How a helicopter glides — and lands — with no engine power.
By the end of this lesson you can:
Explain where the energy comes from in an engine-out descent.
Describe the driving, driven, and stall regions of the rotor disc.
State the two things a pilot protects first when the engine quits.
Read a Height-Velocity diagram and explain why the shaded zones are dangerous.
1 · The big idea
When the engine stops, the helicopter doesn't drop like a rock — it becomes a glider. As the aircraft descends, air flows upward through the main rotor and keeps it spinning. That stored rotor RPM is the pilot's "battery": you trade altitude for rotor RPM on the way down, then trade that RPM back for lift in the flare to cushion the landing. The two things a pilot protects the instant the engine quits: airspeed and rotor RPM.
2 · Watch: the concept explained
Curated reference clip — “What is Autorotation? | Helicopter Emergency Descent Explained,” 3G Heli Prep (YouTube). Embedded with the creator's player; we don't host or alter it.
3 · The rotor disc has three regions
In a steady-state autorotation the spinning disc divides into three zones: the driven (propeller) region near the tips that creates drag, the driving (autorotative) region in the mid-blade that actually sustains rotor RPM, and the small stall region near the hub. The pilot manages collective to keep these balanced so rotor RPM stays in the green. (See the FAA figure referenced below for the classic three-region diagram.)
4 · Watch: a real engine-out demonstration
Curated reference clip — “Strapped Into A Falling Helicopter,” Smarter Every Day #154 (YouTube). A real in-flight autorotation, shown for instructional purposes.
5 · Reference figures — use the authoritative charts
Height-Velocity diagram (the “dead-man's curve”)
Rather than a stylized redraw, study the real charts:
Your aircraft: open your Robinson R44 POH, Section 5 (Performance) — Height-Velocity Diagram. This is the chart that legally applies to N668SA; the shaded "avoid" area is specific to the R44's weight and density-altitude conditions.
✍️ Fill in for the aircraft you fly (N-________)
Value / limit:
R44 POH section & page:
Leave blank until you look it up in your R44 POH (see the reference above) and confirm it with your CFI. Aircraft-specific numbers vary with weight & conditions — don’t guess.
✍️ Fill in for the aircraft you fly (N-________)
Value / limit:
R44 POH section & page:
Leave blank until you look it up in your R44 POH (see the reference above) and confirm it with your CFI. Aircraft-specific numbers vary with weight & conditions — don’t guess.
FAA handbooks are public-domain U.S. Government works. In the published course these exact public-domain figures are embedded inline; your aircraft-specific H-V chart always comes from your POH.
Risk management (the “Consider”): the most common killer isn't the engine failure — it's the delayed reaction. Every second of hesitation lowers rotor RPM and shrinks your options, which is exactly why the Height-Velocity "avoid" zones are dangerous. We drill entries until they're a reflex and brief a landing spot continuously on every flight.
6 · Knowledge check
ACS-coded — framed the way the written test asks it.
Lesson complete ✓
Enjoyed the preview? The full Private (PPL-H) course covers all of ACS-15.