I have followed this thread with interest regarding large aeroplanes flying aerobatic manoeuvres but also with some incredulity over the arguments regarding the 'g' used. If I may feed in some food for thought ...
To a pilot, 'g' is load factor = Lift/Weight. Therefore, if an aeroplane is flying at '1g' Lift=Weight. However, to a physicist, an object subject to 1g has an acceleration in a specified direction of 9.81m/sec2. Therefore, he/she would view an aircraft in straight and level, constant speed flight as being at 0g along all three axes. An accelerometer fitted to an aircraft to measure 'g' should, to a physicist, be calibrated to indicate 0g when level and static but, by convention and to be useful to a pilot as an indicator of load factor, it is calibrated to read +1.
Based on the above, I pose a question to those who have referred to a '1g' loop; what is your frame of reference? If it is 0g when straight and level then you could, if you had enough thrust, theoretically fly a loop with +1g indicated throughout.
For aircraft that have indications of longitudinal or lateral g, note that when at constant speed and under conditions of zero sideforce then the longitudinal and lateral 'g' respectively are both zero and when accelerating/decelerating and sideslipping these are true linear acceleration values.