ILS - Glide Slope angle

[jparnold]

Firstly just wondering in real life if the ILS glide slope can be different (angles) at different runways and if so what is the maximum angle generally used.

Secondly can the Glide Slope angle be set to various values in ADE. I could not find anywhere where it can be changed.

Thanks

 

[glottis]

Firstly just wondering in real life if the ILS glide slope can be different (angles) at different runways and if so what is the maximum angle generally used.

Secondly can the Glide Slope angle be set to various values in ADE. I could not find anywhere where it can be changed.

Thanks

Yes they can, generally they are about 3 degrees, but some charts can show above or below this, afraid i have no idea what the Maximum is......
you will find the angle here:
ADE/List/Navaids click on the runway ILS to bring up the properties to see the Glide Slope Angle

 

[jparnold]

Thanks Ray,

I couldn't find anything in the user manual to suggest that it could be varied, only that it could be turned on or off and ADE is installed on a different PC to the one I am currently using.

Now I need to find out if I can add (or create a separate file for) a fictitious ILS to existing scenery recently downloaded.

It's been around 12 months since I last used ADE to develop/modify airports so it's going to be another learning experience.

 

[TOWSIM]

The normal, standardized glide slope is 3 degrees. This value comes from physical experiences with an aircraft flying 'downhill'. The glide slope shall ensure an acceptable speed control during landing. The lower limit of a glide slope is dictated by the obstacle situation in the final approach segment. In regard to the distance to touchdown, a certain vertical clearance to the highest obstacle must be ensured. If the clearance cannot be ensured for 3 degrees glide slope, the slope angle must be raised or the procedure touchdown must be moved towards the departure end of the runway. The maximum acceptable glide slope is at 6 degrees. It can be flown only with gear down and full flaps before the glide path intercept. Depending on the type of aircraft mainly flown at an aerodrome, it can be necessary to establish an glide slope lower than 3 degrees. This situation is very seldom an depends even on the obstacle situation in the final approach segment. The calculation of glide slope and approach minima is subject of APATC1, PANS OPS and FAA TERPS.
Regards,
Mike

 

[jparnold]

Wow thanks Mike for the very detailed description.
I considered some of what you described but it was good to read it all in context.
With glideslopes I am thinking of the approach to runway 10 at St Barthemeley where pilots have to clear a hill which is (according to Google Earth) around 130 feet above sea level and just 500 feet before the runway threshold which is at 80 feet above sea level. So the pilot must descend a minimum of around 52 feet in 560 feet. What would the 'glideslope' be there? I used a web page I found and got around 5.3 degrees which isn't as great as it looks so not sure if I calculated it correctly.
To make it even more interesting the runway is only about 1000 feet long.
http://www.youtube.com/watch?v=3FrYGqaW94o
I had a go at landing there in a twin beech and made it but a very very bad landing.
I am in the process of creating a fictitious ILS for the runway and seeing how FSX would handle a landing using ILS glideslope.

 

[TOWSIM]

The video looks very interesting. But what I can assume is, that the responsible agency would never approve an ILS procedure for this runway because of the hill, runway length, missing runway lighting...
It seems to be a real adventure to approach this runway in pretty VMC.

 

[jparnold]

I agree.

But that is why I stated that I wanted to create a FICTITIOUS ILS just to see how FSX would handle a landing using that (fictitious) ILS.

Just for fun

 

[GHD]

London City (EGLC) has a 5.5 degree glideslope.

 

[jparnold]

I guess that is because it is in the CBD and tall buildings around?

Googling 'airports with steep glide slopes' brings up a few 'hits' for EGLC.

Also found the following -


Chambéry (LFLB) is 4.46˚, Innsbruck (LOWI) 4.0˚, Lugano (LSZA) 6.65˚.......

The only one I have flown regularly (B737 and B757) is Chambery 18 which is 4.6 deg.. very interesting.. on the 757 you have to be fully configured to land and back at Vapp before intercepting the glideslope because if you ain't you won't be able to slow down so it's a go-around


And there are others. Fascinating.

Have a look at http://www.pprune.org/tech-log/483336-steep-glidesopes.html

 

[TOWSIM]

The minimum allowable glide path for ILS category I can be determined as follows:
Problem:
obstacle distance 9000 feet from GPI
obstacle height above runway elevation 238 feet.

• ROC = required obstacle clearance (vertical distance between top of obstacle and glide slope)
• GS = glide slope angle
• GPI = ground point of intercept (location where glide slope touches the runway)
• OH = obstacle height above runway elevation in feet (238 feet)
• D = Distance from GPI to obstacle in feet (9000 feet)
• RoConClose = constant 0.02366 for distances less than 10975
• RoConFar = constant 0.01866 for distances equal or more than 10975 feet

First, determine the ROC. For the example with a distance of 9000 feet, we take RoConClose

• ROC = D * RoConClose + 20
  232.94 = 9000 * 0.02366 + 20
• Tangent of minimum Glide Slope = (OH + ROC) / D
  0.0522326 = (238 + 232.9) / 9000
• ARC TAN 0.0522326 = 2.99536 degrees minimum glide slope.

This calculation has to be done for each obstacle in the final approach segment to find the controlling obstacle, which dictates the minimum glide slope angle. The dimension of the final approach segment is a trapezoid of 50000´length in maximum
The dimensions of the final approach segment can be seen in the attached image.
See APATC-1 (A) Chapter 9, Instrument landing system
Regards,
Mike