For those of you who can't make the Landscape mode work on their iPhone 6S .... I've found this solution!
Go To:
SETTINGS - DISPLAY & BRIGHTNESS - VIEW (under Display Zoom) and MAKE SURE YOU CHOSE THE STANDARD...
IF your Display setting here is set to ZOOMED then you'll get LANDSCAPE VERSION OF THIS APP IS NOT SUPPORTED ON IPHONES MSG...
Changing this setting to STANDARD make Landscape mode works !!!
Safe flying!