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By way of greeting, I’m a CSI (also CFI/CFII/MEI in airplanes and CFI/CFII in helicopters) at Air Orlando in Central Florida. I have lurked through the forums for some time but haven’t joined the public forums until just now. I am not a COPA member, although our flight school does maintain a COPA membership. Since that name is under our marketing director, Gary Hillyer, I will post under my own name, and only in the public forums for now. Anyway - hello! Good group ya’ll have here.
I wanted to interject my own comments with regards to the discussion between Scott Dennstaedt and Jerrold Seckler about glideslope intercept altitude and acceptable procedures for intercepting the glideslope.
I think there may be a small element of communication breakdown between Jerrold and Scott. Scott’s pretty much got it right when it comes to GSIA and the appropriate (mandatory) GSIA, but what has been completely neglected (unless maybe I missed it!) by both parties is the fact that ATC authorization is required to intercept the glideslope at ANY altitude other than that published on the IAP.
Scott has correctly noted that on some instrument approach procedures, glideslope intercept may occur at altitudes other than the GSIA. However, this requires ATC authorization. To independently choose to intercept the glideslope at any other altitude would be a pilot deviation from an ATC instruction.
In a message dated 6/10 Jerrold stated:
“In each case ATC will turn you on the localizer below the glideslope at that point and give you a minimum altitude until established, or a mandatory crossing altitude. You can hold that altitude until GS interception and fly it down.”
I disagree with this statement. First, there is absolutely no requirement for ATC to vector or route an aircraft onto the final segment of an approach at an altitude below GSIA. A review of the NACO terminal procedures will show a significant number of approaches which feature initial and intermediate segments at altitudes above the published GSIA. ATC’s MVA (minimum vectoring altitude) may also be above GSIA. The minimum altitude until established means exactly that - maintain the assigned altitude until established on the localizer. In fact, the exact verbiage ATC uses is, “Maintain XXXX until established on the localizer/final approach course.” Normally, no mention of glideslope intercept or GSIA is made. If no authorization is given by ATC for intercepting the glideslope at any aItitude other than that published on the IAP, the pilot must intercept the glideslope at that altitude.
Thus, if the aircraft becomes established at an altitude above glideslope intercept, it is incumbent upon the pilot to descend to the published (or assigned) GSIA prior to intercepting the glideslope. The reason for this, among others, is to avoid intercepting the glideslope from above (especially important when flying coupled approaches.)
The AIM provides some guidance on this topic in 1-1-9:
"3. The glide path projection angle is normally adjusted to 3 degrees above horizontal so that it intersects the MM at about 200 feet and the OM at about 1,400 feet above the runway elevation. The glide slope is normally usable to the distance of 10 NM. However, at some locations, the glide slope has been certified for an extended service volume which exceeds 10 NM.
- Pilots must be alert when approaching the glidepath interception. False courses and reverse sensing will occur at angles considerably greater than the published path."
In other words, there’s no way for the pilot to know exactly how far out on the approach the glideslope signal may be used - all that the AIM tells us is that the glideslope is “normally usable” up to 10nm distance from the transmitter, and may be certified for an extended service volume at certain locations. So don’t count on the glideslope indication above GSIA being reliable, folks.
The subsequent advisory is also of interest. Clearly the angle at which the aircraft intercepts the glideslope is of importance; “False courses and reverse sensing will occur at angles considerably greater than the published path.” Intercept at level altitude - at your published or assigned glide slope intercept altitude.
Procedure turns and airline procedures have no real bearing on this discussion. We all follow the same rules. Keep in mind that the approaches the airlines fly are often Cat II or IIIa approaches - completely separate published procedures from what the majority of GA use.
Hope this input is regarded as helpful.