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Discussion in 'Cleared for the Approach' started by Palmpilot, Nov 24, 2017.
Did I hear another voice from the Cirrus early in the recording? Maybe a CFII?
My wife's IFR instructor called that the "pass/fail" button. Get that wrong and you fail the checkride.
I'm stealing that for sure!
Even if you don't have the auto switch, it will blink at you to remind you to switch to VLOC. (not at all speaking from experience....)
I haven't flown with a Garmin for a number of years. Can you join the ILS final in LNAV then change to VLOC and track the localizer prior to the final-approach segment?
A Garmin 400 series lets you switch to VLOC whenever you like, although I think I was told by an instructor that you're supposed to switch to VLOC as soon as you receive a vector to intercept the localizer. (This is consistent with Note 2 in AIM 1-2-3c, which prohibits using RNAV for lateral navigation on a localizer course.)
They call that button the $400 button around here. Forget to push it on the checkride and you'll spend that for a retest.
On a related topic, I've never seen a Garmin 430/530 that was set up to automatically switch from GPS to VLOC, as was mentioned earlier. It must be rare for people to enable that feature.
That is only "without reference to raw localizer data". Is the LOC course not displayed before VLOC is selected?
You could tune in the localizer on a separate VOR receiver, but unless you do that, the "raw localizer data" will not be displayed without selecting VLOC.
You're "supposed to" follow the LOC once you intercept. When you make the switch is a matter of technique. One option is to have your panel GPS set for automatic switching. I do that but, preferring to do it manually, I do the switch on that final instruction to intercept the localizer when being vectored.
Thanks for looking out for another pilot. As a GA pilot, I appreciate that the professional pilots will do what they can to provide assistance.
If you want to be snarky, just say that this guy deprived Cirrus of another CAPS save.
Let's say your on your own navigation on this ILS from over SEAVU. When would you switch from LNAV to the localizer?
I’d switch on a Tuesday. That one intercepts a long way out. Knowing what some localizers do at half that distance I have to ask how straight that localizer really is. Since it’s California the question is probably pointless.
What's the current consensus on this? I've flown with a few different IR rated pilots and instructors recently and there seem to be two schools. One believes that with the GPS counting down the time you are better off planning a smooth even descent to pass your fixes at or above the minimum altitude. The idea is that a.) with tech it is pretty easy to do mental math "okay I need about 700fpm" and b.) that diving and driving gives you more time and opportunity to accidentally drift below the min altitude.
The other school is that it is easy to just drop down at 1,000 fpm and then you don't have to worry about the descent profile until the next fix, at that point just maintain altitude and track. I think I'm in the former camp, but don't have enough IR experience to be an ardent supporter of either
Pretty much what my instructor said as well during our initial instrument lessons. On the GTN plane we fly it *should* switch to VLOC on its own but the way we treat it is to assume it won't switch on its own so we always babysit the GPS/VLOC modes
I’ve always been a fan of the nice, smooth descent rather than chop and drop. Less power, changes, less leveling off. I don’t really like the roller coaster effect. Either way is fine, I just prefer to do/teach a constant descent rate. Nowadays, most planes equipped with GPS will tell you the vertical speed required to reach the next waypoint and pilots don’t even have to do mental math.
There is no consensus. I think it depends on the plane, the pilot and the approach.
For example, in the Cirrus SR20, dive and drive was really easy to pull off and gave you a lot more time when at MDA to look for the runway in margin conditions. However, in the Aerostar, with an approach speed 50% higher, and a lot more happening, a constant descent angle was much more preferable.
Thanks, that's the way my current instructor has been teaching me, but the two other pilots I flew with recently both were big proponents of the "dive and drive." I agree though, I think you are more stabilized and in control of the plane flying it down steady. It's really not hard to do a quick mental math, or like you said, most modern GPS will give you the vertical speed anyway
Thanks, in my case we're talking 1970s spam cans with the occasional Cirrus mixed in (when budget permits). That's a good point on getting more time at the MDA
Fortunately, California doesn't design IFPs.
Also known as the suicide button. Fail to switch and it may be suicide.
Since it's own nav rather than a vector, the advice that (I think) the instructor gave would not apply. I would wait until I was on the final approach course and close enough to receive a stable unflagged localizer signal. (If there is some guidance about where to switch, I would love to hear it.)
The newer Garmin gear switches when the PFAF becomes the active waypoint (provided the VORLOC is on the ILS frequency and the approach mode is selected.) This would be passing SHELL. SHELL is the intermediate fix so prior to that point the approach course has Victor airway widths.
That makes sense; I guess four nm each side of course ought to be enough even for me! However Garmin's autoswitching algorithm seems to be at odds with note 2 of AIM 1-2-3c, which says the following about RNAV substitution, without any mention of how far out on the localizer you are:
"2. These operations do not include lateral navigation on
localizer−based courses (including localizer back−course
guidance) without reference to raw localizer data."
I can't find the reference offhand, but my impression was that the LOC and GS were only required for the final approach segment.
That's what I recall from the info on when and how GPS can be substituted for other approach instruments. The FAF is the defining point for when radio nav must be used on approaches that aren't RNAV. Various reasons for that I guess and flight check is prolly a big one.
I thought that too, but it was a mistake. It's the same reference—AIM 1-2-3(c), or AC90-108, which have the same information: you may NOT use RNAV in lieu of a conventional NAVAID during the final approach segment. You also may NOT use RNAV in lieu of a localizer-based course at any time without reference to raw localizer data.
You might be thinking of Note 4 in the same section:
"4. Pilots may not substitute for the NAVAID (for example,
a VOR or NDB) providing lateral guidance for the final
approach segment. This restriction does not refer to
instrument approach procedures with “or GPS” in the title
when using GPS or WAAS. These allowances do not apply
to procedures that are identified as not authorized (NA)
without exception by a NOTAM, as other conditions may
still exist and result in a procedure not being available. For
example, these allowances do not apply to a procedure
associated with an expired or unsatisfactory flight
inspection, or is based upon a recently decommissioned
Note 2 and note 4 look to me to be independent of each other, which implies that note 4 would not override note 2.
These notes are on page 1-2-7 of the October 12, 2017 edition of the AIM.
I can tell you that the FAA issued a bulletin a few years ago advising airline pilots flying the ILS approaches from the east to use LNAV and Baro VNAV to assure not busting the step-down fixes on a hot day. All the airline equipment does the same as the newer Garmin equipment does: remains in LNAV until crossing the fix prior to the PFAF.
Sounds like the FAA's right hand doesn't know what the left hand is doing.
Or both are doing something we’d rather not watch? LOL.
PS you realize how funny that sounded coming from someone who goes by “Palmpilot”, right?
Good catch Nate!
If you find it easier to navigate the AIM by paragraph instead of page number it's 1-2-3 c.
More on that in AIM 5-4-5 b., note 2.
The recent Garmin equipment I am familiar with will show a shadow LOC and GS while tracking an ILS outside the fix prior to the PFAF. So, that would certainly meet the monitoring of raw data requirement. The monitoring requirement is absurd, though, on an ILS outside the IF. The protected airspace is equivalent to RNAV-2, which is the same as a T or Q route. But, the FAA has been known on occasion to be absurd.
I think I'd probably do it well before FOGLA where it becomes required. I probably wouldn't do it between SEAVU and LYCOM, and just have a peek at my source for 'raw localizer data.'
At least they put out that bulletin you mentioned in post #110 that pretty much says 'we know the letter of the law says use the localizer but go ahead and use LNAV anyway.' I'm wondering how wide the localizer is out there at LYCOM. It's 37 miles out from the antennae which is at the far end of a 2 mile long runway. It's supposed to be 700 feet wide at the runway threshold. I don't know how to do the trigonometry.
When I fly a Skycatcher, my palm is in contact with the joystick!