Pilot misinterprets STAR and leaves assigned altitude.

Attributes
ACN	311990
Time
Date	199507
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dtw
State Reference	MI
Altitude	msl bound lower : 4000 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dtw artcc : zdc
Operator	common carrier : air taxi
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 135
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 80 flight time total : 9600 flight time type : 3800
ASRS Report	311990
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Inbound to dtw I was to fly the polar 1 arrival. After I intercepted the dxo 343 degree radial, I maintained 5000 ft to the polar intersection. I incorrectly descended to 4000 ft as depicted. I know now that is a minimum altitude, I should have maintained 5000 ft that was assigned to me. I believe it would have been helpful if the controller had told me to maintain 5000 ft upon intercepting the depicted radial of the polar 1 STAR. At about 4300 ft the controller asked me what my altitude was. I told him and was instructed to climb back to 5000 ft. This event distracted me and I missed a turn to 130 degrees at the 31 DME scubi intersection by 10 NM. I have since reviewed STAR procedures.

Original NASA ASRS Text

Title: PLT MISINTERPRETS STAR AND LEAVES ASSIGNED ALT.

Narrative: INBOUND TO DTW I WAS TO FLY THE POLAR 1 ARR. AFTER I INTERCEPTED THE DXO 343 DEG RADIAL, I MAINTAINED 5000 FT TO THE POLAR INTXN. I INCORRECTLY DSNDED TO 4000 FT AS DEPICTED. I KNOW NOW THAT IS A MINIMUM ALT, I SHOULD HAVE MAINTAINED 5000 FT THAT WAS ASSIGNED TO ME. I BELIEVE IT WOULD HAVE BEEN HELPFUL IF THE CTLR HAD TOLD ME TO MAINTAIN 5000 FT UPON INTERCEPTING THE DEPICTED RADIAL OF THE POLAR 1 STAR. AT ABOUT 4300 FT THE CTLR ASKED ME WHAT MY ALT WAS. I TOLD HIM AND WAS INSTRUCTED TO CLB BACK TO 5000 FT. THIS EVENT DISTRACTED ME AND I MISSED A TURN TO 130 DEGS AT THE 31 DME SCUBI INTXN BY 10 NM. I HAVE SINCE REVIEWED STAR PROCS.

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.