Originally Posted by
Fareastdriver
The problem with twin rotors is the transmission. Apart from the Belvedere one or more of the gearboxs was dependent on a shaft to drive it. This breaks and you have a fatal disymmetry of lift. Luckily AFIK this hasn't happened yet.
The problem here is that two helicopters are being forced to fly in close formation with each other. They are so ugly that they repel each other, so sometimes the shaft breaks.
The shaft certainly has broken on an RAF Chinook, at Odiham. Thankfully the aircraft was in the low hover and the occupants escaped intact. Mind you, everything else broke, too. The pilot told me that after it fell to the ground like a railway carriage, he naturally reached up to shut the engines down and the engine controls had departed, along with the cockpit roof, which was also missing.