A little more to add to Spunk's post about the fuel tank AD's. This comes from
here and simply states,
Current production R44-series helicopters have a more rugged, environmentally sealed rotor brake switch. This bulletin requires replacement of earlier switches.
From what I have been told, the rotor brake lamp switch (reed switch attached to rotor brake system) is the probable source of the spark that is causing the post crash fires. Simply, as it always has power going to the switch, it becomes the ignition source for the split fuel when the tanks burst!
Yet Robinson describe the change simply as "a more rugged, environmentally sealed rotor brake switch" to disguise its the importance of carrying out this this SB.