Due to system or software limitations, some data items are excluded from the final database for the following products covered under Garmin’s Type 2 LOA. The following lists detail those data items excluded for the 1311 cycle
A statement from Garmin on a US site:
The signature of the problem is an LP approach where the underlying approach does not have a defined vertical angle. LP approaches were not available in the electronic Jeppesen database until January, 2013. The first LP approach without a defined vertical angle appeared in the 1308 (August, 2013) cycle of the Jeppesen navigation database. Each new cycle we receive from Jeppesen is tested for safety and quality purposes and an analysis was done with our avionics which detected the ‘unusual’ approach. Garmin determined that the avionics code was not handling these unusual approaches correctly, therefore Garmin chose to remove them from the database.
Software updates are in progress to accommodate these different type of approaches and when those software upgrades are available and the avionics software can handle these approaches, they will be restored to the database.
I don’t actually know what this means but a lot of the removed approaches are in Europe. See the PDF link.
Apparently the airports being removed are ones which are not capable of having a continuous descent profile FAF-MAP, due to obstacles, and thus need the “dive and drive” method (only). But it’s more complex than that, and to do with obstacles below the MDA.
By my reading of the pdf, no european approaches are affected by this particular issue (do we even have any LP approaches over here?)
There is a long-standing issue with the older 430/530 units and the flightdecks (G1000 et al) that share the same hardware/firmware: for FAF to MAP distances greater than 7 miles on LNAV+V and LNAV/VNAV approaches, CDI scaling is wrong. The upshot is that these are encoded as LNAV-only. This affects a lot of german approaches in particular.
Some care is needed when flying GPS approaches – the same approach can come up as any one of LNAV, LNAV+V, LNAV/VNAV, and LPV depending on coding, installation, RAIM availability, WAAS availability and simple GPS precision. Admittedly its quite unlikely, but there is always a chance of arriving at your destination and finding your nice LPV approach is annunciated as LNAV.
You can also be on the approach and be downgraded to a lower level if something fails – on the GTN units you will always be downgraded straight to LNAV. The “correct” behaviour according to the garmin manuals is to simply continue the approach to LNAV minima: I would always go around unless in good VMC.
> By my reading of the pdf, no european approaches are affected by this particular issue (do we even have any LP approaches over here?)
France has them at least….Calais for one
> I would always go around unless in good VMC.
My initial reaction to losing the glideslope on an ILS (or, more realistically, not getting it at the expected point or failing the distance/OM check; happened to me once so far) is to throw it away, simply because at that point I cannot be sure if it is really the glideslope failing, or me doing something badly wrong such as having the wrong DME tuned or having captured a false glideslope.
But the GPS tells you exactly what it still can do, and the above are not an issue.
How about including the LNAV minima in the approach briefing, and carrying on?
IMHO this is a screw up by AeroNav which is the FAA outfit that charts the US approaches. They design and develop the approaches, then provide the technical data to Jeppesen et al. Recently, new criteria was adopted when obstacles were found in the visual segment that prevented a Constant Angle Non Precision Approach (CANPA) descent to the runway. If flight test considers them an issue, then a note is added to the approach chart, “Descent Angle NA” and the VDA (Visual Descent Angle) is not charted. The note is there because not all FMS/GPS use the descent angle data to determine if an advisory glidepath is provided. A pilot is supposed to read the chart and determine that even though they see a glidepath, it should be ignored. In the case of the Garmin implementation of LP approaches, they don’t currently provide any advisory vertical guidance on these procedures, so it is a moot point. However, someone at AeroNav thought it would prevent GPS/FMS systems from displaying the advisory glidepath if they set the GS angle in the database record to zero. Little did they realize that a zero in this field of the database was not supported. This resulted in the approach not being able to be coded in the database as an unintended consequence. I have raised this as an issue at the Aeronautical Charting Forum/Instrument Procedures Group as it is unnecessarily causing the loss of all approach procedures for some airports.
We have some 15,000+ airports in the US and only 500 or so are used by the airlines. Constant angle descent on a non precision approach is an important safety improvement for turbine equipment. But for piston GA facilities, with short runways, that often don’t have approach lights, and are mostly non towered, constant angle is not always feasible. The so called dive and drive method to these airports is the only way of providing access to these airports in instrument conditions. MITRE did a study comparing the safety of CANPA and DD on both turbine and smaller GA piston aircraft. They found a clear safety benefit with the CANPA for turbine aircraft, but there was no statistical difference for GA piston aircraft (in fact the DD was slightly safer).
By definition, the approach path was not found suitable for vertical guidance if a LP is published, otherwise it would have been a LPV. So it is not unexpected that these LP procedures are published in a more challenging obstacle environment and that they are not well suited to the CANPA method.