Redglyph,
I had both missions working pre-1.5.5 patch release with some workarounds. Tested Mission 5 this morning with the newest patch and the Chinook in Mission 5 still will not land. I even took out the AI troops, and changed the airframe to a UH-1H and still not landing. I have submitted a bug report to ED, hopefully this gets fixed soon. I have also changed different conditions for the land path, duration, etc, nothing seems to work.
Unfortunately, I do not have access to the test builds so I cannot troubleshoot until a patch is released...