Why don't voice radio communications use FM?

Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio? I
realize there's substantial inertia in the installed base of AM
equipment, but surely one could allocate some new frequencies to FM
and use them in parallel for some years to ease the transition.

The reason I ask is that improper and misunderstood radio
communication is a leading cause of accidents, and so it seems that
anything that can make that communication clearer would greatly
improve safety. I can barely understand what I hear on the radio. It
is true that the communication is very standardized, making it easier
to guess what is being said, but the results are pretty unpleasant if
one guesses wrong.

On a related note, it has occurred to me that one could develop
voice-recognition systems that understand the speech of a pilot and
then repronounce what he says in an extremely standard synthetic
voice. This could also improve understanding, especially for
non-Anglophone pilots who speak with heavy accents. The same systems
could clean up the speech so that it is absolutely standard, with no
missing or added words. Of course, the issue here is that the system
would be stuck if it cannot recognize what is being said, or if a
completely non-standard utterance is made by the pilot. A natural
extension of this would be systems that recognize standard phrases in
one language and translate them to another, but that would be even
more dangerous if the system ever failed.

Still another idea is special training systems that listen to a
pilot's speech and transcribe it, and point out any problems with
understandability. Again, this would be most useful for
non-Anglophone pilots, but it would work for anyone. If a machine can
understand a pilot's speech clearly, then a human being should
certainly be able to understand it that much more easily.

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"Mxsmanic" wrote in message
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Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio?


Wouldn't that reduce the available frequencies?

Yeah, Steve, it would. But I think we might be able to swap (on a long term
swap basis) the VHF com band for stuff up between 600 and 900 MHz. that have
very limited usage. Not only could we get way more bandwidth, but the
antenna size is cut by a factor of 6 or so.

Jim


"Steven P. McNicoll" wrote in message
nk.net...

"Mxsmanic" wrote in message
news

Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio?


Wouldn't that reduce the available frequencies?

Steven P. McNicoll writes:

Wouldn't that reduce the available frequencies?

For a given audio bandwidth, FM tends to require somewhat more radio
bandwidth, as I recall, but the audio bandwidth of aviation radio is
already so limited that I don't think this would be an issue. The
gain in clarity would outweigh any loss of audio fidelity, assuming
that the same channel widths were used.

If frequencies were reallocated (instead of allocating new ones), that
would be different. That would also obsolete older equipment much
more quickly, which might not be acceptable. But there must be some
space somewhere that could be added to the frequencies, or perhaps
some band so rarely used that it could be reassigned.

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You recall incorrectly.

Jim


"Mxsmanic" wrote in message
...
Steven P. McNicoll writes:

Wouldn't that reduce the available frequencies?

For a given audio bandwidth, FM tends to require somewhat more radio
bandwidth, as I recall,

RST Engineering writes:

You recall incorrectly.

Perhaps. Theoretically it should require exactly the same bandwidth,
but I seem to recall reading that typical implementations used more
bandwidth. In any case, you don't need much for voice communication.
The advantage of FM would be the reduction of noise. Digital over FM
would be still better.

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Mxsmanic wrote:

The reason I ask is that improper and misunderstood radio
communication is a leading cause of accidents,

A leading cause of accidents? Where did you get this statistic?

but the results are pretty unpleasant if
one guesses wrong.

Guess? If a pilot or controller is not able to comprehend the other side's
transmission, there is no guess. "Say again?" is the phrase of choice and
it is used all over the frequencies.



--
Peter

Peter R. writes:

A leading cause of accidents? Where did you get this statistic?

From the NTSB and several books on the subject.

Guess? If a pilot or controller is not able to comprehend the other side's
transmission, there is no guess. "Say again?" is the phrase of choice and
it is used all over the frequencies.

It's routine in linguistics to unconsciously guess. A person
listening to familiar sounds in a familiar context will "fill in the
blanks" for any sounds that cannot be unambiguously distinguished, and
he will do this without thinking. If he guesses wrong, trouble can
result, and accidents have happened in aviation for this reason (the
most famous probably being the one at Tenerife).

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Mxsmanic wrote:

From the NTSB and several books on the subject.

Have a name of one of these books that claims that aviation communication
is the leading cause of aviation accidents?


It's routine in linguistics to unconsciously guess. A person
listening to familiar sounds in a familiar context will "fill in the
blanks" for any sounds that cannot be unambiguously distinguished, and
he will do this without thinking.

You imply that this is a very common occurrence. Sorry, but I am unable to
accept your premise without some evidence to back up this claim.

If he guesses wrong, trouble can
result, and accidents have happened in aviation for this reason (the
most famous probably being the one at Tenerife).

My understanding of the accident at Tenerife is that it had more to do with
a fateful heterodyne and a captain who was asserting his own way, rather
than misunderstood communications.


--
Peter

Peter R. writes:

My understanding of the accident at Tenerife is that it had more to do with
a fateful heterodyne and a captain who was asserting his own way, rather
than misunderstood communications.

Some of the words on the cockpit recording are impossible to
understand even today. That's pretty strong evidence that
misunderstood communications had an important role in this accident.
In fact, there are several instances of misunderstood radio
communication involved.

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