Hi everyone. I have heard that the FAA allows GPS overlay approaches. From what i gather this allows a pilot to perform an NDB approach using GPS for track guidance. This seems like a great idea. I happened to have done some training on a G1000 equipped aircraft. They don't come with ADF, so during VMC, my instructor and I would practice NDB approaches using track quidance provided by the onboard GPS, which can be made to at as an RMI. I would imagine that GPS track guidance is far more accurate than that provided by an ADF, especially when the onboard equipment has FD/FD & E. Any thoughts? wiki
You guys might be surprised to know that almost all RPT jet aircraft flying in Aus are doing this already. I admit they aren’t called GPS/NDB approaches but the aircraft is following a green line on the nav display that is derived from a GPS/IRS position. The NDB is only there for raw data and isn’t used in any way by the nav system to determine its position in the approach.
I thought overlay approaches were using GPS guidance to follow an NDB or VOR approach track by using the GPS nav line, not using the waypoint bearing pointer on the RMI as you would use the ADF needle as has been suggested here.
Any overlay approaches I know of use a GPS generated track and don't use the waypoint bearing pointer. These approaches benefit from the tracking accuracy which comes with the scaling of the CDI. This accuracy is not possible by just using a bearing pointer.
Perhaps there is more than one style of overlay approach. Using the bearing pointer seems a reasonable option for an NDB approach. The pointer would be nice and steady, there would be no coastal refraction etc.
...that he didn't have a GPS overlay approach for the G1000 to use or a NDB for that matter, but he could use RMI mode on the G1000 to get the same info and do a GPS approach.
You are correct that a NDB/GPS overlay approach is used to fly the NDB IAL track with the superior display/information/accuracy of the GPS unit. And yes, great pity we don't have them here.
You will find the main reason it's allowed over in the states is the fact that they have two geostationary satellites and a bunch of ground based, Wide-area Reference Stations (WRS) to ensure the integrity of the signal, whereas there is just the one over the pacific. (I'm unsure as to how many WRS's we have).
GPS approaches are available for many aerodromes in Australia, providing you're equipped with a TSO-149 certified GPS as this includes WAAS. These approaches often use ground based navigation aids such as a VOR or NDB, I'm unsure if it would any less legal if your GPS simply overlayed the approach on a map...
In Aus there is no dispensation for an overlayed approach, even for Airliners.
When operating an Airliner, technically you do "overlay" the approach through the FMGC but you must monitor the performance though Raw data. In the Airbus for example, the flight manual allows you to operate an NDB appraoch without the NDB, however state regulations revent this.
On the 777 we can use for example an ILS over lay for an NDB approach, Moses Lake Washington is one place this is done. What we do is load the ILS Rwy 32R approach and then in the FMC change the procedure altitude and LOM crossing Altitude at Pelly to the NDB Rwy 32R plate, and also the Min. The aircraft then flys the ILS with same inbound course 324 Degs but crosses the LOM/Pelly at the new NDB ht. You must monitor the NDB raw data. Very nice as the NBD is flown on auto pilot doing all the wind correction stuff and flys the vertical part as with an ILS. You can also use on this approach the ILS missed approach part if it is same as NDB, which in this case it is.
You will find the main reason it's allowed over in the states is the fact that they have two geostationary satellites and a bunch of ground based, Wide-area Reference Stations (WRS) to ensure the integrity of the signal, whereas there is just the one over the pacific.
???? My GPS's (all 3 of them) are usually receiving data from 10 satellites at any one time.
Quote:
GPS approaches are available for many aerodromes in Australia, providing you're equipped with a TSO-149 certified GPS as this includes WAAS. These approaches often use ground based navigation aids such as a VOR or NDB, I'm unsure if it would any less legal if your GPS simply overlayed the approach on a map...
Nope! Where are you getting this stuff from ??? If you wanna be Biggles you will need to get your facts right.
You don't need a TSO-145/6 (not 149) GPS to fly a GPSRNAV Appr in Oz. I fly them regularly with my TSO-129 Garmin 430, perfectly legally!
If you are referring to GPS precision ILS type approaches - then yes, you do need a TSO-145/6 GPS -and you need to be somewhere other than in Oz because even though a TSO-145/6 GPS is WAAS capable (at least that is the case for Garmin 430/530) - WE DONT HAVE WAAS in Oz.
I have flown NDB overlay approaches (or George has anyway) using the Garmin 430 many times in Oz (in VMC) - works like a charm.
An ADF (VOR) will be a handy thing when the GPS signals stop... for whatever reason.
How many times has this happened in the last 10 years?
In 500+ hrs in the Bo in the last 4 years, I have NEVER seen the Garmin 430 loose its satellite signals to the point where it ceased to provide accruate position data.
Garmin III Pilot - yes; Garmin 296 - yes; Garmin 150 - yes; Garmin 496 - not as yet! I suspect they were mostly antenna issues.
I would put another TSO's GPS in my aeroplane before I would waste money replacing the ADF.
I used to fly my NDB approaches when bankrunning in the old PA31. We had a Garmin 430 and just set up the NDB approach in approach section and you could fly it as a HSI mode on the GPS or use the map mode and it would shoot out a big pink line on the final approach course to assist in situational awareness if attempting to look at the poorly lit ADF Best was when you flew with two Garmin 430s so you could do one of each but the only ones with those flash setups where the C208s.
As usual modal awareness if everything. Thats why I watch from the sandwich officer seat on the airbus now watching others enjoy model awreness fun
Doing raw data NDBs are great for traininig and testing but in reality the safer option I think (with the appropriate equipment) is also follow on the NDB and GPS
???? My GPS's (all 3 of them) are usually receiving data from 10 satellites at any one time.
Dr, If you bothered to read my post you'll notice two key words...
Quote:
You will find the main reason it's allowed over in the states is the fact that they have two geostationary satellites and a bunch of ground based, Wide-area Reference Stations (WRS) to ensure the integrity of the signal, whereas there is just the one over the pacific.
.....
If you are referring to GPS precision ILS type approaches - then yes, you do need a TSO-145/6 GPS -and you need to be somewhere other than in Oz because even though a TSO-145/6 GPS is WAAS capable (at least that is the case for Garmin 430/530) - WE DONT HAVE WAAS in Oz.
GPS satellites are NOT geostationary, so the argument that your mighty 3 GPS's receiving 10 satellites is really moot, seeing that you are arguing a point I did not even make!
And where exactly did I say we DID have WAAS??? Did my post not say the states have two, and there is only one over the pacific?
As for the 149 error, I apologise, put it down to posting before my 2nd cup of coffee
Take a deep breath mate and read the initial post - it is about NDB overlay approaches. You don't need geostationary satellites to do them. The TSO'd approach capable GPS equipment that is widely available in aircraft in Oz can be used to fly an NDB overlay approach NOW.
The only impediment is the regulators!
If faced with flying an NDB approach in anger, I would copy the airline boys and girls and let George handle it on the GPS, while monitoring the "raw" data from the ADF - to comply with my legal obligations. Thats how I do the three NDB approaches I fly each year for currency purposes - leaving the one I do each year for my IR renewal as the only one I fly soley by the raw data. This compares with the, on average, 2 x GPSRNAV and 2 x ILS apprs I fly each month.
The only reason for having an ADF in an aeroplane these days is to cover some alternate requirements.
Dr
PS: Wally, was it a TSO'd GPS that lost all the satellites - or a portable?
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