This is good stuff. Interesting postings. What about pure GPS based approaches in the airlines ? – i.e. not traditional ILS of whatever CAT.
Very few “airlines” have any GPS landing capability.
Fly to any airline-airport and listen to which approaches the airlines are asking for.
At ILS airports they all go for the ILS, ignoring any GPS approaches – as would I because my autopilot can take me all the way down on an ILS.
At non-ILS airports, practically all of them refuse the “RNAV” ones (which are mostly GPS/LNAV, and sometimes GPS/LPV i.e. similar to an ILS) and go for the VOR ones. Not because they actually use the VOR but because their FMS can fly an INS-guided overlay of the VOR approach, with an artifically generated glideslope, like an ILS but higher minima.
Peter wrote:
At non-ILS airports, practically all of them refuse the “RNAV” ones (which are mostly GPS/LNAV, and sometimes GPS/LPV i.e. similar to an ILS) and go for the VOR ones. Not because they actually use the VOR but because their FMS can fly an INS-guided overlay of the VOR approach, with an artifically generated glideslope, like an ILS but higher minima.
That is usually because they don’t have the equipment or approvals to do an LPV. Any operator who can do a precision approach with a lower minima in IMC will choose to do it. ILS are done as all aircraft have the equipment, and authorised to do them and they have the lowest minima (in Europe).
Peter wrote:
Very few “airlines” have any GPS landing capability. […] At non-ILS airports, practically all of them refuse the “RNAV” ones
You’re talking about Somalia here, right? For Europe it can’t be true, the vast majority will be able to do RNAV. I could even get you evidence of that by sampling all IFR flight plans in the Eurocontrol system and looking at the equipment string.
Having a GPS and declaring it in the equipment string doesn’t mean your AOC includes approval for RNAV approaches.
This is what I hear on the radio, all the time. They refuse RNAV and go for the ILS (if available) or the VOR one.
Going for the ILS makes perfect sense, obviously – at every level of aviation.
Why is that?
Whenever I have an LPV available I will prefer that any day. No switching from NAV/GPSS to VLOC, Final course set automatically, no side lobes, no ILS maintenance etc. More simple and less errors possible.
Peter wrote:
Having a GPS and declaring it in the equipment string doesn’t mean your AOC includes approval for RNAV approaches.
That is AFAIK correct and usual; however the more modern INS systems use three GPS receivers to do INS corrections. They however still don’t have any GPS navigation capability, let alone GPS landing capability.
Normally INS uses DME-DME for the corrections but that won’t work over oceans etc.
Mind you, if you have INS, you would never use GPS for anything critical like landing. On Sunday I got a total loss of GPS at EGKA, somewhere past the FAF. I switched off all “gadgets” and it didn’t happen again. Very rare but you need only the one…
Can happen with anything, ILS too … but I’d say unlikely to happen with WAAS
Peter wrote:
Mind you, if you have INS, you would never use GPS for anything critical like landing. On Sunday I got a total loss of GPS at EGKA, somewhere past the FAF. I switched off all “gadgets” and it didn’t happen again. Very rare but you need only the one…
That isn’t true. WAAS GPS is incredibly reliable. Your GPS system Peter is is not exactly state of the art. Airliners don’t land on the INS for a precision approach.
