Would it help us to know what sort of outdoor instructor - e.g. outward bound, or gardening? Our replies might be different then. I can think of more than three instances when written work could be necessary, but here are some:
Say it's a gardener and he is training other gardeners.
a) a lesson plan showing what he's going to be teaching them, say during the next week
b) health and safety guidelines in plain English eg about putting a fork through your foot, dealing with chemicals etc, making reports in case anyone does have an accident
c) writing up student reports on progress
The same would apply in principle if it's an outdoor sports person but the context and examples would be different.
I hope this helps.