Helicopter Dynamics · AERO

Low Rotor RPM Decay on Takeoff & Blade Stall Trap

CASA Ref: CASR Part 61 MOS Schedule 3 AD(H) 1.4 · FAA Ref: FAA-S-ACS-15 Area I Task E (Helicopter Aerodynamics)

Scenario & Physics Summary

Over-pitching collective at low power causes rotor RPM to decay below operating limits, leading to rotor stall and rapid descent.

Interactive 3D Visual Plates & Scenario Media

Low Rotor RPM Decay on Takeoff & Blade Stall Trap Plate 1

Plate 1: Low Rotor RPM Decay on Takeoff & Blade Stall Trap

Low Rotor RPM Decay on Takeoff & Blade Stall Trap Plate 2

Plate 2: Low Rotor RPM Decay on Takeoff & Blade Stall Trap

Low Rotor RPM Decay on Takeoff & Blade Stall Trap Plate 3

Plate 3: Low Rotor RPM Decay on Takeoff & Blade Stall Trap

Low Rotor RPM Decay on Takeoff & Blade Stall Trap Plate 4

Plate 4: Low Rotor RPM Decay on Takeoff & Blade Stall Trap

Aerodynamic & Operational Physics

Rotor thrust depends on rotor RPM squared (T ∝ RPM²).
If collective is raised beyond engine horsepower limits, drag exceeds engine torque, decaying rotor RPM.
As RPM drops, pilot pulls more collective to maintain lift, increasing pitch and drag further—entering rotor stall.
Recovery: Immediately LOWER COLLECTIVE to reduce drag and restore RPM.

CASA & FAA Exam Gotcha Alert

CASA / FAA Exam Trap: Pulling collective when rotor RPM is decaying accelerates rotor stall. You MUST lower collective immediately.

Frequently Asked Questions & Exam Explanations

How do you recover from decaying low rotor RPM in flight?

Immediately lower collective to reduce blade drag, roll throttle on, and push forward cyclic to unload the disc.

Master Low Rotor RPM Decay on Takeoff & Blade Stall Trap in the Simulator

Drill targeted CASA and FAA exam questions with step-by-step mathematical decoders and regulatory clause links.

Take free CASA diagnostic test →