"Bucky" wrote in message
oups.com...
I'm not a pilot, just your typical passenger. I don't fly United often,
so I just discovered that they put the ATC on the inflight audio. I was
totally fascinated and want to learn some more. Is there a website that
has some basic ATC protocols? Not some huge reference manual, just the
common phrases that you hear over a commercial flight's radio.

There are a lot of them out there, can't remember what site has them, but i
know JFK, DFW, and a few others are out there, most are realaudio, but a few
can be streamed to windows media player or winamp.

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?

All you hear is very very very bad static, and other noises unpleasant to
the ear, the key to avoid talking over each other is to listen before keying
up the mike, even then it happens now and then, ATC can usually recognize
when they have been talked over and will repeat, and definately know when
two aircraft talk over each other, and will usually have a good idea who was
first cus they've been talking to them earlier, or perhaps they caught a bit
of the transmission before or after being stepped on. When in uncontroled
airspace its common for a third pilot to chime in "Blocked" when they heard
a "step on" to let both pilots know they didnt' get heard.


- It seems that there is no authentication/security, the parties just
identify themselves. Have there been cases of troublemakers making
false impersonations?


Not common for troublemakers, most don't have the brains to know how to
handle an aviation radio, but we did have a NOTAM on our desk here in the
Phoenix Area about a guy pretending to be America West making false reports
of "Traffic in sight" etc. Dunno if they caught him yet, and if they
have/do, i hope they tie him to the nearest cactus.

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

The transponder will send altitude information, but it sends pressure
altitude ( what the altimeter would read if the altimeter setting was
29.92 ) which may differ from the local altimeter setting, sometimes the
difference can be quite large between what the transponder reports, and what
the altimeter on the flight deck reports (unless flying above 18,000', and
even then the error tolerances between the Transponder and Altimeter are
fairly loose). Its possible the ATC tech can be seeing you at 8000' and
300knots (cus the formula for calculating the speed is for groundspeed not
airspeed) when the airplane is actually at 7000 and 250 kts. Just a way for
the tech to double check that they pilot recieved and is following
instructions. Transponder does not send heading info, again like speed
that is calculated by the ATC computers, and is a ground track that does not
take into account wind direction, so an airplane flying a heading of 270
could be getting blown onto a track of 260 or somesuch, and the 260 is what
is reported to the ATC tech. Its also a "polite" way of stating that they
believe the aircraft is off course/altitude/speed and to correct for it.
And the correct answer to "XYZ-2356 state airspeed" when below 10,000 is
ALWAYS "250."

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

Wish they did, I fly regularly on American and Delta, never have heard it on
their radios.