Neither the ADIRU (whether you have a single intergrated unit or 3 individual units) nor the GPS can navigate. they can only tell you where you are (and in the case of ADIRU's only if you accurately tell it where you started)
Knowing your current position is navigation, no need for FMC's, it's simple math. A whole lot better than relying on the whisky. What has happened to piloting skills today? The ADIRU's/IRU's are a whole lot more accurate than the old Delco units. Even W/O GPS position updating.
Back on topic yes 2 ADIRU's are long range navigation systems, just as INU's are. I believe it is an ICAO standard.
Looking for a quote and found this old doccument (1955) warning of increased traffic in the future 1970-1975, and the standards for what we know now as the RNP of the day.
http://www.icao.int/icao/en/nr/1955/pio195512_e.pdf
Here is a good ref. Badically if an aircraft has inu's/iru's and maintains rnp10 it is another standard for GPS.
http://www.icao.int/nacc/meetings/20...TCARWGip03.pdf
3. Aircraft RNP 10 Eligibility Groups Provided For in FAA 8400.12A
A. Eligibility Group 1 – Aircraft Eligibility Through RNP Certification
• RNP compliance documented in the AFM. Typically not limited to RNP 10.
• Example: B747-400 or A-340 incorporating FANS 1/A.
B. Eligibility Group 2 – Eligibility Though Prior Navigation System Certification.
(1) Dual INS or IRU approved in accordance with Part 121, Appendix G (6.2 hour RNP 10 time limit,
unless action taken to extend time)
(2) Dual INS or IRU approved for NAT MNPS or Australian RNAV operations….eligible for RNP
10 with 6.2 hour RNP 10 time limit unless action taken to extend time.
NAT/CAR WG/1 – WP/06
- C3 -
(3) Dual GPS approved for primary means of navigation in oceanic and remote areas….approved in
accordance with AC 20-138 (as amended) (34-minute limit on FDE unavailability)
• GPS/WAAS systems installed in accordance with AC-20-138A incorporate primary means
capability. TSO-C145a and TSO-C146a are applicable.
(4) Multi-sensor systems integrating GPS (GPS integrity provided by RAIM or Aircraft Autonomous
Integrity Monitoring (AAIM))….approved in accordance with AC 20-130A.
(5) Single INS or IRU and single TSO C-129 authorized GPS with approved FDE and exclusion (34-
minute FDE unavailable time)
C. Eligibility Group 3 – Aircraft Eligibility Through Data Collection
(1) Appendix 1 (Sequential Method). Uses Pass/Fail graphs to assess INS or IRU performance and
RNP 10 time limit.
(2) Appendix 6 (Periodic Method). Allows use of hand-held GPS to assess INS or IRU performance
and RNP 10 time limit.
http://www.icao.int/icao/en/ro/nacc/...TCARWGwp06.pdf
This answer..