'Pippa' was originally a navigator, then after a crossover course, became a Vulcan co-pilot. When the Vulcan left service, he was unsuccessful at TWU and was offered a choice of another ME pilot slot, or a FJ navigator slot - he chose the latter.
Not quite accurate. He withdrew from pilot training before re-roling as a navigator. It is true that he was unsuccessful at TWU, but, I believe, indirectly related to his performance in the air. Being a QWI Air Defence and Ground attack on both F4 and Tornado is no mean feat.