Is there a practical way to fly within sight of each other, without freaking out controllers? Not really formation flight (flying formation or flying in formation), but within easy visual range under VMC?
I don’t want to encourage anyone who has not had close formation flight training, to do it anyway. That is not just a casual disclaimer. Untrained formation flight has killed many pilots. Even TRAINED formation flight has killed a lot of pilots; I have watched four very experienced people die doing it (so far). That doesn’t include the major fubars we have all seen on TV, at a few of the world’s major airshows.
Personally, I consider a half-mile separation to be a safe “loose formation” flight, as long as there is continuous cockpit communication and the trailing aircraft always has the lead in sight. You have to select an unused radio channel for air-to-air; normal A-T-A is often too congested. You need prior agreement on who will be Lead, and what the wide-separation plan will be if the Wingman loses sight of Lead. The separation plan has to ensure that you won’t collide while looking for one another. Altitude separation is a key component. There are multiple ways to handle this. Attempts to re-form, when untrained, are the most dangerous aspect. I have personally seen two planes come within a couple of hundred feet of each other, attempting to re-form, with one of the pilots never seeing the other plane as it whipped by. A couple of hundred feet isn’t very much, with a closing rate exceeding 300 knots (about one-half second). On the other hand, if you agree on a common altimeter setting via radio, and agree on each other’s respective separation altitudes with 1,000′ difference, and agree on a GPS position, heading, and groundspeed for a reform position, it can be safely accomplished. Once Wing has Lead in sight, the altitude can be matched back up.
The way to handle this with ATC, both in the USA and in Canada, is to announce a “flight of two”. Lead is responsible for NAV and ATC contact. The Flight will be named by ATC for the Lead, such as “Sierra Flight”, or “Sierra Flight Of Two”. Wing is supposed to turn their transponder to Standby, so that ATC doesn’t have warnings going off all the time. Every Tower, Approach, and Center I have experienced has readily approved Flight Of Two operations, including takeoffs and landings. You matter-of-factly make the call, such as “SGJ Tower, Sierra 18767 Flight Of Two at Kilo with Romeo, ready to taxi for northbound VFR”. They matter-of-factly clear you as requested. You line up on the runway, with the planned separation, when Lead+Flight is cleared to take the active. Ditto for calls to Approach or Tower when inbound.
Loose formation means Wing starts rolling as Lead breaks ground; and Wing touches down as Lead readies to clear the active. Wide runways enable Lead to use the right side while Wing uses the left side. Narrow runways mandate a longer separation. This spacing enables Wing to handle arrival and departure maneuvering while keeping Lead in sight. Lead announces all turns in advance, as well as altitude call-outs. If you pre-plan slight turns to course during climb-out, it makes it easier for Wing to keep up with Lead (by turning slightly inside), and to keep Lead in sight (ahead and above). It is amazing how hard it can be to keep Lead in sight, until you have some experience. If the planes have unequal performance, the slower plane flies Lead. If they have equal performance, Lead climbs on slightly reduced power (again, pre-planned power settings). Lead NEVER maneuvers while looking for Wing; Lead flies the preplanned or announced course, as smoothly as possible. Two planes, with both trying to find one another, is a recipe for disaster.
This is really nothing more than rapid ops, as is performed at nearly all major airshows to accommodate the arrivals and departures, rather than true formation flight. It still requires care and planning, to be safe. Closure rates can far exceed what we ever deal with in day-to-day life, with our reaction times found lacking. The preflight planning has to ensure that you cannot wind up in circumstances that could lead to a collision, no matter what happens (lost comm, weather, lost visual contact, etc.).