Small aircraft came into close proximity to another small aircraft after traffic was issued.

Attributes
ACN	151525
Time
Date	199007
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : alo
State Reference	IA
Altitude	msl bound lower : 2500 msl bound upper : 2550
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : alo
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other
Flight Plan	VFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Flight Plan	VFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
ASRS Report	151525
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : developmental
Events
Anomaly	conflict : airborne less severe non adherence : far other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Miss Distance	horizontal : 1000 vertical : 50
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was working arrival/departure radar with a developmental. We had 8-10 aircraft on the frequency. The developmental issued traffic to both of the aircraft involved. Small aircraft X was circling over the city at various altitudes but was indicating a 2900' MSL when traffic was issued to him as an small aircraft Y sebnd from waterloo at 2500' MSL. Traffic was also issued to small aircraft Y as sebnd flying locally over the city at various altitudes and the pilot reported the other aircraft in sight. 3 or 4 mins later, small aircraft X said an aircraft came very close to him as he had apparently descended from 2900' MSL to about 2550' MSL. Recommendations: we, ATC, should have instructed small aircraft X to stay at 3000' MSL until he had small aircraft Y in sight. Also, small aircraft Y pilot should not have descended his aircraft into the altitude of small aircraft X especially after acknowledging ATC as to the small aircraft Y at 2500' MSL and heading for the area that he was flying in.

Original NASA ASRS Text

Title: SMA CAME INTO CLOSE PROX TO ANOTHER SMA AFTER TRAFFIC WAS ISSUED.

Narrative: I WAS WORKING ARR/DEP RADAR WITH A DEVELOPMENTAL. WE HAD 8-10 ACFT ON THE FREQ. THE DEVELOPMENTAL ISSUED TFC TO BOTH OF THE ACFT INVOLVED. SMA X WAS CIRCLING OVER THE CITY AT VARIOUS ALTS BUT WAS INDICATING A 2900' MSL WHEN TFC WAS ISSUED TO HIM AS AN SMA Y SEBND FROM WATERLOO AT 2500' MSL. TFC WAS ALSO ISSUED TO SMA Y AS SEBND FLYING LOCALLY OVER THE CITY AT VARIOUS ALTS AND THE PLT RPTED THE OTHER ACFT IN SIGHT. 3 OR 4 MINS LATER, SMA X SAID AN ACFT CAME VERY CLOSE TO HIM AS HE HAD APPARENTLY DSNDED FROM 2900' MSL TO ABOUT 2550' MSL. RECOMMENDATIONS: WE, ATC, SHOULD HAVE INSTRUCTED SMA X TO STAY AT 3000' MSL UNTIL HE HAD SMA Y IN SIGHT. ALSO, SMA Y PLT SHOULD NOT HAVE DSNDED HIS ACFT INTO THE ALT OF SMA X ESPECIALLY AFTER ACKNOWLEDGING ATC AS TO THE SMA Y AT 2500' MSL AND HDG FOR THE AREA THAT HE WAS FLYING IN.

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.