Aircraft turned the wrong way on go-around

[flyingfudge]

ROUTE ID: DEFRTE EGFF/12 BCN1B BCN Q63 STU P2 BANBA DCT CRK DCT EIKY/26

As per the title, the aircraft turned right instead of left on the go-around. ( same on v1.6.1 and the Beta version )

Log.txt

[Pils]

Thanks we’ll file it up.

[richjb]

Interesting.... 

This was a real issue in the Collins FMS for software prior to verion 4.x and the J42 database.  It infamously resulted in the "loss of 10,000 instrument approaches from the nav-database".  

This missed approach is coded as a VD leg or heading-to-DME fix leg. It's similar to a VA or heading-to-altitude leg which was the cause of the issue above.  The FMS if it at or above the altitude published for the VA turn (e.g., "climb to 1000 feet then turn right..."), when the FMS saw that the altitude was satisfied, it sequenced the leg and with it, the coded turn direction (e.g, "...then turn right").  The FMS would look at the heading of the aircraft at the time of leg sequence, and if based on its current heading, it would turn in the shortest direction to go to the next waypoint.    In the example, if a heading at the time of leg sequence resulted in a left turn being a shorter distance turn to the next leg, then airplane would turn left instead of right.  The FAA issued and airworthiness directive removing approximately 10,000 approaches from the database until Collins fixed the problem. This circa 2017.  

It was not limited to approaches either.  The Cathedral SID at Palm Springs CA (KPSP) - 00545CATHEDRAL (faa.gov) was removed from the nav-database for similar reason.  When departing runway 31L, the procedure called for flying a 310 heading until crossing the PSP R-268, then a right turn direct to PSP.  In some wind conditions, the FMS would calculate left turn as a shorter direction to get to the PSP VOR.  When the radial crossing was satisfied, the FMS would drop the coded turn direction and turn in the shorter direction, i.e., left turn to PSP VOR.  

There was also an issue with TEMP COMP affecting turn direction, which is why TEMP COMP is not authorized in FMSs without software ver 4.x and J42 database. 

I am going to take a guess that this issue is similar.  The FMS is sequencing legs and, in the process, dropping the coded turn direction.  

Rich Boll