Narrative:

We were in turbulence at FL280 and asked for FL310. ZAB told us to climb to FL290 and to expect FL310 after buckeye. I was looking out the left window as we crossed bxk VOR. The first officer, without saying anything, selected FL310 and started a slow vertical speed climb. My first indication that we were in a climb was when he reset the altitude in the pressure controller. I felt the cabin pressure starting to climb, looked at the rate indicator and saw at 600 FPM climb as the controller tried to catch up. I then saw FL310 set in the pressure controller, looked to the MCP and saw FL310 selected and the autoplt set for a vertical speed climb. I said to the first officer 'I must have been out to lunch because I did not hear you talk to center about climbing to FL310.' he replied, 'I didn't, they told us we could climb after bxk.' I said 'no! We were told to expect the climb. Stop the climb! Stop the climb! Get back down to FL290!' he managed to stop the climb at FL298. As we started back down, the TCASII gave us a TA for an aircraft above us approximately 1200 ft and almost at the same time ZAB asked us to confirm our altitude. I told him that we had a little problem and that we were releveling at FL290. A few mins later, he gave me a phone number to call. The watch supervisor said that he would be sending a follow-up report to the FAA. The snitch horn had gone off. Our company has very solid, definite procedures on how to make and confirm altitude changes. None of them are done silently! Supplemental information from acn 488150: I understand ATC to clear us, prior to bxk VOR, to climb from our cruise altitude of FL280 to FL290 and at bxk VOR cleared to FL310. We complied with this clearance and upon reaching FL299, simultaneously received an aural 'traffic, traffic' from TCASII with a call from ATC requesting our altitude. I immediately descended back to FL290 while clarifying with ATC, what the clearance was supposed to be. The clearance was to FL290 and expect FL310 at bxk VOR.

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Original NASA ASRS Text

Title: ALT EXCURSION NEAR PHX, AZ.

Narrative: WE WERE IN TURB AT FL280 AND ASKED FOR FL310. ZAB TOLD US TO CLB TO FL290 AND TO EXPECT FL310 AFTER BUCKEYE. I WAS LOOKING OUT THE L WINDOW AS WE CROSSED BXK VOR. THE FO, WITHOUT SAYING ANYTHING, SELECTED FL310 AND STARTED A SLOW VERT SPD CLB. MY FIRST INDICATION THAT WE WERE IN A CLB WAS WHEN HE RESET THE ALT IN THE PRESSURE CONTROLLER. I FELT THE CABIN PRESSURE STARTING TO CLB, LOOKED AT THE RATE INDICATOR AND SAW AT 600 FPM CLB AS THE CTLR TRIED TO CATCH UP. I THEN SAW FL310 SET IN THE PRESSURE CONTROLLER, LOOKED TO THE MCP AND SAW FL310 SELECTED AND THE AUTOPLT SET FOR A VERT SPD CLB. I SAID TO THE FO 'I MUST HAVE BEEN OUT TO LUNCH BECAUSE I DID NOT HEAR YOU TALK TO CTR ABOUT CLBING TO FL310.' HE REPLIED, 'I DIDN'T, THEY TOLD US WE COULD CLB AFTER BXK.' I SAID 'NO! WE WERE TOLD TO EXPECT THE CLB. STOP THE CLB! STOP THE CLB! GET BACK DOWN TO FL290!' HE MANAGED TO STOP THE CLB AT FL298. AS WE STARTED BACK DOWN, THE TCASII GAVE US A TA FOR AN ACFT ABOVE US APPROX 1200 FT AND ALMOST AT THE SAME TIME ZAB ASKED US TO CONFIRM OUR ALT. I TOLD HIM THAT WE HAD A LITTLE PROB AND THAT WE WERE RELEVELING AT FL290. A FEW MINS LATER, HE GAVE ME A PHONE NUMBER TO CALL. THE WATCH SUPVR SAID THAT HE WOULD BE SENDING A FOLLOW-UP RPT TO THE FAA. THE SNITCH HORN HAD GONE OFF. OUR COMPANY HAS VERY SOLID, DEFINITE PROCS ON HOW TO MAKE AND CONFIRM ALT CHANGES. NONE OF THEM ARE DONE SILENTLY! SUPPLEMENTAL INFO FROM ACN 488150: I UNDERSTAND ATC TO CLR US, PRIOR TO BXK VOR, TO CLB FROM OUR CRUISE ALT OF FL280 TO FL290 AND AT BXK VOR CLRED TO FL310. WE COMPLIED WITH THIS CLRNC AND UPON REACHING FL299, SIMULTANEOUSLY RECEIVED AN AURAL 'TFC, TFC' FROM TCASII WITH A CALL FROM ATC REQUESTING OUR ALT. I IMMEDIATELY DSNDED BACK TO FL290 WHILE CLARIFYING WITH ATC, WHAT THE CLRNC WAS SUPPOSED TO BE. THE CLRNC WAS TO FL290 AND EXPECT FL310 AT BXK VOR.

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.