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"Glidepath" Vs "Glideslope"?  
User currently offlineTimz From United States of America, joined Sep 1999, 6835 posts, RR: 6
Posted (6 years 10 months 3 weeks 15 hours ago) and read 19127 times:

In the other thread (Reply 46)

3-degree ILS Glideslope Is 3 Deg From What? (by Timz Oct 26 2007 in Tech Ops)

Boeing 7E7 said

"you have in that picture a 3 degree glidepath, but a >3.00 glideslope. The glidepath is what is published as a glideslope on a chart. Only with a flat runway does the GS = GP."

When asked "So you're saying that there is a difference between the meaning of 'glidepath' and 'glideslope'?", he said

"Yes. Glidepath is the path. Glideslope is the instrument."

So it seems the beam that most people call a glideslope is actually a glidepath-- so a glideslope is just a piece of hardware? Or two pieces, one on the ground and one in the plane? Does it have a slope? Defined how?

20 replies: All unread, jump to last
 
User currently offlineLongHauler From Canada, joined Mar 2004, 4972 posts, RR: 42
Reply 1, posted (6 years 10 months 3 weeks 14 hours ago) and read 19117 times:

On the Embraer 175/190 Glideslope (GS) refers to the vertical mode of the ILS receiving information from a ground based station. Glidepath (GP) refers to an aircraft manufactured vertical mode using the VNAV function.


Never gonna grow up, never gonna slow down .... Barefoot Blue Jean Night
User currently offlineTimz From United States of America, joined Sep 1999, 6835 posts, RR: 6
Reply 2, posted (6 years 10 months 3 weeks 5 hours ago) and read 19034 times:

So on the Embraer "glidepath" has nothing to do with the ILS? It can exist at airports that don't have an ILS?

But "glideslope" does refer to the ILS beam, not the hardware that produces it?


User currently offlineLongHauler From Canada, joined Mar 2004, 4972 posts, RR: 42
Reply 3, posted (6 years 10 months 3 weeks 5 hours ago) and read 19024 times:

Quoting Timz (Reply 2):
So on the Embraer "glidepath" has nothing to do with the ILS? It can exist at airports that don't have an ILS?

Yes, exactly. We would only use the VNAV Glidepath at an airport or runway that does not have an ILS, as approach limits are higher. Or sometimes, we would do a GPS "overlay" approach on top of a VOR, or NDB approach, that too would have VNAV Glidepath data.

Of all the approaches, the good old ILS has the lowest limits, right down to CAT 2 or 3!

Quoting Timz (Reply 2):
But "glideslope" does refer to the ILS beam, not the hardware that produces it?

That's a tough one. I guess technically, the "glideslope" is the component of the ground based ILS beam that gives vertical data. The ILS receiver on the aircraft receives it, and displays it to the pilots.

But, on the EMB 175/190 when you arm the approach, among other things, you will see either GS armed for an ILS approach, or GP armed for a RNAV or GPS approach with VNAV data.



Never gonna grow up, never gonna slow down .... Barefoot Blue Jean Night
User currently offlineBond007 From United States of America, joined Mar 2005, 5416 posts, RR: 8
Reply 4, posted (6 years 10 months 3 weeks 4 hours ago) and read 19014 times:

"GLIDEPATH- (See GLIDESLOPE.) "

From FAA Pilot/Controller Glossary (and I'm not omitting anything).

The term 'glideslope' certainly refers to the ILS 'glidepath' beam, but if you look at most FAA documentation, both terms are used interchangeably, and often written as glideslope/glidepath.

The imaginary line in space that they are describing is the same .... waiting to be corrected on that  Wink

My understanding is the glideslope/localizer is the ILS beam/equipment defining the glidepath.

From AIM:

"The term 'glide path' means that portion of the glide slope that intersects the localizer. "


Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineSilverComet From Mauritius, joined Apr 2007, 85 posts, RR: 0
Reply 5, posted (6 years 10 months 3 weeks 3 hours ago) and read 18995 times:

Didn't think there was a specific definition to 'glidepath' as opposed to 'glideslope'. The way I always understood it was 'glidepath' was just the general term for the vertical path followed by the aircraft on final for any kind of approach, be it ILS, non-precision or visual. 'Glideslope' to me refers to the vertical guidance portion of an ILS.

But I may be wrong.


User currently offlineIAHFLYR From United States of America, joined Jun 2005, 4790 posts, RR: 22
Reply 6, posted (6 years 10 months 3 weeks 2 hours ago) and read 18988 times:

Or simply use the phrase "vertical path" and confuse even more!  Smile


Any views shared are strictly my own and do not a represent those of any former employer.
User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 7, posted (6 years 10 months 3 weeks 2 hours ago) and read 18979 times:

Quoting Bond007 (Reply 4):
The term 'glideslope' certainly refers to the ILS 'glidepath' beam, but if you look at most FAA documentation, both terms are used interchangeably, and often written as glideslope/glidepath.

The imaginary line in space that they are describing is the same .... waiting to be corrected on that



Quoting SilverComet (Reply 5):
Didn't think there was a specific definition to 'glidepath' as opposed to 'glideslope'. The way I always understood it was 'glidepath' was just the general term for the vertical path followed by the aircraft on final for any kind of approach, be it ILS, non-precision or visual. 'Glideslope' to me refers to the vertical guidance portion of an ILS.

[
I would say you guys are correct. I've always just referred to the descent line to the rnwy as the glidepath.

Quoting LongHauler (Reply 3):
on the EMB 175/190 when you arm the approach, among other things, you will see either GS armed for an ILS approach, or GP armed for a RNAV or GPS approach with VNAV data.

I would say that's just nomenclature. On the MD-11 an RNAV app will just say "prof ' meaning profile glidepath to mins there's also FPA "Flight Path Angle" which is a pilot selected flight path which is normally set to 3 deg.


User currently offlineMir From United States of America, joined Jan 2004, 21624 posts, RR: 55
Reply 8, posted (6 years 10 months 2 weeks 6 days 22 hours ago) and read 18921 times:

Quoting SilverComet (Reply 5):
The way I always understood it was 'glidepath' was just the general term for the vertical path followed by the aircraft on final for any kind of approach, be it ILS, non-precision or visual. 'Glideslope' to me refers to the vertical guidance portion of an ILS.

That's the way I look at it as well.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 9, posted (6 years 10 months 2 weeks 6 days 20 hours ago) and read 18901 times:

My understanding is that the original term was glidepath, i.e. flight path on final approach to landing. In the old days before flaps were invented the engines would be idling, hence glidepath. When ILS was developed the term glideslope was used to identify the vertical guidance signal provided to put the aircraft on the glidepath.

Just my assumption, but I'm pretty sure the term glidepath is much older than glideslope.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineBond007 From United States of America, joined Mar 2005, 5416 posts, RR: 8
Reply 10, posted (6 years 10 months 2 weeks 6 days 20 hours ago) and read 18887 times:

Quoting SilverComet (Reply 5):
Didn't think there was a specific definition to 'glidepath' as opposed to 'glideslope'. The way I always understood it was 'glidepath' was just the general term for the vertical path followed by the aircraft on final for any kind of approach, be it ILS, non-precision or visual. 'Glideslope' to me refers to the vertical guidance portion of an ILS.

Yes, that's a good description .... although I still say a 'glidepath' is a predefined angle/path (here we go again!) ... not just the descent path the aircraft happens to be taking... albeit a VASI glidepath, RNAV, or ILS.

So if you are high on the approach, you may be above the VASI glidepath, or RNAV glidepath ... or ILS glideslope  Smile

Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineBio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 11, posted (6 years 10 months 2 weeks 6 days 19 hours ago) and read 18884 times:

AIM - PILOT / CONTROLLER GLOSSARY:

GLIDEPATH
-- (See Glideslope)

GLIDEPATH [ICAO] -- A descent profile determined for vertical guidance during a final approach.

GLIDESLOPE -- Provides vertical guidance for aircraft during approach and landing. The glide slope / glide path is based on the following:

a. Electronic components emiting signals which provide vertical guidance by reference to airborne instruments during instruiment approaches such as ILS/MLS, or

b. Visual ground aids, such as VASI, which provide vertical guidance for a VFR approach or for the visual portion of an instrumen approach and landing.

c. PAR. Used by ATC to inform an aircraft making a PAR approach of its vertical position (elevation) relative to the descent profile. (See ICAO term Glidepath)

----

According to these definitions:

- The FAA does not distinguish among Glidepath and Glideslope.
- ICAO defines both term separately.

Here is my interpretation of ICAO's term definition:



Due to the terms being used, the ICAO definition seems much more logical. a "PATH" is just that. It doesn't imply a definite angle or straight lines, but just a path being flown or intended to be flown. On the other hand, the term "SLOPE" is a mathematical term that defines an angle. For aviation purposes, the vertical slope for most approaches is 3°. This can not be changed, and is used just as a guidance for aircraft during the final approach phase, regardless of the path intended to be flown or being flown by the aircraft.

Alfredo


User currently offlineBond007 From United States of America, joined Mar 2005, 5416 posts, RR: 8
Reply 12, posted (6 years 10 months 2 weeks 6 days 19 hours ago) and read 18880 times:

Quoting Bio15 (Reply 11):
a "PATH" is just that. It doesn't imply a definite angle or straight lines, but just a path being flown or intended to be flown.

Yes, which may explain why the term "glidepath" is used for RNAV/GPS approaches where the path may change it's angle.

Quoting Bio15 (Reply 11):
On the other hand, the term "SLOPE" is a mathematical term that defines an angle.

Which explains it's use with the ILS, since the ILS is a defined angle.

Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineBoeing7E7 From , joined Dec 1969, posts, RR:
Reply 13, posted (6 years 10 months 2 weeks 6 days 17 hours ago) and read 18853 times:

From TERPS....

Descending on a Precision Glidepath. The
obstacle evaluation method for descent on a glidepath
is the application of a descending OCS below
the glidepath. The vertical distance between the
glidepath and the OCS is ROC; i.e., ROC =
(glidepath height) - (OCS height). The ROC
decreases with distance from the final approach fix
as the OCS and glidepath converge on the
approach surface baseline (ASBL) height
(see figure 1-2). The OCS slope and glidepath
angle values are interdependent: OCS Slope =
102 ÷ glidepath angle; or glidepath angle = 102 ÷
OCS slope. This relationship is the standard
that determines the ROC value since
ROC =(glidepath height)- (OCS height) .

Threshold Crossing Height (TCH).
A height as low as 32 feet for military airports may be used at
locations where special consideration of the glidepath
angle and antenna location are required.


Obviously, the "antenna" is the "glideslope antenna".

[Edited 2007-11-01 18:56:47]

User currently offlineIAHFLYR From United States of America, joined Jun 2005, 4790 posts, RR: 22
Reply 14, posted (6 years 10 months 2 weeks 6 days 5 hours ago) and read 18799 times:

Quoting Bio15 (Reply 11):
Here is my interpretation of ICAO's term definition:

Ahhh the ole ILS 4 at HOU!!! Why did you pick that??  Big grin



Any views shared are strictly my own and do not a represent those of any former employer.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 15, posted (6 years 10 months 2 weeks 6 days 1 hour ago) and read 18757 times:

The ILS beam is most definitely a glide path, as that is the term used in ICAO Annex X Vol 1. Coincidentally, it is also the term used by people who make their living working with ILS systems.

You are on a glide slope anytime you are descending, in my dictionary, but that's not cross referenced to anything. Only an opinion.

All attempts to claim that the glide slope is an instrument or whatever, with nothing to do with the path the aircraft is flying, would be a symptom of the foot in mouth confuscation disease.

The obstacle clearances surfaces and the glide path angle are connected, but the glide path is not set according to the obstacle clearances surfaces, contrary to what some people might try to imply at times. The obstacle clearance surfaces are set to cater for the glide path. If this cannot be done you can displace the threshold or, uncommonly as it is undesirable for many reasons, increase the GP angle. Lower GP angles are not all that uncommon though, at least not in my part of the world. This is typically when the ILS systems were originally installed to cater for various air forces, which for some reason seem to prefer a shallower approach.

Cheers,
/Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineBond007 From United States of America, joined Mar 2005, 5416 posts, RR: 8
Reply 16, posted (6 years 10 months 2 weeks 5 days 21 hours ago) and read 18733 times:

Quoting FredT (Reply 15):
All attempts to claim that the glide slope is an instrument or whatever, with nothing to do with the path the aircraft is flying, would be a symptom of the foot in mouth confuscation disease.

Well .... might be from the UK perspective, but the FAA clearly defines it as such ... see earlier post above.

Quoting Bio15 (Reply 11):
Provides vertical guidance for aircraft during approach and landing.

Otherwise you'd never be 'above' or 'below the glideslope' would you .... if it was just the path the aircraft is flying?

It is a predefined glide path.


Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 17, posted (6 years 10 months 2 weeks 5 days 20 hours ago) and read 18723 times:

Quoting Bond007 (Reply 16):
Well .... might be from the UK perspective, but the FAA clearly defines it as such ... see earlier post above.

Hmmm... I am in fact agreeing with what the above FAA/ICAO quotes. Perhaps not in the clearest of wordings, admittedly, but still agreeing.  Smile



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineBond007 From United States of America, joined Mar 2005, 5416 posts, RR: 8
Reply 18, posted (6 years 10 months 2 weeks 5 days 19 hours ago) and read 18707 times:

Quoting FredT (Reply 17):
Hmmm... I am in fact agreeing with what the above FAA/ICAO quotes. Perhaps not in the clearest of wordings, admittedly, but still agreeing.

Agreed.. I think I mis-interpreted your comment.  Smile

Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineBoeing7E7 From , joined Dec 1969, posts, RR:
Reply 19, posted (6 years 10 months 2 weeks 5 days 15 hours ago) and read 18681 times:

Quoting FredT (Reply 15):
The obstacle clearances surfaces and the glide path angle are connected, but the glide path is not set according to the obstacle clearances surfaces, contrary to what some people might try to imply at times. The obstacle clearance surfaces are set to cater for the glide path. If this cannot be done you can displace the threshold or, uncommonly as it is undesirable for many reasons, increase the GP angle. Lower GP angles are not all that uncommon though, at least not in my part of the world. This is typically when the ILS systems were originally installed to cater for various air forces, which for some reason seem to prefer a shallower approach.

If you are implying this is incorrect...

Quoting Boeing7E7 (Reply 13):
Descending on a Precision Glidepath. The
obstacle evaluation method for descent on a glidepath
is the application of a descending OCS below
the glidepath. The vertical distance between the
glidepath and the OCS is ROC; i.e., ROC =
(glidepath height) - (OCS height). The ROC
decreases with distance from the final approach fix
as the OCS and glidepath converge on the
approach surface baseline (ASBL) height
(see figure 1-2). The OCS slope and glidepath
angle values are interdependent: OCS Slope =
102 � glidepath angle; or glidepath angle = 102 �
OCS slope. This relationship is the standard
that determines the ROC value since
ROC =(glidepath height)- (OCS height) .

Then you should call the FAA and ICAO. Its their words, and their standard. Not mine.

[Edited 2007-11-02 20:36:20]

User currently offlineTimz From United States of America, joined Sep 1999, 6835 posts, RR: 6
Reply 20, posted (6 years 10 months 2 weeks 4 days 22 hours ago) and read 18606 times:

Don't see where he said anything that disagrees with your quote. The quote tries to specify the relationship between the two surfaces-- it doesn't say anything about which surface determines the other.

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