Cape Town RNAV(GNSS) RWY19

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Cape Town RNAV(GNSS) RWY19

Unread post by ppakotze » Tue Oct 17, 2017 7:18 am

Seems FACT also have an GNSS approach now. Anyone used it yet?

Might be useful for training as well.
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by Float_flyer » Tue Oct 17, 2017 2:52 pm

Interesting to see the 44C maximum temperature limit. How often does it become a factor?
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by ppakotze » Tue Oct 17, 2017 3:29 pm

And also 0deg C minimum. That is for the VNAV or BaroVNAV part of it. In simple terms a altimeter is used for vertical guidance part.

APV BARO-VNAV procedures are not permitted when the
aerodrome temperature is below the promulgated minimum aerodrome temperature for the
procedure, unless the RNAV system is equipped with approved cold temperature
compensation for the final approach
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by apollo11 » Tue Oct 17, 2017 6:04 pm

I'm thinking for a GA single pilot IF these approaches would be loaded with potential to induce errors as besides the approach plate correctly setting up the IFR GPS correctly , the GNSS approach plates appear rather cluttered?

So how does this work will the database (assuming it's 100% current) when selecting this GNSS approach for example do all those way points show up automatically for the approach selected, I'm assuming they will similar to an ILS frequency selection automatically showing GS and localiser, so what happens if the GPS system fails (very unlikely I know) at some point flying the procedure, I'm assuming then the missed approach pertaining to the related ILS or VOR approach is then followed.
There is the normal mention of comms failure but what about GPS failure?

In my humble opinion the standard ILS approach appears a lot more simpler and less prone to making selection errors via the nav ILS or GPS.
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by Hop Harrigan » Tue Oct 17, 2017 10:01 pm

Hi Apollo,
One may only use a GNSS approach which is loaded from the Nav database ie it is not legal to insert the points manually into the GPS. On loading the approach, the appropriate points, depending on the entry point selected, are loaded into the GPS at the end of the current FPL as though they are additional GPS waypoints. The FPL is then flown manually, or more usually on the autopilot using these waypoints. The points are usually ‘flyby’ points ie the turn is initiated at an appropriate time ahead of the turn in order to line up with the following waypoint.
So there’s nothing odd about the method, it’s just flying from GPS waypoint to waypoint.
Vertical guidance is either manual (as in a normal VOR approach) or automatic if the system is equipped to do so ie coupling of the baro alt to the GPS. Not all Navcomms can handle the vertical guidance and in this case a flag is displayed indicating ‘HNAV only’.
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by apollo11 » Wed Oct 18, 2017 8:41 am

Hi Hop, thank you for taking time to explain, makes sense, I'm relieved that it's not legal to insert way points in manually.

I can appreciate that one will fly the little airplane icon overlay over the indicated approach resulting in pretty much decent situational awareness.

What happens if there is an equipment failure, a GPS outage in general or on board failure I see there is no procedure to revert to traditional navaids?
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by Swampdonkey » Wed Oct 18, 2017 9:01 am

apollo11 wrote:Hi Hop, thank you for taking time to explain, makes sense, I'm relieved that it's not legal to insert way points in manually.

I can appreciate that one will fly the little airplane icon overlay over the indicated approach resulting in pretty much decent situational awareness.

What happens if there is an equipment failure, a GPS outage in general or on board failure I see there is no procedure to revert to traditional navaids?
In most cases the same philosophy applies to any type of approach, imagine if one were flying an ILS, and either the on board equipment or the ground based facility were to fail? In this case one should immediately execute a missed approach and fly to a holding position and once in a stable, safe aircraft state, re-brief for another IAP like an ILS or a VOR/D, or consider a diversion.

Remember Fly, recover the aircraft into a safe and stable condition, Navigate, execute the appropriate missed approach procedure and then fly to a safe place (like a holding pattern), and Communicate advise ATC of your intentions or requests.
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by apollo11 » Wed Oct 18, 2017 9:17 am

Point Swampmonkey :oops:
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by tansg » Mon Oct 23, 2017 7:51 am

Was in a briefing by Honeywell on GPS Ground Based Augmentation System (GBAS) implementation and it is now even more obvious the days of ILS are rapidly coming to a close due to cost, the need to calibrate, separation restrictions, interference issues and the obsolescence of the technology and procedures.
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by ppakotze » Tue Oct 24, 2017 6:55 am

tansg wrote:Was in a briefing by Honeywell on GPS Ground Based Augmentation System (GBAS) implementation and it is now even more obvious the days of ILS are rapidly coming to a close due to cost, the need to calibrate, separation restrictions, interference issues and the obsolescence of the technology and procedures.
Tansg why the replace ILS with GBAS, also a ground based navigation source? Would SBAS not give the same precision, without the need for localised ground based infrastructure? With SBAS you could get national or regional (SADC) coverage for similar or less infrastructure with national oversight?

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Re: Cape Town RNAV(GNSS) RWY19

Unread post by tansg » Tue Oct 24, 2017 8:39 am

ppakotze wrote:
tansg wrote:Was in a briefing by Honeywell on GPS Ground Based Augmentation System (GBAS) implementation and it is now even more obvious the days of ILS are rapidly coming to a close due to cost, the need to calibrate, separation restrictions, interference issues and the obsolescence of the technology and procedures.
Tansg why the replace ILS with GBAS, also a ground based navigation source? Would SBAS not give the same precision, without the need for localised ground based infrastructure? With SBAS you could get national or regional (SADC) coverage for similar or less infrastructure with national oversight?

Regards
P.
Good question and the differences are explained in an easily identifiable way very often and I will try and encapsulate the major factors so you can understand the differences in point form below:

1. Cost:
ILS expensive as it requires precision earthworks, very clean electricity supply and back up, very expensive antennae and electronics.
SBAS expensive as it requires a regional network of monitoring stations and an uplink facility to the satellites (yes more than 1 as a back-up) and very expensive satellite access time.
GBAS cheap requires minimum 4 antennae with a GPS receiver mounted on them, 2 x base station (1 for back-up), can be contained on an airfield (so no access agreements etc), uses VHF to transmit the corrections.
2. Accessibility:
ILS serves 1 runway end, can go down to CAT 3C approaches, has limited traffic capacity due to signal interference behind of the aircraft using the ILS so forced separation distances between aircraft on approach, does not rely on aircraft databases.
SBAS can serve multiple runway ends in a region, at best can get to a CAT1 approach, allows reduction of separation between aircraft, however relies on the procedure to be coded within the aircraft database.
GBAS serves up to 48 runway ends within about a 80Nm radius (depending on the geographical layout and other technical issues), can achieve Cat 3 levels with 3C under development, allows reduction of separation between aircraft, is independent of aircraft database as the approach is uplinked from the ground for each approach.
3. Accuracy:
ILS a couple of metres laterally and about 20' vertically depending how far out you are and the CAT of the system.
SBAS a metre or so laterally and about 20' vertically wherever you are on the approach.
GBAS millimetres laterally and less than 5' vertically wherever you are on approach.
4. Continuity:
ILS subject to interference from ground movements in the "sensitive areas", needs a "good" power supply, equipment needs air conditioning and is susceptible to lightning strikes.
SBAS reliant on the network of monitoring stations all over the region that need electricity, aircons, connectivity (usually microwave links) with uplink station, connectivity to the satellites and susceptible to space weather (GPS and SBAS signals)
GBAS only reliant on the minimum 4 antennae on the field, designed to be operated with solar power and battary back-up, connectivity (can be microwave or even optical/cable if the distances from the base station are not to great) and less susceptible to space weather (GPS only)
5. Reliability:
ILS complex system which requires 6 month/1year (depending on CAT) calibration, high level of maintenance
SBAS relatively complex system relying on outstations and satellite uplinks, only requires regional signal in space checks (no special equipment required can be done with any aircraft, a laptop, software and to window sticker GPS antennae)
GBAS a simple system based on the airfield (most cases), plug and play components with only localised signal in space checks checks required (no special equipment required can be done with any aircraft, a laptop, software and to window sticker GPS antennae)
6. Security:
ILS very susceptible to any sort of signal or electrical interference, interruptions in power supply or physical interference of antennae
SBAS susceptable to interfence at all monitoring stations 9including theft, electricity supply interruptions (cable theft), etc),space weather, satellite interference, signal interference (ITCZ causing scintillation in the ionosphere) and satellite outages.
GBAS resilient system that can work with only 3 antennae operable for a limited time, has built in battery back-up to the solar, susceptible to space weather interference of the GPS signal.

Operationally GBAS gives all the advantages of RNP AR without the organisational restrictions and cost.

Hope that answers some of your questions. If not feel free to ask I will attempt to answer them as best I can in hopefully simple terms as some of the concepts can become complex.
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Re: Cape Town RNAV(GNSS) RWY19

Unread post by ppakotze » Tue Oct 24, 2017 10:18 am

The SBAS case study for SA I have seen shown about 7 reference stations deployed on existing airfields in SA, so the location of GBAS and SBAS equipment could both be on the airfield? The benefit of SBAS is that you not only get coverage on the airfield where deployed like GBAS but for every little field in-between. From your example ILS precision through SBAS from Porterville, Prieska through to Polekwane all with the same hardware deployed?

What am I missing? The US has WAAS (SBAS) which gives them that, what is their use of SBAS vs GBAS?

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Re: Cape Town RNAV(GNSS) RWY19

Unread post by tansg » Wed Oct 25, 2017 11:17 am

ppakotze wrote:The SBAS case study for SA I have seen shown about 7 reference stations deployed on existing airfields in SA, so the location of GBAS and SBAS equipment could both be on the airfield? The benefit of SBAS is that you not only get coverage on the airfield where deployed like GBAS but for every little field in-between. From your example ILS precision through SBAS from Porterville, Prieska through to Polekwane all with the same hardware deployed?

What am I missing? The US has WAAS (SBAS) which gives them that, what is their use of SBAS vs GBAS?

Regards
P.
:D I was one of the contributors to that case study. Yes we tried to make the reference stations as efficient as possible bearing in mind the South African challenges.

I need to correct you you are not going to get an ILS Precision approach you are going to get a 3-D APV approach which at best will give you ILS Cat1 minimas. There is a difference. Where SBAS is useful is that it provides a better than LNAV/VNAV approach independent of aerodrome ground based equipment which is very useful in Africa. It is also ideal as a back-up to GBAS or ILS. The downside is it is in relative terms expensive and requires states to cooperate on a regional basis to make it effective. The present iteration in the form of EGNOS's performance is also severely affected by the thunderstorms and the sintillation caused by them in the ionisphere. This should be mitigated in EGNOS II. So here in Africa the operational reliability could be an issue. The nice bit about it is that the EGNOS data is supperimposed on the GPS signals so the EGNOS satellite acts as an extra GPS and your FMS/GPS receiver in theory only will require a software upgrade. Is this still true? If anyone knows better please update me.

In the US case WAAS was rolled out quite a while ago and there was an active program by the FAA to put WAAS procedures into as many airfields as possible, prioritising those which had scheduled traffic but which were still only served by conventional nav aids and RNAV (GNSS) procedures i.e. non-ILS airfields. This was subsequently extended to the ILS fields as a back-up to the ILS. GBAS is a whole new kettle of fish. It has been developed over the last 10 years or so specifically to replace ILS and is sometimes referred to as GLS. Therefore the system architecture and operation are vastly different to SBAS and need to be to satify the requirements for a 3-D Precision approach.

Here a few webpages and videos which are rather informative:

https://aerospace.honeywell.com/en/~/me ... em-bro.pdf

https://aerospace.honeywell.com/en/pres ... n-republic

https://www.youtube.com/watch?v=bsiDpyj5gec

https://www.youtube.com/watch?v=w04B8lRnOM0

https://www.faa.gov/about/office_org/he ... AS_FAQ.pdf

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