What stability issue can result from negative longitudinal stability?

Negative longitudinal stability means that when the aircraft experiences a pitch disturbance, it will not return to its original attitude but instead will continue to move away from it. This can lead to significant problems in controlling the aircraft, particularly during critical phases like a stall.

In the context of stall recovery, negative longitudinal stability can result in the aircraft becoming more difficult to control when attempting to recover from a stall. When the aircraft stalls, it may not respond predictably to control inputs because of its inherent instability. Pilots rely on the predictable behavior of the aircraft to perform maneuvers safely. If a plane has negative longitudinal stability, the actions taken to recover from a stall may not be effective, and the aircraft could continue to behave erratically or worsen the situation instead of regaining controlled flight.

The other options describe issues that are either not directly linked to negative longitudinal stability or refer to characteristics typically associated with different stability parameters or flight conditions. For instance, the inability to recover from increased altitude, loss of control during high-speed maneuvers, and enhanced efficiency in climb rates do not directly correlate with the inherent instability characteristics introduced by negative longitudinal stability.