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Bumps During Helicopter Flight Can Prove Fatal

Rotorcraft are like another country because they do things differently there.

Tour helicopters are common along the scenic but inaccessible Na Pali Coast in Hawaii. [Adobe Stock]
Tour helicopters are common along the scenic but inaccessible Na Pali Coast in Hawaii. [Adobe Stock]
Gemini Sparkle

Key Takeaways:

  • Mast bumping is a catastrophic aerodynamic phenomenon specific to two-bladed helicopters (e.g., Robinson, some Bell models), occurring when the main rotor is "unloaded" in low or zero-G conditions, causing the rotor to flail and damage the airframe.
  • This phenomenon is typically initiated by severe turbulence or abrupt pilot inputs (like pitching down) and is disproportionately seen in Robinson helicopters, potentially due to their design, prevalence in training, and pilot demographics.
  • Pilot awareness, adherence to operational limits, and proper training are crucial to mitigate the risk of mast bumping, which has disastrous, often fatal, consequences.
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I learned to fly helicopters long ago, in a Bell 47, the little bug-headed two-seater familiar to viewers of M*A*S*H. Once I had the rating I seldom flew them again.

I did visit the nearby Robinson Helicopters factory from time to time, however, and the amiable Frank Robinson would send one of his pilots up with me to scuff some of the thick rust off my skills. On one occasion Robinson himself flew with me in an R22, and I remember his telling me that fixed-wing pilots transitioning into helicopters faced a special hazard because their instinctive reaction in certain circumstances, like suddenly noticing traffic on a collision course, was to pitch down. Pitching down was fine in an airplane but could have disastrous effects in a helicopter. 

Peter Garrison

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, ""Technicalities"" and ""Aftermath,"" with FLYING readers.

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