Hot from the current CAO....
Civil Aviation Order 82.0
Definitions
adequate aerodrome, for an aeroplane, means an aerodrome which:
(a) meets the physical requirements set out in Appendix 2; and
(b) provides facilities and services for the aeroplane type, including:
(i) meteorological forecasts; and
(ii) at least 1 suitable authorised instrument approach procedure.
Note It is not necessary that an en route adequate aerodrome within the threshold time must meet the requirements for an EDTO alternate aerodrome unless the flight is dispatched as an EDTO flight.
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EDTO alternate aerodrome means an adequate aerodrome that:
(a) is listed in the AOC holder’s EDTO safety operational specifications as being an aerodrome that may be designated as an alternate in the event of a diversion during an EDTO; and
(b) for an aerodrome inside Australian territory — is one for which radio carriage is required under regulation 166E of the Civil Aviation Regulations 1988; and
for an aerodrome outside Australian territory — has:
(i) air traffic control or air traffic services (with not more than 30 minutes’ notice); and
(ii) rescue and firefighting services to Manual of Standards Part 139H category 4 (with not more than 30 minute’s notice); and
from the earliest to the latest time of landing at the aerodrome — has a meteorological forecast at or above:
(i) for flight planning and aeroplane dispatch — 1 of the aerodrome planning minima set out in Table 1 in clause 7 of Appendix 5 (Standard EDTO alternate aerodrome planning minima) as applicable for the facilities available at the aerodrome; and
Note A departure or destination aerodrome is not required to meet the relevant Standard EDTO alternate aerodrome planning minima unless it happens also to be an EDTO alternate aerodrome.
(ii) before passing the EDTO entry point — the approved aerodrome landing minima for the expected approach during the estimated period of use of the EDTO alternate aerodrome; and
has a forecast cross-wind component, including gusts, for the landing runway expected to be used, of not more than whichever of the following is the lowest:
(i) the maximum demonstrated cross-wind component specified in the AFM;
(ii) the maximum demonstrated cross-wind component specified in the OEM operations manual;
(iii) the maximum operational cross-wind component specified in the OEM operations manual; and
for the expected runway surface conditions, wind conditions, aeroplane landing configuration, and aeroplane landing weight, at the aerodrome — has a landing distance available that is not less than that required in accordance with subsection 11 of Civil Aviation Order 20.7.1B.
This definition applies for flight planning and does not limit the discretion of the pilot in command during flight.
Civil Aviation Order 82.0
Appendix 2
Adequate aerodrome — physical requirements
1 The landing distance available must be not less than that required for an aeroplane under subsection 11 of CAO 20.7.1B.
2 The surface and strength of the manoeuvring area must allow the aeroplane to land without the likelihood of:
(a) damage to the aeroplane; or
(b) the aerodrome being rendered unusable for other operations.
3 The taxiways and apron areas must allow the aeroplane to park so that it is clear of the remaining movement areas and does not render the aerodrome unusable for other operations.
4 The aerodrome lighting must be as set out in AIP En Route under the heading “Suitability of Aerodromes”.
As as you can see, no requirement for visual or electronic slope guidance (you do need at least one suitable IAP though).
However, always check your ops manual. Your company may have gone above/beyond the regulations and require it (unlikely though).
Additionally, if there is an airport-specific requirement that approach slope guidance is required (the only place I can think of is YPXM for high-capacity ACFT, see ERSA), then I would say if you are using that airport for EDTO adequate coverage, then in that specific instance you would require its PAPI to be operational. It could probably be argued that under the direct EDTO rules as quoted you wouldn’t need the PAPI at YPXM, but the smart money is you’d still want them operable at this location for the EDTO coverage anyway, even if it wasn’t legally required.