What risk is associated with excessive aircraft weight at takeoff?

Excessive aircraft weight at takeoff significantly increases the risk of a stall during flight. When an aircraft is heavier than its optimal weight, it requires a longer distance to achieve the necessary lift for takeoff. As the aircraft accelerates down the runway, the margins for error become diminished; if the angle of attack exceeds the critical value before sufficient lift is generated, the wings may not produce enough aerodynamic lift, leading to a stall.

In contrast, the other choices do not accurately describe the effects of excessive weight. Increased stall risk is a direct consequence of having a heavier aircraft because it alters the lift-to-weight ratio. Decreased fuel consumption is not associated with increased weight; rather, heavier weights typically lead to higher fuel consumption due to increased drag and a more powerful thrust requirement. Enhanced lift is not achievable with excessive weight; instead, it can hinder the lift generated, making it harder to reach necessary flight parameters. Lastly, excessive weight does not shorten the takeoff roll; it typically extends it because the aircraft requires more speed to achieve lift.