Definition
A crosswind component equal to 20 percent (0.2) of an airplane's stalling speed in the landing configuration (VSO). The FAA uses this value as a guideline for the maximum demonstrated crosswind component an airplane is required to handle during certification testing.
Plain English
Take the airplane's stall speed when it is set up to land (flaps and gear down), and multiply that number by 0.2. The result is the crosswind speed the airplane was tested against during certification.
Context Anchor
Seen when planning or evaluating takeoffs and landings in crosswind conditions, especially when comparing the wind across the runway with a conservative limit.
Derivation
VSO comes from aviation shorthand: V for velocity, S for stall, and O for the landing configuration (gear and flaps fully extended, often pictured as the 'O' for 'open' or as the bottom of the flight envelope). The 0.2 is simply a multiplier — twenty percent of that stall speed.
Why Pilots Care
Provides a simple rule-of-thumb threshold for deciding whether a crosswind requires a modified landing technique or warrants delaying the flight.
Grounding Statement
If the airplane’s VSO is 50 knots, then 0.2 VSO is 10 knots, so a 10-knot crosswind would meet this rule-of-thumb limit.
Intuition Check
0.2 VSO does not mean 0.2 knots, and it is not a separate published aircraft speed. It means multiply VSO by 0.2 to get a crosswind speed reference.
Example Sentence 1
If an airplane stalls at 50 knots in the landing configuration, its 0.2 VSO crosswind value works out to 10 knots.
Example Sentence 2
For this airplane, 0.2 VSO equals about 11 knots, giving a clear limit for normal crosswind landings.