Class B · speeds and engine failure

Distinguish stall, control and performance limits on single- and multi-engine propeller aeroplanes.

What protects the margin above the stall?

VS is a stalling or minimum steady-flight speed in the stated configuration; VS0 is the landing-configuration value and VS1 is a specified-configuration value. VR begins rotation, the speed at 50 ft belongs to the take-off demonstration, and VREF is the landing reference speed. They have different roles and may use different stall references.

Know what each speed promises

For common legacy CS-23 class-B examination data, single-engine VR is at least VS1, and the speed at 50 ft is at least 1.2 VS1; normal landing VREF is at least 1.3 VS0. For a conventional multi-engine legacy case, VR is at least 1.05 VMC and 1.10 VS1; the 50-ft speed is at least 1.10 VMC and 1.20 VS1. Use the most restrictive applicable term. These ratios are linked to the stated legacy certification basis; use the given AFM for actual type speeds and any different category/amendment case.

Control is not climb

The critical engine is the one whose failure most adversely affects performance or handling. On many conventional twins with both propellers rotating clockwise as seen by the pilot, failure of the left engine leaves the larger right-engine asymmetric yawing moment; counter-rotating designs may have no critical engine in that sense.

A windmilling propeller increases drag; feathering reduces it when approved. An engine failure also introduces yaw and trim drag and reduces available power. VMC reflects directional controllability under specified conditions, not a guaranteed climb. In a normally aspirated twin, high density altitude can reduce asymmetric thrust and VMC while simultaneously worsening climb. Lower VMC therefore does not mean safer terrain clearance.

Can you make the performance decision?

Four original questions. Work from the stated conditions and review the reasoning.