Near midair collision.

Attributes
ACN	133385
Time
Date	199001
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : dpa
State Reference	IL
Altitude	msl bound lower : 1700 msl bound upper : 1700
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tower : dpa
Operator	general aviation : instructional
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	descent : approach
Flight Plan	None
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent : approach
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 9 flight time total : 214 flight time type : 103
ASRS Report	133385
Person 2
Affiliation	Other
Function	flight crew : single pilot
Events
Anomaly	conflict : nmac
Independent Detector	other flight crewa
Resolutory Action	none taken : insufficient time
Consequence	Other
Miss Distance	horizontal : 50 vertical : 200
Supplementary
Primary Problem	Flight Crew Human Performance

Narrative:

I was returning home after a flight to bloomington, il (bmi), 92 NM ssw. After getting ATIS, I called the tower at oswego, about 15 NM ssw. I was told to report 2 NM south. There was heavy congestion on the tower frequency. Many aircraft were arriving at dupage at about the same time at dusk. I reported 2 south. While on left downwind for 28, I saw one aircraft on very short final. The tower told me that my traffic was on a right base. A few moments later, I saw another aircraft on final, which I took to be my traffic that had turned from base to final. After extending my downwind slightly, and seeing no traffic, I turned base. As I was turning high final, I saw another aircraft pass about 200' below me, also in a position to turn final. This must have been my traffic. I had mistaken the previous aircraft for my traffic. Contributing factors: 1) heavy congestion on tower frequency. 2) fading light at dusk. 3) proximity of previous aircraft to expected path of my traffic. Human performance considerations: I should have asked the tower for permission to turn base, instead of assuming that my traffic was the previous aircraft I had last seen on final.

Original NASA ASRS Text

Title: NMAC.

Narrative: I WAS RETURNING HOME AFTER A FLT TO BLOOMINGTON, IL (BMI), 92 NM SSW. AFTER GETTING ATIS, I CALLED THE TWR AT OSWEGO, ABOUT 15 NM SSW. I WAS TOLD TO REPORT 2 NM S. THERE WAS HEAVY CONGESTION ON THE TWR FREQ. MANY ACFT WERE ARRIVING AT DUPAGE AT ABOUT THE SAME TIME AT DUSK. I REPORTED 2 S. WHILE ON LEFT DOWNWIND FOR 28, I SAW ONE ACFT ON VERY SHORT FINAL. THE TWR TOLD ME THAT MY TFC WAS ON A RIGHT BASE. A FEW MOMENTS LATER, I SAW ANOTHER ACFT ON FINAL, WHICH I TOOK TO BE MY TFC THAT HAD TURNED FROM BASE TO FINAL. AFTER EXTENDING MY DOWNWIND SLIGHTLY, AND SEEING NO TFC, I TURNED BASE. AS I WAS TURNING HIGH FINAL, I SAW ANOTHER ACFT PASS ABOUT 200' BELOW ME, ALSO IN A POSITION TO TURN FINAL. THIS MUST HAVE BEEN MY TFC. I HAD MISTAKEN THE PREVIOUS ACFT FOR MY TFC. CONTRIBUTING FACTORS: 1) HEAVY CONGESTION ON TWR FREQ. 2) FADING LIGHT AT DUSK. 3) PROX OF PREVIOUS ACFT TO EXPECTED PATH OF MY TFC. HUMAN PERFORMANCE CONSIDERATIONS: I SHOULD HAVE ASKED THE TWR FOR PERMISSION TO TURN BASE, INSTEAD OF ASSUMING THAT MY TFC WAS THE PREVIOUS ACFT I HAD LAST SEEN ON FINAL.

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.