Narrative:

The san diego airport's venerable baret 4 arrival STAR has been around for many yrs. I've flown this arrival many times in several non-glass and glass transport category aircraft. There are 2 issues with this arrival that need to be addressed: 1) incompatibility with the airbus FMGC vertical navigation system, and 2) unpredictable and random socal approach controller modifications to crossing altitudes specified on the STAR. The airbus FMGC (A319, 320, 321) is incapable of computing a vertical descent profile that correctly reflects the published crossing restr 'expect to cross 25 NM northeast of pgy VOR at 12000 ft.' although the lateral (LNAV) track is correctly stored in the airbus FMGC, the above vertical crossing restr is not a defined latitude/longitude waypoint, as '25 NM northeast of pgy VOR' falls somewhere on the 190 degree heading leg of the arrival from the northeast, and that heading leg ground track will move around due to descent winds. The airbus computer creates a 'conditional' waypoint at the intersection of the 190 degree heading leg with the pgy inbound radial. Any attempt to insert a 'place-bearing-distance' waypoint upstream of this intersection that reflects a position 25 NM northeast of the pgy VOR causes the FMGC to link directly to baret, instead of intercepting the pgy 043 degree radial as published. Unlike the boeing FMS (smith industries) and collins-equipped cpr aircraft, the airbus FMGC (honeywell) does not have a 'fix page' capability, wherein a defined distance from a NAVAID like pgy can be superimposed on the existing route, which then allows a vertical crossing restr to be inserted into the flight plan. The pillo crossing restr from the imperial VOR is a defined latitude/longitude waypoint, and the airbus FMGC can be programmed for this crossing restr without any difficulties. The solution here would be to change the northeast transition routing between karro and baret to a defined ground track (not a heading leg) and to create a fixed latitude/longitude waypoint (similar to pillo) that reflects the desired crossing altitude. The second problem with this STAR is the inconsistency of the actual crossing restr as stated by the socal controller on duty. Although the STAR clearly states, 'expect to cross 25 NM northeast of the pgy VOR at 12000 ft MSL,' I have most likely never received that exact clearance in yrs! What typically happens is the socal approach controller issues the following: 'cleared direct to baret, cross 10/12/15 (take your choice, every controller does it differently) NM northeast of baret at 12000 ft.' doing the math, you can see that the controller issued 10/12/15 NM crossing restrs are actually 28/30/33 NM from the pgy VOR, far more restrictive than the expected published crossing altitude. Since we have commenced our descent from cruise altitude based on the 25 NM crossing restr, we are now 'high and fast' and must use a fuel inefficient speed brake assisted descent profile to make the new crossing restr. The solution here is the same as the proposed solution above. Have the controllers decide on a common restr, tie it to a fixed latitude/longitude waypoint, and stick with it. In summary, the first problem stated herein is unique to the airbus FMGC system. The lack of an 'along-track displacement' waypoint capability is a known and much-lamented deficiency of the honeywell FMC system. The second problem affects all aircraft using the baret 4 arrival STAR from the tnp, eed, and pke vors.

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Original NASA ASRS Text

Title: AN A320 CHK AIRMAN'S RPT ON THE INCOMPATIBILITY OF THE ACFT'S FMS-FMGC TO COMPUTE A VERT DSCNT PROFILE BASED UPON THE RESTRS CITED FOR THE ALT XING RESTR WITHIN THE BARET 4 STAR, 25 NE OF PGY, CA.

Narrative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

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.