VOR Accuracy

[nippy31]

Hey folks,
Heres a good question my student asked me. I'll share my thoughts on it too. Let me know what you all think?

How accurate is a VOR?
A vor radial is accurate to 1 degree, however when we test them in our planes, our instrument is allowed to have a variance of 4-6 degrees, depending on how you test them. Therefore, a VOR is accurate to +- 6 degrees.

Would this be accurate?

Thanks

[tgrayson]

Originally Posted by nippy31

A vor radial is accurate to 1 degree

Unfortunately, not true.

Therefore, a VOR is accurate to +- 6 degrees.

At best.


See this article:

http://www.terps.com/ifrr/oct95.pdf

[JDMcFly]

Accurate by about 1nm?

I dunno!

[nippy31]

AC 61-27 chapter 8 is where it say the VOR is accurate to 1 degree. I am still trying to find my AC 61-27 This answer came from the ASA Oral exam guide.

[MidlifeFlyer]

Originally Posted by nippy31

AC 61-27 chapter 8 is where it say the VOR is accurate to 1 degree. I am still trying to find my AC 61-27 This answer came from the ASA Oral exam guide.

AC 61-27 was superseded in 2004 by FAA-H-8083-15A - Instrument Flying Handbook.

In Chapter 7, of the IFH, it does say that "The accuracy of course alignment of the VOR is generally plus or minus 1°". But that is in the context of the larger picture that the VOR facility itself part of a larger system that also includes the accuracy of the equipment in the airplane.

The same 1° for the =radial= accuracy appears in the Pilots Handbook of Aeronautical knowledge, but goes on the say, "The accuracy of course alignment of VOR radials is considered to be excellent. It is generally within plus or minus 1°. However, certain parts of the VOR receiver equipment deteriorate, and this affects its accuracy. This is particularly true at great distances from the VOR station." (my emphasis)

You can go deeper (tgrayson?) but, as one example, AC20-130A talks about navigation systems and describes the tolerance for VOR in one section as 1.4° for the ground equipment and 3° for the airborne equipment. That translates to an overall 4.4° system error.

[MidlifeFlyer]

Originally Posted by JDMcFly

Accurate by about 1nm?

I dunno!

Since the CDI is calibrated in degrees, distance in nm isn't relevant unless you also talk about distance from the station. Assuming 1° of accuracy, that 1 nm accuracy would take place at 60 nm from the station. That one of the reasons the CDI reading for GPS and VOR are so different. CDI deviation for GPS translates directly to degrees. 120 miles from a station/VOR waypoint, a very small CDI deviation in the VOR setting can translate to a very large one if you switch the CDI to GPS mode, even if both systems are dead on.