listening to ATC on United Airlines

Bucky wrote:

A few questions I had while listening:

- What happens if 2 people try to talk at the same time? Do you hear
both voices or neither? How do they avoid talking over each other?

Usually they block each other out with a loud squeal and have to repeat
their transmissions. How do "they" avoid it...that's been the age old
question. Mostly with experience in the system, pilots and controllers
become very good at anticipating when each other is done talking.

- It seems that there is no authentication/security, the parties just
identify themselves.

True, but at some "sensitive" airports, additional procedures have been
in effect since 9/11.

Have there been cases of troublemakers making
false impersonations?

Yes, however, it's very rare.

- They ask pilots their speed, altitude, and heading a lot. Can't the
transponder send that information?

When a controller wants "speed", they are asking for the pilot's
INDICATED airspeed. Controller's can only see GROUND speed on their
radars.

When a controller asks for altitude, he/she is verifying the altitude
he/she sees on their radar with what the pilot is seeing on their
altimeter. It's a backup and safety thing so that there is no confusion
and to verify the transponder is sending accurate information.

When a controller ask for heading, they are asking for the compass
heading the aircraft is flying. Controllers can only see the TRACK the
aircraft is flying.

- Do any other airlines put ATC on the inflight audio?

Yes, but I can't tell you which ones do and don't.

BJ