Runway take-off phases: the lift-off distance is defined as the distance along the runway centerline from the start of the take-off roll up to which characteristic point?

Introduction / Context:
Take-off performance is split into ground roll, lift-off, and climb segments. Accurate definitions matter for declared distances, obstacle clearance, and performance charts. “Lift-off distance” pinpoints the instant the aircraft transitions from rolling to flying.

Given Data / Assumptions:

• Runway centerline reference.
• Standard take-off phases: ground run → rotation → lift-off → climb.

Concept / Approach:
Lift-off occurs when aerodynamic lift exceeds weight sufficiently and the main wheels leave the runway. Distances to other reference heights (e.g., screen height 10.7 m) belong to separate definitions (take-off distance to 35 ft) and must not be confused with lift-off distance.

Step-by-Step Solution:
Identify phase transition: wheels-off-ground point = lift-off.Exclude runway end/stopway: these are infrastructure limits, not performance milestones.Exclude the 10.7 m height: this is screen height for obstacle clearance, not lift-off.Select the airborne point definition.

Verification / Alternative check:
Aircraft performance manuals distinguish lift-off distance (ground run to airborne) from take-off distance to screen height and balanced field length used in field limiting calculations.

Why Other Options Are Wrong:

• Runway end/stopway: physical boundaries, not aerodynamic milestones.
• 10.7 m height: relates to take-off distance over a screen height, not lift-off.

Common Pitfalls:

• Mixing “rotation” point with “lift-off”; rotation precedes lift-off.

Final Answer:
The point where the aircraft first becomes airborne (wheels leave the ground).