Jonathan Jenkins will run the equivalent of five-and-a-half marathons across the Sahara Desert in the Marathon Des Sables.
He will have to carry all his provisions except water with him as he traverses the sandy terrain in temperatures of up to 50 degrees - it's little wonder some 10% of runners fail to complete the extreme endurance test.
But Mr Jenkins, who is CEO of the Social Investment Business, which helps finance charities and social enterprises, cannot wait to embark on the challenge on April 8.
'Wife was fed up of wearable media and Vaseline'
"I have always wanted to run the ultimate marathon – the Marathon Des Sables – but marriage, two young kids and a wife that was fed up of wearable media and Vaseline meant this ambition had to be parked," said the 45-year-old, who has already completed 10 London Marathons .
"I've never directly needed the help of London's Air Ambulance, nor have any of my friends and family, but as a very proud Londoner, it struck me that the work, the stories and the ambitions of the charity resonated deeply with me."
He is already halfway towards his £10,000 target for the charity , which treats on average five critically injured patients across the capital each day.
London's Air Ambulance CEO Graham Hodgkin praised him on behalf of the charity's many patients for taking on such a "crazy endeavour".
You can donate at Jonathan's JustGiving page here.