bookworm... the Initial Segment of a Base Turn procedure normally ends upon completion of the turn. It goes without saying that there may, or may not, be an IF in such a procedure. However, I believe it would be a very bad idea to be 2.5 NM off track at the end of the outbound leg because :
- If the aircraft is on the outside of the procedure, there may not be a lot of obstacle clearance. As you correctly state, an obstacle in the secondary area can be higher than in the primary area, so the pilot may have 100 feet, OR LESS, of clearance above it. This situation could easily remain true all the way through the turn.
- If the aircraft is on the inside of the procedure, it's unlikely that there will be any chance of intercepting the inbound track directly, even at an extreme bank angle. Thus a severe overshoot is highly likely to occur. This might well place the aircraft out in the secondary area and, at the same time, increase the time needed for the intercept - thereby reducing the time available for descent on the inbound leg.
Neither of these situations are desireable and it needs to be remembered that the splay angle between outbound and inbound tracks is based on a particular maximum speed, as
reynoldsno1 appropriately points out. If the aircraft is not close to the outbound track at the end of the outbound leg, an overshoot of the inbound track is almost certain. There are only a few circumstances in which a procedure will keep an aircraft within the primary protection area and still allow an efficient intercept of the inbound track.