En route glide slope?

Dave S wrote
Sounds like his enroute flight takes place above FL 180

Sounds as if you have never flown outside of the USofA.
Notice that he WAS posting from "ch".

Bob Moore

"Stefan" wrote in message
...

Uh... Icebound..., the altimeter *always* indicates pressure altitude.
To get useful information, you must set the altimeter appropriately, of
course. Appropriately may or may not mean 1013.

You two are just arguing about terminology. I've always thought the norm is
to refer to an altitude measured on an altimeter (rather than another
instrument like a GPS) as "barometric altitude", with "pressure altitude"
reserved for the indicated altitude with 1013/29.92 set.

Julian Scarfe
..

Mike Rapoport wrote:

Many, if not most, turbine airplanes have this but it requires an airdata
computer system. You can set it to arrive at a particular point at a
specific altitude. You need an airdata system as long as you are climbing
or descending to a pressure altitiude. WAAS could only guide you to a GPS
altitude.

Perhaps I'm missing something basic, but don't we specifically adjust the
kollsman window to convert values provided by a barometric altimeter to a
true altitude (at least below 18,000')? Of course, you're quite right that
the GPS would need "correction" to yield the pressure altitude used above
18,000 (which I didn't consider because I've never flown there myself {8^).

- Andrew

"Andrew Gideon" wrote in message
online.com...
Mike Rapoport wrote:

Many, if not most, turbine airplanes have this but it requires an airdata
computer system. You can set it to arrive at a particular point at a
specific altitude. You need an airdata system as long as you are
climbing
or descending to a pressure altitiude. WAAS could only guide you to a
GPS
altitude.

Perhaps I'm missing something basic, but don't we specifically adjust the
kollsman window to convert values provided by a barometric altimeter to a
true altitude (at least below 18,000')? Of course, you're quite right
that
the GPS would need "correction" to yield the pressure altitude used above
18,000 (which I didn't consider because I've never flown there myself
{8^).

- Andrew
You are right and as Julian points out, I should use the term barometric
altitude. Barometric altitude (with the correct kollsman setting) is only
correct if the temperature lapse rate is 2C/1000'. It is also affected by
airflow over mountains and can be off by 1,000' in extreme conditions (I've
read). My point is that there is no way to "convert" GPS altitude to
barometric altitude since the barometric altitude is subject to a host of
errors. Everybody needs to be on the same "system" and that is barometric.

Mike
MU-2

It drives the flight director and the autopilot follows the flight director.
I don't know for certain if it drives the GS needle. I am pretty sure it
does.

Mike
MU-2

"Julian Scarfe" wrote in message
...
"Mike Rapoport" wrote in message
k.net...
Many, if not most, turbine airplanes have this but it requires an airdata
computer system. You can set it to arrive at a particular point at a
specific altitude. You need an airdata system as long as you are
climbing
or descending to a pressure altitiude. WAAS could only guide you to a
GPS
altitude.


Does it really drive the glideslope needle?

Some of the more sophisticated GPSs have VNAV functionality, and turbine
aircraft FMSs almost certainly do too, based on a barometric altitude
input.
But I always thought there was a reluctance to put the information on the
GS
needle because the glideslope of an ILS is generally associated with a
trajectory with terrain clearance -- something that simple VNAV can't
guarantee.

Julian Scarfe

Bob Moore wrote:

Dave S wrote

Sounds like his enroute flight takes place above FL 180


Sounds as if you have never flown outside of the USofA.
Notice that he WAS posting from "ch".

Bob Moore

Nope.. Never have.

Dave

Julian Scarfe wrote:

You two are just arguing about terminology. I've always thought the norm is
to refer to an altitude measured on an altimeter (rather than another
instrument like a GPS) as "barometric altitude", with "pressure altitude"
reserved for the indicated altitude with 1013/29.92 set.

Ah! I wasn't aware of that. Of course I meant barometric altitude.

Stefan

It would require extensive (read expensive) modifications to achieve what
you wish. First of all the CDI is driven by a VHF omni range or Localizer
signal while the GS indicator is driven by a UHF signal from the glide slope
transmitter. In the beginning use of ILS there were 2 separate receivers
to be tuned.... one for the Localizer VHF frequency and one for the GS UHF
frequency. Then they paired up LOC/GS frequencies so that tuning the
localizer automatically tunes for the GS. Much the same way that tuning in
VHF VOR stations automatically tunes the paired UHF tacan DME receiver for
VOR stations that have DME.

--

Darrell R. Schmidt
B-58 Hustler History: http://members.cox.net/dschmidt1/
-

"Andrew Gideon" wrote in message
online.com...
I was staring at the VOR-head during a flight a while back, and started
wondering why we only use half of it most of the time. Whether by GPS or
VOR, the CDI provides us with lateral navigation. But the glide slope
needle sits unused until the very end of the flight (if then {8^).

Why?

Using older technology, why not have an altitude bug and let the bug and
altimeter feed the GS needle, providing VNAV information en route?

Will WAAS-ified GPSs be able to drive the GS needle en route?

Curiously...

Andrew