reported AP CPL Bugs utilizing TACAN - MAG vs True Heading Modes

[Mikaa]

Apologies if this is already reported. I couldn't find anything specific to this when searching the forums.

 

While spending time looking at another TACAN-ism (the TOD discussion) I came across this bug when utilizing the CPL function of the Autopilot in conjunction with a TACAN station. While in Mag HDG Mode (under the Data, A/C submenu), the aircraft does not properly track to the waypoint, despite the HUD and HSI heading information as well as the HUD Great Circle Steering Cue indicating correctly. This however, does not appear to be an issue when the HSI is switched to True Heading Mode. When in TRUE HDG, the autopilot correctly tracks toward the station (seemingly within a degree or so of the HUD indication). Additionally, the HSI bearing information changes for Waypoints when swapping between Mag and True HDG modes, but it does not change for the TACAN information - I believe this should reflect the current units (Mag or True, whichever is selected under the Data, A/C submenu). 

Next, I attempted to see if a manually selected course would track TO/FROM the station along a selected radial using the CRS rocker and CSEL. Both the HSI and HUD CDI cues are incorrect in True HDG, even if the course is manually slewed to center over the a/c's current radial (which should prompt it to capture and track to the station). This also doesn't match the HSI indications of the course line. The True Heading mode seems to have conflicting information as it eventually will violently roll towards the full scale CDI needle (TAC BLIM) but then rolls in the opposite direction, as if to track an incorrect radial. This cyclical error pattern is endless while in True HDG mode, regardless of the radial chosen. Mag HDG as far as I can tell, seems to be operating somewhat correctly, however it often will develop a significant bank angle while attempting to track the selected radial, or will begin to oscillate laterally in an attempt to correct for drift. Something may be amiss, but it is difficult to tell without further investigation.  

 

As a sanity check, I conducted this same test utilizing Waypoints instead of TACAN with the same Freeflight Instant Action in Nevada. I just boxed the waypoint for Nellis (WP 5) and conducted the same checks. This seems to be working as intended from my cursory run through. True/Mag swap works correctly, with correct indications on HUD and HSI, as does the selection and tracking of a manually selected course in both True and Mag. At present I feel this is only a TACAN issue. 

Reproduceable on other maps, however the errors are most apparent on NTTR due to the high degree of Mag Variation. 

Please let me know if you need more tracks. 

F-18C TACAN CPL Bug.trk

[BIGNEWY]

I have asked the team to check the behaviour of CPL TACAN when using MAG 

thanks