Tinkering with the rules, are we? Why yes, yes I am! While I find Check Your 6! to be a fairly comprehensive rules system, at times things "just don't seem right for the times." Hence, like many other gamers, I have found that a few adjustments here and there bring a bit of clarity or added realism without adversely impacting the game flow. To that end, what follows are a few modifications we use - some are from other sources, and a couple are original (as far as I know) from the Check Your 6! Southwestern Ohio Group.

I will say right out of the gate that utilization of the narrow arc of fire is a must for me. While I have read the designer's notes about the wider arc, and understand the reasoning behind using same, the standard fire arc still feels a bit too wide for my purposes. As others have pointed out, planes with a higher maneuverability rate benefit from using the narrow arc, and as that leans more towards historic results, plus helps to make games last a bit longer, I am up for the narrow arc for all my CY6! games, and for front, side, and rear arcs.
Another rule I have tinkered with - out of ammunition results seem to happen a bit too frequently for my tastes. Perhaps it is the dice we use that seem to roll doubles more frequently than average, but we receive a lot of out of ammo results in our games. Upon reading first person and other accounts (being an an avid reader/researcher), what happened more frequently is some guns ran out of ammo, or some guns jammed, but not an all or nothing proposition. As a result, we often have gone to a quick house rule in which we roll a die to determine the actual number of guns that are out of ammunition, and by type if there is more than one type of gun firing. I have been using something like this: 1 - ignore out of ammo result, 2-5 - half the guns of the same caliber are out of ammo, 6 - apply the out of ammo result. If a second set of qualifying doubles are rolled later in the game, the aircraft is completely out of ammunition. If a single gun of a specific caliber is firing, then I apply this methodology: 1-3 - ignore the out of ammo result, 4-6 - apply the result.
This next rule comes from a few different places, but mainly from the Battles Above series of scenario books: aircraft may fire at targets one TAL higher which are moving at the same speed or faster with a -1 die roll modifier. This is another area in which I have come across many mentions of pulling up lower than the target and firing a burst. Granted, there is not usually a large different in altitude between target and attacker, but having this option from one TAL below makes sense.
Next, Strafing attacks must be made from three or less hexes away from the target and only at TAL 1 or 2, within the SURFACE LOW CAB. I believe this is another one from the Battles Above books.
Again, from Battles Above - for added playability, planes with a maximum speed of three, when taking engine damage, reduce their maximum speed to two instead of one. Who in the heck wants to be stuck with a plane that moves but one hex per turn?
Aircrew quality, or the lack thereof, as portrayed in the Korean War scenario book, should probably be used more often for certain nationalities. Examples during World War II might include some Chinese, early Soviet, and several satellite countries where training was often rudimentary. Therefore, poor (-1) aircrew are treated as green (+0) but take a minus one (-1) die-roll penalty when making aircrew checks and firing.
And a new one that has been bandied about a bit by the group: changing the dice used for damage. Leave LMGs as a D4, early or less effective HMGs as a D6, bump up the highly effective .50 caliber to a D8, leave the "normal" 20mm cannon as D10, but take the better performing British 20mm to a D12, and then the heavy stuff still comes in at a D20. This is an easy way to replicate weapons that performed at a higher standard. We have not tried this one yet, but in reading reports of pilots using .50 machine guns and how they would chew up about anything they hit leads me to believe they should deliver damage results closer to a standard 20mm.

When an aircraft is destroyed, the rules call for an aircrew survival check using the same damage results. This has given us many game examples of United States Korean War pilots rarely surviving, yet the historical record was that many U. S. pilots during that conflict, even with their planes holed with Soviet rounds, survived were able to be rescued. However, using the same damage results rarely yields a crew survival. Therefore we have been thinking that a survival roll should be a basic aircrew check (with no modifiers for crew quality as an ace has no better chance to survive a shootdown than does a rookie), but use a nationality modifier. Therefore those U. S. pilots during Korea might gain a positive modifier while nations with a poorer or even nonexistent search and rescue process would have a detrimental roll. We still have to try this, but it seems to make sense.
I would be curious to see other "house rules" so please feel free to leave a comment below with ones that you utilize or have created.