h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I believe that the statement about the lower aircraft being told to descend isn't 100% accurate.

I -believe- that I've read somewhere that the system can also take into account current climb/descent data to deal with the situation where although the lower plane is lower, he's in a steep climb, and although the higher plane is higher, he's descending. In such a situation the TCAS systems advise the climbing plane to climb even FASTER, and the descending plane to descend even FASTER, so that they shoot past each other.

This is because a descending plane cannot suddenly stop descending (unless of course it has some way of violating the laws of physics and in the process flattening everyone on the plane like a pancake), nor can a climbing plane suddenly level off.

I think this is in reference to a crossing resolution advisory which is where one aircraft is directed to pass through the altitude of the other aircraft. The aural warning in this case should use the word "crossing" as I recall.

"Resolution Advisory" is what the system tells the planes to do to avoid each other.