General aviation pilots reported that while in formation flight one pilot performed an unexpected maneuver that resulted in an NMAC with one of the other aircraft.
Synopsis
General aviation pilots reported that while in formation flight one pilot performed an unexpected maneuver that resulted in an NMAC with one of the other aircraft.
Narrative
I was the flight lead of a formation during an airshow. All were in a briefing the day of the show. We entered the brief with plans to do a formation. Mid way through the Brief; it was determined it would be better if the military trainers flew single ship vs. a formation since the Pyrotechnics Guy wanted to detonate after fast-movers passed. Just before the Brief ended; the Air Boss said we could make 1 pass in formation and then split up for single ship passes. We were told to 'keep it tight' so we could get possibly more than 1 pass. Jets were in a group in a pattern with an altitude block (on the downwind) from 800-1000' AGL. Formation passes at 300' and Single Ship passes at 200' down the runway were approved. Jets were at the bottom of the stack and would fly first; then the middle stack above us; then the high stack above other military trainers (2300-2600' AGL). Our group took off as a formation and immediately entered our Pattern; came down the runway at 400' and turned crosswind back into our pattern altitude. Speed was approximately 200 KIAS. I moved Aircraft Y to the left wing and we increased speed on the downwind. We had briefed a 10 second break for our single ship fly-by's at full power. I turned in as Lead with Smoke On as I entered the fly-by 500' line. I passed center at 320 KIAS and 200' AGL. I turned crosswind and was climbing (very fast) to the downwind. I turned well in front of the formation group that was holding at 1500 - 1800' AGL. When I rolled out on the downwind I realized I was at 1200' AGL and immediately pushed over to get back under 1000' AGL. I asked the Air Boss on the downwind if we had another pass and he said no and directed us to land. I slowed the jet and set up for landing. In the de-brief back on ramp; Aircraft Y indicated that he got in my smoke and the black (pyro) smoke and thought he was too low so he pulled up and entered the cross-wind and climbed above 1000' on the downwind as well forgetting about the ceiling. Aircraft Z indicated he lost sight of Aircraft Y on the fly-by and when he saw Aircraft Y's nose climbing to the right (to enter the crosswind); he had to pull harder to avoid Aircraft Y which put him up even higher (crosswind to downwind?) near around 1750' AGL. Aircraft Z came within 100' of their formation belly up to them. I can't explain how Aircraft Z was so close to Aircraft Y and had to pull up to avoid Aircraft Y. A 10 second break and full power (as Aircraft Y indicated he was) should have created sufficient distance between Aircraft Y & Aircraft Z. This was a severe screw up that could have ended in a mid-air disaster. Although each of us were briefed on the airspace and cautioned to remain inside it at all times; we all exceeded 1000' AGL on the downwind putting others above us at risk. This can never happen again.In retrospect; I could have reiterated that if anyone loses sight of the aircraft in front of them; they should call it; hit their speed brakes and simply fly straight ahead; contact the air boss to get back in sequence vs. pulling up. We could have flown our single ship fly-bys at a much slower airspeed (vs. full power) which would have help avoid the high g and climb rate on the crosswind to downwind turn. Both Aircraft Y and Aircraft Z had flown elsewhere and said their instinct at the time was to pull up vs. remembering the 1000' ceiling that was briefed in the briefing.Jets are made to go fast and are exciting. Things also happen much quicker (higher climb rate than a slow mover). I would suggest putting the JETS up to the top of the stack so when it's their time to do fly-bys; there are NO aircraft above them and no chance this could happen in the future; whether a pilot deviated from the Brief or not.
Second reporter narrative
Chain of events: How the problem aroseDuring the flight; our 3 jets were assigned to take off and immediately enter the lowest flyby circuit of runway XXR at ZZZ [airport]. The height of the pattern was to be no lower than 200 feet over the taxi way and no higher than 1000 feet (800 preferred) behind the spectators.Our three aircraft launched as a formation takeoff; immediately turned right and entered the flyby pattern. One pass was in formation; as briefed we broke to base with 10 second interval spacing and accelerated to max forward speed during the descent to 200 feet. Upon reaching the threshold for the flyby each aircraft agreed to put on our smoke trail.As Aircraft Z; I rolled out on a one and a half miles final and on centerline of the flyby threshold at approximately 700 feet and I expected to see Aircraft Y most of the way through his pass below and in front of me. I saw the aircraft ahead pulling up as expected but a split second later the aircraft color confirmed I was looking at Aircraft X. Aircraft X's smoke trail obscured the flyby pattern and now I think also Aircraft Y. I stopped my descent at 400 feet and searched for Aircraft Y. During his accelerating descending base turn Aircraft Y had gotten wide and his larger turn radius and slower acceleration allowed me to close our spacing. As Aircraft Y corrected back toward the flyby path and with the ground munitions and Aircraft X's smoke obscuring his view he climbs and I lose sight of him as he goes under my nose. Having SA (Situational awareness) on the formation in the circuit above and chose to climb away from my threat from below; knowing that passing close behind the formation above I would not be a conflict for any formation following them.Contributing factors: Absolute boundaries. Runway XXR separates the flyby patterns at the airshow; this runway is treated by all crews as a brick wall not to be crossed. So the flyby pattern (Taxiway for XXR).The spectator area; cannot be flown over under 1000 ft. The ceiling of the low flyby pattern is 1000ft. Basically meaning a tunnel the flyby pattern is a tunnel 200 feet wide and 600 feet tall.Our 10 second spacing at 300 knots and 'then accelerate to full power' in the descending break to final was our mistake.Corrective Action: Brief speeds to fly once formation separates; not what we did 'wide open or full power'. Our Briefs at airshows need to include 'what if' scenarios. Human Performance Considerations - judgementWith the brick wall - spectators - and an aircraft merging out of sight; my decision to climb into blue sky near but close behind the formation above was the action I took and believe was the safest course of action.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.