Da-20 pilot reported flying formation with an aircraft that was unaware of his intentions.

Attributes
ACN	1268878
Time
Date	201506
Place
Locale Reference	ZLA.ARTCC
State Reference	CA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	DA20-A1 Katana
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	None
Flight Plan	VFR
Aircraft 2
Make Model Name	Champion Citabria Undifferentiated
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Person 1
Function	Single Pilot Pilot Flying
Qualification	Flight Crew Private
Experience	Flight Crew Last 90 Days 30 Flight Crew Total 500 Flight Crew Type 200
Events
Anomaly	Conflict NMAC Deviation - Procedural FAR Deviation - Procedural Published Material / Policy
Miss Distance	Horizontal 50 Vertical 10

Narrative:

I was flying and saw my formation buddy's plane. I joined on his wing then he joined on mine. We flew together for about a minute or two. Later [I found] out from my friend that was not his plane and he was not flying that day. The plane we joined is the same model citabria and exact paint scheme with the same tail markings. Both planes are completely identical and I mistakenly joined on the wrong plane.

Original NASA ASRS Text

Title: DA-20 pilot reported flying formation with an aircraft that was unaware of his intentions.

Narrative: I was flying and saw my formation buddy's plane. I joined on his wing then he joined on mine. We flew together for about a minute or two. Later [I found] out from my friend that was not his plane and he was not flying that day. The plane we joined is the same model Citabria and exact paint scheme with the same tail markings. Both planes are completely identical and I mistakenly joined on the wrong plane.

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.