Readers may be familiar with the phenomenon known as 'ground resonance'. Wikipedia has an article about it, but briefly, the dynamic balance of a helicopter's rotor system may become disturbed, leading to distortion between its axis of rotation and the system's center of gravity. This places excessive strain on the helicopter, which can lead to serious damage or even total destruction of the aircraft.
That's what happened to a rescue helicopter this week during a landing in Brazil. The Telegraph reports:
Brazil's Regional Service for the Investigation and Prevention of Aeronautical Accidents is looking into the reasons why a rescue helicopter disintegrated shortly after landing in the northern state of Para on Wednesday.
. . .
Officials believe the helicopter experienced what is known as ground resonance, a condition that happens when the aircraft's rotor is working while the helicopter is on the ground.
Four people that were travelling aboard the helicopter were injured.
Here's how it looked to a nearby cameraman.
I'm glad I wasn't aboard at the time! You can see more videos of ground resonance on YouTube.