VX, best angle of climb speed

VX is the designated airspeed for the best angle of climb. At VX, an aircraft gains the most altitude for a given horizontal distance. Pilots use it when obstacle clearance requires the steepest climb path, subject to the aircraft's POH or AFM procedures and limitations.

What it is used for

VX is an indicated airspeed, normally published in KIAS. It is aircraft-specific and can change with configuration, weight, altitude, and model or serial-number variant. The value may also change with altitude in some aircraft. Do not substitute a remembered value from another aircraft or model.

Best angle and best rate are different objectives. VY produces the greatest altitude gain over time. VX generally provides a steeper path but a lower climb rate than VY. The aircraft handbook explains how to use each speed during takeoff and climb.

Example

A POH may publish a VX value for a specific aircraft configuration and weight range. During an obstacle departure, the pilot uses the procedure and speed specified by that POH, then transitions to the applicable climb speed when the obstacle requirement no longer controls. This example does not supply a generic speed because values vary by aircraft.

Why it matters

Using an incorrect VX can change the aircraft's climb path, engine cooling, controllability, and runway or obstacle margins. The speed is not a guarantee of obstacle clearance. Runway slope, wind, density altitude, loading, aircraft condition, and pilot technique also affect performance.

Read the applicable POH or AFM before using VX. This glossary entry provides terminology only and does not replace aircraft-specific performance data.

Related terms and tools

• VY, best rate of climb speed
• Indicated airspeed
• FAA Pilot's Handbook of Aeronautical Knowledge