An experimental aircraft has an near midair collision with a piper at dpa.

Attributes
ACN	610546
Time
Date	200403
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : dpa.airport
State Reference	IL
Altitude	msl single value : 1500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : dpa.tower
Operator	general aviation : personal
Make Model Name	Experimental
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	approach : traffic pattern arrival : vfr
Flight Plan	VFR
Aircraft 2
Controlling Facilities	tower : dpa.tower
Operator	general aviation : personal
Make Model Name	Piper Aircraft Corp Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	climbout : initial climbout : intermediate altitude
Route In Use	approach : traffic pattern
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 30 flight time total : 1100 flight time type : 500
ASRS Report	610546
Person 2
Affiliation	other
Function	flight crew : single pilot
Events
Anomaly	conflict : nmac non adherence : far
Independent Detector	other flight crewa
Miss Distance	horizontal : 300 vertical : 0
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Ambiguous

Narrative:

I was inbound for landing at dupage airport from the west. I called in 10 mi out and received 'left downwind for runway 28, report the river.' at the river, I called, and got no response. 1/2 mi later, I tried again, and was cleared to land, runway 28. Shortly thereafter, as I was on left downwind, (eastbound), a plane (that apparently had taken off from dpa) crossed from left to right, right in front of me, (sbound) same altitude, a few hundred ft ahead. I saw the other plane and was able to cross behind him. I don't know exactly how this close call came to happen, but somehow the tower sequencing had to be involved, unless the other plane was somewhere they were not supposed to be. I don't recall the tower's interactions with that plane through its takeoff.

Original NASA ASRS Text

Title: AN EXPERIMENTAL ACFT HAS AN NMAC WITH A PIPER AT DPA.

Narrative: I WAS INBOUND FOR LNDG AT DUPAGE ARPT FROM THE W. I CALLED IN 10 MI OUT AND RECEIVED 'L DOWNWIND FOR RWY 28, RPT THE RIVER.' AT THE RIVER, I CALLED, AND GOT NO RESPONSE. 1/2 MI LATER, I TRIED AGAIN, AND WAS CLRED TO LAND, RWY 28. SHORTLY THEREAFTER, AS I WAS ON L DOWNWIND, (EBOUND), A PLANE (THAT APPARENTLY HAD TAKEN OFF FROM DPA) CROSSED FROM L TO R, RIGHT IN FRONT OF ME, (SBOUND) SAME ALT, A FEW HUNDRED FT AHEAD. I SAW THE OTHER PLANE AND WAS ABLE TO CROSS BEHIND HIM. I DON'T KNOW EXACTLY HOW THIS CLOSE CALL CAME TO HAPPEN, BUT SOMEHOW THE TWR SEQUENCING HAD TO BE INVOLVED, UNLESS THE OTHER PLANE WAS SOMEWHERE THEY WERE NOT SUPPOSED TO BE. I DON'T RECALL THE TWR'S INTERACTIONS WITH THAT PLANE THROUGH ITS TKOF.

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.