Narrative:

While cruising at FL370 sfo-lax, I was talking to the flight attendants on the interphone and was not actively monitoring the VHF frequency although I had it on at a lower volume. The captain was talking to ATC about some turbulence and I did overhear the mention of FL350 as I ended my communication with the flight attendant. At that time the captain selected 35000 ft in the altitude window. I confirmed that 35000 ft was set in the window in accordance with SOP, but since I was not actively monitoring ATC at that time (I was as soon as I ended my communications with the flight attendant) I advised ATC that we were leaving FL370 for FL350 and the controller rogered my communication. Leaving 36300 ft the controller instructed us to make an immediate 40 degree left turn and maintain FL370 due to traffic at FL350 (to whom he also gave a 40 degree turn). I acknowledged and advised him that we were climbing to FL370. When the controller instructed us to make a 40 degree left turn, the captain disengaged the autoplt and rolled into a 45 degree angle of bank and attempted to start a climb which resulted in moderate buffet (accelerated stall). I stated loudly 'don't stall' and he released the back pressure and we recovered. We rolled out on the assigned heading and climbed to FL370. I don't now if we were even cleared to FL350 and when I later stated to the controller that I advised him we were leaving FL370 for FL350, he said he was working 2 frequencys. The remainder of the flight was uneventful. Comments: the captain overreacted. A 45 degree bank at 36000 ft was excessive. Don't create an emergency to avoid a potential emergency. When in doubt, ask for a confirmation of clearance. To endanger the aircraft to avoid breaking the 5 mi bubble was unwise (at no time did we receive a TA or RA on the TCASII).

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION FROM ASSIGNED. TEMPORARY LOSS OF ACFT CTL DURING RADAR VECTORING AND ATTEMPT TO CLB BACK TO ALT.

Narrative: WHILE CRUISING AT FL370 SFO-LAX, I WAS TALKING TO THE FLT ATTENDANTS ON THE INTERPHONE AND WAS NOT ACTIVELY MONITORING THE VHF FREQ ALTHOUGH I HAD IT ON AT A LOWER VOLUME. THE CAPT WAS TALKING TO ATC ABOUT SOME TURB AND I DID OVERHEAR THE MENTION OF FL350 AS I ENDED MY COM WITH THE FLT ATTENDANT. AT THAT TIME THE CAPT SELECTED 35000 FT IN THE ALT WINDOW. I CONFIRMED THAT 35000 FT WAS SET IN THE WINDOW IN ACCORDANCE WITH SOP, BUT SINCE I WAS NOT ACTIVELY MONITORING ATC AT THAT TIME (I WAS AS SOON AS I ENDED MY COMS WITH THE FLT ATTENDANT) I ADVISED ATC THAT WE WERE LEAVING FL370 FOR FL350 AND THE CTLR ROGERED MY COM. LEAVING 36300 FT THE CTLR INSTRUCTED US TO MAKE AN IMMEDIATE 40 DEG L TURN AND MAINTAIN FL370 DUE TO TFC AT FL350 (TO WHOM HE ALSO GAVE A 40 DEG TURN). I ACKNOWLEDGED AND ADVISED HIM THAT WE WERE CLBING TO FL370. WHEN THE CTLR INSTRUCTED US TO MAKE A 40 DEG L TURN, THE CAPT DISENGAGED THE AUTOPLT AND ROLLED INTO A 45 DEG ANGLE OF BANK AND ATTEMPTED TO START A CLB WHICH RESULTED IN MODERATE BUFFET (ACCELERATED STALL). I STATED LOUDLY 'DON'T STALL' AND HE RELEASED THE BACK PRESSURE AND WE RECOVERED. WE ROLLED OUT ON THE ASSIGNED HDG AND CLBED TO FL370. I DON'T NOW IF WE WERE EVEN CLRED TO FL350 AND WHEN I LATER STATED TO THE CTLR THAT I ADVISED HIM WE WERE LEAVING FL370 FOR FL350, HE SAID HE WAS WORKING 2 FREQS. THE REMAINDER OF THE FLT WAS UNEVENTFUL. COMMENTS: THE CAPT OVERREACTED. A 45 DEG BANK AT 36000 FT WAS EXCESSIVE. DON'T CREATE AN EMER TO AVOID A POTENTIAL EMER. WHEN IN DOUBT, ASK FOR A CONFIRMATION OF CLRNC. TO ENDANGER THE ACFT TO AVOID BREAKING THE 5 MI BUBBLE WAS UNWISE (AT NO TIME DID WE RECEIVE A TA OR RA ON THE TCASII).

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.