Narrative:

While flying as first officer as the PF from lax to jfk, we experienced an altitude deviation. We were flying the lendy 4 arrival to jfk. ATC cleared us to cross harty intersection at FL230. I made the descent from cruise altitude using the flight director but no autoplt. We descended at the proper time and made the crossing restr without a problem. I initiated the leveloff as we approached FL230 using the flight director but still no autoplt. As I leveled off I began to increase power. At that time I noticed that the #3 engine was slow to respond. Due to a slightly different rigging from the other engines, this throttle needed to be pushed up further than the other 3 in order to produce the same power. As I was making this power adjustment I glanced back over to my flight instruments and noticed that I had descended to FL225. At this same time the captain noticed my altitude and advised me to 'watch the altitude.' I immediately pulled the nose up and quickly got back to FL230. At that time ATC called us to 'say your altitude.' since we were now back at FL230 we replied 'FL230.' the controller then told us to 'disregard.' the remainder of the flight was uneventful. This deviation was caused by my allowing myself to become distraction by the #3 throttle and subsequently allowing the altitude to deviation. Had I used the autoplt while I was adjusting the throttle this altitude deviation would have been prevented. Also, had either the captain or the flight engineer's brought the altitude to my attention sooner, this might have been avoided.

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Original NASA ASRS Text

Title: ACR B747 AFTER MEETING A DSCNT XING RESTR DSNDS BELOW ASSIGNED ALT WHILE MAKING PWR ADJUSTMENT TO #3 ENG.

Narrative: WHILE FLYING AS FO AS THE PF FROM LAX TO JFK, WE EXPERIENCED AN ALTDEV. WE WERE FLYING THE LENDY 4 ARR TO JFK. ATC CLRED US TO CROSS HARTY INTXN AT FL230. I MADE THE DSCNT FROM CRUISE ALT USING THE FLT DIRECTOR BUT NO AUTOPLT. WE DSNDED AT THE PROPER TIME AND MADE THE XING RESTR WITHOUT A PROB. I INITIATED THE LEVELOFF AS WE APCHED FL230 USING THE FLT DIRECTOR BUT STILL NO AUTOPLT. AS I LEVELED OFF I BEGAN TO INCREASE PWR. AT THAT TIME I NOTICED THAT THE #3 ENG WAS SLOW TO RESPOND. DUE TO A SLIGHTLY DIFFERENT RIGGING FROM THE OTHER ENGS, THIS THROTTLE NEEDED TO BE PUSHED UP FURTHER THAN THE OTHER 3 IN ORDER TO PRODUCE THE SAME PWR. AS I WAS MAKING THIS PWR ADJUSTMENT I GLANCED BACK OVER TO MY FLT INSTS AND NOTICED THAT I HAD DSNDED TO FL225. AT THIS SAME TIME THE CAPT NOTICED MY ALT AND ADVISED ME TO 'WATCH THE ALT.' I IMMEDIATELY PULLED THE NOSE UP AND QUICKLY GOT BACK TO FL230. AT THAT TIME ATC CALLED US TO 'SAY YOUR ALT.' SINCE WE WERE NOW BACK AT FL230 WE REPLIED 'FL230.' THE CTLR THEN TOLD US TO 'DISREGARD.' THE REMAINDER OF THE FLT WAS UNEVENTFUL. THIS DEV WAS CAUSED BY MY ALLOWING MYSELF TO BECOME DISTR BY THE #3 THROTTLE AND SUBSEQUENTLY ALLOWING THE ALT TO DEV. HAD I USED THE AUTOPLT WHILE I WAS ADJUSTING THE THROTTLE THIS ALTDEV WOULD HAVE BEEN PREVENTED. ALSO, HAD EITHER THE CAPT OR THE FE'S BROUGHT THE ALT TO MY ATTN SOONER, THIS MIGHT HAVE BEEN AVOIDED.

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.