Hi there, Usually when ATC issues your final vectors for intercepting the localizer, they will end their transmission with " maintain "X" altitude until established on the localizer" (FS2002). I always wondered if this was correct since I thought that your final altitude would be maintained until the glideslope was intercepted. Can someone enlighten me on whether or not this is a technically correct instruction from ATC (i.e. should it be "maintain "X" altitude until established on the glideslope)Thanks for any responseJ.C. (MYNN)

You normally don't want to descend unless you have some sort of course guidance. In this case it's the localizer. You need the localizer because without it you don't know exactly where you are. The altitudes that ATC assigns or that are published in the approach plate are designed to keep you out of the terrain because you can see them in IMC. So if you do descend before you have course guidance, then you run the risk of colliding with terrain.So the instruction from FS ATC to "maintain xxx until established" is correct. When you're flying along on your approach, and the glideslope starts descending, but you're not established on the localizer then you need to double-check to see where you are.But normally with the controller vectoring you, you will see the localizer come alive before the glideslope does.CheersWoodreau / KMVL

This is correct.Since the controller manual states that aircraft will be vectored onto an precision approach course at or below the glideslope, you will be established on the localizer at the controller's altitude(hopefully) before the glideslope starts moving.The reason for intercepting the glideslope from below is that this prevents receiving false glideslope signals usually found above the real glideslope.http://mywebpages.comcast.net/geofa/pages/Geofdog2.jpg

> should it be "maintain "X" altitude until>established on the glideslopeYes you should.The sequence is this: you first hold the given altitude, then intercept the localizer and then when you intercept glideslope you start descent. In other words your final let down can't start until you are established on both - localizer and glideslope.Michael J.http://www.reality-xp.com/community/nr/rsc/rxp-higher.jpg

Thanks for all the responses.J.C. (MYNN)

>>> should it be "maintain "X" altitude until>>established on the glideslope>>Yes you should.>The sequence is this: you first hold the given altitude, then>intercept the localizer and then when you intercept glideslope>you start descent. In other words your final let down can't>start until you are established on both - localizer and>glideslope.>er, actually, no ... the controller will often vector you at an altitude which is higher that the glideslope intercept altitude. So you might be vectored at 2000' to an approach where you need to descend to 1800' for glideslope intercept. Once you've got lateral guidance (localizer) you follow altitude guidance from the published procedure.

I am not sure if I am mis reading your post-but from the faa atc controllers handbook (section 2b below)this might clarify it:http://www2.faa.gov/atpubs/ATC/Chp5/atc0509.html#5-9-15-9-1. VECTORS TO FINAL APPROACH COURSE Except as provided in para 7-4-2, Vectors for Visual Approach, vector arriving aircraft to intercept the final approach course: a. At least 2 miles outside the approach gate unless one of the following exists: 1. When the reported ceiling is at least 500 feet above the MVA/MIA and the visibility is at least 3 miles (report may be a PIREP if no weather is reported for the airport), aircraft may be vectored to intercept the final approach course closer than 2 miles outside the approach gate but no closer than the approach gate. 2. If specifically requested by the pilot, aircraft may be vectored to intercept the final approach course inside the approach gate but no closer than the final approach fix. b. For a precision approach, at an altitude not above the glideslope/glidepath or below the minimum glideslope intercept altitude specified on the approach procedure chart. c. For a nonprecision approach, at an altitude which will allow descent in accordance with the published procedure. http://mywebpages.comcast.net/geofa/pages/Geofdog2.jpg

Martin and Geofa,Actually you're both correct.For a precision approach, the controller must vector you to intercept below the glideslope. So if the published GS intercept is 1800 and the controller's MVA (Minimum Vectoring Altitude) is 2000, then he would need to vector you to join further outside the approach gate so you would still be below the GS at 2000. However, once you join the localizer you could theoretically descend to 1800 prior to capturing the GS (assuming 1800 is the published MIA prior to the marker).Actually this occurance is far more common with non-precision approaches. For example, there is an NDB approach in my airspace that has an MIA of 2200; but my MVA is 3000. When vectoring to this approach, the clearance is "maintain 3000 until established on the final approach course...." Once the pilot joins the final, he can descend to 2200 prior to the FAF.I hope that's as clear as mud :-),Marc