predicitability being one thing that the terrorist community seems to value.

It would be far more practical for a terrorist or terrorist-wannabe to obtain and use a shoulder-fired rocket.