C402 pilot has altitude deviation while en route.

Attributes
ACN	703796
Time
Date	200607
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zab.artcc
State Reference	NM
Altitude	msl single value : 15000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zab.artcc
Operator	common carrier : air taxi
Make Model Name	Cessna 402/402C/B379 Businessliner/Utiliner
Operating Under FAR Part	Part 135
Flight Phase	cruise : level
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zab.artcc
Make Model Name	Baron 58/58TC
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : multi engine pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 100 flight time total : 3500 flight time type : 800
ASRS Report	703796
Person 2
Affiliation	government : faa
Function	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

Flying at 15000 ft MSL ZAB advised traffic 10-11 O'clock position 5 mi at 14000 ft. I responded with 'looking for traffic.' center advised baron 'twin cessna 1-2 O'clock position.' baron advised 'traffic in sight.' then I saw the baron and advised center; 'traffic in sight.' controller advised 'expect further descent to 12000 ft after traffic has passed.' we watched each other go by. I started a descent after a few mins. The frequency was busy and I was able to call 'descend to 12000?' controller; '12000 affirmative.' my altimeter read 14500 ft at that time. 500 ft altitude deviation.

Original NASA ASRS Text

Title: C402 PLT HAS ALTDEV WHILE ENRTE.

Narrative: FLYING AT 15000 FT MSL ZAB ADVISED TFC 10-11 O'CLOCK POS 5 MI AT 14000 FT. I RESPONDED WITH 'LOOKING FOR TFC.' CTR ADVISED BARON 'TWIN CESSNA 1-2 O'CLOCK POS.' BARON ADVISED 'TFC IN SIGHT.' THEN I SAW THE BARON AND ADVISED CTR; 'TFC IN SIGHT.' CTLR ADVISED 'EXPECT FURTHER DSCNT TO 12000 FT AFTER TFC HAS PASSED.' WE WATCHED EACH OTHER GO BY. I STARTED A DSCNT AFTER A FEW MINS. THE FREQ WAS BUSY AND I WAS ABLE TO CALL 'DSND TO 12000?' CTLR; '12000 AFFIRMATIVE.' MY ALTIMETER READ 14500 FT AT THAT TIME. 500 FT ALTDEV.

Data retrieved from NASA's ASRS site as of January 2009 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.