What maneuvers are permitted in ET (III)?

The correct answer highlights the specific maneuvers that are permitted in the ET (III) stage of training, which focuses on safe and controlled aerobatic flight within a formation context. The modified Cuban 8, loop, cloverleaf, and barrel roll are maneuvers that maintain a level of safety and control suitable for formation flying. These maneuvers are designed to be executed with precision and coordination among the formation members, ensuring that the formation remains tight and within safe parameters during performance.

In contrast, maneuvers such as flat spins are highly risky and do not maintain the controlled environment necessary for formation flying, making them inappropriate for this stage of training. Additionally, while speed brake deployment can be a part of flight operations, it typically does not fall under aerobatic maneuvers, hence its exclusion from the list of permitted actions. Wingtip rolls, often more extreme in nature, also do not align with the controlled maneuvering that ET (III) requires. Thus, the selected answer reflects the essential need for safety and discipline in aerobatic maneuvers conducted in formation.