An air carrier B757 flight crew descended below their assigned altitude when the flight crew became ...

Attributes
ACN	391210
Time
Date	199801
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : 3l3
State Reference	CA
Altitude	msl bound lower : 4600 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : lax tower : las
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 180 flight time total : 18000 flight time type : 1500
ASRS Report	391210
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : far
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:

Copilot was hand flying and we were cleared to 5000 ft. All was stable at 5000 ft and then I was having trouble adjusting my seat for the approach (my head was down). Then I heard the altitude alert go off and I saw we were in a very shallow/smooth descent passing through 4700 ft MSL. The descent was checked at 4650 ft MSL and we returned to 5000 ft. Shortly after the altitude alert approach control came up and very matter of factly told us to maintain 5000 ft at which I replied 'roger.' that describes the whole event. No traffic conflict arose and approach control did not seem alarmed. The copilot was very upset. He said he was looking outside for traffic (very clear VFR day over the ocean between santa catalina island and the mainland) and he had not noticed the descent. It never fails, the moment you get distracted (my seat) something occurs. I know this pilot to be top notch and very conscientious as well as being very disciplined. To prevent this from ever occurring again I believe using the autoplt to maintain altitude during traffic watch would have been the best course of action.

Original NASA ASRS Text

Title: AN ACR B757 FLC DSNDED BELOW THEIR ASSIGNED ALT WHEN THE FLC BECAME DISTRACTED.

Narrative: COPLT WAS HAND FLYING AND WE WERE CLRED TO 5000 FT. ALL WAS STABLE AT 5000 FT AND THEN I WAS HAVING TROUBLE ADJUSTING MY SEAT FOR THE APCH (MY HEAD WAS DOWN). THEN I HEARD THE ALT ALERT GO OFF AND I SAW WE WERE IN A VERY SHALLOW/SMOOTH DSCNT PASSING THROUGH 4700 FT MSL. THE DSCNT WAS CHKED AT 4650 FT MSL AND WE RETURNED TO 5000 FT. SHORTLY AFTER THE ALT ALERT APCH CTL CAME UP AND VERY MATTER OF FACTLY TOLD US TO MAINTAIN 5000 FT AT WHICH I REPLIED 'ROGER.' THAT DESCRIBES THE WHOLE EVENT. NO TFC CONFLICT AROSE AND APCH CTL DID NOT SEEM ALARMED. THE COPLT WAS VERY UPSET. HE SAID HE WAS LOOKING OUTSIDE FOR TFC (VERY CLR VFR DAY OVER THE OCEAN BTWN SANTA CATALINA ISLAND AND THE MAINLAND) AND HE HAD NOT NOTICED THE DSCNT. IT NEVER FAILS, THE MOMENT YOU GET DISTRACTED (MY SEAT) SOMETHING OCCURS. I KNOW THIS PLT TO BE TOP NOTCH AND VERY CONSCIENTIOUS AS WELL AS BEING VERY DISCIPLINED. TO PREVENT THIS FROM EVER OCCURRING AGAIN I BELIEVE USING THE AUTOPLT TO MAINTAIN ALT DURING TFC WATCH WOULD HAVE BEEN THE BEST COURSE OF ACTION.

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.

An air carrier B757 flight crew descended below their assigned altitude when the flight crew became distracted.