Definition
VYI is the helicopter airspeed that produces the greatest gain in altitude per unit of time when the aircraft is climbing from an in-ground-effect (IGE) hover. It is the rotorcraft equivalent of a fixed-wing VY but referenced to a departure made from a low hover where ground effect is still available at the start of the climb.
Plain English
It's the speed a helicopter should fly to climb the most feet per minute when starting the climb from a low hover near the ground.
Context Anchor
Seen in helicopter instrument procedures, including copter GPS approaches and missed approach climb-performance discussions.
Derivation
V stands for velocity (speed), Y is the standard aviation code for best rate of climb, and I indicates the climb begins from an in-ground-effect hover. So VYI reads as 'velocity, best rate of climb, in-ground-effect.'
Why Pilots Care
Provides the fastest altitude gain when climbing out of an approach in low visibility or after a missed approach.
Intuition Check
Do not assume VYI is always the same as ordinary VY. The I means the speed is tied to instrument-flight climb use, so use the value published for that helicopter.
Example Sentence 1
After lifting into a low hover, the pilot accelerated to VYI to climb out at the best rate of climb.
Example Sentence 2
The procedure called for maintaining VYI until reaching the published climb altitude.