I wish I could just change the title to IFR questions as I'm finding a few more.

1.Can someone please help explain the difference between these two to me? I know the MOCA is minimum obstruction clearance which gives obstruction clearance and navaid reception for 22nm(from vor). Is that the difference between the two? The MORA gives no reception? Why would you use one over the other?

2.VORTAC tells me that a VOR has DME ability because of the TAC, even though the TACAN is for military use, correct?

3. (looking at Jepp enroute chart legend) Why do the charts show Class A? The sample I'm looking at is p61 of the Jepp introduction fyi. Just wondering why it would ever be changed from FL18-FL60

Thanks
Duck

 

1. You're right about the MOCA. The Minimum Off-Route Altitude (MORA) provides obstruction clearance 10NM on either side of the route centerline including a 10NM radius beyond the radio fix reporting or mileage break defining the route segment. It doesn't say anything about how much altitude of clearance you get, my guess would be 2000 ft mountainous and 1000 non-mountainous. Also, doesn't say if navaid reception is garunteed.

2. VORTAC is a VOR and TACAN combination and it does have DME because of the TACAN, so you're correct about that.

3. I'm not sure about this one.....Anybody else?

 

A MOCA is classified as a minimum IFR altitude. It will keep you 1000' above the highest obstacle in non-mountainous terrain and 2000' above the highest obstacle in mountainous terrain. Moutainous terrain is defined as a 3000' change in elevation within a 10 mile distance.

A MORA is a JEPPESEN derived (non-official) altitude. "Route MORA values clear all reference points by 1000' in areas where the highest reference points are 5000' MSL or lower. Route MORA values clear all reference points by 2000' in areas where the highest referene points are 5001' feet MSL or higher." (Jepp Intro page 10)

 

The class A example found on page 61 would occur outside the US airspace system. It is an ICAO classification of airspace and can vary throughout the world.

 

Thanks a bunch guys. I had no clue it was a Jepp only term I was having a hard time finding info on it. Thanks for the posts!

 

From the AIM Re: VORTAC

...A VORTAC is a facility consisting of two components, VOR and TACAN, which provides three individual services: VOR azimuth, TACAN azimuth and TACAN distance (DME) at one site. Although consisting of more than one component, incorporating more than one operating frequency, and using more than one antenna system, a VORTAC is considered to be a unified navigational aid. Both components of a VORTAC are envisioned as operating simultaneously and providing the three services at all times.

...Operating frequency range of a DME according to ICAO Annex 10 is from 960 MHz to 1215 MHz. Aircraft equipped with TACAN equipment will receive distance information from a VORTAC automatically, while aircraft equipped with VOR must have a separate DME airborne unit.

...There's more, check out AIM 1-1-5 & 1-1-6, I'm too tired to look through it all for anything else that may pertain to your question.

 

DME was developed for the military, and is an inherent part of any TACAN or TACAN receiver. The civvies thought it was a good idea and developed their own stand-alone receivers, and also added the DME component of TACAN to many VORs.

1) VOR: VOR only, no DME
2) VORDME: VOR w/ DME
3) VORTAC: VOR w/ TACAN (which includes DME).

2) & 3) are the same as far as civilian aircraft are concerned.

Basically we prefer VORs that have more letters at the end.

 

Stumped me at first too, but if you look at both the examples/explanations below the Class A, one is for Stavanger, and one is for London....so I kinda just assumed it was referring to international. As you stated above, the vertical limits for Class A in the US are FL180-FL600

Doubt you will be asked that on an interview, unless you looking at international charts