This should provide a synthetic glideslope on a WAAS GPS. No need for LPV.
I am quite sure I have flown GNSS LNAV approaches with a non-WAAS G1000 and had advisory glideslope (baro-VNAV). The only hesitation I have is whether this actually took place in the simulator, in which case the GPS may have been WAAS.
I have also flown the LPV into LFPT with a GTN650 (WAAS)
It is true you will need better visibility for a CDFA procedure compared to a “dive and drive” approach.
Yes and no. Before CDFA we were supposed to calculate a DTL-point (decision to land) from which you either would continue towards the threshold on a 3-degree slope or go-around if nothing in sight. So even with a dive and drive approach you would have had to decide at exactly the same point as we do now following that 3-degree path all the time. Of course some people would always continue to fly towards the runway at MDA and then hammer the aircraft somehow onto the tarmac from 400ft above the threshold. But this is not what the regulators and insurers want to see any longer.
A great explanation from NCYankee about the subtle difference between LPV and +V…
I wonder how much of an OAT departure you would need to breach the vertically protected area? Would it be the same under TERPS as PAN-OPS?
I wonder how much of an OAT departure you would need to breach the vertically protected area?
In cases where that might be a problem it is printed on the Jeppesen charts. For example my once-per-week GPS approach to RWY 25 at EDAB has a caption “Baro VNAV not authorized below -15°C”.
But this is why really LPV is superior to Baro VNAV. We should be flying GPS derived glideslopes which can be surveyed and flown regardless, temp etc. It might reduce my ability to see the runway but I will take a constant descent profile any day over dive and drive.
It is true you will need better visibility for a CDFA procedure compared to a “dive and drive” approach. OTOH I find CDFA so much easier to fly that for me it is worth it. In fact when I first did a CDFA it was like a revelation — I asked myself why NPAs haven’t been done like that all the time?
Simply put, not all NPA approaches to all runways are suited for CDFA. If the obstacle environment supports an LPV, it is a superior approach and in most cases will offer lower minimums, but not always. If there is an obstacle that blocks a CDFA to the runway, a step down fix can permit the aircraft to descend to a lower altitude once the obstacle is passed. This works for a dive and drive, but you can’t have an approach with dual glideslopes. In the US, there are two kinds of airports, those that serve the airlines and those that serve GA. The approaches to airports that serve the airlines typically have a control tower, an approach light system, longer and wider runways, an ILS and in general meet tougher obstacle requirements. If these same criteria were used at all GA airports, probably 3/4 would lose their IFR approach access.. The runways are shorter and narrower, have more obstacle issues, are un-lit, do not have a tower, and are hidden by trees, hills, Walmart parking lots. etc. Locating one of these runways when the visibility is good is difficult, make the visibility 1 SM and it is going to take some time while the aircraft is stabilized at the MDA before you positively verify what you are looking at is actually a runway.
The FAA has added additional flight testing for NPA and flies an advisory glidepath with one dot fly up. If the flight test crew determines that this is too hazardous or they get a TAWS alert, they make a note in the flight test report. If the note is present, the advisory GS is deleted from the chart and the database providers eliminate the advisory GS from the approach. This is an ongoing effort and will take years to go thru the entire inventory of NPA. In the mean time, flying the advisory glidepath below the MDA is not permitted and can ruin your day.
I too enjoy flying the LPV and use the advisory glidepath on NPA, but I understand its limitations. They are certainly easier to fly and for aircraft equipped with GS tracking are very nice. But in low visibility they are less likely to result in a safe landing, which is the primary purpose of conducting the approach in the first instance. One size does not fit all.
I wonder how much of an OAT departure you would need to breach the vertically protected area?
Using WAAS for vertical advisory guidance, temperature won’t cause a breech of obstacle clearance as the GS is relatively fixed in space. What moves with temperature is the MSL indication. There are two reasons why, particularly hot days cause an issue with a WAAS advisory glidepath. The first is regulatory, one is not permitted to bust the MSL minimum altitude. In other words, if the GS takes you below the minimum, you must obey your altimeter and abandon the GS. The second has to do with vertical separation from traffic above. Vertical separation is based on MSL and there are cases in the US where vertical separation has been lost, particularly following a GS outside of the FAF. Differences of 300 feet in MSL will be detected by radar and can and have resulted in a pilot deviation. Differences of 100 feet will cause a bust on a check ride.
Interestingly enough, Baro-VNAV systems without temperature correction don’t have this issue, because both the altimeter indication and the GS move in space in tandem as they use the same vertical source. Of course, then temperature limits are placed on using these type of systems. A LNAV/VNAV APV may be flown by an aircraft equipped with Baro VNAV or WAAS in the US, the Baro VNAV system is limited by temperature, whereas the WAAS system is not on the same approach.
Locating one of these runways when the visibility is good is difficult, make the visibility 1 SM and it is going to take some time while the aircraft is stabilized at the MDA before you positively verify what you are looking at is actually a runway.
That’s precisely it. Since I have normal 430s only, I can only fly LNAV approaches here in Europe. And if the vis is poor, I really like to have as much time as possible at the MDA to scan the area for the runway.
Also what_next, please always consider (and mention) that what you are doing is often dictated by company procedures. 95% of us here are not restricted by such. Just to make it clear: whilst certain “bodies” may have a preference for CDFA, it is entirely legitimate to fly dive and drive, even in Europe.
I think I can see the subtle argument with the +V glideslope.
One is supposed to watch the SDF altitudes on the way down and must not breach any of them.
The glideslope is GPS-derived so is not temperature dependent, which is good.
But the SDFs are specified in terms of baro altitude and as the air warms up they will rise up in true height, and eventually will pierce the temperature-independent GPS derived glideslope. At that point, you cannot just fly the glideslope anymore. Well, you can, because nothing physical has actually changed, but you will fail your IR checkride!
But isn’t this argument disingenuous? What matters to safety is your actual obstacle clearance, not whether you are complying with barometric altitudes.
Well, maybe the trees will be taller when it’s warmer and might expand and pierce the GPS glideslope 
Everything gets bigger when it’s warmer 
Also what_next, please always consider (and mention) that what you are doing is often dictated by company procedures.
Not company procedures. All commercial operators under EU OPS (1.430) and now EASA OPS have to fly non-precision aproaches as CFDA down to a decision altitude.
As private pilot you must respect the rules of your country of registration and those of the country where you are flying. In many countries, CFDA is manadatory. Have no idea about Germany, the last time I looked into the AIP was before EU Ops.
NB: This website here explains CFDA and “dive and drive” quite well and may be worth a look: Link
