EGLL 09L RNAVZ arrival

[marcus holmes]

I was arriving into EGLL yesterday and the controller ask if I would like a RNAVZ arrival into 09L. Can someone tell me the difference between a 09L ILS arrival and a 09L RNAVZ arrival?

 

Been on Vatsim awhile, but always learning, that is what I love about this hobby.

[Torben Andersen]

Just as there can be different ILS approaches to one runway (these are labeled Z, Y, W - so you have ILSZ rwy xx), sometimes there are different RNAV arrivals to the same runway. Labeled RNAVZ or RNAVY rwy 09L.

 

To see the differences between the RNAVZ 09L and RNAVY 09L you need to find the charts in the AIP or Navigraph.

An ILS approach utillizes ground equipment to give you localizor beam and glideslope. So you use the VHF radio to tune into the ils. RNAV uses satellites (GPS), so you use LNAV/VNAV to guide you in. Usually you'll find that the DA is higher on an RNAV app than on an ILS app.

 

Regards

Torben

[Andreas Fuchs]

On the charts it is actually labelled RNAV Z 09L:

Did the controller really ask you for "RNAVZ" or for "RNAV Zulu" (by voice)? Even in writing a controller should leave a space between the type of approach and the "version", so "RNAV Z 09L" would be better to help pilot understand.

[Simon Kelsey]

As Torben says, an RNAV approach utilises your aircraft's internal navigation sensors (e.g. GPS/IRS etc) -- exactly like the way you will have navigated en-route using LNAV and VNAV (or equivalent depending on your aircraft type). This is in contrast to an ILS approach which uses a ground-based radio navigation aid to project horizontal ('localiser') and vertical ('glideslope') 'beams' which can be received by a suitable receiver on the aircraft and the aircraft's displacement from the centre of those beams displayed on an instrument. The pilot, or autopilot, can then track these beams down to the runway.

 

The main difference is that the ILS beams are by definition essentially fixed in space and entirely independent from the aircraft's own navigation systems, which makes the ILS extremely precise and reliable, to to the point where in many cases it can be used to facilitate fully automatic landings in near-zero visibility.

 

RNAV approaches, on the other hand, are considered 'non-precision' approaches and you cannot autoland off them (yet!). Amongst the reasons for this are the fact that being based on the aircraft's own internal navigation sensors and database, any errors in the aircraft's sensed position or height will naturally result in an offset from the actual centreline or glidepath, and when a few metres either way could make all the difference this is problematic! That said, the accuracy of most modern RNAV systems is extremely high.

 

There are a number of reasons you might be offered an RNAV approach. Heathrow ATC generally will offer the RNAV to an aircraft following an A380 as the A380 is known to cause disturbances to the ILS signal for following aircraft - using the RNAV gets around this, if the weather conditions are suitable for the RNAV minima which are slightly higher than the ILS minima (if the ILS is a necessity due to the weather then additional spacing would need to be given, resulting in delays). The other reason could be if the ILS is not operational for whatever reason.

 

There are two RNAV approaches published for each runway at Heathrow, labelled Z and Y respectively. The RNAV Z is the 'normal' RNAV approach. The RNAV Y approaches are trial procedures utilising a 'slightly steeper' 3.2 degree glidepath - the object of the trial being to [Mod - Happy Thoughts]ess whether this reduces noise levels under the approach path whilst being achievable for aircraft including complying with the 160 kt to 4 DME speed restriction and also meeting company stablilised approach criteria (typically: fully configured for landing with all checklists etc complete and at Vapp by 1000 ft radio). I don't believe ATC are offering the RNAV Y but pilots are encouraged to request it (mainly BA I think?) if they wish and the weather conditions are conducive.

 

How you fly an RNAV approach will depend upon the specific aircraft you are flying but very broadly speaking they are typically flown in LNAV and VNAV or equivalent modes.

[marcus holmes]

Many thanks for the detailed answer to my question.

 

So just following up, if I was to accept an RNAV Z approach into EGLL would ATC still vector to me on to the approach or would it be the pilots responsibility to do that?

[Simon Kelsey]

The likelihood (certainly at LHR) is that you would still be radar vectored for sequencing. The difference is that rather than clearing you for the ILS and asking you to report established, instead you will at the appropriate moment be instructed to route direct to the IF (ABAVI for the RNAV Z 09L) and cleared for the RNAV approach. At this point you would do a 'direct to' ABAVI in the FMC and fly the RNAV approach per your aircraft's operating procedures.

[marcus holmes]

Many thanks for your help Simon.

 

It all makes sense now. I think next time I fly into EGLL I will request the RNAV Z 09L, if he 09s are in use on the day, just to give it a try.

 

It is always great learning something new in aviation, even after flying on Vatsim for many years.

[Trevor Hannant]

You can do it on the 27's also...

 

https://www.aurora.nats.co.uk/htmlAIP/Publications/2019-10-10-AIRAC/html/eAIP/EG-AD-2.EGLL-en-GB.html#EGLL-AD-2.24