Why don't voice radio communications use FM?

Emily writes:

And yes, the official probable cause lists the heterodyne.

No, it does not, at least not if you're thinking of the NTSB reports.
The probable causes a

- Pilot in command - failed to follow approved procedures, directives,
etc. (KLM)
- Pilot in command - failed to abort takeoff (KLM)

- Personnel - Miscellaneous-personnel: Pilot of other aircraft (Pan
Am)

The first report is DCA77RA014, the second is DCA77RA014. For the KLM
flight, the probable-cause report also lists "Pilot in command -
misunderstanding of orders or instructions" as a factor.

I thought you would have known that, seeing as you know allegedly
read all these accident reports.

You can read them yourself with the NTSB IDs above.

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Mxsmanic wrote:
Emily writes:

And yes, the official probable cause lists the heterodyne.

No, it does not, at least not if you're thinking of the NTSB reports.
The probable causes a

- Pilot in command - failed to follow approved procedures, directives,
etc. (KLM)
- Pilot in command - failed to abort takeoff (KLM)

- Personnel - Miscellaneous-personnel: Pilot of other aircraft (Pan
Am)

The first report is DCA77RA014, the second is DCA77RA014. For the KLM
flight, the probable-cause report also lists "Pilot in command -
misunderstanding of orders or instructions" as a factor.

I thought you would have known that, seeing as you know allegedly
read all these accident reports.

You can read them yourself with the NTSB IDs above.


I wasn't reading the NTSB report.

Dan,

He's got a ton of it to spread around.


He must be Skylune ;-)

--
Thomas Borchert (EDDH)

Mxsmanic,

So I guess you can point to the accidents caused by Windows-based glass
cockpits as well as you pointed to sources for accidents caused by AM
radios?


--
Thomas Borchert (EDDH)

Emily writes:

He didn't hear ANYTHING but a heterodyne.

Not so. The transmission was hard to make out, but it was not
completely obliterated.

And even if he had heard only that, a squeal is not a take-off
clearance. Either he was deliberately negligent, or he heard
something he wanted to hear.

The actual situation was more complex, but misunderstanding was a key
part of it.

If you want to say he heard
the heterodyne as clearance to take off, fine, but that's not what we're
talking about.

That counts as hearing what you want to hear.

The OP stated that AM results in poor transmission quality and
therefore pilots will hear what they want to hear.

Yes. When a transmission is ambiguous, pilots will hear what they
want to hear.

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Emily writes:

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

Only the first part has been established. Nobody knows why he heard
what he wanted to hear; it may or may not have been unintelligible
transmission.

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Emily writes:

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

I can expect others here to have at least a basic knowledge of how
such communications work.

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Emily writes:

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

Famous last words again. OEMs that work with cutting-edge technology
are particularly prone to mess up.

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writes:

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.

Not so. The major causes of environmental noise in AM affect the
amplitude of the signal. FM modulates frequency, so changes in
amplitude are not important. Noise that changes frequency is much
more rare in the environment, so FM has less noise. That's the key
advantage of FM.

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.

With a lot of background noise, additional noise in the channel is
even more of a problem, since the margin of safety is smaller.

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

But the merit of that is that the transmission is either clean or not
there at all. Errors are rare or nonexistent.

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.

The world seems to be cooperating pretty well on aviation so far.

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.

If people are speaking with accents, noise reduction is even more
important, as the redundancy of language is even more reduced.

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...!

So nobody from the USA can fly in Europe now?

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Emily schrieb:

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.

Ok. And I'm saying that the heterodyne didn't cause anything at all.
More precisely, it caused that the Panam couldn't warn the KLM that they
were still on the runway, which maybe could have prevented the accident
in the last second, agreed. But the fatal misunderstanding occured in
perfect radio conditions and was probably caused by the overall
confusion of the situation (at all participants) and by the desire of
the KLM crew to continue their trip.

Stefan