with PBN routing is that an effort was made to improve aircraft energy management while
flying PBN routes. On the older conventional STARs, terminus altitudes on the downwind were
often higher but created unstable approaches with high energy if ATC turned the aircraft early
on VMC days (and it's simply a fact we have more VMC days than IMC at most locations). On
the newer PBN procedures, industry asked to use existing ground tracks on VMC days to figure
a STAR terminus altitude that would remove the high energy, unstable approach problems we
saw with the conventional procedures. Let's look at a practical example of this problem, then
look at some potential solutions:
KIAH in East configuration using the SKNRD RNAV Arrival with the ILS RWY 08R. Using the north
downwind, the SKNRD RNAV Arrival ends at CASST at 6,000 feet.
When the pilot goes to load the ILS RWY 08R, the only relevant options from CASST is to load
the FMC from EELPO (no transition) or LASSY transition. Most pilots would know they will likely
not get turned in by EELPO and therefore would want to load the LASSY transition to be
prepared to be turned onto final further out. The only problem is that the LASSY transition
starts at 7,000 feet which is higher than the STAR terminus of 6,000 feet. In this case, the pilot
will not be able to EXEC this routing into the FMC without some modification. Since most
operators train pilots not to modify approach attributes in the FMC, and we of course cannot
modify the bottom altitude of the STAR, this leaves little options for the pilots to work with.
