Hio local controller describes a near midair collision where an aircraft is told to follow an aircra...

Narrative:

Aircraft X was IFR and released from P80. I told the aircraft cleared for takeoff. Aircraft Y was on final and I cleared it for a touch and go with a wake turbulence cautionary. I told aircraft Z who was on final too that he was number 2 on final and cleared touch and go. Aircraft a called me on the left downwind and I told the pilot 'aircraft a; number three; follow cessna three mile final; runway 31 cleared to land.' aircraft a replied; 'follow cessna; clear to land three one.' I then made other transmissions to other aircraft and then scanned for aircraft a to make sure it had turned base. I saw the aircraft on base but was not sure if he was going to follow aircraft Z mainly because of the visibility. In the background there were dark clouds and it was hard to spot some of the airplanes and also judge distances. I asked aircraft a if he had the cessna ahead and to his right on final in sight because at that moment I thought he was in a base turn that would cut off aircraft Z. He said he had the cessna in sight but I did not know if he was referring to aircraft Z or aircraft Y who was short final. I told aircraft Z to turn left so that he would turn away from the final; but instead aircraft a took evasive action and climbed the aircraft to avoid hitting aircraft Z. That's when aircraft Z said on frequency that he wanted to report that. I told aircraft a to proceed northbound and then I told him to head towards the airport and he was cleared to land. He landed safely. I don't have any recommendations. I thought when I gave aircraft a his sequence and clearance to land he knew which aircraft to follow.

Original NASA ASRS Text

Title: HIO Local Controller describes a NMAC where an aircraft is told to follow an aircraft type on final; while there are two of the same type of aircraft on final. Downwind traffic turns in to follow wrong aircraft.

Narrative: Aircraft X was IFR and released from P80. I told the aircraft cleared for takeoff. Aircraft Y was on final and I cleared it for a touch and go with a wake turbulence cautionary. I told Aircraft Z who was on final too that he was number 2 on final and cleared touch and go. Aircraft A called me on the left downwind and I told the pilot 'Aircraft A; number three; follow Cessna three mile final; runway 31 cleared to land.' Aircraft A replied; 'Follow Cessna; clear to land three one.' I then made other transmissions to other aircraft and then scanned for Aircraft A to make sure it had turned base. I saw the aircraft on base but was not sure if he was going to follow Aircraft Z mainly because of the visibility. In the background there were dark clouds and it was hard to spot some of the airplanes and also judge distances. I asked Aircraft A if he had the Cessna ahead and to his right on final in sight because at that moment I thought he was in a base turn that would cut off Aircraft Z. He said he had the Cessna in sight but I did not know if he was referring to Aircraft Z or Aircraft Y who was short final. I told Aircraft Z to turn left so that he would turn away from the final; but instead Aircraft A took evasive action and climbed the aircraft to avoid hitting Aircraft Z. That's when Aircraft Z said on frequency that he wanted to report that. I told Aircraft A to proceed northbound and then I told him to head towards the airport and he was cleared to land. He landed safely. I don't have any recommendations. I thought when I gave Aircraft A his sequence and clearance to land he knew which aircraft to follow.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1221807
Time
Date	201412
Local Time Of Day	0001-0600
Place
Locale Reference	HIO.Tower
State Reference	OR
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	Light Transport Low Wing 2 Turbojet Eng
Flight Phase	Takeoff
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Aircraft
Flight Phase	Final Approach
Person 1
Function	Local
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 1.2
Events
Anomaly	Conflict NMAC Deviation - Procedural Clearance Deviation - Track / Heading All Types

Hio local controller describes a near midair collision where an aircraft is told to follow an aircraft type on final; while there are two of the same type of aircraft on final. Downwind traffic turns in to follow wrong aircraft.