■ The objective for this particular flight was recurrent formation training for me with the assistance of the pilot of a second aircraft…based at another nearby airport.… We agreed that we would rendezvous in a particular location, that he would fly lead, and I would join off his wing there. We further agreed on a time, altitude, frequency, and callsigns. As I approached the practice area, I observed at my 12 o’clock position, at approximately 3,500 feet MSL, an [aircraft] heading in the same direction…to the center of the practice area. On…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.

■ The weather was VFR with rain directly over the field, and the winds were favoring Runway 25.… I planned for…and briefed the Runway 25 RNAV approach before the descent started.… I leveled at 2,500 feet, …was configured with flaps 5, and speed was set. I was given a heading…to intercept the final approach course about 6 miles from the Final Approach Fix and cleared for the RNAV [Runway] 25. As the autopilot was intercepting the inbound [course],…we experienced a 15-knot loss of indicated airspeed and moderate turbulence.

■ [I] arrived at the aircraft and completed preflight items for a maintenance ferry flight…for the purpose of parking the aircraft…due to the COVID-19 economic downturn. During pre-flight, I determined that there was not a current maintenance release form in the aircraft logbook. I called Maintenance on the radio and requested a new maintenance release. Maintenance said that we did not need a maintenance release form because we were flying a maintenance ferry flight and we only needed a maintenance ferry document, which should be in the aircraft logbook. There was no maintenance ferry document in the aircraft logbook or in the flight plan paperwork.

■ I was Pilot Flying and set thrust for takeoff, pressed the TOGA button to engage takeoff thrust, and noticed the right thrust [lever] did not fully advance. I called, “Check thrust.” The Captain noticed that the Number 2 Engine would not achieve takeoff thrust.

■ As I approached the [aircraft] 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] 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.… 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.… 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] in view and asked if that was my training partner’s aircraft.… He replied that he was flying a different aircraft, and the mistaken identity suddenly was clear to us both.

At that point, I broke off formation with…[that aircraft], and…the rest of the flight proceeded normally.

Contributing factors to this confusion included:

The remarkable coincidence that the mistaken [aircraft] 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 so.

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 lead.

My electing to join from a trail position, which denied my flight lead a chance at a visual until later in the process.

My expectation bias that, because of Corona, there would be few, if any, other aircraft, and that this must have been my training partner.

■ I immediately disconnected the autopilot and the autothrottles, simultaneously rolled wings level, and [advanced] the throttles. I pitched up when I was confident that the airspeed was recovered to a safe speed. I asked the FO to inform the Approach Controller that we aborted the approach. We maintained…heading and climbed up to 4,000 feet. We flew out for approximately 10 miles. After 10 minutes, we received radar vectors for a right base and a visual approach without incident.

■ I called Dispatch and requested a new maintenance release and was told all I needed was the maintenance ferry document. I told Dispatch that I did not have one anywhere on the aircraft and I needed him to send me one. The Dispatcher told me that he couldn’t cut and paste the maintenance ferry document into ACARS, but that he could take a picture and send it to me on my phone. He sent me a picture of the maintenance ferry document.

I had never seen a maintenance ferry document, and therefore, had no idea if the Dispatcher had sent me the proper documentation. Per the flight plan, we were dispatched Part 91, and having been told by both Maintenance and Dispatch that we had what we needed, we proceeded to operate the flight safely and on time.…

It was only an hour after our arrival…that we were contacted by…Flight Operations and were told that we had departed without the proper maintenance release form. I sent a picture of the maintenance ferry document from Dispatch and a copy of the flight plan and told her I would file a report.

■ [The Captain] called, “100 knots,” but I noticed he was heads down at the engine gauges, and I called, “V1.” I achieved Vr, and he called for a rejected takeoff. I said, “Negative, we are past V1.” He pushed the thrust levers to full thrust, and we rotated without incident. I disconnected autothrottles and was able to achieve climb thrust for the climb to cruise altitude. At cruise, the Captain called Maintenance Control to discuss the issue, and they told us that the aircraft [recently] had a similar incident.… We continued the flight without incident and debriefed the situation at cruise. We talked about the fact that we were at such a light weight and the speeds V1 and Vr came so much earlier than normal.