Narrative:

Air carrier X misunderstood clearance. Mso cleared us to 11000' at the mso VOR to maintain FL210. All the charts refer to crossing the VOR at/or above MEA to 11000' for V187 due to high terrain in the area. Took off of runway 29 went outbnd on the 291 degree right till 9600' or 16 NM as recommended. Started left turn direct to mso VOR. While climbing through 12500' mso approach asked us to cross 8 northeast on V187 at 11000'. I responded that it would be no problem, we were already above 11000'. The controller stated that we were to maintain 11000' till the mso and now to maintain 11000' till 8 northeast of mso VOR on V187. Both the first officer and myself were surprised because of the charts and terrain implied that it was an at/or above clearance. I explained that both pilot had understood the clearance to mean to cross mso VOR at/or above 11000' for terrain. I suggested the clearance be more obvious and due to terrain considerations and charting that it was easy to be misunderstood. I recommend a phrase like, 'maintain 11000' till reaching mso VOR then cleared to climb and maintain 11000' till reaching mso VOR, then climb and maintain FL210.' in any case it was probably our mistake however, and an easy trap to fall into. We descended immediately to 11000'. Supplemental information from acn 155642: controller stated that the clearance was read back to clearance delivery appropriately, indicating we had not had a communication problem. I believe the depicted procedures on the company departure plate influenced our interpretation of the clearance to be one of a minimum rather than a hard altitude. The controller stated at some point that this was a new procedure, though how new not mentioned. This was my first trip into mso and so my first departure so the supposed change of procedure was irrelevant to me.

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Original NASA ASRS Text

Title: ACR X FLT CREW FAILED TO COMPLY WITH ATC CLRNC. PLT DEVIATION.

Narrative: ACR X MISUNDERSTOOD CLRNC. MSO CLRED US TO 11000' AT THE MSO VOR TO MAINTAIN FL210. ALL THE CHARTS REFER TO XING THE VOR AT/OR ABOVE MEA TO 11000' FOR V187 DUE TO HIGH TERRAIN IN THE AREA. TOOK OFF OF RWY 29 WENT OUTBND ON THE 291 DEG R TILL 9600' OR 16 NM AS RECOMMENDED. STARTED LEFT TURN DIRECT TO MSO VOR. WHILE CLBING THROUGH 12500' MSO APCH ASKED US TO CROSS 8 NE ON V187 AT 11000'. I RESPONDED THAT IT WOULD BE NO PROB, WE WERE ALREADY ABOVE 11000'. THE CTLR STATED THAT WE WERE TO MAINTAIN 11000' TILL THE MSO AND NOW TO MAINTAIN 11000' TILL 8 NE OF MSO VOR ON V187. BOTH THE F/O AND MYSELF WERE SURPRISED BECAUSE OF THE CHARTS AND TERRAIN IMPLIED THAT IT WAS AN AT/OR ABOVE CLRNC. I EXPLAINED THAT BOTH PLT HAD UNDERSTOOD THE CLRNC TO MEAN TO CROSS MSO VOR AT/OR ABOVE 11000' FOR TERRAIN. I SUGGESTED THE CLRNC BE MORE OBVIOUS AND DUE TO TERRAIN CONSIDERATIONS AND CHARTING THAT IT WAS EASY TO BE MISUNDERSTOOD. I RECOMMEND A PHRASE LIKE, 'MAINTAIN 11000' TILL REACHING MSO VOR THEN CLRED TO CLB AND MAINTAIN 11000' TILL REACHING MSO VOR, THEN CLB AND MAINTAIN FL210.' IN ANY CASE IT WAS PROBABLY OUR MISTAKE HOWEVER, AND AN EASY TRAP TO FALL INTO. WE DSNDED IMMEDIATELY TO 11000'. SUPPLEMENTAL INFO FROM ACN 155642: CTLR STATED THAT THE CLRNC WAS READ BACK TO CLRNC DELIVERY APPROPRIATELY, INDICATING WE HAD NOT HAD A COM PROB. I BELIEVE THE DEPICTED PROCS ON THE COMPANY DEP PLATE INFLUENCED OUR INTERP OF THE CLRNC TO BE ONE OF A MINIMUM RATHER THAN A HARD ALT. THE CTLR STATED AT SOME POINT THAT THIS WAS A NEW PROC, THOUGH HOW NEW NOT MENTIONED. THIS WAS MY FIRST TRIP INTO MSO AND SO MY FIRST DEP SO THE SUPPOSED CHANGE OF PROC WAS IRRELEVANT TO ME.

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.