Following the GS

[Donsa320]

Avbug

Tell ya what, big guy. Next time I'll include pictures so you can follow along.

All better?

Well, they say a picture is worth a thousand words. In your case I would have to agree. <grin>

D.C.

 

[snoopy_1]

Maybe if you put down the MS Flight Sim long enough and read a book, you will understand the difference.

Come on, MS Flightsim 2004 is really improving my inverted ILS approaches http://forums.avsim.net/dcboard.php?az=show_topic&forum=147&topic_id=173752&mesg_id=173752&page=

 

[corpflunkie]

according to an airways facilities friend of mine, the glideslope antenna is the same for catI, catII or catIII. The difference is the localizer antenna array. GS is accurate to the height the antenna is from the ground (10-12ft) unless there is some obstacle that may distort the beam ie the restriction at a place like KMEM

 

[Donsa320]

according to an airways facilities friend of mine, the glideslope antenna is the same for catI, catII or catIII. The difference is the localizer antenna array. GS is accurate to the height the antenna is from the ground (10-12ft) unless there is some obstacle that may distort the beam ie the restriction at a place like KMEM

I'm wondering what your friend means by that. The glide slope signal is bounced off of the ground in front of the antenna. This is to suppress any "fly down" side lobe signals that otherwise might be below the useable glide slope. Hopefully all the signal BELOW the useable glide slope will be "fly up".

Here in snow country we frequently lose the glide slope when the reflective plane gets enough snow on it to screw up the reflective angle. The monitor then trips the glide slope off 'till the snowplows clear the reflection zone. Not too handy. <g>

D.C.

 

[prpjt]

I included avbugs post in an example of why we were discussing GS between DA and 100' I took exeption to these words, " It's not flightchecked"

I took those words to infer that the GS was not tested inside the point where DA exists on the GS centerline. I don't think that is what he meant, but that's how I read it.

I'm using the word flightchecked to mean tested.The flightcheck has nothing to do with wether the signal is approved for use inside a particular point.. And the GS in fact is tested inside the DA point. The type of test for fly up signal depands on the type of Cat I approach. I was unaware that there was more than 1 type of cat I ILS.

A sincere thanks to Avbug for the reference to the FAA Order. And I'm not being a smarta$$. Thanks.

I would like to ask a question regarding some terms used in that order. Either an answer or a reference would be appreciated.

What makes a GS restricted or unrestricted.
How is it determined wether a Cat I ILS will be "for use below 200" or "not for use below 200" (those are the 2 types of Cat I ILS, and GS is tested differently)

And donsa is correct that heavy snow can render a GS useless and initiate an OTS Notam.

 

[avbug]

During periods of heavy snow accumulation, Airway Facilities personnel may NOTAM glide slope facilities as "due to snow on the XXX (appropriate identifier), glide slope minima temporarily raised to localizer only." Category II/III operations are not authorized during the snow NOTAM.

During periods when the snow NOTAM is in effect, the approach is flight inspected for localizer only. If the glide slope supports Category II/III approach procedures, the glide slope will only be evaluated to Category I tolerances. Restoration of Category II/III facilities, after the snow NOTAM is removed, will be considered as a periodic overdue inspection.

 

[avbug]

Prpjt,

A Squared is probably a better source on your question; he's a lot better versed in TERPS.

The approach category, and the corresponding DH, is set by several things. Volume 3, Chapter 3, Paragraph 3.7 stipulates that the minimum DH for a category 1 approach is 200'. Per TERPS, minimums may be raised due to precipitous terrain, the requirement for a remote altimeter setting source (RASS), unusual typical wind conditions in excess of 20 knots, and obstructions and climb gradients required for the missed approach. Decision altitude is also adjusted for obstacle penetration into the obstacle clearance slope (OCS).

The concept is straightforward; if obstacles are close to the final approach course, the decision altitude is raised, and often the visibility required, to permit adequate time and space to see and avoid these obstacles. In the case of missed approach criteria, the decision altitude is placed farther out and higher up in order to permit a lesser climb gradient requirement. Often aircraft that can meet a higher climb gradient criteria are issued lower minimums.

Per TERPS, numerous considerations are in effect. By example, directly prior to the runway is the Precision Obstacle Free Area, which dimensions are 200' long and 400' either side of the centerline. If this area is not clear, the minimum HAT is 250', and the minimum visibility is 3/4 mile. Various boundaries and zones exist on each approach segment, and any terrain or obstacle penetration into those areas raises that segment altitude. This has an effect on decision altitude for the final approach segment.

Aside from the physical considerations of the approach, the aircraft, the pilot and the operator must also be approved for lower than standard operations. Thus, four criteria must be met in order to use lower than standard, or lesser than Category 1 and published minimae.

The aircraft must have equipment capable of conducting the approach to lesser minimums. The pilot must be qualified and current to do so, and the operator or individual must have authorization, which comes in both the form of a straight authorization, or operations specifications for certificate holders.

 

[prpjt]

That points me in the right direction, Thanks.