Q. about "Flight Level"

Hi.

I have heard some military comms on my scanner (not that I understand
everything I hear).

If I understand correctly, "Flight Level" or FL is used to describe
altitude. So, FL400 would be 40,000 feet?

My question is, if an airplane is way up there, can I hear the plane down
here? (I can hear them on the radio, but I mean, can I actually hear the
engine of the jet, as in the sound that a jetliner makes when it goes
overhead.)

At the speeds used up that high, wouldn't I hear a sonic boom?

"TeleTech" wrote in message
. 193.32...
Hi.

I have heard some military comms on my scanner (not that I understand
everything I hear).

If I understand correctly, "Flight Level" or FL is used to describe
altitude. So, FL400 would be 40,000 feet?

My question is, if an airplane is way up there, can I hear the plane down
here? (I can hear them on the radio, but I mean, can I actually hear the
engine of the jet, as in the sound that a jetliner makes when it goes
overhead.)

At the speeds used up that high, wouldn't I hear a sonic boom?

You'll hear them at 40,000ft. That's only 7 miles away and there's nothing
to get in the way.

If they were travelling at mach speeds you'd hear the boom but they don't
tend to do that over land, or at least over populated areas.

On Sun, 11 Jul 2004 16:39:11 GMT, TeleTech
wrote:

Hi.

I have heard some military comms on my scanner (not that I understand
everything I hear).

If I understand correctly, "Flight Level" or FL is used to describe
altitude. So, FL400 would be 40,000 feet?

Altitude, measured traditionally by an altimeter, requires a
barometric pressure reading for a base. For most low altitude work,
the local barometric pressure is set in the altimeter and it then
reads field elevation in feet above mean sea level (MSL). As you
climb, the pressure is reduced and the instrument reads your altitude.

For high altitude operations, where aircraft will be transitioning
barometric pressure gradients, it is necessary to use a standard
altimeter setting so that all aircraft get the same altitude readings
and can maintain separation. This standard setting is 29.92 inches of
mercury. During climb out at the designated transition altitude,
altimeters are reset to standard then altitudes above that are
reported as flight level.

And, you are correct, FL400 is 40,000 feet.

My question is, if an airplane is way up there, can I hear the plane down
here? (I can hear them on the radio, but I mean, can I actually hear the
engine of the jet, as in the sound that a jetliner makes when it goes
overhead.)

If 6000 feet is a nautical mile, then the airplane is six and a half
miles away. Could you hear four jet engines at that distance?
Probably.

At the speeds used up that high, wouldn't I hear a sonic boom?

Only if the aircraft is supersonic. Typically airliners are operating
in the .85-.88 Mach airspeed region. Even tactical jets are probably
cruising sub-sonic. No booms for you.


Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
Smithsonian Institution Press
ISBN #1-58834-103-8

Hi.

I have heard some military comms on my scanner (not that I understand
everything I hear).

If I understand correctly, "Flight Level" or FL is used to describe
altitude. So, FL400 would be 40,000 feet?

Nope.

http://en.wikipedia.org/wiki/Flight_level


My question is, if an airplane is way up there, can I hear the plane down
here? (I can hear them on the radio, but I mean, can I actually hear the
engine of the jet, as in the sound that a jetliner makes when it goes
overhead.)

What you hear is the sound of the engines. It is louder than the "sound that a
jetliner makes"

At the speeds used up that high, wouldn't I hear a sonic boom?


Not when the plane isn't going supersonic.

Wait til high school. Your physics teacher will explain.

TeleTech wrote in
. 193.32:

[snip]

At the speeds used up that high, wouldn't I hear a sonic boom?

Not if they are subsonic.
Most classic jet aircraft cruise in the high 0.7-0.8 Machs.
Some cruise closer to 0.9 than 0.8 but thats not in the shock
producing region.
I used to lie on my back in the back yard with the radio tuned
to an air band. Every once in a while we'd hear a call sign
Speedbird ( British Airways ) reporting their altitude as FL5X0
to NY ARTCC. Only one airplane in the world that could be (Concorde)
By the time they would be below Mach 1 and no longer generating
a shock wave. So never heard a sonic boom.
Lived two years near Langly AFB and never heard a boom either

IBM

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"TeleTech" wrote in message
. 193.32...

Hi.

I have heard some military comms on my scanner (not that I understand
everything I hear).

If I understand correctly, "Flight Level" or FL is used to describe
altitude. So, FL400 would be 40,000 feet?


"Flight Level" means a level of constant atmospheric pressure related to a
reference datum of 29.92 inches of mercury. Each is stated in three digits
that represent hundreds of feet. For example, flight level (FL) 250
represents a barometric altimeter indication of 25,000 feet.



My question is, if an airplane is way up there, can I hear the plane down
here? (I can hear them on the radio, but I mean, can I actually hear the
engine of the jet, as in the sound that a jetliner makes when it goes
overhead.)


I don't know if they're audible to the human ear at that height, but you
probably couldn't hear them over normal background noise anyway.



At the speeds used up that high, wouldn't I hear a sonic boom?


Only if they actually exceed the speed of sound. I remember hearing them
fairly often growing up in the sixties, haven't heard one in a very long
time.

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

"TeleTech" wrote in message
. 193.32...

Hi.

I have heard some military comms on my scanner (not that I understand
everything I hear).

If I understand correctly, "Flight Level" or FL is used to describe
altitude. So, FL400 would be 40,000 feet?


"Flight Level" means a level of constant atmospheric pressure related to a
reference datum of 29.92 inches of mercury. Each is stated in three digits
that represent hundreds of feet. For example, flight level (FL) 250
represents a barometric altimeter indication of 25,000 feet.


Flight Level is an altitude of sorts but it is measered against a
theoretical datum. FL400 would be 40000 feet above theoretical Mean Sea
Level. When flying at an altitude you are actualy flying above a physical
reference point.
29.92 Inches or 1013(.2) Millibars is the altimiter setting used when you
are told to fly at a flight level. If you are told to use any other
altimeter setting then you are no longer flying at a flight level but an
altitude. In the US, all aircraft above 12500 feet (I think) should be using
flight levels. In Europe, it varies. In England FL as low as FL 35 is
possible.
As an aside, above flight level 290 you will only get odd numbers as 2000
feet separation is required, so FL400 does not exist UNLESS you are flying
in airspace which uses RVSM or reduced vertical separation Minima. This has
recently been introduced in Canada and across the Altlantic. I am not 100%
sure but I dont think it is used in the USA.




My question is, if an airplane is way up there, can I hear the plane
down
here? (I can hear them on the radio, but I mean, can I actually hear the
engine of the jet, as in the sound that a jetliner makes when it goes
overhead.)


I don't know if they're audible to the human ear at that height, but you
probably couldn't hear them over normal background noise anyway.

Not a chance at FL 400 and very unlikely even at FL250.



At the speeds used up that high, wouldn't I hear a sonic boom?


Only if they actually exceed the speed of sound. I remember hearing them
fairly often growing up in the sixties, haven't heard one in a very long
time.
Supersonic flight is not permited over land (in peacetime operations)

"gary pearson" wrote

I don't know if they're audible to the human ear at that height, but you
probably couldn't hear them over normal background noise anyway.

Not a chance at FL 400 and very unlikely even at FL250.

Hogwash. I hear them every day. As a matter of fact, I hear them about
20 miles after they pass overhead. You have to look where they might be
now, instead of straight up where you hear the sound.

gary pearson wrote:

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

"TeleTech" wrote in message
. 193.32...

Hi.

I have heard some military comms on my scanner (not that I understand
everything I hear).

If I understand correctly, "Flight Level" or FL is used to describe
altitude. So, FL400 would be 40,000 feet?


"Flight Level" means a level of constant atmospheric pressure related to a
reference datum of 29.92 inches of mercury. Each is stated in three digits
that represent hundreds of feet. For example, flight level (FL) 250
represents a barometric altimeter indication of 25,000 feet.


Flight Level is an altitude of sorts but it is measered against a
theoretical datum. FL400 would be 40000 feet above theoretical Mean Sea
Level. When flying at an altitude you are actualy flying above a physical
reference point.
29.92 Inches or 1013(.2) Millibars is the altimiter setting used when you
are told to fly at a flight level. If you are told to use any other
altimeter setting then you are no longer flying at a flight level but an
altitude. In the US, all aircraft above 12500 feet (I think) should be using
flight levels.

Unless it's changed in the last 15 years or so, Flight Level usage starts at or
above 18,000 ft. MSL, which is to say FL 180 or higher, depending on the
barometric pressure. The applicable FAR used to be 91.81, "Altimeter settings,"
with other sections such as 91.109 "VFR cruising altitude or flight level", and
91.119 "IFR cruising altitude or flight level", based on it.

Guy

"D. Strang" wrote in
news:q4IIc.23480$r3.15887@okepread03:

"gary pearson" wrote

I don't know if they're audible to the human ear at that height,
but you probably couldn't hear them over normal background noise
anyway.

Not a chance at FL 400 and very unlikely even at FL250.

Hogwash. I hear them every day. As a matter of fact, I hear them
about 20 miles after they pass overhead. You have to look where they
might be now, instead of straight up where you hear the sound.

Shock waves are funny things. They can reflect and travel long
distances. There were reports for years of mysterious
"sonic booms" on the east coast of Canada for many years which
I believe have a weak but not insignificant correlation with
Concorde schedule.

IBM

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