it could be 1 of 3 things
1. it might not be a current model (i.e. it was designed for an earlier flight simulator)
2. it could be a bad model (as in the designer forgot or messed up on the animations)
3. it could be a problem with your computer (graphic card related)

if you could give us a link to the file, or some more details, it would be much easier to find the problem and to fix it

My favorite Huey is the excellent Bell 205A-1 Evergreen Helicopters on Amphibian Floats by Lynn Rogers.

You can get it here:

[url]http://www.simviation.com/fs2004helicopters3.htm[/url]

There is also another Huey with extended amphibian floats in Stratford Helicopters paint by the same author available here:

[url]http://www.simviation.com/fs2004helicopters4.htm[/url]

These models are very detailed -- they both come with opening pilot's and passenger's doors as well as a good 2D panel and a Huey Sound package.  They don't come with a virtual cockpit or interior cabin views, however, I can live without these.  They're lots of fun.  Try one or the other--or both!  You won't be disappointed.