I read this back in the late 1970's as a young teen.

I think it was set in the Caribbean and involved a couple of down on their luck pilots.  One pilot had just been released from prison after a people smuggling scheme went bad in England and resulted in a death (a Chinese VIP tried to run off the wing when police arrived and fell into the prop) for which he was held responsible.  He had taken the job to make some quick cash for his young wife.

The pilots were old friends and got involved in some kind of jewel smuggling caper with a ruby I think was called the Coeur de Leon.  Anyway, the ex-con pilot ends up getting killed and his friend goes after the gang that killed him.  I think.

I just remember liking the book and I've been rereading some of the books of my misspent ute.  I had also recently seen "The Man Who Would Be King" and I imagined Sean Connery as the bitter driven ex-con and Michael Caine as his friend watching him spiral down.

I cannot remember the title for the life of me!  I thought is was "The Heart of the Lion" or "The Lion's Heart" but neither have turned anything up on Google...

Help me, Arf Komenobi, you're my only hope!

Anyone?