AirTalk.org Aviation discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  En route glide slope? Goto page 1, 2  Next          AirTalk.org Forum Index -> Aviators (General Discussions) View previous topic :: View next topic   Author Message Andrew Gideon Guest Posted: Fri Nov 19, 2004 8:08 pm    Post subject: En route glide slope? 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 Back to top Nathan Young Guest Posted: Fri Nov 19, 2004 11:06 pm    Post subject: Re: En route glide slope? On Fri, 19 Nov 2004 15:08:56 -0500, Andrew Gideon <ag7337 (AT) gideon (DOT) org> wrote: Quote: 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? Not trying to be argumentative, but a simple look at the altimeter provides all the info you need to know. I do not see much value add by having a GS needle tell me I am 100 feet too high (enroute), when I can look at the altimeter and get the same info. Another issue: The setting of the enroute cruise altitude introduces an opportunity for error - where the pilot sets the wrong cruise altitude. Of course, this issue already exists with the more advanced altitude preset autopilots. I wonder if setting the wrong altitude is a problem with those? -Nathan Back to top Stefan Guest Posted: Fri Nov 19, 2004 11:22 pm    Post subject: Re: En route glide slope? Nathan Young wrote: Quote: Will WAAS-ified GPSs be able to drive the GS needle en route? Not trying to be argumentative, but a simple look at the altimeter provides all the info you need to know. Even more to the point, a look at the altimeter provides you with the correct information, namely pressure altitude. Stefan Back to top Icebound Guest Posted: Sat Nov 20, 2004 1:00 am    Post subject: Re: En route glide slope? "Stefan" <stefan (AT) mus (DOT) _INVALID_.ch> wrote Quote: Nathan Young wrote: Will WAAS-ified GPSs be able to drive the GS needle en route? Not trying to be argumentative, but a simple look at the altimeter provides all the info you need to know. Even more to the point, a look at the altimeter provides you with the correct information, namely pressure altitude. Uh... Stefan..., a look at the altimeter provides you with *indicated* altitude. It only shows *pressure* altitude if the altimeter setting is set to 29.92 Back to top Michelle P Guest Posted: Sat Nov 20, 2004 1:51 am    Post subject: Re: En route glide slope? Andrew, The software on my Pocket PC provides you with a highway in the sky if you feed it the altitude you want for each leg. Michelle Andrew Gideon wrote: Quote: 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 -- Michelle P ATP-ASEL, CP-AMEL, and AMT-A&P "Elisabeth" a Maule M-7-235B (no two are alike) Volunteer Pilot, Angel Flight Mid-Atlantic Volunteer Builder, Habitat for Humanity Back to top Dave S Guest Posted: Sat Nov 20, 2004 2:53 am    Post subject: Re: En route glide slope? Icebound wrote: Quote: "Stefan" <stefan (AT) mus (DOT) _INVALID_.ch> wrote in message news:cnlv6v$pp5$1 (AT) newshispeed (DOT) ch... Nathan Young wrote: Will WAAS-ified GPSs be able to drive the GS needle en route? Not trying to be argumentative, but a simple look at the altimeter provides all the info you need to know. Even more to the point, a look at the altimeter provides you with the correct information, namely pressure altitude. Uh... Stefan..., a look at the altimeter provides you with *indicated* altitude. It only shows *pressure* altitude if the altimeter setting is set to 29.92 Sounds like his enroute flight takes place above FL 180 Dave Back to top Mike Rapoport Guest Posted: Sat Nov 20, 2004 4:42 am    Post subject: Re: En route glide slope? Many, if not most, turbine airplanes have this but it requires an airdata computer system. You can set it to arrive at a particular point at a specific altitude. You need an airdata system as long as you are climbing or descending to a pressure altitiude. WAAS could only guide you to a GPS altitude. Mike MU-2 "Andrew Gideon" <ag7337 (AT) gideon (DOT) org> wrote Quote: I was staring at the VOR-head during a flight a while back, and started wondering why we only use half of it most of the time. Whether by GPS or VOR, the CDI provides us with lateral navigation. But the glide slope needle sits unused until the very end of the flight (if then {8^). Why? Using older technology, why not have an altitude bug and let the bug and altimeter feed the GS needle, providing VNAV information en route? Will WAAS-ified GPSs be able to drive the GS needle en route? Curiously... Andrew Back to top Mike Rapoport Guest Posted: Sat Nov 20, 2004 4:45 am    Post subject: Re: En route glide slope? "Icebound" <ice_bound (AT) rogers (DOT) !!!EXTRACT!!!.com> wrote Quote: "Stefan" <stefan (AT) mus (DOT) _INVALID_.ch> wrote in message news:cnlv6v$pp5$1 (AT) newshispeed (DOT) ch... Nathan Young wrote: Will WAAS-ified GPSs be able to drive the GS needle en route? Not trying to be argumentative, but a simple look at the altimeter provides all the info you need to know. Even more to the point, a look at the altimeter provides you with the correct information, namely pressure altitude. Uh... Stefan..., a look at the altimeter provides you with *indicated* altitude. It only shows *pressure* altitude if the altimeter setting is set to 29.92 All altitudes shown on an altimeter are "pressure altitudes" (as opposed to true altitudes) since the altimeter is an air pressure guage marked in feet. Mike MU-2 Back to top Julian Scarfe Guest Posted: Sat Nov 20, 2004 9:18 am    Post subject: Re: En route glide slope? "Mike Rapoport" <rapoportnospam (AT) earthlink (DOT) net> wrote Quote: 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 Back to top Stefan Guest Posted: Sat Nov 20, 2004 12:29 pm    Post subject: Re: En route glide slope? Icebound wrote: Quote: Uh... Stefan..., a look at the altimeter provides you with *indicated* altitude. It only shows *pressure* altitude if the altimeter setting is set to 29.92 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. On the other hand, your GPS always gives you GPS altitude, which is of no value in flight. Stefan Back to top Bob Moore Guest Posted: Sat Nov 20, 2004 2:42 pm    Post subject: Re: En route glide slope? Dave S <DoggtyredRN (AT) earthlink (DOT) net> wrote Quote: 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 Back to top Julian Scarfe Guest Posted: Sat Nov 20, 2004 7:26 pm    Post subject: Re: En route glide slope? "Stefan" <stefan (AT) mus (DOT) _INVALID_.ch> wrote Quote: 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 .. Back to top Andrew Gideon Guest Posted: Sat Nov 20, 2004 9:02 pm    Post subject: Re: En route glide slope? Mike Rapoport wrote: Quote: 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 Back to top Mike Rapoport Guest Posted: Sat Nov 20, 2004 10:20 pm    Post subject: Re: En route glide slope? "Andrew Gideon" <ag7337 (AT) gideon (DOT) org> wrote Quote: 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 Back to top Mike Rapoport Guest Posted: Sun Nov 21, 2004 2:19 am    Post subject: Re: En route glide slope? 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" <julian (AT) avbrief (DOT) com> wrote Quote: "Mike Rapoport" <rapoportnospam (AT) earthlink (DOT) net> wrote in message news:bXznd.413$uV6.105 (AT) newsread3 (DOT) news.pas.earthlink.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. 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