Narrative:

We were flying the pebble 2 departure out of san diego. The captain was flying and I was the PNF. ZLA gave us a climb clearance to FL190. The captain was flying a 305 degree heading to intercept the mission bay 293 degree radial as depicted on the departure. We were advised of traffic at our 1 O'clock position at an altitude, if my memory serves me right, of FL210. I acknowledged the traffic in sight. As the traffic passed from our right to our left, center gave us a heading clearance of 310 degrees. I read back to the center heading 310 degrees. A few seconds later, I glanced at my HSI and noticed that the captain was still flying a heading of 305 degrees. I reminded him that we were assigned a 310 degree heading. He then pointed to the altitude alerter stating that we were cleared to FL310. The captain had selected FL310 in the altitude alerter and began a climb. I then noticed we were leaving FL193 and again I reminded him that we were assigned a 310 degree heading. He then pointed to the altitude alerter stating that we were cleared to FL310. The captain had selected FL310 in the altitude alerter and began a climb. I then noticed we were leaving FL193 and again I reminded him that we were assigned a heading of 310 degrees. He then told me to verify our clearance with center while he continued to climb. The frequency was busy and before I could call center, he called us and asked for our altitude. I then asked center if we were cleared to FL310. He said negative. I then told center we were descending back down to FL190. Our altitude now was approximately FL197. About that time we received a TCASII RA advising us to monitor our vertical speed which was associated with the previous acknowledged traffic that was now behind us and to our left and moving away. The captain began a descent back down to FL190. Before we reached FL190, center cleared us to FL210. I acknowledged FL210. Seconds later, center again cleared us to FL190. After we reached FL190, I called center to verify our clearance of heading 310 degrees and FL190. He acknowledged affirmative. A few mins later we were cleared to our cruise altitude and continued to sjc without further incident. I can easily see how the captain mistook the heading clearance for an altitude clearance since the number '310' can be either a heading or an altitude. However, SOP was not followed when the captain selected FL310 in the altitude alerter, thereby taking me out of the loop for an altitude clearance verification. As we all know, the PNF selects the new altitude and the PF acknowledges the altitude. I also could have helped in avoiding this incident if I would have glanced at the MCP to verify the heading change instead of just my HSI, the error may have been caught sooner. I also believe that when there is a question between the 2 pilots as to their clearance, the aircraft should remain on or immediately be corrected back to the original clearance, until a clarification can be made. Supplemental information from acn 536714: I thought I heard we were cleared to FL310 and set FL310 in the altitude window. The departure controller had given us a heading change of 20 degrees to 310 degrees. The first officer read it back to him as a heading change and I as the captain and flying the aircraft thought he gave us an altitude change to FL310. The TCASII never went off and I can only assume the other aircraft in question was the one that passed overhead and was heading away from us on our left.

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Original NASA ASRS Text

Title: A B737-500 FLC LEAVE THEIR ASSIGNED ALT WHEN THE PIC BELIEVES THAT THE HDG ASSIGNMENT RECEIVED WAS AN ALT CHANGE WHILE ON FREQ WITH ZLA, CA.

Narrative: WE WERE FLYING THE PEBBLE 2 DEP OUT OF SAN DIEGO. THE CAPT WAS FLYING AND I WAS THE PNF. ZLA GAVE US A CLB CLRNC TO FL190. THE CAPT WAS FLYING A 305 DEG HDG TO INTERCEPT THE MISSION BAY 293 DEG RADIAL AS DEPICTED ON THE DEP. WE WERE ADVISED OF TFC AT OUR 1 O'CLOCK POS AT AN ALT, IF MY MEMORY SERVES ME RIGHT, OF FL210. I ACKNOWLEDGED THE TFC IN SIGHT. AS THE TFC PASSED FROM OUR R TO OUR L, CTR GAVE US A HDG CLRNC OF 310 DEGS. I READ BACK TO THE CTR HDG 310 DEGS. A FEW SECONDS LATER, I GLANCED AT MY HSI AND NOTICED THAT THE CAPT WAS STILL FLYING A HDG OF 305 DEGS. I REMINDED HIM THAT WE WERE ASSIGNED A 310 DEG HDG. HE THEN POINTED TO THE ALT ALERTER STATING THAT WE WERE CLRED TO FL310. THE CAPT HAD SELECTED FL310 IN THE ALT ALERTER AND BEGAN A CLB. I THEN NOTICED WE WERE LEAVING FL193 AND AGAIN I REMINDED HIM THAT WE WERE ASSIGNED A 310 DEG HDG. HE THEN POINTED TO THE ALT ALERTER STATING THAT WE WERE CLRED TO FL310. THE CAPT HAD SELECTED FL310 IN THE ALT ALERTER AND BEGAN A CLB. I THEN NOTICED WE WERE LEAVING FL193 AND AGAIN I REMINDED HIM THAT WE WERE ASSIGNED A HDG OF 310 DEGS. HE THEN TOLD ME TO VERIFY OUR CLRNC WITH CTR WHILE HE CONTINUED TO CLB. THE FREQ WAS BUSY AND BEFORE I COULD CALL CTR, HE CALLED US AND ASKED FOR OUR ALT. I THEN ASKED CTR IF WE WERE CLRED TO FL310. HE SAID NEGATIVE. I THEN TOLD CTR WE WERE DSNDING BACK DOWN TO FL190. OUR ALT NOW WAS APPROX FL197. ABOUT THAT TIME WE RECEIVED A TCASII RA ADVISING US TO MONITOR OUR VERT SPD WHICH WAS ASSOCIATED WITH THE PREVIOUS ACKNOWLEDGED TFC THAT WAS NOW BEHIND US AND TO OUR L AND MOVING AWAY. THE CAPT BEGAN A DSCNT BACK DOWN TO FL190. BEFORE WE REACHED FL190, CTR CLRED US TO FL210. I ACKNOWLEDGED FL210. SECONDS LATER, CTR AGAIN CLRED US TO FL190. AFTER WE REACHED FL190, I CALLED CTR TO VERIFY OUR CLRNC OF HDG 310 DEGS AND FL190. HE ACKNOWLEDGED AFFIRMATIVE. A FEW MINS LATER WE WERE CLRED TO OUR CRUISE ALT AND CONTINUED TO SJC WITHOUT FURTHER INCIDENT. I CAN EASILY SEE HOW THE CAPT MISTOOK THE HDG CLRNC FOR AN ALT CLRNC SINCE THE NUMBER '310' CAN BE EITHER A HDG OR AN ALT. HOWEVER, SOP WAS NOT FOLLOWED WHEN THE CAPT SELECTED FL310 IN THE ALT ALERTER, THEREBY TAKING ME OUT OF THE LOOP FOR AN ALT CLRNC VERIFICATION. AS WE ALL KNOW, THE PNF SELECTS THE NEW ALT AND THE PF ACKNOWLEDGES THE ALT. I ALSO COULD HAVE HELPED IN AVOIDING THIS INCIDENT IF I WOULD HAVE GLANCED AT THE MCP TO VERIFY THE HDG CHANGE INSTEAD OF JUST MY HSI, THE ERROR MAY HAVE BEEN CAUGHT SOONER. I ALSO BELIEVE THAT WHEN THERE IS A QUESTION BTWN THE 2 PLTS AS TO THEIR CLRNC, THE ACFT SHOULD REMAIN ON OR IMMEDIATELY BE CORRECTED BACK TO THE ORIGINAL CLRNC, UNTIL A CLARIFICATION CAN BE MADE. SUPPLEMENTAL INFO FROM ACN 536714: I THOUGHT I HEARD WE WERE CLRED TO FL310 AND SET FL310 IN THE ALT WINDOW. THE DEP CTLR HAD GIVEN US A HDG CHANGE OF 20 DEGS TO 310 DEGS. THE FO READ IT BACK TO HIM AS A HDG CHANGE AND I AS THE CAPT AND FLYING THE ACFT THOUGHT HE GAVE US AN ALT CHANGE TO FL310. THE TCASII NEVER WENT OFF AND I CAN ONLY ASSUME THE OTHER ACFT IN QUESTION WAS THE ONE THAT PASSED OVERHEAD AND WAS HDG AWAY FROM US ON OUR L.

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.