what is RNAV?

[eagle737]

some STAR charts show that "only for RNAV equipped aircraft", so what is "RNAV equipped"? is B737-300/500 "RNAV equipped"?
I just know RNAV stand for AREA NAVIGATION.

[Genghis the Engineer]

It's a variation upon VOR/DME.

The aircraft is equipped with a navigation system which allows you to define artificial waypoints in terms of a VOR radial and a DME distance. It will then display those on the CDI and DME readout (using a bit of basic trig that is easy for a small computer, but too complex to do manually whilst flying) as if each waypoint was a discrete VOR/DME transmitter in it's own right.

I'm not an instrument pilot, but I'd guess in the context of a STAR chart that it's requiring you to have the ability to define a user waypoint in your nav box allowing you to fly the approache referenced to a defined point in space.

GPS will do the same thing equally well of-course, but is not necessarily approved for primary nav in most parts of the world. But, in a fit of pragmatism, most airfield plates will show VRPs as both a lat-long (GPS or INS) and as a VOR/DME relationship so effectively either (or both) is/are useable.

In light aircraft the King KNS-80 is probably the most commonly found RNAV device and used in a lot of training establishments. If the kit is fitted into many school PA28s and C172, it's probably a reasonable guess that you'll find something that'll do the job in most 737s - I'm sure there's a 737 driver in the house who can confirm or deny that.

G

[OzExpat]

The expression "RNAV" began life with the meaning Random NAVigation. The idea was that the system was capable of navigation on random tracks. This concept was fairly short-lived because of the confusion that the term generated among pilots and ATCOs. Thus, the expression was modified to mean "Area Navigation", but I'm not sure that this is a real improvement... :}

Anyway, RNAV can be either VOR/DME or DME/DME. If it is based on VOR/DME, you must only use the specified VOR/DME and, indeed, your self-contained nav system - IRS or GPS - will do just that. If the chart allows DME/DME, the nav system will use all the DME facilitiesit can find. This can be a bit of a problem to the person designing the procedure as the system is quite capable of picking a DME that it beyond reception range or, worse, outside of a viable angle with the track. :eek:

Anyway, whichever system the procedure is designed to use will be shown on the chart. I suspect that most RNAV procedures are VOR/DME rather than DME/DME, due to the above problem. I have an idea that RNAV can also be construed as GNSS so that you only need to use a TSO 129A/145A/146A GPS Receiver, but I could stand to be corrected about that.

In any event, I'd be very surprised if the nav system installed in a late-ish model 737 can't handle RNAV.

[Genghis the Engineer]

DME/DME will only be useful for a finely defined and followed procedure - the joy of VOR/DME is that you can correct from anywhere within receiving range of the beacon. If you are far-enough out on DME/DME you could default to the wonrg point - as OXP says, it's going to be a bit of a headache to whoever is trying to define the procedure.

G

[reynoldsno1]

There are 4 basic types of RNAV procedures available:
VOR/DME
DME/DME
GNSS
RNP (Required Navigation Performance)

The 1st three specify the source of navigation data to be used - the last specifies the accuracy to be achieved, and doesn't care how you do it - therefore allowing the full capabilities of the aircraft to be untilised. Any of the 1st three can be assigned an RNP value.

[Blacksheep]

More confusion - there are several standards of RNAV!

Apart from the Basic RNAV there are precision RNP10/RNP5 standards and the not yet introduced RNP1/3 that will be combined with ADSB. I suppose it is the basic RNAV that eagle737 noticed marked on the charts, but I know that some airports - Frankfurt for example - have some PRNAV approach options for aircraft equipped for precision RNAV.

Notwithstanding the physical aircraft fit, within EuroControl, each individual aircraft is required to carry a certificate issued by the airworthiness authority in the country of registration, stating the compliance standards of the navigation equipment carried, including with ACAS/TCAS II Ch 7, RVSM and RNAV. Obtaining the certificate is generally a paperwork exercise but it includes proving that the company Operations Manual includes procedures for using the equipment to operate in the designated airspace.

Unless the navigation fit is certified for RNAV you should not fly designated RNAV flight paths, regardless of one's opinion of the equipment carried. It is easy to discover the certified installation of the aircraft you are flying as the navigation performance certificate is carried on the flight deck, along with the certificate of airworthiness, radio station licence, certificate of insurance etc.

[reynoldsno1]

The terms BRNAV and PRNAV are essentially confined to Europe. BRNAV = RNP 5, PRNAV = RNP1.0. (The values are in NM). Terminal operations are RNP1.0 or less. NPA are RNP 0.5 or less (0.3 is the lowest).
Most modern commercial air transport avionic fits will be RNP certified at installation (and many are RNP 0.1 or less)...

[Blacksheep]

Oops! Sorry! Got my own knickers in a knot there...

Yes RNP10/5 is Basic RNAV and RNP1 and below are PRNAV. Although some equipment fits allow PRNAV down to one tenth of a nautical mile, these are meant mainly for terminal operations - somehow, I don't think they'll ever be used for en-route horizontal separations of a few hundred yards! Europe does intend to reduce horizontal separations as a means of dealing with increased congestion, though; leading to progressive introduction of RNP1 with ADSB as a minimum performance requirement for huge areas of controlled airspace.

Although current use is mainly confined to Europe, these are international standards; they could, and probably will be introduced anywhere that traffic gets a tad congested.