Small aircraft Y failed to follow ATC instructions. Near midair collision. Pilot deviation.

Attributes
ACN	126728
Time
Date	198910
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : prc
State Reference	AZ
Altitude	agl bound lower : 1000 agl bound upper : 1500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : prc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent : approach descent other other
Route In Use	approach : straight in
Flight Plan	None
Aircraft 2
Make Model Name	Small Aircraft, High Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other other
Route In Use	enroute : on vectors
Flight Plan	None
Person 1
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Experience	controller non radar : 5
ASRS Report	126728
Person 2
Affiliation	Other
Function	flight crew : single pilot
Events
Anomaly	conflict : nmac non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : took evasive action other
Consequence	Other
Miss Distance	horizontal : 0 vertical : 200
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft X reported humpty inbound on ILS/DME 21 approach and was instructed to report 4.3 DME. Small aircraft Y reported 2 mi left base and was instructed to turn to the left downwind to follow aircraft X approaching a 3 mi final. Small aircraft Y acknowledged the instruction. I noticed small aircraft Y continuing on the base leg, I again issued the instructions to turn right and enter the left downwind. Small aircraft Y still did not follow instructions. It was no longer feasible for small aircraft Y to turn right because of this position in relation to the final approach course. I then instructed small aircraft Y to turn towards the runway. Small aircraft Y began to turn right and aircraft X descended rapidly to avoid small aircraft Y. Due to the volume of traffic and student pilots at prescott it is paramount that instructors insure the student complies with instructions when they are first issued.

Original NASA ASRS Text

Title: SMA Y FAILED TO FOLLOW ATC INSTRUCTIONS. NMAC. PLT DEVIATION.

Narrative: ACFT X REPORTED HUMPTY INBND ON ILS/DME 21 APCH AND WAS INSTRUCTED TO REPORT 4.3 DME. SMA Y REPORTED 2 MI LEFT BASE AND WAS INSTRUCTED TO TURN TO THE LEFT DOWNWIND TO FOLLOW ACFT X APCHING A 3 MI FINAL. SMA Y ACKNOWLEDGED THE INSTRUCTION. I NOTICED SMA Y CONTINUING ON THE BASE LEG, I AGAIN ISSUED THE INSTRUCTIONS TO TURN RIGHT AND ENTER THE LEFT DOWNWIND. SMA Y STILL DID NOT FOLLOW INSTRUCTIONS. IT WAS NO LONGER FEASIBLE FOR SMA Y TO TURN RIGHT BECAUSE OF THIS POSITION IN RELATION TO THE FINAL APCH COURSE. I THEN INSTRUCTED SMA Y TO TURN TOWARDS THE RWY. SMA Y BEGAN TO TURN RIGHT AND ACFT X DESCENDED RAPIDLY TO AVOID SMA Y. DUE TO THE VOLUME OF TFC AND STUDENT PLTS AT PRESCOTT IT IS PARAMOUNT THAT INSTRUCTORS INSURE THE STUDENT COMPLIES WITH INSTRUCTIONS WHEN THEY ARE FIRST ISSUED.

Data retrieved from NASA's ASRS site as of August 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.