As Achim said: The RWY starts right at a 200 ft cliff – I’ve been there too. There’s really no room to put it anywhere else.
That airport has a rock below the MDA, so if you bust the minima and continue a +V “GS” past the MAP, you hit the rock.
But why on earth do you chart (even on the original FAA plate) a nominal GS that you can’t follow below the MDA without hitting terrain? And without any kind of note on the plate!
Flying an NPA using the advisory glidepath will place the aircraft when arriving at the MDA at the point where a continued descent to the runway would commence (continue), typically 3 degrees. Past this point the descent will have to be steeper. Most smaller piston aircraft can easily handle 6 degrees and for my Bonanza in the high drag configuration, power off is close to 8 degrees. If the ceiling and visibility are close to minimums, I will choose DND rather than CDFA. To get the best chance of completing the approach, I don’t want to treat the MDA as a DA, because of the single instant in time it provides me to see the runway or initiate a climb. I also have to give up at least 50 feet and use a DDA instead of the MDA to account for the sink thru after my decision is made, because I am still in a descent and have to decide early, higher, and further from the runway in order to not bust the MDA, which is treated as a hard floor. Since I am a single pilot operation, I don’t have a PF and a PNF looking outside for the runway. This means I may have to increase the DDA to provide me some time. I could level off at the MDA, in a hybrid maneuver, using the advisory guidance down to a DDA, and then leveling at the MDA and continue at the MDA to the MAP. However, this doesn’t buy me what I want, which is more time to search for the runway. Leveling off and stabilizing the aircraft at the MDA takes priority over searching for the runway, and this takes a substantial amount of time and attention so that I don’t bust the MDA. Once stable at or near the MDA, I can divide my attention and search for the runway while making sure I don’t bust the MDA. I would prefer to get to the MDA sooner and complete the level off stabilization sooner, so I can start my search for the runway. Ideally I will be stabilized at the MDA by the time or I reach the VDP or sooner. Remember that in low visibility, without lights, at an unfamiliar airport, with a narrow and unmarked runway, it will take some time after seeing what I believe to be a runway is in fact one and that it is safe to commence my descent. If I don’t spot the runway or am not in a position to land when I do spot it, I continue to the MAP. I am already level, so at the MAP, I don’t have a descent rate to overcome and I can just commence my missed approach climb and follow the missed approach procedure.
On the other hand, if the reported weather is 500 feet above my MDA and visibility is well above minimums, I will choose to use the advisory glidepath to make my descent and expect to break out without much difficulty spotting the runway. If the weather turns out to be worse than reported, I will start the level off above the MDA and continue to the MAP.
But why on earth do you chart (even on the original FAA plate) a nominal GS that you can’t follow below the MDA without hitting terrain? And without any kind of note on the plate!
Good question. All this stuff evolved over time. Until about 10 years ago, there were no charted VDA (Visual Descent Angle) on NPA charts. Then standards were changed to include them first on all RNAV NPA procedures and later on all NPA procedures. NPA TERPS does not in any way account for descent to the runway, there is a single ROC (Required Obstacle Clearance) value on the final approach segment, typically 250 feet. NPA approaches are evaluated for the visual segment against two inclined planes, one with a 20 to 1 slope and the other with a 34 to 1 slope. The 20 to 1 slope affects the minimum visibility permitted and whether or not night operations are permitted. The 34 to 1 slope is the same one that is used for an ILS. It is charted as a stipple symbol on the government charts and not charted at all on the Jeppesen Charts. The NPA was designed for DND, full stop. To descend below the MDA, the pilot must visually see the runway and avoid all objects. Airlines and business jets have had baro VNAV vertical guidance for some time. An opspec has been developed to utilize a DDA or DA in lieu of an MDA on NPA for these operators, but not applicable to part 91 operators. These runways have to meet specific criteria, for example if the runway had an ILS, it would be OK to fly a NPA to the same runway. Jeppesen provides a specific note on the Chart to the operator that the runway is suitable to use a DA in lieu of the MDA.
So in 2007 we started getting the first WAAS units. As an optional feature, the TSO permitted the vendor adding an advisory glidepath on NPA RNAV approaches. However, an attempt was made to make it clear that the advisory glidepath had no standing and that using it below the MDA could be hazardous to your health. The folks that designed approaches did not change their criteria to consider this optional feature of some manufacturer, as it was only an aid to the pilot and in no way changed the rules for flying the approach. A few years ago, a SouthWest 737 reported that they got a TAWS alert flying a NPA in to KBHM. FAA Flight Test re-flew the procedure, and did not get a TAWS alert if they flew it as designed as a DND. But they did get the TAWS alert when they flew it as CDFA. This started a lot of discussion in the FAA and industry. I participated in the discussion as a GA pilot. The end result was that Flight test now evaluates flying the NPA using the advisory GS at 1 dot fly up along the center line of the NPA final approach path. If they get a TAWS alert or determine that obstacles in the visual segment create a hazard, they report this on the test report. Government charting then added a note on the chart “Descent Angle NA” and removed the charted angle and TCH from the chart. Jeppesen removed the charted angle and TCH from the chart and totally reevaluated their current standard for their DA as MDA note to only apply to part 139 airports (the biggest that serve the airlines and meet stringent criteria). In addition, the database definition was changed to allow for disabling the advisory glidepath on specific approaches. The process of evaluating all approaches to the new standards will take many years, so N23 is still there. So far, the advisory glidepath has been removed from over a hundred approaches and more will come over time. In addition, the criteria for night use of approaches has been stiffened considerably and well over 500 procedures have had notes added NA at night.
Exactly. When you have an explicit MDA value you can continue at that altitude to the MAPT. But without MDA and DA instead you go around immediately regardless of your position. MDA and DA a computed differenty and it may not be safe to fly at DA (best example being an LPV to 200ft AGL which is certainly not a safe altitude for the last to miles of a dive&drive procedure.)
The LPV is not a non-precision approach. To the best of my knowledge, DA for an NPA flown using CDFA has always been calculated by taking the MDA and adding a buffer value to account for the sink after decision at DA. There’s been a lot of debate as to what the buffer should be, from 50 ft to 0, but I’ve never seen a proposal that it should be negative, i.e. that DA is less than MDA.
Can you offer a counterexample?
Well, my aircraft just did it’s acceptance test flight this afternoon and will now be certified for LPV as well. Garmin 430W, plus S-Tec 55x with Flight Director and Autotrim plus Aspen EFD1000 Pro. The flight test crew were VERY happy with the performance of all components and particularly the autopilot performance, to their surprise actually, as one of them knows the S-Tec installation from his SR22. He said the performance in this installation is way better than what he remembers. Really happy camper here at the moment :)
Pic I took 2 days ago while still in the hangar during first live tests of the systems.
Aspen EFD 1000 Pro with Flight Director
Ready for test flight.
I must say I was very happy with the way the installation and certification was handled, also by the FOCA, very helpful, good advice and good people working with us. The people at Avionitec and Seiferle Aviation did an excellent job on this.
What we did is:
- GNS430 WAAS upgrade
- S-Tec 55x Autopilot with Autotrim and Flight Director
- Avionic Straubing Altitude Preselect
- Aspen EFD 1000 Pro.
Now waiting for the paperwork to be finalized and we can start flying.
Ouuuh… Sexy!
Awesome! The autopilot especially is really going to transform IFR for you (and VFR)…
But… you left out the really essential thing. You missed the chance to replace those 1944 toggle switches with proper milspec ones
Very nice! But I would not want to see the invoice …
Still a lot less than a new airplane Flyer59…. I am looking forward to see the TAS values off the Aspen, test pilot today reported 147 kts TAS @ FL65 with about 65% power… for a C’ Model I’ll take that any time.
Peter, LOL, well, none of them ever gave me trouble so don’t fix what works I suppose.
