![]() Even if everything goes right it requires a pretty good rate of descent to make it work, now factor in the fudge factor plus a wind out of the southeast quadrant that's delaying your final approach course intercept while blowing you closer to the airport and it could be tempting to call yourself "established" and start descending early.until you think about that huge (tall) grain elevator So you see, in some cases it's best to know exactly at what point it's safe to consider yourself "established". Now let's say our estimating and timing is perfect and we intercept inbound at 8 miles, to descend 1420' from PT altitude of 4300' to MDA at 2880' in the five miles that'd put us on a 1 mile final to runway 29 for a straight in. Also note the NDB is located about a mile & a half beyond the center of the airport. Keep in mind that you're determining distance outbound by the imprecise method of estimating groundspeed for timing so you prob'ly should fudge it a little on the short side to insure you don't go outside the ten mile limit. Back in the "good ol' days" the procedure turn minimum altitude was a few hundred feet lower than it is now but it was pushed up to 4300 about fifteen years ago to allow for a huge (tall) concrete grain elevator that was built out in the PT area. Now you're flying this one the purist way, ADF and timing to determine how far to go outbound while insuring you remain within 10 miles of the beacon. Here's a good reason to understand at what point you should consider yourself "established" on the final approach course and OK to start descending to MDA, link is to the NDB 29 approach to Wolf Point, Montana. However, you cannot leave your last assigned 2000 for the intermediate segment/GS intercept altitude of 1600 until you are established on that segment, i.e., the needle is within half scale and stable. The controller has you at 2000 feet (the MVA in that area), and you get the following "final vector" call: "Cessna 123, 4 miles from WEGRO, turn right heading 010, maintain 2000 until established, cleared ILS 4 approach." Since you are only 5 miles from WEGRO, you know you're inside RIKME and the segment altitude once established is 1600. Imagine you are being vectored to join the ILS 4 at Easton MD (KESN). With no more than one quarter scale deflection maintained, the aircraft will be aligned with the runway. This sensitivity permits accurate orientation to the landing runway. In that case, you cannot safely (or legally) leave the last assigned altitude for the published intermediate segment altitude until "established" on the localizer. With this course width, a full-scale deflection shows when the aircraft is 2.5° to either side of the centerline. In those places, you may be vectored to join the localizer with the last vectoring altitude being higher than the published altitude for the intermediate segment you are joining. ![]() So the term 3/4 scale deflection for an ILS means that at all times during the approach procedure, the needles must not exceed 3.75 dots (or 75% of the available space) on both lateral and vertical guidance needles.Click to expand.There are many places where you are vectored to join a localizer only a few miles outside the FAF. This is true for both vertical guidance (glideslope) and lateral guidance (localiser). Should you be doing an ILS, as explained above, the instrument abides by a cone, so the closer you get to the ILS beacon - the smaller the scale (hence the smaller the movement required to regain / lose track). (meaning no more than 7.5 degrees off course) The term 3/4 scale deflection for VOR tracking means that at all times during your tracking, you must not stray more than 3.75 dots either side of the centreline. ![]() I used the VOR because the scale remains constant, and it was an easy way to describe the term "scale deflection". ![]() Hence 3/4 scale deflection would be 7.5 degrees off course (or 3.75 dots either side). Half scale deflection means that I am 5 degrees off course (or 2.5 dots either side). (Hence I must turn right to regain track).įor you to understand the scale, full scale deflection whilst tracking a VOR means that I am 10 degrees or more off the desired track (as the instrument has 5 dots either side, each dot is 2 degrees hence 10 degrees ). So if I am tracking the 240 degrees TO the VOR, then if my needle is on the second dot to the right of the centreline of the instrument, then that means that I am 4 degrees to the left of the desired track. When your CDI/OBS/HSI is tuned to (and identified) a VOR station, you can see 5 dots on either side of the centreline of the instrument. As what you quote seem like limits, I will attempt to explain it in as easy a way as I can. But I am not sure anyone explained what this "3/4 scale deflection" means.
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