If you need an animated camera to look vertically upward or downward, use a free camera.
If you use a target camera you might run into a problem of unexpected movement. 3ds Max constrains a target camera's up-vector (its local positive Y axis) to be as close as possible to the world positive Z axis. This is no problem when you are working with a static camera. However, if you animate the camera and put it in a nearly vertical position, either up or down, 3ds Max flips the Camera view to prevent the up-vector from becoming undefined. This creates sudden changes of view.