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Reported loss of separation when flight crew of air carrier B737 miscopies descent altitude and conflicts with unknown traffic at 11000 ft.
| Attributes | |
| ACN | 393200 |
| Time | |
| Date | 199802 |
| Day | Fri |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : bsr |
| State Reference | CA |
| Altitude | msl bound lower : 11800 msl bound upper : 13000 |
| Environment | |
| Flight Conditions | IMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zoa |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other |
| Flight Phase | cruise other descent other |
| Route In Use | arrival other arrival star : star enroute : on vectors enroute airway : zoa |
| Flight Plan | IFR |
| Aircraft 2 | |
| Make Model Name | Any Unknown or Unlisted Aircraft Manufacturer |
| Operating Under FAR Part | other : unknown |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : commercial pilot : cfi pilot : flight engineer pilot : instrument pilot : atp |
| Experience | flight time last 90 days : 219 flight time total : 21712 flight time type : 18400 |
| ASRS Report | 393200 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : instrument pilot : atp pilot : commercial |
| Experience | flight time last 90 days : 210 flight time total : 7900 flight time type : 3200 |
| ASRS Report | 393322 |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance non adherence : far non adherence : required legal separation other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified other controllera |
| Resolutory Action | controller : issued new clearance other |
| Consequence | faa : reviewed incident with flight crew |
| Miss Distance | vertical : 800 |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
As we descended on the STAR north of bsr we were given a vector by ZOA to a heading of 260 degrees and descent clearance to 13000 ft. After several mins on the 260 degree heading we were given a rapid series of clrncs: 'direct eugen, hadly 2 arrival, cross eugen one-one-thousand and 250 KTS.' the first officer and I confirmed between ourselves that the fix was eugen and the altitude was 11000 ft and I read back 'direct eugen, hadly arrival 11000 ft.' hearing no objection from ATC I set 11000 ft in the mode control panel altitude window. The published crossing restr on the hadly 2 STAR is to expect eugen at 11000 ft and 250 KTS. As we approached eugen we were both intent on accomplishing the difficult intercept and crossing restr. At this time we received a TCASII alert of traffic below us. As we descended out of 12000 ft we were told by ATC to 'maintain present altitude.' the first instructions we had heard from ATC since the clearance direct eugen. After that we were cleared for the hadly 2 arrival, 12000 ft and turned over to bay approach. Bay approach requested that we call ZOA after landing. When we called we were told that ZOA had had a 'loss of separation' and that they showed that we had only been cleared to 13000 ft on the STAR at that time. Up until the time of the TCASII alert, both the first officer and I believed that we were complying with ATC instructions to cross eugen at 11000 ft. We thought that we heard and read back eugen at 11000 ft. The ATC method of using 'one-one' and 'one-three' phraseology rather than the more clearly differentiated 'eleven' and 'thirteen' may have been a problem with a fix at which the expected crossing restr is 11000 ft. Callback conversation with reporter revealed the following information: reporter indicated that in the call to the center supervisor, he heard a portion of the tape where the controller issued the descent clearance to 13000 ft and not 11000 ft as they thought they heard.
Original NASA ASRS Text
Title: RPTED LOSS OF SEPARATION WHEN FLC OF ACR B737 MISCOPIES DSCNT ALT AND CONFLICTS WITH UNKNOWN TFC AT 11000 FT.
Narrative: AS WE DSNDED ON THE STAR N OF BSR WE WERE GIVEN A VECTOR BY ZOA TO A HDG OF 260 DEGS AND DSCNT CLRNC TO 13000 FT. AFTER SEVERAL MINS ON THE 260 DEG HDG WE WERE GIVEN A RAPID SERIES OF CLRNCS: 'DIRECT EUGEN, HADLY 2 ARR, CROSS EUGEN ONE-ONE-THOUSAND AND 250 KTS.' THE FO AND I CONFIRMED BTWN OURSELVES THAT THE FIX WAS EUGEN AND THE ALT WAS 11000 FT AND I READ BACK 'DIRECT EUGEN, HADLY ARR 11000 FT.' HEARING NO OBJECTION FROM ATC I SET 11000 FT IN THE MODE CTL PANEL ALT WINDOW. THE PUBLISHED XING RESTR ON THE HADLY 2 STAR IS TO EXPECT EUGEN AT 11000 FT AND 250 KTS. AS WE APCHED EUGEN WE WERE BOTH INTENT ON ACCOMPLISHING THE DIFFICULT INTERCEPT AND XING RESTR. AT THIS TIME WE RECEIVED A TCASII ALERT OF TFC BELOW US. AS WE DSNDED OUT OF 12000 FT WE WERE TOLD BY ATC TO 'MAINTAIN PRESENT ALT.' THE FIRST INSTRUCTIONS WE HAD HEARD FROM ATC SINCE THE CLRNC DIRECT EUGEN. AFTER THAT WE WERE CLRED FOR THE HADLY 2 ARR, 12000 FT AND TURNED OVER TO BAY APCH. BAY APCH REQUESTED THAT WE CALL ZOA AFTER LNDG. WHEN WE CALLED WE WERE TOLD THAT ZOA HAD HAD A 'LOSS OF SEPARATION' AND THAT THEY SHOWED THAT WE HAD ONLY BEEN CLRED TO 13000 FT ON THE STAR AT THAT TIME. UP UNTIL THE TIME OF THE TCASII ALERT, BOTH THE FO AND I BELIEVED THAT WE WERE COMPLYING WITH ATC INSTRUCTIONS TO CROSS EUGEN AT 11000 FT. WE THOUGHT THAT WE HEARD AND READ BACK EUGEN AT 11000 FT. THE ATC METHOD OF USING 'ONE-ONE' AND 'ONE-THREE' PHRASEOLOGY RATHER THAN THE MORE CLEARLY DIFFERENTIATED 'ELEVEN' AND 'THIRTEEN' MAY HAVE BEEN A PROB WITH A FIX AT WHICH THE EXPECTED XING RESTR IS 11000 FT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR INDICATED THAT IN THE CALL TO THE CTR SUPVR, HE HEARD A PORTION OF THE TAPE WHERE THE CTLR ISSUED THE DSCNT CLRNC TO 13000 FT AND NOT 11000 FT AS THEY THOUGHT THEY HEARD.
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.