Ibra wrote:
Why 3D LPV does not have a separate redundancy requirement? (other than RAIM/SBAS satellites)
You said it yourself. RAIM/SBAS!
Ibra wrote:
On 3D ILS, the DME reading at FAP or navigatiom fix is yoyr sort of “ILS RAIM” once that checked you will slide untill DH no matter what happens
That depends. Some ILSes have you check the DME distance at the FAP. Other ILSes have you check it when you’re halfway down. In any case, you need the DME distance to make the check.
How come people in the US manage to get valid glide paths for ILS without DME checks?
Ibra wrote:
How come people in the US manage to get valid glide paths for ILS without DME checks?
Either they have marker/locator beacons or they use radar fixes – or GPS. The whole start of this (sub)discussion what that the FAA permits substitution of GPS for DME while EASA does not.
Intellectually, it would be interesting to know how it’s done in practice without DME? and why it’s relvant there but not here? after all the FAA pilots & EASA pilots tend to have similar number of grey cells
DME/GPS substitution is what it is: not allowed in EASA land and one has to bolt one in their cockpits at 15k
In FAA as Airborne _Again pointed out there are still marker beacons, or an approved IFR database GPS overlay.
There is also the practice in non jet ops of dive-and-drive (subject to intermediate MDAs). One of the positive practices of EASA is the use of CDFA in the context of non precision approaches. This is one safety practice which the USA might adopt from EASA.
RobertL18C wrote:
This is one safety practice which the USA might adopt from EASA.
CDFA is taught in USA, particularly for Turbine aircraft. However, it is not mandated. Most US pilots prefer to have an advisory GP, but there are times when D&D makes sense as It can provide for a lower visibility and a lower MDA as there is no need for a derived DA buffer. This is important at thousands of US airports without towers or approach lighting. Your new to you Bonanza can easily descend still requiring some power using a six degree slope and still land on a relatively short runway, so a three degree slope of a CDFA is not needed. Also, although CDFA is clearly safer for Turbine aircraft, it has not been demonstrated to be so for piston aircraft. MITRE did a study and found that with piston aircraft, approaches with vertical guidance had a slightly higher accident rate than those without, although the difference was not statistically significant.
Marker beacons are becoming obsolete in the US. Many ILS are being revised without an outer marker or a OM locater NDB. Localizer procedures are often based on ILS DME. GPS substitution for DME makes having a DME in an aircraft redundant. AT my airport KUZA, there are two ILS procedures, both with the same final approach ILS course. One is an ILS Y with a hybrid TAA using GPS to join the procedure and the ILS Z which uses VOR and DME conventional facilities to join the procedure. The FAF is recommended to be used to confirm the crossing altitude when following the GS agrees with the chart. The altitude comparison is primarily to catch a miss set altimeter and would also might catch a gross GS error. By the time one is crossing the FAF at a non towered airport, ATC has already cleared the aircraft for the approach and switched them to the local CTAF frequency.
NCYankee wrote:
Most US pilots prefer to have an advisory GP, but there are times when D&D makes sense as It can provide for a lower visibility and a lower MDA as there is no need for a derived DA buffer.
Does the FAA demand a DDA? EASA does not. (And with good reason.)
Also, although CDFA is clearly safer for Turbine aircraft, it has not been demonstrated to be so for piston aircraft.
For me personally, the main advantage with CDFA is not safety but that it is so much easier to fly compared to d’n’d.
Airborne_Again wrote:
Does the FAA demand a DDA?
No, that is a pilot choice. However, approach procedures are designed assuming DDA to get the lowest MDA/visibility and to support all equipment capabilities. For the FAA charts, a VDA and TCH are charted for a straight in approach as long as there the obstacle environment below the MDA is not found to have obstacles that require the note: “Visual Segment – Obstacles”. Jeppesen takes a contrary approach and charts the VDA and TCH in addition to the note if applicable. The note is only determined by a flight test if maneuvering is required below the MDA on the VDA/TCH defined path to avoid obstacles in the visual segment. An NPA procedure just uses a single level OCS surface (250 feet for an RNAV (aka RNP APCH) procedure and does not eliminate the approach if there are obstacles in the visual segment. Some NPA procedures will have a step down fix inside the FAF to obtain a lower MDA.
Airborne_Again wrote:
For my personally, the main advantage with CDFA is not safety but that it is so much easier to fly compared to d’n’d.
I think most pilots would agree, but there are occasions where this reduces the chances of completing the approach with a landing when conditions are close to or at minimums.
