TACAN pointer problem

Hello,

In this video please watch 34:00. There is a TACAN station to the east of my position. But the needle points in wrong direction (west).

When I unset and reset my TACAN channel at 34:15 it becomes corrected.

hello , Same thing with Senaki Tacan 31X . Just turn Off then On and it Work .

I think this needs a fix. Or is it normal?

In the video at 33:15 you can see the TACAN pointing to correct direction at DME 19. Then there is a left roll (which may be the cause) and you can again see the pointer at 34:00 is wrong. I will try to reproduce it and save track.

https://drive.google.com/open?id=0BzkYV8K2tmevYzdFMWZEWTI2U3c

Okay I could reproduce the problem multiple times. Here is the track file. The problem is observable after the first 5 minutes of the flight. I go away like 30NM from Groom Lake and see the TACAN behavior on the way back.

I wonder if this is ED modeling the 40 degree TACAN lock-on error? If so I would be very impressed. Your clip makes it hard to see if the needle is pointing West and reacting, or just pointing exactly west and not reacting to azimuth change.

See here for some info on the TACAN azimuth error:

http://navyflightmanuals.tpub.com/P-305/Figure-1-17-Tacan-Azimuth-Cone-Of-Confusion-35.htm

The article says it's unusual in modern day TACAN sets, but "modern day" is a very loose term. It's not that uncommon. At any rate, this is interesting. Even if it's a bug, it's not unlike the kinds of problems you deal with when using real TACAN sets.

aaron what you mention is I think related to flights passing over the TACAN station. I was flying about 20-30NM away.

No, I wasn't referring to the cone of confusion... the 40 degree lock error is an error inherent in the signal design of TACAN. (Make sure you're reading 4a)

On closer inspection of your video however, I don't see the pointer reacting in any way, it is fixed on 270. It doesn't appear to be the 40-degree azimuth lock error. This is more indicative of unlock due to line of sight issues, and that would have been apparent if I had backed up the video on my first viewing. Notice how initially the pointer was reacting normally, but as you flew lower and into more restricting terrain (33:30) it lost the azimuth lock. When the bearing pointer in your video was pegged on 270, that was TACAN's way of showing you "hey man, I'm not tracking anymore." This is actually really impressive on ED's part, it shows both the line of sight restriction, and the channelized nature of TACAN. (Looks like the DME functioned normally however, and I would expect that to unlock as well, but I've never personally experienced these errors in a real airplane.) EDIT: It's important to note that unlike a VOR which will continue receiving signal (or no signal) on a particular frequency without stopping, TACAN will only tolerate about 10 seconds without signal, at which time it will simply stop trying until it is reset.

Summary: This is normal operation. You cannot use TACAN without a line of sight to the station. If a signal is disrupted for a period of time, the receiver in your airplane will "unlock" from the TACAN channel and need to be reset just as you did in your video. This is the normal procedure upon suspecting a TACAN lock error. TACAN is not designed to provide navigation for low-level flying, it is designed for instrument rules flight.

I am also having problems with NELLIS Tacan, on the 300 radial 90nm it starts first to cut out then reverse the station indicator and then bugs out completely (Altitude 20 000 - 30 000 ft. MSL) happened two times now (in the Maple Flag BFM Campaign) last flight I started to pick it up at only when I was at 30 nm or so.