Date: 202004
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Small Aircraft
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Training
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: UNICOM ZZZ
Second aircraft: Small Aircraft
Reporter organization: Personal
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Situational Awareness; Other / Unknown; Confusion; Communication Breakdown
Anomaly: Conflict Airborne Conflict; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Contributing factors: Environment - Non Weather Related; Human Factors
Primary problem: Human Factors

Narrative: The objective for this particular flight was recurrent formation training for me; with the assistance of the pilot of a second aircraft (an occasional training partner; based at another nearby airport).  Per our telephonic briefing on the ground; we agreed that we would rendezvous in a particular location and that he would fly lead and I would join off his wing there.  We further agreed on a time; altitude; frequency and call signs.As I approached the practice area I observed at my 12 o'clock position at approximately 3;500 MSL an [Aircraft Y type] heading in the same direction -- i.e. to the center of the practice area.On the air-to-air frequency; I then made my first call to check in and to ask the flight lead if he was in position.  He responded that he was approaching the practice area.  I told him I thought I had him in sight.He then asked me my position; and I said I was at his 6 o'clock; several miles in trail.  I told him he could maintain his heading and I would close from the rear.As I approached the [Aircraft Y type] in front of me; I suggested over the air-to-air frequency that my training partner make a shallow turn to help me close; and he acknowledged.  A moment later; the [Aircraft Y type] in front of me began a gentle turn to the left.Once I was established in the turn and began to close; my partner asked for my current position; I indicated that I was moving from trail to his right wing.  During this time I moved into a loose fingertip off the lead aircraft.  About this time my partner asked again for my position and said he could not see me.  I replied that I was off his right wing; and thought for a moment that possibly I was partly blocked by the window/door framing.  To help with his field of view; I moved slightly forward to a more visible bearing line; and then radioed to ask if he had a clear visual.  He responded that he still did not; and at that point it suddenly occurred to me that I might be flying formation off the wrong aircraft.  Over the air-to-air frequency I read the N number of the [Aircraft Y type] in view; and asked if that was my training partner's aircraft (we had been using call signs; so I had not had any prior occasion to reference his N number).  He replied that he was flying a different aircraft; and the mistaken identity suddenly was clear to us both.At the point; I broke off formation with the [Aircraft Y type]; and switched back to  tower (whose airspace was fairly close -- some ~8NM away -- to explain the mistaken identity and to ask if he was talking with the other [Aircraft Y type].  The tower controller indicated that he was not talking with that aircraft but said he would relay the message if the [Aircraft Y type] should check in.That was the end of the mistaken/unsafe condition and the rest of the flight proceeded normally.Contributing factors to this confusion included:1) The remarkable coincidence that the mistaken [Aircraft Y type] was in exactly the right place at the right time and the right altitude; and that it subsequently began a turn exactly when I requested my flight lead to do so2) My failure to ask my training partner to utilize TCAS/ADS-B to firmly establish me on his PFD prior to my moving in on what I thought was the flight lead3) My electing to join from a trail position; which denied my flight lead a chance at a visual until later in the process4) My expectation bias that; because of Corona; there would be few if any other aircraft and that this must have been my training partner (as it happens; the mistaken [Aircraft Y type] and the intended [Aircraft Y type] were the only two aircraft I saw or heard in the sky all day).




Synopsis: GA pilot reported flying formation with the wrong aircraft. Reporter cited a number of contributing factors that led to this confusion.