A complicated RNAV Question

[C172s]

I don't know if I should have this on this forum or the questions forum but anyway..please be gentle as I am asking this question on behalf of someone else so I may not present it in the proper manner.

It concerns a certain old aircraft ( American made of course and beautifully big, :) ) which has 3 INS's on board but is not RNP5 certified.

The question is can 'Legal' (FAA/JAA) RNAV approaches be made on DME/DME information with positions updated from the INS's. What is the accuracy index? Also, what does RNP5 and B-RNAV stand for?

I'd appreciate help on any of this which will satisfy the most humble of pilots. If the questions do not make sense, please ask.

Thanks for your help in advance.

C172s...putt...putt..putt

[HotDog]

RNP5 is required navigation performance grade 5. Further info, see:

http://www.eurocontrol.int/cns/cns_annex2.html

B(asic)-RNAV defines European RNAV operations which satisfy a required track keeping accuracy of ±5NM for at least 95% of the flight time. This level of navigation accuracy is comparable with that which can be achieved by conventional navigation techniques on ATS routes defined by VOR/DME, when VORs are less than 100 NM apart.

For further info, see:

http://users.forthnet.gr/ath/mpang/whatis.htm

[BOAC]

C172 - if it is any help, where I 'live', the 737 3/4/5 (which rely on DME/DME for FMC update), are not permitted to fly RNAV approaches unless the RNAV waypoints can be located by 'conventional' means.

[scrubba]

C172s,

No, you won't be able to do rnav approaches. Read this link:

http://www.ecacnav.com/rnav/default.htm

in the sequence presented and all will be revealed. my guess is the navigation system presently on board will meet rnp5. however, rnp1 will soon be required for terminal area nav and that is the standard most likely to get you to the final fix. beyond that, rnp0.3 will be required for final approach. most boxes without gps will never get the tick and with the world wide trend to disabling the ground based aids in favour of spaced based systems, no valid updates will be available to get ins/irs even close.

[Blacksheep]

In response to the original question, you can fly to B-RNAV/RNP5 quite satisfactorily with INS and DME/DME updating (Rho/Rho Navigation) In European airspace this is required for flight above FL100 generally - with some variation between contracting states. For RNAV approaches you should be using PRNAV/RNP1 or 1/3 and you won't get that accuracy without GPS. In European airspace, airways charts have been redrawn to WGS84 to ensure that waypoints coincide with the GPS coordinates.

In response to scrubba's comment, VOR and NDB are being phased out already (target is 2005!) but there is so far no intention to shut down the DME equipment that is co-located with most VORs and some Localisers. RNP5 will be with us for quite some time...

**************************
Through difficulties to the cinema

[GlueBall]

None of our airplanes equipped with triple INSs and "triple-mixed" through the FMS is certified for RNAV approaches.