An air carrier B727 flight crew operating with a block 'V' autoplt, in moderate turbulence, descended below their assigned altitude when it failed to capture it.

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Attributes
ACN	401930
Time
Date	199805
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : fqf
State Reference	CO
Altitude	msl bound lower : 18600 msl bound upper : 19000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv tracon : myr
Operator	common carrier : air carrier
Make Model Name	B727-200
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 15000 flight time type : 5000
ASRS Report	401930
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot non adherence : far non adherence : clearance other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Descending to FL190 with a clearance to cross thompson intersection at FL190 at 250 KTS. At approximately FL200 encountered moderate turbulence. At approximately FL195, rate of descent was 2000 FPM and we were capturing the inbound course and meeting the altitude restr. I confirmed with the captain at FL195 that FL190 was our final altitude. He acknowledged affirmative. By the time it was obvious our block 'V' autoplt wasn't going to capture the altitude in time and with the moderate turbulence we descended below FL190 approximately 400 ft.

Original NASA ASRS Text

Title: AN ACR B727 FLC OPERATING WITH A BLOCK 'V' AUTOPLT, IN MODERATE TURB, DSNDED BELOW THEIR ASSIGNED ALT WHEN IT FAILED TO CAPTURE IT.

Narrative: DSNDING TO FL190 WITH A CLRNC TO CROSS THOMPSON INTXN AT FL190 AT 250 KTS. AT APPROX FL200 ENCOUNTERED MODERATE TURB. AT APPROX FL195, RATE OF DSCNT WAS 2000 FPM AND WE WERE CAPTURING THE INBOUND COURSE AND MEETING THE ALT RESTR. I CONFIRMED WITH THE CAPT AT FL195 THAT FL190 WAS OUR FINAL ALT. HE ACKNOWLEDGED AFFIRMATIVE. BY THE TIME IT WAS OBVIOUS OUR BLOCK 'V' AUTOPLT WASN'T GOING TO CAPTURE THE ALT IN TIME AND WITH THE MODERATE TURB WE DSNDED BELOW FL190 APPROX 400 FT.

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.