DME requirement for ARC - what about altitude
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Since DME is a slant range from your jet to a TACAN station, altitude matters in figuring out the slant range. If I am at 40.000 ft or 20.000 ft, I will not have the same slant range and thus different DME measurements.
I am looking for input into what the DME instrument should show, to ensure I am properly on the Arc. When a chart states to fly a 20 DME Arc, does it mean 20 DME at ground level, so when I am at altitude my instrument should read, say, 22 DME ?
Thx,
JB -
You need to read the DME chart. That will give you the altitudes you need for certain waypoints.
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The chart always tells you what altitude to be at for each Waypoint. You shouldn’t have to figure it out.
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When the chart says an arc of X DME then you fly X DME. You don’t compensate for altitude to try to make an X mile radius of ground track. Whoever made the approach knows and has planned for the radius to be whatever it is. As others say the vertical position in the approach is specified in the approach chart. E.g. ILS 18 for Soeul is a 13 DME arc at 3700’. In all the civil charts I could find the altitude is also written on the arc itself in the upper area.
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Thanks, I see that the ILS approach charts clearly states the different altitudes. My question came about due to the Coyote Three Departure chart for Kunsan - is the required altitude on the arc 14.000 as stated in “TRANS ALT” at the top ?
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Thanks, I see that the ILS approach charts clearly states the different altitudes. My question came about due to the Coyote Three Departure chart for Kunsan - is the required altitude on the arc 14.000 as stated in “TRANS ALT” at the top ?
Transition altitude is the altitude at which you change from your current altimeter setting to the standard one. The altitude on the arc is here not stated, but a hint is that when reaching wolf you are not in VMC (visual meteorological conditions) you enter the hold as published and it says that the MHA is 13000 feet, which means that the minimum holding altitude is 13000 feet. So it means that when you takeoff you slowly climb to 13000 feet minimum.
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Published numbers are to be flown as indicated on your instruments. No Flight Agency expects you to do that kind of trigonometry on the fly (pardon the pun).
Also, since separation under IFR conditions is the responsibility of ATC that know where you are (RADAR or position transponders), as long as you are close to the published approach/departure, they will instruct you and others more appropriately if required.
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Since DME is a slant range from your jet to a TACAN station, altitude matters in figuring out the slant range. If I am at 40.000 ft or 20.000 ft, I will not have the same slant range and thus different DME measurements.
I am looking for input into what the DME instrument should show, to ensure I am properly on the Arc. When a chart states to fly a 20 DME Arc, does it mean 20 DME at ground level, so when I am at altitude my instrument should read, say, 22 DME ?
Thx,
JBWhen they say 14 DME, they mean you should have a slant range of 14 miles. Yes, that does mean that at higher altitudes, you will be horizontally closer to the station for a given slant range. 20 DME means 20 DME on the instrument, regardless of altitude.
Some charts will state that you can use GNSS instead of DME. GNSS ranging is horizontal distance, not slant distance, so you can have some issues there. Some charts will only allow GNSS, and others, only DME, for this reason.
When last I looked, the F-16 was not yet RNAV approach approved. However, this was some years ago, and this may have changed by now. At the time, you could fly ILS approaches, and if the ILS approach specifies a certain distance DME, that means on the DME - no substituting with an INS provided horizontal value.
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OK, 20 DME as per the instrument it is. So for the Coyote Three departure that would mean that depending on altitude I may not directly overfly the INS location of WOLF, but be close enough.
Thanks all
JB -
Alltidues are given are given for Approach Charts. So for Kunsan 18 you start the Arc at TOLCI 8000ft DME15 descending to JEWEL DME15 3500ft
And btw if you do the math disance over ground DME15 at 8000ft is 14.98NM at 3500ft is 14.94NM so not even noticeable on your instrument
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Good point, the DME vs ground deviation is maybe .1 or .2 for a 20DME arc. So no big deal.
Approach charts will always tell you the altitude, I found that some departure charts may not. That is probably by design cf. the “resume own navigation” call that one gets once airborne
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So on the coyote departure you are given a crossing altitude for the initial point. It is assumed you will continue your climb to your flight planned altitude. There is also a restriction that you must hold if not at safe altitude and IMC. This ensures that you can avoid any obstacles before proceeding on course. In the Viper you should be well above all minimum safe altitudes before reaching Wolf.