Narrative:

This being a very noise sensitive airport, our company has developed a noise abatement procedure that must be done exactly right to avoid exceeding the established noise limits (and risk losing operating authority). 80% power is set prior to brake release. At vr a positive rotation to 20 degrees anu is initiated to maintain V2+10. We were at maximum weight for this runway. At 500' AGL I asked for autoplt on (still in FGS takeoff mode). First officer bumped vertical speed wheel, which caused FGS to enter vertical speed mode just as autoplt was switched on. This caused a momentary period of confusion, as we investigated what had happened. During this interval, speed decreased to V2 before I reduced the vertical speed and accelerated back to V2+10. The next step in the noise profile is cutback (climb) power at 800' AGL, which we were late accomplishing, due to the autoplt situation. This probably resulted in a noise bust, but it could have been worse. An engine failure occurring at V2 at 500' may have rendered the airplane uncontrollable (I may give it a try in the simulator sometime...). An alternative procedure would be waiting until 1000' for the autoplt on command, when we could use the IAS mode. It is hard enough to avoid ringing the bells when everything goes right (it happens on too many flts as it is). It sure doesn't take much to screw up the rhythm.

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Original NASA ASRS Text

Title: ACR MLG FAILED TO FOLLOW NOISE ABATEMENT PROC ON DEP.

Narrative: THIS BEING A VERY NOISE SENSITIVE ARPT, OUR COMPANY HAS DEVELOPED A NOISE ABATEMENT PROC THAT MUST BE DONE EXACTLY RIGHT TO AVOID EXCEEDING THE ESTABLISHED NOISE LIMITS (AND RISK LOSING OPERATING AUTHORITY). 80% PWR IS SET PRIOR TO BRAKE RELEASE. AT VR A POSITIVE ROTATION TO 20 DEGS ANU IS INITIATED TO MAINTAIN V2+10. WE WERE AT MAX WT FOR THIS RWY. AT 500' AGL I ASKED FOR AUTOPLT ON (STILL IN FGS TKOF MODE). F/O BUMPED VERT SPD WHEEL, WHICH CAUSED FGS TO ENTER VERT SPD MODE JUST AS AUTOPLT WAS SWITCHED ON. THIS CAUSED A MOMENTARY PERIOD OF CONFUSION, AS WE INVESTIGATED WHAT HAD HAPPENED. DURING THIS INTERVAL, SPD DECREASED TO V2 BEFORE I REDUCED THE VERT SPD AND ACCELERATED BACK TO V2+10. THE NEXT STEP IN THE NOISE PROFILE IS CUTBACK (CLB) PWR AT 800' AGL, WHICH WE WERE LATE ACCOMPLISHING, DUE TO THE AUTOPLT SITUATION. THIS PROBABLY RESULTED IN A NOISE BUST, BUT IT COULD HAVE BEEN WORSE. AN ENG FAILURE OCCURRING AT V2 AT 500' MAY HAVE RENDERED THE AIRPLANE UNCONTROLLABLE (I MAY GIVE IT A TRY IN THE SIMULATOR SOMETIME...). AN ALTERNATIVE PROC WOULD BE WAITING UNTIL 1000' FOR THE AUTOPLT ON COMMAND, WHEN WE COULD USE THE IAS MODE. IT IS HARD ENOUGH TO AVOID RINGING THE BELLS WHEN EVERYTHING GOES RIGHT (IT HAPPENS ON TOO MANY FLTS AS IT IS). IT SURE DOESN'T TAKE MUCH TO SCREW UP THE RHYTHM.

Data retrieved from NASA's ASRS site as of August 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.