Lead changes may not be accomplished with the formation in which position?

Lead changes in formation flying are crucial for maintaining effective and safe communication and navigation among aircraft. In a fingertip formation, the aircraft are very close together, with the wingmen maintaining a specific distance and alignment to the lead. This tight spacing is designed primarily for visual formation flying and allows for effective maneuvering and display.

However, the tight proximity in fingertip formation also limits the ability for smooth lead changes. The adjustment required for a wingman to transition to the lead position without disrupting the flow and maintaining the necessary distance and alignment can be challenging. This close-knit configuration does not provide the necessary room for the lead aircraft to move to another position, which can cause disruptions in the formation.

In contrast, positions such as line abreast, tactical, and trail allow for the flexibility needed to make lead changes safely. These formations are designed with enough spacing to facilitate a shift in the lead without compromising the integrity of the formation. Therefore, fingertip formation is not suitable for lead changes due to its restrictive nature, making it the correct answer.