Why don't voice radio communications use FM?

On Sun, 03 Sep 2006 13:39:09 +0200, Mxsmanic
wrote:

Larry Dighera writes:

--- cut-----

Anything that isn't signal is noise. AM transmissions are fuzzy and
hard to hear. In fact, aviation AM radio is probably the noisiest
type of radio voice communication still in use. Most other types of
radio communication today are FM.


This thread is becoming a lot of guessing and not based on facts!
I doubt anybody has evaluated AM compared to FM in an aircraft so
won't know what the effects are when tried side by side.

There is absolutely no difference in qualilty between AM & FM if they
are designed to the same specification. If you modulate an AM or FM
transmitter with up to 3KHx of audio they will sound identical. What
you put into the transmitter comes out of the receiver assuming there
isn't a fault.

FM maintains a low background noise longer than AM and the only
difference is at low signal levels when FM very quickly becomes
totally unreadable. AM can still be heard and understood, depending on
the ability of the person listening. With all the noise in an aircraft
a little bit of low level background noise is not significant.

Digital has some merit but again when the signal reaches a threshold
it stops completely.

The whole thread is futile as the centre of the 'aviation universe'
may well be the US but you aren't going to get the rest of the world
to change. Even having regultions which are supposed to be accepted
worldwide doesn't work. Most counties have exceptions.

About the only thing which is standard is the use of the English
language. Even then the locals will use their own language! Have you
ever worked controllers with Spanish English, Finnish English,
Canadian English, New Zealand English, Cyprus English, Bahamian,
Caribbean or even Amereican English. That's where the differences can
be heard. AM radio is adequate for the job and if you don't think so
then get your installation checked out by a qualified engineer, you
may be suprised.

As for increasing the number of frequencies Europe has introduced
8.3KHz spacing. Fortunately at the lower GA flight levels it's not
required but the higher commercials now require new radios.

Most radios are dual NAV/COM so not only would you need a new COM but
a new NAV too... It isn't going to happen...!

James Robinson wrote:
Emily wrote:

The tower told the KLM aircraft to stand by at the same time the Pan
Am aircraft transmitted, which resulted in a blocking of both
transmissions. There were many other steps in the accident chain, but
Tenerife was most certainly not caused by a pilot hearing what he
wanted to hear.

Then why did the aircraft start its takeoff roll, if the pilot didn't hear
what he wanted to? The tower only issued the ATC clearance, and the KLM
captain seems to have taken that as permission to take off. What else is
that but hearing what he wanted to?

He didn't hear ANYTHING but a heterodyne. If you want to say he heard
the heterodyne as clearance to take off, fine, but that's not what we're
talking about. The OP stated that AM results in poor transmission
quality and therefore pilots will hear what they want to hear. In this
case, the pilots heard nothing, and a high ranking captain blatantly
ignored both ATC and his own f/e.

Mxsmanic wrote:
Vaughn Simon writes:

Actually, not much does change in aviation compared with other fields of
human endeavor.

I don't think that is necessarily a bad thing. It does worry me that
the things that change in aviation are things that I'd rather see
stable. I have my doubts about fly-by-wire systems or glass cockpits,
which seem to be increasingly designed for the convenience of
programmers who grew up with Windows rather than for the convenience
of pilots.

Do you have any connection to aviation at all?

Mxsmanic wrote:
Emily writes:

They were misunderstood a) because people were stepping on other people
and b) because the KLM crew had heavy Dutch accents.

The reasons why they were misunderstood have never been ascertained,
and there are several possibilities. It's not even clear how much was
understood or misunderstood, since a number of the people involved are
dead. The common point to all the possible scenarios is misunderstood
radio communication.

Because of a heterodyne, NOT poor radio transmission quality. As
someone else already pointed out, FM doesn't even have this useful quality.

And yes, the official probable cause lists the heterodyne. I thought
you would have known that, seeing as you know allegedly read all these
accident reports.

(And since one full flight crew survived, that's pretty good eyewitness
account)

Mxsmanic wrote:
Thomas Borchert writes:

Sorry, but that's just plain BS.

Famous last words.


Speaking as someone who works for an OEM that works with the latest
cutting edge technology, Thomas is entirely correct.

Stefan wrote:
Emily schrieb:

There were many other steps in the accident chain, but Tenerife was
most certainly not caused by a pilot hearing what he wanted to hear.

Actually, the KLM captain hearing what he wanted to hear was most
certainly the main cause for that accident.

As a consequence of this misunderstanding, the word "take-off" shall now
only be used in "cleared for take off" and in the read-back of this
clearance, or, at uncontrolled airfields, when a pilot says that he is
taking off. No more "ready for take off", "stand by for take off" and
the like, and no taking off before you are absolutely positively sure
that you have heard and read back the word.

But all this had nothing to do with the readability of the radio
transmissions.

Stefan
That was my point. He heard what he wanted to hear, but not because of
jarbled radio transmission.

Mxsmanic wrote:
Larry Dighera writes:

You'll have to cite a source for this nugget of knowledge.

FAA AIMs and CFRs make it pretty clear that communications involving a
controller are pilot-controller exchanges, not pilot-pilot exchanges.

Are you familiar with Common Traffic Advisory Frequency (CTAF)?

Yes, but it and similar schemes don't involve a controller, so
obviously the communication is between aircraft directly.


But you just said that all communications are air-ground. You can't
back pedal.

Emily schrieb:

He didn't hear ANYTHING but a heterodyne.


Wrong. Please read the NTSB report before making such statements.


1705:53.4 APP KLM eight seven * zero five uh you are cleared to the
Papa Beacon climb to and maintain flight level nine zero right turn
after take-off proceed with heading zero four zero until intercepting
the three two five radial from Las Palmas VOR. (1706:08.2)

1706:09.6 KLM Ah roger, sir, we're cleared to the Papa Beacon flight
level nine zero, right turn out zero four zero until intercepting the
three two five and we're now (at take-off). (1706:17.9)


Of course this has nothing to do with the readablility of the transmission.

Stefan

"Mxsmanic" wrote in message
...

Wait and see.

I try to remain civil here on the Usenet, but you have proven all through
this thread to not be someone worth wasting time on. You get the last word, but
thanks to technology I won't be seeing it.

Bye
Vaughn


Transpose mxsmanic and gmail to reach me by e-mail.
Why would I want to do that?

Stefan wrote:
Emily schrieb:

He didn't hear ANYTHING but a heterodyne.


Wrong. Please read the NTSB report before making such statements.

I have read the report, and I don't see where readability came in.

1705:53.4 APP KLM eight seven * zero five uh you are cleared to the
Papa Beacon climb to and maintain flight level nine zero right turn
after take-off proceed with heading zero four zero until intercepting
the three two five radial from Las Palmas VOR. (1706:08.2)

1706:09.6 KLM Ah roger, sir, we're cleared to the Papa Beacon flight
level nine zero, right turn out zero four zero until intercepting the
three two five and we're now (at take-off). (1706:17.9)

I think there was some confusion here. I wasn't saying that he never
heard ATC at all, just that the transmission confusion was due to the
heterodyne, not static or poor transmission quality.