Narrative:

ZJX issued us a clearance to descend to cross jayja intersection at FL270. I started the aircraft down a little bit early because we were experiencing light to occasional moderate chop. Because I started down early; I used less rate of descent than required to make the restr in order to catch back up to the final descent profile. I was distraction by multiple task saturation and did not notice the aircraft going high on the FMC descent profile until the captain noticed it first. I increased the rate of descent to try to make the crossing restr. As the aircraft approached FL270; the altitude hold either failed to acquire FL270 or overshot FL270 and we descended below our assigned altitude. When I saw the aircraft approaching FL270 and it was not appearing to be in the process of leveling off; I secured the autoplt and manually climbed the aircraft back to a level FL270. The duration of the deviation was less than 10 seconds and the aircraft resumed altitude hold on the autoplt without any further incident. I should not have allowed other cockpit tasks to distract me from my primary mission of flying the aircraft; as I was the PF. In the future; I will aviate first; navigation second; and communication third. The high descent rate probably contributed to the overshoot of the leveloff altitude; but if I had stayed on the descent profile; this would not have been an issue. Supplemental information from acn 649390: the frequency was congested so we couldn't talk to center. Nothing was said by ATC.

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Original NASA ASRS Text

Title: A B737-300 CREW MISSED A DSCNT ALT CONSTRAINT BECAUSE OF DISTRS CAUSED BY TURB AND DSCNT PLANNING.

Narrative: ZJX ISSUED US A CLRNC TO DSND TO CROSS JAYJA INTXN AT FL270. I STARTED THE ACFT DOWN A LITTLE BIT EARLY BECAUSE WE WERE EXPERIENCING LIGHT TO OCCASIONAL MODERATE CHOP. BECAUSE I STARTED DOWN EARLY; I USED LESS RATE OF DSCNT THAN REQUIRED TO MAKE THE RESTR IN ORDER TO CATCH BACK UP TO THE FINAL DSCNT PROFILE. I WAS DISTR BY MULTIPLE TASK SATURATION AND DID NOT NOTICE THE ACFT GOING HIGH ON THE FMC DSCNT PROFILE UNTIL THE CAPT NOTICED IT FIRST. I INCREASED THE RATE OF DSCNT TO TRY TO MAKE THE XING RESTR. AS THE ACFT APCHED FL270; THE ALT HOLD EITHER FAILED TO ACQUIRE FL270 OR OVERSHOT FL270 AND WE DSNDED BELOW OUR ASSIGNED ALT. WHEN I SAW THE ACFT APCHING FL270 AND IT WAS NOT APPEARING TO BE IN THE PROCESS OF LEVELING OFF; I SECURED THE AUTOPLT AND MANUALLY CLBED THE ACFT BACK TO A LEVEL FL270. THE DURATION OF THE DEV WAS LESS THAN 10 SECONDS AND THE ACFT RESUMED ALT HOLD ON THE AUTOPLT WITHOUT ANY FURTHER INCIDENT. I SHOULD NOT HAVE ALLOWED OTHER COCKPIT TASKS TO DISTRACT ME FROM MY PRIMARY MISSION OF FLYING THE ACFT; AS I WAS THE PF. IN THE FUTURE; I WILL AVIATE FIRST; NAV SECOND; AND COM THIRD. THE HIGH DSCNT RATE PROBABLY CONTRIBUTED TO THE OVERSHOOT OF THE LEVELOFF ALT; BUT IF I HAD STAYED ON THE DSCNT PROFILE; THIS WOULD NOT HAVE BEEN AN ISSUE. SUPPLEMENTAL INFO FROM ACN 649390: THE FREQ WAS CONGESTED SO WE COULDN'T TALK TO CTR. NOTHING WAS SAID BY ATC.

Data retrieved from NASA's ASRS site as of January 2009 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.