Bl@@dy calculators! :ouch:

Bloggs:

The FAA cancels any overlay approach to a given runway at the time they chart a straight-in RNAV IAP to that runway. The two VOR IAPs at KGGW were titled "VOR or GPS Rwy XX" when they were overlays.

https://www.faa.gov/air_traffic/flig...lts&nasrId=GGW

Thanks aterpster. That should put sillypeople's mind at ease. :}

Down Under, we never had overlays. We went straight to proper GPS NPAs (as they were called at the start).

Well I think some guys get caught up in the terminology...we all know what a technical overlay is...technically they are the same approach with both approaches depicted.

In this case, it's just obvious that the GPS approach was built off of the VOR approach, being a straight in, they had to line up for a straight in, vs what is best for a circling approach. Given that both approaches have only a difference in inbound headings of ten degrees, its a given for me that if your on the GPS approach and lose the box at say 4k, why not have the inbound VOR radial dialed in as a back, for better situational awareness, as another way to depicts the MAP, then simply side step to the 293 inbound to 2880.

Other guys standing there stomping their feet that it's not an overlay, translates into the box going dead, they miss...but miss to what? They don't have a GPS signal?

Now I guess they should have thought about putting that VOR in as back up and having that approach chart out.

It's not the argument that is the problem...is the guys arguing a point that in the real world, if they lost the GPS they wouldn't know where the hell they were...not a problem if by themselves...but this is beyond stupid for the guys that carry people for a living. Food for thought.

Sorry, but just because the approach is straight in doesnt make it an overlay. The procedures are completely different, in design and in use.

In the near future, navaids like a VOR, NDB, and ILS will be just a repressed memory.

Sillypeoples:

Nope, when the U.S. had overlays there was only one chart.

The RNAV IAPs were designed from a clean sheet, with all the technical stuff that goes with LPV and LNAV/VNAV.

The FAA premise is that there is so much airspace in a conventional RNAV IAP that the pilot can dead reckon the missed approach in that very unlikely event.

But, not so with RNP AR unless it is basic RNP 0.30 with a conventional TERPS missed approach. Otherwise, you have to have at least one IRU for extraction in that very unlikely event GPS is lost. RNP AR approaches with RNP missed approach procedures "telescope" in width in accordance with IRU drift rate assumptions.

Using GGW as an example that VOR will be shut down as time goes on.

I don't think it's very smart to dump ground based Navaids. Relying on one system down to minimums with terrain all around, furthermore subject to the military playing games because they think Iran is using GPS to fly a drone around that day, thinking that one little box in your aircraft is 'enough' to get you from point a to b is 'hopeful'.

Maybe I have been flying in the soup to long, but I have seen GPS 'problems' and I am more comfortable having multiple systems backed up telling me where I am and where I am going.

sillypeoples:

The big boys all have IRUs. :)

In a way i understand your concern Sillypeoples, probably unlike the US some european states actually build new DMEs or VORDMEs as a backup system for GPS to enable DME/DME operation which is good down to RNP 0.3, of course in a multisensor-system with IRUs.

On the other hand it is much cheaper to just use SBAS and GPS and no further ground based navaids, although a satellite segment needs maintenance as well and as far as i know GPS maintenance is far behind schedule.

The GBAS will likely replace SBAS, by the time you build enough ground stations for the SBAS, and the data centers, and sats, you might just as well install a GBAS.

With CAT III cert, and the curved path GBAS signal, it will be a tough system to beat.

There is also some traction in using the cell towers to broadcast as well.

IRU's are about to take a quantum leap forward as well, when coupled with the intent bus, you have a real nice system.

Well when I read the transcript of AF447, it sounded like they lost situational awareness...maybe the computers were rebooting after a lighting strike...or the tubes all went red...either way....not having anything else as a reference, just tv screens, all relying on one computer, make you ponder having one mechanical peanut gyro and and ILS head. It's old school, but it's also peace of mind.

I carry a handheld GPS as a back up, surprisingly accurate, barely doable for an approach but better then trying to do it at night in a dark aircraft with no electrical.