[FG28_Kodiak]

yes its possible.

    public int GetSumAllPlanes()
    {
        int planeCount = 0;
        List<AiAirGroup> allAirgroups = new List<AiAirGroup>();

        if (GamePlay.gpAirGroups(1) != null)
            allAirgroups.AddRange(GamePlay.gpAirGroups(1));

        if (GamePlay.gpAirGroups(2) != null)
            allAirgroups.AddRange(GamePlay.gpAirGroups(2));


        allAirgroups.ForEach(item =>
            {
                foreach (AiAircraft ac in item.GetItems())
                {
                    planeCount++;
                }
            });

        return planeCount;
    }

before loading a new mission you can check for example

if(GetSumAllPlanes() < maxPlanes)

You can also use AiAirgroup 's NOfAirc but it seems buggy in the current Clod Version, it sometimes not show the correct Numbers of Airplanes in a group. So it's better to add the Aircrafts like above.