RNAV vs GPS

[malecontrol]

How does an RNAV approach differ from a GPS approach? Can you clear an aircraft for an RNAV approach and when it reaches the final approach fix ask to report established on the ILS? If the ACFT commences an RNAV or GPS approach will it intercept the ILS at any time or will it be the GPS all the way to the touch down?

[BaldEd]

GPS approaches are now called RNAV approaches. An RNAV approach and an ILS approach are 2 completely different approach procedures, each with different minima.

The RNAV approach charts will usually specify the type of equipment to be used eg "RNAV (GNSS) RWY 05" or "RNAV (RNP) RWY 05). Each of these approaches will have different procedures, minima and missed approach procedures. There is no requirement for any ground based guidance aid for an aircraft to carry out an RNAV approach.

At many airports there are also RNAV ARRIVAL procedures, eg. "RNAV (GNSS) ARRIVAL RWY 05" or "RNAV STAR 05" which will define the initial arrival route an aircraft is to take to reach the point where either an RNAV approach or an ILS approach starts.

Global Navigation Satellite Systems (GNSS) is the standard generic term for satellite navigation systems.

[Gumaaark]

In Aust, we have RNAV approach, (which are also called GNSS) and GPS arrival. Your question says GPS approach, which does not exist.
do you mean GPS arrival? (described below)
or do you mean GNSS aproach? (described in previous post-see also RNAV approach!)
(This bit above added, as I may have misread the question)

It might depend a bit on where you are. i was under the impression that in Australia, there are still GPS arrival which are VERY different to an RNAV approach, unless this has changed in the last 12 months.

The RNAV description as above is accurate as a runway approach, the 'RNAV arrival' sounds like what we could call a 'STAR' (Standard arrival route), which (as described) would take you to the IAF of an instrument arrival (which may be an ILS, RNAV, VOR or NDB approach).

a GPS arrival (in Aust) is mostly the same as a DME arrival, in that the GPS must be tuned to the lat and long of a vor/ndb, and the pilot descends based on distance from that navigation aid. Usually the gps arrival is broken into sectors, with different steps (ie distances at which you can descend) depending on where the aircraft is coming from.

The biggest differenc, is that with an RNAV, pilot is following a 'line in the sky' (usually aligned with a runway), and should be on a constant profile (such as with an ILS).
With a Gps arrival, the pilot can manouver prior to crossing the FAF (final approach fix), and may not be runway aligned- a much less precise approach, but useful as they can be used to get below cloud without going significantly off track (if at all). Though in Really bad weather, an RNAV would be preferred for it usually has a lower minima.

Clear as Mud?

[malecontrol]

Yeah it's a little muddy.

You say a GPS approach is something that does not exist? This really confuses me because here we have GPS approach charts in our AIP labelled GPS approach and a GPS arrival is mentioned no where.

You say an RNAV approach is a constant descend profile. Does this mean that ATC cannot or shouldn't interrupt the descend until the aircraft reaches the FAF? Or it should go all the way to the touch down uninterrupted?

Can ATC ask the aircraft to intercept the ILS after having cleared it on an RNAV arrival/approach or GPS arrival? I am asking this because as far as I know an ILS approach is a completelt different approach from the RNAV and GPS so asking the pilot to intercept the ILS would mean asking him to switch the approach he was cleared to. And since these approaches are mostly done by the autopilot, FMS cannot execute 2 different approaches at the same time, i.e, RNAV and ILS, if I am not mistaken.

Thanks
Ahmad

[caucatc]

I have just got a question about RNAV , we were told that if controller vector aircraft leave the RNAV ,we should tell pilot direct to a fix when we want aircraft back to the procedure rather than a heading,like "XXX,direct to AA111 ,join DOGAR7A" ,but I asked a pilot if he can join the procedure if I just give him a heading not a fix ,the answer was affirm and he really did it ,the point he intercept the procedure is not any fix of the procedure ,can anybody tell me why can not use a heading to intercept the procedure ?