Retreating blade stall

In helicopters, a hazardous flight condition where the retreating blade stalls due to excessive angle of attack. Retreating blade stall occurs at high forward airspeeds and is one of the factors limiting helicopter airspeed. Retreating blade stall is more likely to occur when the following conditions exist at high forward airspeed:

• High gross weight
• Low rotations per minute
• High density altitude
• Steep or abrupt turns
• Turbulent air

The stall reaction is rapid and violent resulting in pitch up and roll towards the retreating blade. In most cases recovery is not possible.

References

Basic Helicopter Handbook, US Department of Transportation, Federal Aviation Administration