Lokuttara Paṭicca-samuppāda and the Spiral Path

The doctrine of paṭicca-samuppāda, or dependent arising, forms one of the core teachings of the Buddha. The Theravāda commentarial text Nettipakaraṇa divides the applications of this doctrine into two major categories. The first category, ‘lokiya paṭicca-samuppāda’ is very well known, representing ‘worldly’ conditionality as a sequence of twelve nidānas. The second category, called ‘lokuttara paṭicca-samuppāda’, creates a model of the process of liberation from the same lokiya paṭicca-samuppāda at the point of ‘jarā- maraṇa’, a term that is curiously replaced by ‘dukkha’, suffering. Applications of the second category are also referred to as the ‘Spiral Path’ after the coinage of Sangharakshita, the pre-eminent modern exponent of this aspect of Buddhist doctrine. I have some queries regarding this: The Upanisā Sutta that deals with lokuttara paṭicca-samuppāda in detail, traces the chain of this transcendental conditionality step-by- step in a retrograde fashion from the ‘Destruction of the Cankers’ to ‘Faith’ and it is easy to understand how each such nidāna becomes the supporting condition of the next. However, I am unable to make out how ‘Suffering’ forms the supporting condition for ’Faith’ to arise. Could this be clarified? The second query is why is lokuttara paṭicca-samuppāda also called the ‘Spiral Path’ by Bikśu Sangharakshita? Lastly, why is the nidāna of jarā- maraṇa replaced by the more general term dukkha in the concept of lokuttara paṭicca-samuppāda?