GBAS

Airborne_Again wrote:

Isn’t GBAS is supposed to be useable (eventually) for Cat III autoland?

Yes (allegedly), but GBAS will have local stations on-site and so that bit is supposed to be unaffected by the environmental factors that much.

How about approving Cat2 operations outside places without Cat2 ILS, problem solved?

Now I may not able to claim English as my first language but @Airborne_Again I do believe @Ibra in a lighthearted way suggested a CAT II LPV? Hopefully a native speaker qualified in semantics will drop by and advise?

On the non – WAAS boxes once the box carried out the RAIM on the run into the FAF, am I correct it would then suspend a Loss of Integrity message past the FAF (ie integrity had been satisfied before the FAF), because a. It wouldn’t or isn’t programmed to check and b. it would use ded reckoning if there was a loss of GPS. What would happen on a WAAS LPV especially if it had GBAS? Is it continuous integrity monitoring with LoI warnings announced as late as DA?

RobertL18C wrote:

What would happen on a WAAS LPV especially if it had GBAS? Is it continuous integrity monitoring with LoI warnings announced as late as DA?

Ignoring GBAS as I have no clue how it works on SBAS GPS when flying LPV, RAIM is not required as long as SBAS is available, the final segment is coded to have continuous self monitoring to keep “LPV annunciation”:
- It can degrade to LNAV before 1000ft or FAF, then you fly LNAV MDA
- It can degrade to LNAV after 1000ft or FAF, then you fly MAP on RNAV1
- It can degrade to LOI near DA, then you fly MAP on DR

When you have gone past MDA, DA, MAPT, TCH, TDZ (depending if you are landing, circling, going missed or doing low pass from LPV)
1) if you press SUSP, TERM will get annunciation for flying MAP on RNAV1 = no internal monitoring
2) if you stay UNSUSP, LPV keeps annunciation forever = internal checks running with RNP0.3

In theory, you could get LOI after DA while you are doing a low pass, landing, circling or landing or going missed

Ibra wrote:

Ignoring GBAS as I have no clue how it works

Technically it basically works the same as SBAS – the navigator gets a correction signal which it is applies to the raw GPS position. The difference from SBAS is that the correction signal is computed and transmitted from a ground station (thus the G in GBAS) on or very near the airport itself.

Airborne_Again wrote:

Ibra wrote: Ignoring GBAS as I have no clue how it works

Technically it basically works the same as SBAS – the navigator gets a correction signal which it is applies to the raw GPS position. The difference from SBAS is that the correction signal is computed and transmitted from a ground station (thus the G in GBAS) on or very near the airport itself.

Small correction – the data is sent very differently – according to Wikipedia: https://en.wikipedia.org/wiki/Local-area_augmentation_system#Operation

Local reference receivers are located around an airport at precisely surveyed locations. The signal received from the GPS constellation is used to calculate the position of the LAAS ground station, which is then compared to its precisely surveyed position. This data is used to formulate a correction message which is transmitted to users via a VHF data link. A receiver on the aircraft uses this information to correct the GPS signals it receives. This information is used to create an ILS-type display for aircraft approach and landing purposes. Honeywell’s CAT I system provides precision approach service within a radius of 23 NM surrounding a single airport. LAAS mitigates GPS threats in the Local Area to a much greater accuracy than WAAS and therefore provides a higher level of service not attainable by WAAS.

So it is VDL, therefore can only be done Transport-category aircraft and a very few a/c outside that category.
How many avionics suits exist for non-PART25 a/c that support VDL?
G3000 and that is it?

I guess GBAS correction is way more accurate but the challenge is to receive that GBAS signal all the way at every point of approach & flare & missed?

The SBAS correction is less accurate (this is relative) but you should always receive it if EGNOS satellite is above in the z-axis, maybe I am lucky with GPS-W accuracy:Paris Observatoire 34th RIMS station is 15nm away from runway (I sleep 1100m away from it ), I guess the reliability & quality of the correction depends on the location of runway threshold & ranging station?

What if RIMS station in on the airfield, any technical reason why that will not make SBAS as close to GBAS on the airfield? are they running on similar specs: error rounding, broadcast times…? (I mean practical engineering differences (joke) not some obvious theoretical Sunyaev–Zeldovich effect it’s analogy on how large scale things impact tiny ones: universe expansion impacts spectrum of high energy electrons when hit by big bang photons)

https://en.wikipedia.org/wiki/Sunyaev%E2%80%93Zeldovich_effect

A pity Dave Philips isn’t around anymore; this was his day job.

arj1 wrote:

Small correction – the data is sent very differently – according to Wikipedia: https://en.wikipedia.org/wiki/Local-area_augmentation_system#Operation

Local reference receivers are located around an airport at precisely surveyed locations. The signal received from the GPS constellation is used to calculate the position of the LAAS ground station, which is then compared to its precisely surveyed position. This data is used to formulate a correction message which is transmitted to users via a VHF data link. A receiver on the aircraft uses this information to correct the GPS signals it receives.

That’s what I wrote, is it not? Except that I didn’t specify the frequency band of the transmission.

Airborne_Again wrote:

That’s what I wrote, is it not? Except that I didn’t specify the frequency band of the transmission.

Sorry! I meant to say “clarification” not “correction” – just wanted to emphasize that GBAS requires VDL and an extra VHF radio, doesn’t work like SBAS with just a single navigator…

RobertL18C wrote:

On the non – WAAS boxes once the box carried out the RAIM on the run into the FAF, am I correct it would then suspend a Loss of Integrity message past the FAF (ie integrity had been satisfied before the FAF), because a. It wouldn’t or isn’t programmed to check and b. it would use ded reckoning if there was a loss of GPS.

Robert,

RAIM needs to be available at the FAF in order for the approach to proceed. If RAIM is available, the algorithm continues to operate and can produce an integrity fault along the FAS, in which case the approach must be abandoned, however, if RAIM becomes unavailable, the approach may continue. RAIM being unavailable means the inputs to the algorithm are insufficient for the RAIM algorithm to check integrity. That is a different state from the RAIM algorithm determining an integrity fault. That is why if RAIM is still available at the FAF, the approach can continue, even if it is lost on the FAS.