I have an RCA 61310 hdtv, why is it when I play certain dvds in the "full" mode(which is the mode for playing 16:9 material, some dvds such as "Glory" , "The Natural, Castaway, will fill the entire screen with a great picture with no bars top and bottom while others such as Titanic and other movies will have a great picture but will have the bars top and bottom to varying degrees depending on the particular movie. I am playing these movies in 16:9 mode and not pan/scan.

Because different movies are made in different aspect ratios.

Another way of saying 16:9 is 1.78:1. That means the screen is 1.78 times as wide as it is tall.

The movies that you mention as filling the screen were shot in the aspect ratio 1.85:1, which is almost the same as your widescreen TV. The others were made in the wider 2.35:1 format. To preserve that wider picture, you'll still have slight bars at the top and bottm.

This is normal.

Plus you will always have black bars on Titanic because it is letterboxed, not anamorphic.

You can always zoom in on your DVD player to fill the screen but you will lose picture quality and cut off the sides of the picture.