Tom P writes:

Cell phones do generate a lot of electronic RFC noise, so I can
understand why they are not allowed.

That's not why they are prohibited. They are prohibited because the FCC has a
regulation that forbids the use of cell phones in flight (47 CFR § 22.925).
The FCC's original concern was not interference with avionics, but simply the
risk of overlading base stations on the ground. In fact, that situation did
not materialize, but the regulation is still on the books, and airline crews
cannot override it.

The FAA has a regulation (14 CFR § 121.306, for airlines) that prohibits the
use of electronic portable devices unless the operator (airline) has
determined them to be safe. The regulation is only partly obeyed by airlines,
in part because of an Advisory Circular issued by the FAA (AC 91-21-1B). Cell
phones fall under this regulation, but since they are completely forbidden in
flight by the FCC regulation already, the FAA regulation is moot.

What annoys me is being forbidden to turn on a GPS receiver in flight.
This is a totally passive electronic device.

Many flight attendants are stupid; sometimes their employers are stupid as
well. Stupid people often incorrectly believe that GPS units are transmitters.

AFA not being a threat, the question is, are devices certified as not
being a threat? As long as there is no certification, that's the end of
the story.

The regulations require that airlines determine devices to be safe. Airlines
generally don't want to spend time or money doing this, so they treat all
devices as unsafe, and under the regulations that means that their use must be
forbidden throughout the flight. However, the FAA's Advisory Circular suggests
that its own regulation can be ignored at certain times for many devices, a
tacit recognition of the fact that these devices really cause no problems at
all. Airlines may or may not follow the suggestions in the circular. The
regulation itself provides no wiggle room--a strict interpretation would even
require that batteries be removed from wris****ches during flight.