There are very specific rules on the legal right for the pilot to defend himself / the aircraft or the occupants thereof, but then again it is not in flight so they may not apply. As a pilot you inherit the powers of a constable which is along the lines of any means necessary. I should look them up, it's in the airlaws book and online.
Any powers gained as a pilot are in addition to those available to the general public. And any member of the public may use reasonable and proportionate force as appropriate and as specified by law - can't recall the NT law but it's Section 462a of the Crimes Act here in Vic. So yes, the pilot could have defended themselves or their pax, regardless of any pilot-specific laws.
Police are not permitted to use "more" force in defending themselves than the general public - they merely have more legal use of force options (spray, baton, firearm etc.).
If a pilot was somehow legally carrying a firearm, and had a reasonable belief that his/her life was under imminent threat from the machete-wielding idiot, then they could legally discharge that firearm to protect themselves - same as police.
Where Police use-of-force differs is they are able to use it for more than defence of themselves or others - to effect an arrest, regardless of the imminent threat to themselves, for example (of course, still has to be reasonable, proportionate and necessary). Similarly, pilots have additional arrest powers in-flight.
Defending the aircraft itself on the ground is another matter.