Narrative:

Phx-bur approximately 20 mi east of hec level FL310. ZLA issued a descent clearance which we read back, 'descend to cross hec at or below FL280, pilot discretion down to FL240.' (we descended to and crossed hec at 280 planning to continue lower to meet STAR restrictions.) we switched to another ZLA frequency and reported on '...at FL280 pilots discretion to 240.' center then acknowledged our report. Later (still level 280) lax questioned our altitude and said '...descend to 270.' we complied and asked if the pilots discretion to 240 still applied, or was requested? He asked what our previous clearance was and we repeated the original 'cross hec at or below 280 pilots discretion to 240.' after a few mins ATC asked us to call ZLA after arrival at bur and that a possible pilot deviation had occurred. We called and talked with the area supervisor and he advised us that the clearance was 'descend to cross hec at or below 280 descend and maintain FL240.' he also said we had read back 'descend to cross hec at or below 280 down to FL240.' I replied that we read back pilots discretion, were following that clearance and when reporting on the new frequency again said pilots discretion to 240, which was accepted. He replied we had in fact reported pilots discretion to 240 on the new frequency and agreed it wasn't challenged, accepted at first, but that there wasn't any way for the controller to verify our pilots discretion clrncs as opposed to a descend to and maintain clearance. He also said that he would have to turn the matter over to the quality assurance department. After discussing the matter with our company ATC liaison (who has been in contact with lax), he informed us nothing would be filed or was disputed because we had in fact reported on the new frequency with pilots discretion to 240 and it had been accepted. He also suggested we file this NASA report. Miscom in a very busy area with several altitude changes caused confusion. We plan for the normal expected crossing restrictions on the arrival (STAR). But they are often preempted by other descent clrncs making it difficult to plan a normal descent or input into a flight management computer. Recommendations: 1) issue and use a STAR with a profile descent or at least don't issue last min extra intermediate altitude crossing restrictions on the published STAR. 2) have ATC mark their strips and radar screens denoting 'pilot's discretion' clrncs as well as 'descend to' clrncs on all handoffs (which I thought they did) to avoid confusion. 3) when a pilot's discretion clearance is issued require 'pilot's discretion' be read back not 'pd' to ensure understanding of the clearance.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR MLG ALTDEV UNDERSHOT. FLC FAILED TO CONTINUE DSCNT THINKING THEY HAD 'DISCRETION' ABOUT WHEN TO START DOWN.

Narrative: PHX-BUR APPROX 20 MI E OF HEC LEVEL FL310. ZLA ISSUED A DSCNT CLRNC WHICH WE READ BACK, 'DSND TO CROSS HEC AT OR BELOW FL280, PLT DISCRETION DOWN TO FL240.' (WE DSNDED TO AND CROSSED HEC AT 280 PLANNING TO CONTINUE LOWER TO MEET STAR RESTRICTIONS.) WE SWITCHED TO ANOTHER ZLA FREQ AND RPTED ON '...AT FL280 PLTS DISCRETION TO 240.' CENTER THEN ACKNOWLEDGED OUR RPT. LATER (STILL LEVEL 280) LAX QUESTIONED OUR ALT AND SAID '...DSND TO 270.' WE COMPLIED AND ASKED IF THE PLTS DISCRETION TO 240 STILL APPLIED, OR WAS REQUESTED? HE ASKED WHAT OUR PREVIOUS CLRNC WAS AND WE REPEATED THE ORIGINAL 'CROSS HEC AT OR BELOW 280 PLTS DISCRETION TO 240.' AFTER A FEW MINS ATC ASKED US TO CALL ZLA AFTER ARR AT BUR AND THAT A POSSIBLE PLTDEV HAD OCCURRED. WE CALLED AND TALKED WITH THE AREA SUPVR AND HE ADVISED US THAT THE CLRNC WAS 'DSND TO CROSS HEC AT OR BELOW 280 DSND AND MAINTAIN FL240.' HE ALSO SAID WE HAD READ BACK 'DSND TO CROSS HEC AT OR BELOW 280 DOWN TO FL240.' I REPLIED THAT WE READ BACK PLTS DISCRETION, WERE FOLLOWING THAT CLRNC AND WHEN RPTING ON THE NEW FREQ AGAIN SAID PLTS DISCRETION TO 240, WHICH WAS ACCEPTED. HE REPLIED WE HAD IN FACT RPTED PLTS DISCRETION TO 240 ON THE NEW FREQ AND AGREED IT WASN'T CHALLENGED, ACCEPTED AT FIRST, BUT THAT THERE WASN'T ANY WAY FOR THE CTLR TO VERIFY OUR PLTS DISCRETION CLRNCS AS OPPOSED TO A DSND TO AND MAINTAIN CLRNC. HE ALSO SAID THAT HE WOULD HAVE TO TURN THE MATTER OVER TO THE QUALITY ASSURANCE DEPT. AFTER DISCUSSING THE MATTER WITH OUR COMPANY ATC LIAISON (WHO HAS BEEN IN CONTACT WITH LAX), HE INFORMED US NOTHING WOULD BE FILED OR WAS DISPUTED BECAUSE WE HAD IN FACT RPTED ON THE NEW FREQ WITH PLTS DISCRETION TO 240 AND IT HAD BEEN ACCEPTED. HE ALSO SUGGESTED WE FILE THIS NASA RPT. MISCOM IN A VERY BUSY AREA WITH SEVERAL ALT CHANGES CAUSED CONFUSION. WE PLAN FOR THE NORMAL EXPECTED XING RESTRICTIONS ON THE ARR (STAR). BUT THEY ARE OFTEN PREEMPTED BY OTHER DSCNT CLRNCS MAKING IT DIFFICULT TO PLAN A NORMAL DSCNT OR INPUT INTO A FLT MGMNT COMPUTER. RECOMMENDATIONS: 1) ISSUE AND USE A STAR WITH A PROFILE DSCNT OR AT LEAST DON'T ISSUE LAST MIN EXTRA INTERMEDIATE ALT XING RESTRICTIONS ON THE PUBLISHED STAR. 2) HAVE ATC MARK THEIR STRIPS AND RADAR SCREENS DENOTING 'PLT'S DISCRETION' CLRNCS AS WELL AS 'DSND TO' CLRNCS ON ALL HDOFS (WHICH I THOUGHT THEY DID) TO AVOID CONFUSION. 3) WHEN A PLT'S DISCRETION CLRNC IS ISSUED REQUIRE 'PLT'S DISCRETION' BE READ BACK NOT 'PD' TO ENSURE UNDERSTANDING OF THE CLRNC.

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.