Originally Posted by
The Sultan
The noise being discussed is consistent with a blade tip coming apart. It recures at 6.56 Hz, but is made up of higher frequencies in the audible range.
Yes, it wasnt 5Hz mike my first guess but around 6.7 Hz for the initial three thumps using a analyze tool. 6.56-6.57 hz would bee the 1/rev sound from a 206L. Not a too bad match.
The time increases between the pulses after around 5 of them.
Breaking a blade loosing more than a little of the tip and getting very high imbalance would explain the input drive shaft from engine breaking, or the motor stopping to produce torque = reducing Nr just like the increased time between each sound pulse.
It would also probably explain the detachment of the MGB with the ripping of the roof and tail bom loss.