Apparently a Multiflight aircraft operating out of Leeds Bradford. The only R22 registered to their name is G-FIRS, which is white in colour and this would coincide with the colour of the aircraft shown in the picture of the wreckage. RIP and again my thoughts are with his family and friends.
'Loud crack' is only one mans interpretation of the noise and could be any number of things and so speculation in this area won't really gain anything, however all I can say is that, if the engine was still running, it must have been a very loud crack for somebody to have heard it from a fair distance.