John Stanoch's Squadrons uses the same basic movement system and other basic mechanics as his later Blue Sky rules series although there may be some minor differences. The principal difference, as I recall, is that Squadrons uses D6 for firing while the Blue Sky rules use D10s. There also may be some "theater" specific rules in some of the Blue Sky series-I never compared them so I don't know for sure.
Black Cross/Blue Sky is the replacement for Squadrons, but it is considerably more expensive as it included plastic flight stands and cardboard aircraft cutouts to make it a complete game in a box, while the other Blue Sky rules were miniatures rules only without the aircraft or flight stands.
John's Blue Sky rules are theater and period specific. So, for example, Squadrons (and later Black Cross/Blue Sky) are essentially Battle of Britain rules, while the others are eastern front, war in the Pacific and so on.
Although the basic flight and shooting mechanics are the same over the series (with possibly some mods for specific theaters and with the difference for Squadrons as mentioned above) the main difference, and reason for the various sets of rules is that each contains the aircraft stats for only those used in the theater and time period represented by the rules. So, for example, you won't find aircraft stats for the Mitsubishi AM-6M 'Zero in White Star/Blue Sky (8th AF rules).
Now for the good news; Marty Fenelon at MSD Games LLC has most of the Blue Sky rules in stock-not Squadrons or Black Cross/Blue Sky. More important though, he also has available as downloads the Blue Sky system stats for what seems to be all aircraft. So if you want to try Blue Sky you should be able to get some rules and most or all aircraft stats from MSD Games.
Also, you might want to read this past thread from TMP:
TMP link
