Stupid Question Alert

[minitour]

One of those days...

on the High Enroute charts...if you've got a DME fix, do they take into consideration the "slant range" error in the DME when they set up a DME fix?

I guess on the lows too...if you're high enough it could affect you by a mile or two...

sorry in advance

-mini

 

[Kream926]

hummm, good question

im kinda wondering myself now. well, slant range is the greatest when you are over the navaid right? or is that only for groundspeed

 

[User546]

If you have a fix at 17 DME for instance, when your DME is reading 17 in the cockpit, that's what your going for!

If your asking about slant range in the design of charts, I think it would be wise to assume that it's already been taken into account for. Because they're going to expect you to do your thing at that specified DME, without taking in account for anything.

Remember, keep it simple!

 

[A Squared]

What are we really talking about here?

Much is made of "slant range error" but it ususally isn't put into perspective. Here's some perspective: At 30,000' and 15 NM from the station, slant range error will be about 0.8 NM. That's it. 0.8 nm really isn't much, especially when you consider that the TERPS assumes DME to be only accurate to 0.5 NM Yes, it is worth keeping in mind that when you are very close to or directly over the station there may be substantial error, otherwise, it's just not a big deal. As for the origianal question, I beleive that the DME fixes on charts are the acual DME distance.

 

[minitour]

Thanks guys...sorry to dumb the place down...back to your regularly scheduled posting

 

[MTpilot]

We might need a stupid question forum!

I've got one, If the MEA is 13000 and the MOCA is 8500 why do they even bother giving you the moca, is it just for lost comm situations. They are telling you that below 13000 you won't have reliable nav on the airway, so why bother telling me that I won't hit things at 8500 on the airway when I won't have any way to know whether I'm on it or not. Like Minitour said, sorry in advance.

 

[minitour]

I've got one, If the MEA is 13000 and the MOCA is 8500 why do they even bother giving you the moca, is it just for lost comm situations. They are telling you that below 13000 you won't have reliable nav on the airway, so why bother telling me that I won't hit things at 8500 on the airway when I won't have any way to know whether I'm on it or not. Like Minitour said, sorry in advance.

GPS nav?

You might not have reliable signal between the VOR/NDBs, but the GPS could work....it's the best I got right now...I'm pooped

-mini

 

[banned username 2]

One of those days...

on the High Enroute charts...if you've got a DME fix, do they take into consideration the "slant range" error in the DME when they set up a DME fix?
-mini

Yes, you cross at the DME as indicated on your DME, there is no additional calculations needed... Remember, if you are using GPS, the distance readout will differ from your DME... (DME is slant range, GPS is horizontal distance)

 

[FracCapt]

I've got one, If the MEA is 13000 and the MOCA is 8500 why do they even bother giving you the moca, is it just for lost comm situations. They are telling you that below 13000 you won't have reliable nav on the airway, so why bother telling me that I won't hit things at 8500 on the airway when I won't have any way to know whether I'm on it or not. Like Minitour said, sorry in advance.

That's primarily for GPS/RNAV. You can be on that airway below the altitude at which you have reliable nav/comm, but still have obstacle clearance.

 

[nosehair]

That's primarily for GPS/RNAV. You can be on that airway below the altitude at which you have reliable nav/comm, but still have obstacle clearance.

....except back in the old days, before GPS/RNAV, the MOCA was good to know when you couldn't maintain altitude (ice, engine,etc) how low can you go, and you don't necesarily lose the nav signal immediately, and if you're paying attention to your established crab angle, dead reckoning helps, the point is to know how low you can go if absolutely necessary.