Flight Crew Last 90 Days 172; Flight Crew Type 6958
Confusion; Situational Awareness
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Human Factors; Procedure
Inbound to LAX; we were set up for an approach to 24R off of the RIIVR 2 Arrival.  We were then told to descend via the RIIVR 2 and cleared the ILS 25L.  That was no problem since we had adequate time to reprogram the box and pull out the new approach plate.  While on final; we were given a speed change (don't remember the details) and were told we were cleared direct TAANK for the ILS 25R.  This put us in a jam since we were in a -300 and had to find the appropriate approach plate and reprogram the box.  By the time we got the box programmed; the course indicator didn't make sense to me since I now realize we were already past TAANK.  In the heat of the moment; I felt like I was flying blind and did not have good situational awareness.  At one point the Controller asked about our location and the Captain said something about just finishing the reprogramming and were correcting.  He also said the field was in sight and we were cleared visual approach 25R.  Since I lost situational awareness momentarily; I believe I may have drifted right slightly and gotten slightly low on the approach at or above altitudes. We eventually 'got back into the Green;' but it was very uncomfortable!  I believe we worked well as a crew and did our best to adjust to this last-minute change.  I don't understand why this happens so often.  Please relay to the controllers that these last-minute changes can really throw us into a fur ball.  It is not good business to switch us like that in such a busy environment.  It takes a while to recover and; in that time; bad things can happen with fast moving airplanes.
B737-300 Fist Officer reports a last minute change from runway 24R to 25L then to 25R at LAX which causes confusion and possible altitude and track deviations. The Captain reports the field in sight and is cleared for the visual.