B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 167
Confusion
Other Unwanted situation
Airspace Structure; Chart Or Publication; Company Policy; Human Factors
This is a warning; not a report of a violation. I have seen; perhaps even been party to selecting an RNAV approach when told to expect an ILS (or visual) approach to numerous airports in the system. Many (if not most) different types of approaches have the same IAF and FAF positions; names; altitudes; etc. all to the same runway. Approach Control generally tells us to expect an ILS approach. (Denver is a notable exception) or we get a Descend Via clearance and then are cleared for a particular ILS approach to follow.Flt Ops/Training has encouraged us to request; fly; and report RNAV approaches when appropriate. Here's the hazard caught by my PF's [as a result of his SOP] CDU LEGS page review. On the SEAVU and RIIVR Arrivals to LAX; the transition from RIIVR to the ILS 24R & 24L approach is different than to the RNAV approaches (JAXEV or JINAN transition). From SEAVU; the transition to the ILS 24L and RNAV Y 24L are the same; but the RNAV Z 24L goes to a different point (PFILA). Same for 24R; the ILS and RNAV Y transition to a different point than the RNAV Z (SKOLL).On the south side of the airport; the same discrepancy exists. The RIIVR transition feeds directly into the same point for all approaches to 25L. The SEAVU transition is unique only for the RNAV Z (KRAIN). For 25R; the RIIVR transition is different between approaches but the SEAVU is the same. I'm sure someone more visually inclined could chart out an informative diagram of the similarities and differences between each approach and transition for these two arrivals into LAX. Sometimes ILS and RNAV transitions are the same. Sometimes; they are different. A system was designed that creates distinct single points of failure among a host of arrival and approach choices that otherwise are almost entirely similar. My Jepp FD-Pro has 17 arrivals and 19 approaches listed for LAX.The difference between the RIIVR transition to the ILS and RNAV Z 24R can't be significant. My geometry is rusty; but the sum of the dogleg entry segment lengths (5.5+3.8) is the same as the direct leg (9.3). The different entry creates opportunities for (insignificant) navigational errors. I presume there are similar disparities at other airfields.
A B737-700 Captain reported his concern about his training departments suggestion that; for familiarization; flight crews request and fly RNAV approaches when appropriate when ATC is advertising and assigning other approaches (ILS's for example) to runways that have both options. He points out that transitions from STARs are not always identical; citing LAX RIIVR and SEAVU as examples.