An air carrier B767-300 flight crew descended below their assigned altitude and quickly recovered.

Attributes
ACN	431429
Time
Date	199903
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : atl.vortac
State Reference	GA
Altitude	msl bound lower : 22700 msl bound upper : 23000
Environment
Flight Conditions	Mixed
Weather Elements	Ice Turbulence
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : ztl.artcc
Operator	common carrier : air carrier
Make Model Name	B767-300 and 300 ER
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : sinca.sinca 3
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : ztl.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 150 flight time total : 4500 flight time type : 2000
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : instrument pilot : flight engineer pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 150 flight time total : 20000 flight time type : 5000
ASRS Report	431131
Events
Anomaly	altitude deviation : overshoot non adherence : clearance non adherence : far non adherence : company policies
Independent Detector	aircraft equipment : tcas other flight crewa
Resolutory Action	flight crew : returned to original clearance
Consequence	Other
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Level at FL240 on radar vector. I turned to speak to flight attendant. When I looked forward, ATC had given us a turn direct husky. I responded. When I looked at MCP altitude read FL225 and we were descending through FL230. I asked captain what our altitude should be. He said FL230 and corrected the MCP and began to get vertical speed to climb. (We had received a 1000 ft descent while I was talking to the flight attendant and captain had responded and initiated descent by setting FL230 on MCP and vertical speed of 1000 ft descent.) we received a TA and then an RA. Captain disconnected autoplt and climbed manually. Lowest altitude I saw on altimeter was FL227. Altitude deviation lasted less than 30 seconds.

Original NASA ASRS Text

Title: AN ACR B767-300 FLC DSNDED BELOW THEIR ASSIGNED ALT AND QUICKLY RECOVERED.

Narrative: LEVEL AT FL240 ON RADAR VECTOR. I TURNED TO SPEAK TO FLT ATTENDANT. WHEN I LOOKED FORWARD, ATC HAD GIVEN US A TURN DIRECT HUSKY. I RESPONDED. WHEN I LOOKED AT MCP ALT READ FL225 AND WE WERE DSNDING THROUGH FL230. I ASKED CAPT WHAT OUR ALT SHOULD BE. HE SAID FL230 AND CORRECTED THE MCP AND BEGAN TO GET VERT SPD TO CLB. (WE HAD RECEIVED A 1000 FT DSCNT WHILE I WAS TALKING TO THE FLT ATTENDANT AND CAPT HAD RESPONDED AND INITIATED DSCNT BY SETTING FL230 ON MCP AND VERT SPD OF 1000 FT DSCNT.) WE RECEIVED A TA AND THEN AN RA. CAPT DISCONNECTED AUTOPLT AND CLBED MANUALLY. LOWEST ALT I SAW ON ALTIMETER WAS FL227. ALTDEV LASTED LESS THAN 30 SECONDS.

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.