first thank you for this wonderful aircraft, by far the most realistic I have in my hangar.
As the title says, I have a very strange issue with the rotating beacon.
I am running FSX SE and W7pro
I will try to be synthetic
Aircraft state:
Master switch On
Engine running
Alternator charging
Tested with and without tip tanks
DEFAULT landing lights (sharp triangular pattern on ground)
1-Beacon switched ON (strobe OFF landing lights OFF ) :
the texture of the beacon changes slightly, it comes from dark red to a more saturated (steady) red.
2-Strobe switched ON (beacon ON LDG light OFF):
the beacon start flashing at the same rate than the strobe light. The intensity of the flashes varies cyclicaly probably at the rhythm of the rotating.
If NAV lights are ON, both tail lights start flashing at strobe rate. (white steady base with flashing overlay)
3-At least one of the landing light switched ON (beacon ON, strobe ON or OFF):
the beacon has a realistic rotating effect, independantly from the strobe flashing rate
If NAV lights are ON, tail lights become steady white.
Same conditions with custom landing lights (softer pattern on ground)
Same behaviour as above (point 1 and 2) but landing lights switching OFF or ON has no influence at all.
the beacon flashes and tail Nav lights flash at the strobe rate.
Is it serious, doctor?
The DX10 preview was an unfinished feature of FSX; however, it's possible to use it reliably with the (payware) third party 
