Air carrier flight crew looking for trafic has altitude deviation.

Attributes
ACN	146331
Time
Date	199005
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : bwi
State Reference	MD
Altitude	msl bound lower : 7700 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bwi
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Retractable Gear
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 100 flight time total : 11500 flight time type : 3500
ASRS Report	146331
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 150 flight time total : 7500 flight time type : 3000
ASRS Report	146335
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
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were cleared to descend from 11000' to 8000' MSL. Visibility was 15 to 20 mi. During the descent, approach control alerted us to traffic, (an small aircraft) at 2 O'clock climbing from 6700' to 7500'. We located the traffic visually. While all 3 crew members were watching the traffic, we inadvertently descended to 7700'. We called approach to advise the traffic was in sight. Approach answered and asked us to comfirm that we were at 8000'. We climbed back to 8000' from 7700' as we confirmed our altitude. The small aircraft reported having us in sight and we did the same. There was no near miss conflict. Incident would have been prevented had one of us been looking at the altimeter, instead of all 3 of us looking outside for traffic.

Original NASA ASRS Text

Title: ACR FLT CREW LOOKING FOR TRAFIC HAS ALT DEVIATION.

Narrative: WE WERE CLRED TO DSND FROM 11000' TO 8000' MSL. VISIBILITY WAS 15 TO 20 MI. DURING THE DSNT, APCH CTL ALERTED US TO TFC, (AN SMA) AT 2 O'CLOCK CLBING FROM 6700' TO 7500'. WE LOCATED THE TFC VISUALLY. WHILE ALL 3 CREW MEMBERS WERE WATCHING THE TFC, WE INADVERTENTLY DSNDED TO 7700'. WE CALLED APCH TO ADVISE THE TFC WAS IN SIGHT. APCH ANSWERED AND ASKED US TO COMFIRM THAT WE WERE AT 8000'. WE CLBED BACK TO 8000' FROM 7700' AS WE CONFIRMED OUR ALT. THE SMA RPTED HAVING US IN SIGHT AND WE DID THE SAME. THERE WAS NO NEAR MISS CONFLICT. INCIDENT WOULD HAVE BEEN PREVENTED HAD ONE OF US BEEN LOOKING AT THE ALTIMETER, INSTEAD OF ALL 3 OF US LOOKING OUTSIDE FOR TFC.

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.