B737-200 flight crew descends below assigned altitude.

Attributes
ACN	322580
Time
Date	199511
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : stl
State Reference	MO
Altitude	msl bound lower : 6400 msl bound upper : 7000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : stl artcc : rctp
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time total : 12000
ASRS Report	322580
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 220 flight time total : 6000 flight time type : 700
ASRS Report	321738
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Cleared to 7000 ft. Descended to 6400 ft before realizing below assigned altitude. This was a B737-200 without altitude capture. I was hand flying because the autoplt was jerky in the pitch axis. Supplemental information from acn 321738: we were on arrival to st louis and were cleared to 7000 ft (MSL). Captain was flying so I selected 7000 ft in the altitude select (B737-200). As we passed 8000 ft I called 1000 ft to go. The captain didn't really respond, but that's really not uncommon. (He appeared to be listening to a ball game on the ADF.) I was looking for my airport diagram when I heard the altitude alert go off. I told the captain that we were only cleared to 7000 ft. At this point we were at 6400 ft. The captain promptly climbed back to 7000 ft. At about 6800 ft, stl approach told us to check our altitude. We said thank you. He then gave us a frequency change and the next guy gave us a clearance to 6000 ft. No harm came from this, however, there was a breakdown in CRM and complacency played a big part.

Original NASA ASRS Text

Title: B737-200 FLC DSNDS BELOW ASSIGNED ALT.

Narrative: CLRED TO 7000 FT. DSNDED TO 6400 FT BEFORE REALIZING BELOW ASSIGNED ALT. THIS WAS A B737-200 WITHOUT ALT CAPTURE. I WAS HAND FLYING BECAUSE THE AUTOPLT WAS JERKY IN THE PITCH AXIS. SUPPLEMENTAL INFO FROM ACN 321738: WE WERE ON ARR TO ST LOUIS AND WERE CLRED TO 7000 FT (MSL). CAPT WAS FLYING SO I SELECTED 7000 FT IN THE ALT SELECT (B737-200). AS WE PASSED 8000 FT I CALLED 1000 FT TO GO. THE CAPT DIDN'T REALLY RESPOND, BUT THAT'S REALLY NOT UNCOMMON. (HE APPEARED TO BE LISTENING TO A BALL GAME ON THE ADF.) I WAS LOOKING FOR MY ARPT DIAGRAM WHEN I HEARD THE ALT ALERT GO OFF. I TOLD THE CAPT THAT WE WERE ONLY CLRED TO 7000 FT. AT THIS POINT WE WERE AT 6400 FT. THE CAPT PROMPTLY CLBED BACK TO 7000 FT. AT ABOUT 6800 FT, STL APCH TOLD US TO CHK OUR ALT. WE SAID THANK YOU. HE THEN GAVE US A FREQ CHANGE AND THE NEXT GUY GAVE US A CLRNC TO 6000 FT. NO HARM CAME FROM THIS, HOWEVER, THERE WAS A BREAKDOWN IN CRM AND COMPLACENCY PLAYED A BIG PART.

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.