LD1
Epic Contributor
That's what is called a 'barber-chair'. Certain species of tree with specific grain structures are especially prone to this, ash being one of them. Leaners are even more prone to this, because of the extra stress on the holding wood during the backcut.
See this thread for a good explanation and some tips: http://www.arboristsite.com/tree-care-videos/177328.htm
With a lean you need to make your face cut then plunge through to make your hinge (being careful of kickback and not leaving your hinge too thin) then cut from hinge to the back instead of from the back in.
You can also chain the tree above your cut to help prevent it from splitting out.
:thumbsup::thumbsup:
I cant add much.