GLS Dot deviation
 

Hi guys,

I was looking on the web and on company's manuals but I haven't found anything yet.

GLS (GBAS Landing System) is now being introduced, on trial, in the airline I work for and I can't find what's the value of 1 Dot deviation on the PFD/ND.

Any info?

Thanks

BTS

As far as i remember from our operational GLS use (its been a few years) on the 737NG, it is exactly the same as for an ILS, which means 1 dot equals 1 degree, and for the expanded display one dot equals 0.5 degrees.

The PFD basically did not care what it displayed, the values were calculated by the MMR to give the exact same indications as for an ILS. For the autoflight system it therefore was a normal precision ILS signal and it allowed autoland and automatic rollout. Which was not approved of course, but in a testing effort for the german DLR it was used for that and worked absolutely flawlessly, especially considering that no protected areas were needed. In operational use we used it exactly like an ILS, and it seemed to have better beam stability and integrity (no fluctuation of the LOC/GS whatsoever). The only "downside" was, that it was limited to CAT I use.

GLS is LPV on steroids. So much better than the 1940s ILS.

It might be, but it is certified to CAT I only, not CAT IIIb, the standard for ILS over here.

And technically it is not really LPV, as it is completely independent of an onboard database set, you just need the channel number, the trajectory is transmitted by the GBAS ground station.

GBAS will shortly be CATII/III approved, LPV in its current version will not be lower than CATI.

I understand the difference. Poor choice of words. GLS with eventually be CAT III. The issue is getting the airlines to equip.

Why would any airline with CATIII via ILS and GPS based backup approach capability choose to fork out for a GPS based alternate to ILS for it's low vis system?

If you have one set of eggs in the GPS basket better put the others somewhere else I would have thought!

GBAS is a no cost option on Boeing 737-Next Generation (737-800/-900), Airbus A320, A330/340, A350 and A380 aircraft.

Using Honeywell’s SmartPath Ground-Based Augmentation System (GBAS), Boeing used its ecoDemonstrator 787, a flight test airplane that in 2014 served to assess more than 25 technologies to reduce aviation’s environmental footprint, to complete 12 CAT III approaches and landings at Boeing’s test facility in Moses Lake, Washington.

SEATAC has a proposal to install a CATIII system.

I worked for the operator that had the first operational approval for GLS in europe. And the same company used both 737NGs and Airbus A320 aircraft. Only the 737 was GLS equipped as it was a no-cost option. Although at some point it was decided to phase out the 737 in favor of a pure A320 fleet, the A320 never got GLS approval with that operator. Once asked why, the management told us that there, at that time (until 2016) there was no cost free option available on the A320, in fact it was only as a retrofit that cost around 250k per airframe. That might have changed, and i would expect it to change with the NEO as GLS/GBAS will be more widely used.

Not because it necessarily saves airlines, money, although it might be, as it can, in theory, allow CAT I/II/III curved approach trajectory. No, because it will save money for airport operators. One installation (with a back up set of of course) can serve several runways at once, obsoleting a lot of singular ILS installations. And of course, since it does not need traditional protected areas and more separation for that reason, higher movement numbers are possible, especially once it becomes low vis certified.

And of course, as long as the relevant signals are compatible, and i believe they are between GPS, Galileo and BeiDou, it can even provide higher reliability for a much lower price. Which of course translates in less delays and therefore saved money. So yes, there is a business case for GLS, actually a quite huge one. Now, we do have the egg/hen problem, but there are several airports that already have it installed, including some mildly larger ones like FRA or ZRH for example, next step is for the airlines to decide to get it installed.

Many thanks for the quick replies ;)

To get to Multi Frequency/Multi Constellation you need an appropriate GBAS ground station and airborne receiver equipment. Apart from the SESAR MC/MF test facilities in Europe, I think the only GBAS systems that are multi Constellation are the NPPF Spectr ground stations in Russia that use GLONASS and GPS.