Differences between GLS and APV/SBAS

[paulmadejong]

I am currently researching GLS landing applications for the near/mid future (now - 2020). For what I understand, the following definitions hold;
APV: Approach using Vertical Guidance. Basically an approach with a vertical profile provided by either barometric pressure (baro-VNAV), GPS (SBAS) and GPS + LAAS (GBAS+SBAS).
GLS: GPS Landing System, basically an ILS using GPS for lateral and vertical guidance.My question now is, what is the difference between a APV/SBAS or GBAS and GLS approach? Is it a matter of definition or design criteria? Both approaches are precision approaches, right? Your help is much appreciated!

[Denti]

GLS is a general precision approach procedure based on gps (later on galileo and/or glonass). In europe GLS approaches will be done solely with a GBAS (ground based augmentation system) until galileo is working, which might be never. A GLS is a precision approach system, and usually the presentation to the pilot is ILS like, however you can design approaches that are not usually possible with a normal ILS like curved approaches or approaches with different approach angles in different phases of the approach. If a GBAS is used it transmits not only the GPS differential correction information but also geometrical approach information, which is indeed similar to an ILS. However unlike an ILS current installations support several approaches at once, depending on installation somewhere around 20 to 30 approaches in up to 48NM around the GBAS installation. Theoretically GBAS based GLS approaches are capable of CAT IIIc including roll-guidance on the ground, current installations support close to CAT I only.

I am not familiar with your first family of approaches, however barometric based approaches won't be able to stay within limits of what is required from a precision approach, one hP is a resolution which is way too granular for precision approach needs based on barometry.

Googling will give you a wealth of information, and of course since GLS/GBAS is standard equipment on 737s and optional on a wide range of other aircrafts including Qantas A380s you should be able to get some information from boeing and airbus about it, as well as from operators using that (i know of Qantas, FedEx Air Berlin, there might be more).

[paulmadejong]

For more information regarding APV approaches: http://www.ecacnav.com/downloads/RNAV%20Approaches%20Leaflet.pdf

Unfortunately, the exact details regarding APV approaches is limited and even classified in certain cases, that's why I am hoping for answers on this board.