Narrative:

Confusion on part of crew to what altitude to descend to on the profile descent into toronto, canada. The captain and first officer reviewed their charts for several mins and were cautious in their descent. The first sign of irregularity was when toronto center asked what altitude we were flying. Our response was 10500', and we were asked to maintain 11000' (to our surprise). After further review of the commercial charts it shows the area we were in had a base of 11000'. Later we were told we were not the first aircraft to make that mistake. The profile descent runway 24L and 24R was the clearance. The commercial charts are very confusing the way it is depicted and is a major factor in this event. Supplemental information from acn 108441: aircraft had been cleared the brany 4 arrival, runway 24 profile descent. NOTAMS for yyz asked crews today close attention to the yyz arrival procedure. En route to yyz the crew separately studied the arrival and then discussed the arrival. Both pilots failed to realize their sector required an altitude of 11000' at 25 DME arc. Both pilots saw a 10000' sector altitude which was for the next sector. The crew was descending to 10000', passing 10500' when yyz center (128.27) told them to climb back to 11000'. The flight landed normally after landing and standing the profile descent for several mins, crew realized their mistake. If the sector lines had been drawn in a bolder darker line, or a special note warned of the differing sector altitudes, the crew may not have misread the chart. A phone conversation with yyz indicated a large number of altitude violations during the 4 days since a new chart had been issued by commercial chart. They further stated that the charts used by canadian pilots apparently was drawn in a different manner which made the procedure easier to understand. Supplemental information from acn 108453: had been cleared brany 4 arrival, runway 24L profile descent into yyz. NOTAMS have asked flight crews to pay close attention to the new page of the profile descent. Both pilots reviewed the page en route and discussed the procedure, but did not realize the sector line's depicting the altitude and airspeed blocks were for another sector. Crew was descending through 10500' for 10000' when yyz approach told the crew to climb back to 11000'. Flight landed normally. After further study of the chart crew realized the error. If the sector lines were darker print or a special note that 10000' was for turbo propellers. The crew may not have misread the chart. Yyz center said numerous aircraft had made the same mistake since the arrival was changed.

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Original NASA ASRS Text

Title: LGT DESCENDED BELOW PROFILE DESCENT ALT DUE TO FLT CREW MISINTERP.

Narrative: CONFUSION ON PART OF CREW TO WHAT ALT TO DSND TO ON THE PROFILE DSCNT INTO TORONTO, CANADA. THE CAPT AND F/O REVIEWED THEIR CHARTS FOR SEVERAL MINS AND WERE CAUTIOUS IN THEIR DSCNT. THE FIRST SIGN OF IRREGULARITY WAS WHEN TORONTO CENTER ASKED WHAT ALT WE WERE FLYING. OUR RESPONSE WAS 10500', AND WE WERE ASKED TO MAINTAIN 11000' (TO OUR SURPRISE). AFTER FURTHER REVIEW OF THE COMMERCIAL CHARTS IT SHOWS THE AREA WE WERE IN HAD A BASE OF 11000'. LATER WE WERE TOLD WE WERE NOT THE FIRST ACFT TO MAKE THAT MISTAKE. THE PROFILE DSCNT RWY 24L AND 24R WAS THE CLRNC. THE COMMERCIAL CHARTS ARE VERY CONFUSING THE WAY IT IS DEPICTED AND IS A MAJOR FACTOR IN THIS EVENT. SUPPLEMENTAL INFO FROM ACN 108441: ACFT HAD BEEN CLRED THE BRANY 4 ARR, RWY 24 PROFILE DSCNT. NOTAMS FOR YYZ ASKED CREWS TODAY CLOSE ATTN TO THE YYZ ARR PROC. ENRTE TO YYZ THE CREW SEPARATELY STUDIED THE ARR AND THEN DISCUSSED THE ARR. BOTH PLTS FAILED TO REALIZE THEIR SECTOR REQUIRED AN ALT OF 11000' AT 25 DME ARC. BOTH PLTS SAW A 10000' SECTOR ALT WHICH WAS FOR THE NEXT SECTOR. THE CREW WAS DSNDING TO 10000', PASSING 10500' WHEN YYZ CENTER (128.27) TOLD THEM TO CLB BACK TO 11000'. THE FLT LANDED NORMALLY AFTER LNDG AND STANDING THE PROFILE DSCNT FOR SEVERAL MINS, CREW REALIZED THEIR MISTAKE. IF THE SECTOR LINES HAD BEEN DRAWN IN A BOLDER DARKER LINE, OR A SPECIAL NOTE WARNED OF THE DIFFERING SECTOR ALTS, THE CREW MAY NOT HAVE MISREAD THE CHART. A PHONE CONVERSATION WITH YYZ INDICATED A LARGE NUMBER OF ALT VIOLATIONS DURING THE 4 DAYS SINCE A NEW CHART HAD BEEN ISSUED BY COMMERCIAL CHART. THEY FURTHER STATED THAT THE CHARTS USED BY CANADIAN PLTS APPARENTLY WAS DRAWN IN A DIFFERENT MANNER WHICH MADE THE PROC EASIER TO UNDERSTAND. SUPPLEMENTAL INFO FROM ACN 108453: HAD BEEN CLRED BRANY 4 ARR, RWY 24L PROFILE DSCNT INTO YYZ. NOTAMS HAVE ASKED FLT CREWS TO PAY CLOSE ATTN TO THE NEW PAGE OF THE PROFILE DSCNT. BOTH PLTS REVIEWED THE PAGE ENRTE AND DISCUSSED THE PROC, BUT DID NOT REALIZE THE SECTOR LINE'S DEPICTING THE ALT AND AIRSPD BLOCKS WERE FOR ANOTHER SECTOR. CREW WAS DSNDING THROUGH 10500' FOR 10000' WHEN YYZ APCH TOLD THE CREW TO CLB BACK TO 11000'. FLT LANDED NORMALLY. AFTER FURTHER STUDY OF THE CHART CREW REALIZED THE ERROR. IF THE SECTOR LINES WERE DARKER PRINT OR A SPECIAL NOTE THAT 10000' WAS FOR TURBO PROPS. THE CREW MAY NOT HAVE MISREAD THE CHART. YYZ CENTER SAID NUMEROUS ACFT HAD MADE THE SAME MISTAKE SINCE THE ARR WAS CHANGED.

Data retrieved from NASA's ASRS site as of August 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.