Suppose that you feel a "bump" in flight. One "bang", judder of the airframe, no loss of power or lift, engine running fine afterwards and no sign of vibration or loss of control.
Would you auto, MAYDAY and power-on land in a public park in a large city?
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YES is the right answer.
Is it?
The example John gives has "no loss of power or lift, engine running fine afterwards and no sign of vibration or loss of control", so why the Mayday and why auto into the park full of people who don't know whats happening?
How about a Pan or Mayday and straight in to City Airport. You know, that place just over a mile away with the fire crews etc ready and waiting and practised in matters aviation! After all, no loss of power etc.
Why autorotate into the park full of people, oblivious to what's about to come down from the sky around them
John, I don't think it is the right answer in your example...to be honest it sounds like a glancing birdstrike!
In the referenced incident, the pilot had an apparent loss of power;
In this incident, "The pilot said there was a loud bang and then the helicopter started to drop", darn right...Mayday, Mayday Mayday.... But what's going on when there was time to call the Fire Brigade, who subsequently got the park cleared and then guided them in?
Firefighters from Millwall Station were called to clear the park and help guide the pilot to safety at around 5.30pm.
The big issue that needs addressing with this may be; Could this aircraft have 'alighted' without danger to persons or property on the surface if it really was a Mayday?