Definition
A rule of thumb for selecting a safe minimum approach speed in a single-engine airplane on a stabilized final approach in calm or near-calm wind. The recommended approach speed is approximately 1.3 times VSO, where VSO is the airplane's stalling speed in the landing configuration (full flaps, gear down, power off) at maximum landing weight. Multiplying VSO by 1.3 yields a target final approach speed that provides a safe margin above the stall while remaining slow enough for a controlled landing. Manufacturer-published approach speeds, when given, take precedence over this rule of thumb.
Plain English
A quick way to figure out a safe speed for final approach: take the airplane's landing-configuration stall speed and multiply it by 1.3. That gives you a final approach speed with a comfortable cushion above the stall.
Context Anchor
Seen in FAA handbook discussions that use formulas involving stall speed or airplane performance.
Derivation
VSO is a standard FAA airspeed code: V for velocity, S for stall, and the subscript 0 indicating the landing configuration (flaps and gear fully extended, power off). The 1.3 multiplier comes from long-standing certification and handling practice as a safe margin above the stall.
Why Pilots Care
Knowing the actual stall speed at the current load factor prevents an unintentional stall during turns or recovery from unusual attitudes.
Analogy
If V_SO were 50, then V_SO² would be 50 times 50, not 50 times 2.
Intuition Check
Do not read “VSO 2” as a second kind of V_SO or as V_SO multiplied by 2. In this formula notation, the 2 means squared: V_SO multiplied by itself.
Example Sentence 1
With a landing-configuration stall speed of 50 knots, the pilot used the 1.3 VSO formula to set a target approach speed of 65 knots.
Example Sentence 2
The pilot applied the VSO 2 formula before entering the traffic pattern to confirm adequate margin above stall in the planned turn.