B757 FLC TALE OF AN ALT OVERSHOOT THAT WAS PROMOTED BY A FAILURE OF THEIR AUTOTHROTTLE SYS AND OTHER DISTRS. NEITHER PLT LIKES THE NOISE ABATEMENT PROC AT SNA.

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THE NOISE ABATEMENT TKOF FROM SNA IS DEMANDING WHEN EVERYTHING GOES RIGHT. WHEN SOMETHING MINOR GOES WRONG; THINGS GET BUSY REAL QUICK. AFTER TKOF WITH THE FMC AND AUTOTHROTTLES PROGRAMMED CORRECTLY; THE PWR DID NOT REDUCE WHEN VNAV WAS SELECTED AT 800 FT. THE CAPT FLEW THE PROFILE WHILE I ATTEMPTED TO GET THE PWR REDUCED. WE WERE HANDED OFF TO SOCAL DEP. THEY GAVE US A WESTERLY HDG AND A CLB TO 10000 FT. I WAS STILL WORKING WITH THE THRUST MGMNT COMPUTER AND THE MCP AS WE APCHED 10000 FT. WHEN I LOOKED UP; WE WERE AT 10300 FT AND CLBING. THE CAPT IMMEDIATELY DSNDED TO 10000 FT AS I CHKED ON ANOTHER FREQ. NO MENTION WAS MADE BY ATC AND WE WERE CLRED TO 16000 FT. OUR MAX ALTDEV WAS 500 FT. SNA IS BY FAR THE MOST DIFFICULT DEP IN OUR SYS. NOT BECAUSE THE PROC IS THAT DIFFICULT; BUT BECAUSE IT IS COMPLETELY DIFFERENT FROM ANYTHING ELSE IN OUR SYS. IT IS A MAJOR DEP FROM NORMAL SOPS THAT CAUSES DISTRS NOT ONLY IN THE DEP AREA BUT WELL BEYOND. THE NTSB AND FAA SHOULD RE-EVALUATE THE SAFETY OF THIS PROC DICTATED TO MANY AIRLINES BY ONE CITY IN THE COUNTRY. SUPPLEMENTAL INFO FROM ACN 380202: THE ACFT WAS VERY LIGHT CLBING AT 5000 FPM AND TO A CLRED ALT OF 10000 FT. PASSING ABOUT 9000 FT WE WERE SWITCHED TO ZLA. AT THE SAME TIME WE ENCOUNTERED UNEXPECTED MODERATE CLR AIR TURB. FO WAS IN THE PROCESS OF SWITCHING FREQS AND DID NOT NOTICE CAPT'S FAILURE TO LEVEL AT 10000 FT. WHEN ZLA ANSWERED OUR CHK-IN THEY IMMEDIATELY CLRED US TO A HIGHER ALT. THE CREW ALLOWED THEMSELVES TO BECOME OVERLY OCCUPIED WITH THE ANTICIPATED PROB OF NOISE EXCEEDANCE AND FAILED TO ADEQUATELY FOCUS ON THE CONTINUING CLBOUT. THE HIGH RATE OF CLB; AUTOTHROTTLE PROB; FREQ CHANGE; MODERATE TURB; ALL WITHIN THE FIRST 2 MINS OF FLT; RESULTED IN A VERY HIGH WORKLOAD SIT. THE WORKLOAD COULD HAVE BEEN MODERATED IF THE AUTOPLT HAD BEEN ENGAGED; BUT IT WAS NOT. THE SNA NOISE SIT IS AN EXAMPLE OF HOW PRIORITIES CAN BE MISPLACED WHEN THERE IS ANY GLITCH IN THE PLANNED DEP; SUCH AS OUR AUTOTHROTTLE PROB.