Theories of Lift

I just completed giving two end-of-course checks to flight instructor applicants during which the candidates explained lift, at least in part, by presenting the so-called equal transit time theory. That is, when a pair of air molecules encounters the leading edge of an airfoil, the molecule flowing over the curved top of the wing must travel a longer distance than its companion moving beneath the wing. The molecule on top must therefore move faster to meet its companion at the trailing edge. Pressure drops as a fluid’s speed increases, Bernoulli’s principle, and so forth.

Unfortunately, the equal transit time explanation is wrong, and has long been recognized as an error (see, e.g., Babinsky’s Demonstration: The Theory of Flight and Its Historical Background [PDF]). There’s no physical process that would require the two molecules to meet (we’re not talking quantum entanglement here). In fact, numerous wind tunnel studies and other demonstrations confirm that, while the air flowing over the top of the wing does indeed speed up, and its pressure does in fact drop, particles that start together at the leading edge don’t meet. A molecule taking the (typically slightly) longer upper path in fact ends up far ahead of its cohort that follows the shorter path below. The video below shows the physical reality.

This longer video provides additional details. This one’s good, too.

Indeed, as Doug MacLean (see below) explains, the typical difference in the length of the pathways above and below an airfoil is about an order of magnitude too small to produce the actual observed lift. Moreover, symmetrical airfoils, and even flat planes, provided they meet a stream at an angle of attack, produce lift (more or less efficiently, to be sure) despite the fact that the distances the molecules must travel are effectively equal.

Clearly something (or somethings) else is (are) going on.

Doug MacLean, a retired Boeing aerodynamicist, quotes a former colleague, Philipe Spalart, who said: “It’s easy to explain how a rocket works, but explaining how a wing works takes a rocket scientist.”

(See MacLean in this YouTube video. Warning: There’s math late in the presentation. Triple integrals…)

Here’s a recent, accessible article from Scientific American about various theories of how airfoils create lift. It’s a good read that explains several key points. A teaser:

…Adding to the confusion is the fact that accounts of lift exist on two separate levels of abstraction: the technical and the nontechnical. They are complementary rather than contradictory, but they differ in their aims. One exists as a strictly mathematical theory, a realm in which the analysis medium consists of equations, symbols, computer simulations and numbers. There is little, if any, serious disagreement as to what the appropriate equations or their solutions are. The objective of technical mathematical theory is to make accurate predictions and to project results that are useful to aeronautical engineers engaged in the complex business of designing aircraft.

But by themselves, equations are not explanations, and neither are their solutions. There is a second, nontechnical level of analysis that is intended to provide us with a physical, commonsense explanation of lift. The objective of the nontechnical approach is to give us an intuitive understanding of the actual forces and factors that are at work in holding an airplane aloft. This approach exists not on the level of numbers and equations but rather on the level of concepts and principles that are familiar and intelligible to nonspecialists.

It is on this second, nontechnical level where the controversies lie. Two different theories are commonly proposed to explain lift, and advocates on both sides argue their viewpoints in articles, in books and online. The problem is that each of these two nontechnical theories is correct in itself. But neither produces a complete explanation of lift, one that provides a full accounting of all the basic forces, factors and physical conditions governing aerodynamic lift, with no issues left dangling, unexplained or unknown. Does such a theory even exist?

Read the article for a more complete discussion. You can also find excellent visualizations and explanations via the Lippisch videos, discussed in The Secret of Flight–Dr. Alexander Lippisch.

In the meantime, it seems the best we can do as flight instructors is explain that airfoils are shapes that efficiently produce lift as they move through the air (or the air moves over them). Pressure does in fact drop above an airfoil at a positive AoA resulting in an upward force. The air around an airfoil also is deflected and therefore accelerated (it has a change in velocity, by definition an acceleration), and, as MacLean argues, Newton’s Second Law (F=ma), not so much the Third Law (equal and opposite forces) applies. Lift and drag are the results, and we as pilots can control lift and drag by using the elevator control to change AoA, extending flaps, etc.

But the smart people who try to understand what causes these phenomena still can’t agree on complete theory of lift. As the Scientific American article concludes:

“One apparent problem is that there is no explanation that will be universally accepted,” [Drela] says. So where does that leave us? In effect, right where we started: with John D. Anderson, who stated, “There is no simple one-liner answer to this.”

Redefining Designated Mountainous Areas

FAA is working on a long-term project to redefine Designated Mountainous Areas, a change that could allow lower IFR altitudes in many parts of the western U.S. and in sections of higher terrain in the East. The project was a topic at the October 2020 session of the Aeronautical Charting Meeting; the images below come from an FAA presentation at that meeting.

First, some background. The current Designated Mountainous Areas (DMA) are described in 14 CFR Part 95 Subpart B (originally published in 1963). The references that apply to the continental U.S. are:

  • §95.13   Eastern United States Mountainous Area.
  • §95.15   Western United States Mountainous Area.

Figure 5-6-3 from the AIM shows these areas highlighted in blue. In general, the western third of the U.S., with a couple of exceptions in the Central Valley of California and part of the Puget Sound region near Seattle, is designated as a mountainous area. Another swath covers the high terrain from Alabama to New England, with exceptions in New York and Maine.

In a DMA, the minimum altitudes for IFR flight (explicitly defined in 14 CFR §91.177) must be 2,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown. Because the current DMA, especially in the West, covers such a large area, the MEAs for airways and minimum IFR altitudes that ATC must use can be unnecessarily high in regions such as central Washington and Oregon and similar wide valleys and basins in other states. This issue has become more important as we evolve to GPS navigation that supports direct RNAV routes and as ATC applies ADSB to its surveillance capabilities.

The FAA project seeks to redefine mountainous areas more specifically as:

Designated mountainous areas include those areas having a terrain elevation differential exceeding 3,000 feet within 10 nautical miles within those one arc-second quadrangles overlying terrain or U.S. territorial waters.

This new definition would also align with that used by ICAO.

Illustrations from the presentation at the ACM meeting help clarify the proposed change. These images (not to scale) show how the terrain in each quadrangle is evaluated.

For example, here’s a depiction of how the DMA in the West would change under the new rule. The shaded blue area shows the current DMA. The new definition would require the designation only for the orange-brown areas.

The DMA in the East would also shrink.

The practical effects of the change would alter the requirements for different phases of IFR flight. For example, pilots of piston-powered aircraft could have more flexibility in choosing IFR routes at comfortable altitudes, whether flying airways or RNAV direct. The new DMA could also provide more options when avoiding icing and allow new IFR departure procedures.

For example, when planning an off-airways route under IFR, you must consider the OROCA (although an OROCA is not, in itself, a legal minimum IFR altitude; see 14 CFR §91.177). The AIM defines OROCA thus:

OROCA is an off−route altitude which provides obstruction clearance with a 1,000 foot buffer in non-mountainous terrain areas and a 2,000 foot buffer in designated mountainous areas within the U.S. This altitude may not provide signal coverage from ground−based navigational aids, air traffic control radar, or communications coverage.

ATC must also apply minimum IFR altitudes when clearing you direct off-airways and other published route segments. As the AIM explains:

The minimum vectoring altitude [or minimum IFR altitude (MIA)] in each sector provides 1,000 feet above the highest obstacle in non-mountainous areas and 2,000 feet above the highest obstacle in designated mountainous areas. Where lower MVAs are required in designated mountainous areas to achieve compatibility with terminal routes or to permit vectoring to an IAP, 1,000 feet of obstacle clearance may be authorized with the use of Airport Surveillance Radar (ASR). The minimum vectoring altitude will provide at least 300 feet above the floor of controlled airspace.

Departure procedures are also constrained by DMA. When FAA develops ODPs and SIDs, the AIM explains, planners must evaluate obstacles around an airport:

The 40:1 obstacle identification surface (OIS) begins at the departure end of runway (DER) and slopes upward at 152 FPNM until reaching the minimum IFR altitude or entering the en route structure. This assessment area is limited to 25 NM from the airport in non-mountainous areas and 46 NM in designated mountainous areas.

The expanded OIS required in current DMA can result in steep climb gradients, course changes, and other requirements that can make IFR departures challenging, even when an airport is located in a broad valley or basin.

The effort to redefine DMA is a long project. The timeline below shows that work began in 2017.

A draft NPRM is scheduled for publication in February 2021, but the date may slip due to COVID. And at present, there’s no date for implementation. Changing the DMA would require extensive coordination and updates to legally defined routes, all types of IFR charts, databases, ATC resources and procedures, and FAA publications, including IFR training handbooks. Nevertheless, the effort is a welcome sign of progress as we adopt new navigation technologies and avionics.

A Busy, Blustery Day at Boeing Field

Even on a windy, bumpy Sunday afternoon, Boeing Field (KBFI) in Seattle can be a busy place.

I wanted to get some practice wrestling with crosswinds, so I took a short hop to nearby Bremerton, WA (KPWT) and then back to KBFI. Bremerton wasn’t busy. The wind there was 20-30 degrees off the runway heading and gusting to about 30 knots.

I was surprised on the return to KBFI, however, to find that the tower frequency was hopping. As you can hear in the first video above, one controller was working the two parallel runways on separate frequencies, herding a mix of VFR and IFR traffic, single-engine pistons and jets, helicopters and amphibs.

The wind at KBFI wasn’t quite as strong and it was more closely aligned with the runway, but Boeing Field lies in a valley, and the wind strength and direction often change dramatically as you descend to traffic pattern altitude and then to the runway.

Enjoy the ride. More flying videos at my YouTube channel: BruceAirFlying.

Traffic Pattern Calls: TMI

Lately, it seems that I hear many pilots at nontowered airports announcing their intentions like this:

Generic Traffic, Cessna 123A, 8 miles to the south, setting up for a 45 to the downwind, runway 27. Generic.


Generic Traffic, Cessna 123A on the downwind for base, runway 27. Generic.

Radio calls that include two or more legs of the traffic pattern grate on the ear (almost as much as “Any traffic in the area…“). More importantly, they could easily confuse other pilots, especially when the CTAF is busy and transmissions are cut off or lost in the static of multiple position reports:

Did that Cessna say, “On the 45” or “On downwind?”

Perhaps my noticing such CTAF calls is an example of the frequency illusion called the Baader-Meinhof phenomenon:

Baader-Meinhof phenomenon, or Baader-Meinhof effect, is when your awareness of something increases. This leads you to believe it’s actually happening more, even if that’s not the case.

Whatever the actual frequency of the announcements, they don’t help. When transmitting your position and intentions, provide the essential information, not a detailed description of your plan. For example, I teach this sequence of calls on the CTAF:

Podunk Traffic, Cessna 123A, one-zero miles south, planning left/right traffic runway 27. Podunk.

Podunk Traffic, Cessna 123A, on the 45, left/right traffic, runway 27. Podunk.

Podunk Traffic, Cessna 123A, [turning] left/right downwind runway 27 [full stop/touch and go]. Podunk.

Podunk Traffic, Cessna 123A, [turning] final runway 27 [full stop/touch and go]. Podunk.

Stating the direction of the traffic pattern (left or right) is especially important at airports with non-standard patterns or parallel or intersecting runways. It’s also helpful to tell other pilots that you’re planning a touch-and-go, full-stop, stop-and-go, or low approach.

AC 90-66B: Non-Towered Airport Flight Operations provides more details about this topic, and AIM 4-1-9, Traffic Advisory Practices at Airports Without Operating Control Towers includes additional specific examples such as:

Strawn traffic, Apache Two Two Five Zulu, (position), (altitude), (descending) or entering downwind/base/final (as appropriate) runway one seven full stop, touch−and−go, Strawn.

Note the forward slashes: downwind/base/final as in “downwind or base or final.”

And as for “Any traffic…please advise,” see both the AIM and the AC:

Pilots stating, “Traffic in the area, please advise” is not a recognized Self−Announce Position and/or Intention phrase and should not be used under any condition. (AIM)

Note: Pilots are reminded that the use of the phrase, “ANY TRAFFIC IN THE AREA, PLEASE ADVISE,” is not a recognized self-announce position and/or intention phrase and should not be used under any condition. Any traffic that is present at the time of your self-announcement that is capable of radio communications should reply without being prompted to do so. (AC 90-66B)

For more details, see Operations at Non-Towered Airports.

Unusable Airways, Routes, and Segments

Consider the following excerpt from the FAA low-altitude IFR enroute chart (L-33 / L-34) in upstate NY.

The light gray, EKG-like line that overlays V293/T295 is appearing more often as the FAA continues the MON program to decommission about one-third of the VORs in the continental U.S.

The zigzag line means that the underlying segment of an airway or route is unusable. That word, unusable, has a specific legal meaning in the FAA regulations. It also affects how you can operate under IFR in the area so depicted on a chart.

The combination of the symbol and its underlying meaning continues to confuse many pilots who fly RNAV-capable aircraft, typically using GPS to navigate even along VOR-based airways and routes.

The Aeronautical Chart User’s Guide describes the zigzag symbol thus:

For clarity, I’ve reproduced the caption below:

Pilots should not file a flight plan for or accept a clearance that includes navigation on any route or route segment depicted as unusable. Pilots using RNAV may request ATC clearance to fly point-to-point between valid waypoints or fixes, even those on routes depicted as unusable (refer to AC 90-108 for RNAV eligibility).

The AIM also addresses this issue, although somewhat obliquely.

For example, a note in AIM 1-2-3 Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes explains:

Unless otherwise specified, a suitable RNAV system cannot be used for navigation on procedures that are identified as not authorized (“NA”) without exception by a NOTAM. For example, an operator may not use a RNAV system to navigate on a procedure affected by an expired or unsatisfactory flight inspection, or a procedure that is based upon a recently decommissioned NAVAID.

That’s the legal answer, tied to the legal description of a Victor airway, which is explicitly defined by VOR radials (see 14 CFR Part 71, 14 CFR §91.181 Course to be flown, and FAA Order 7400.11).

For example, if a VOR is decommissioned or temporarily out of service, or if a radial or range of radials that define one or more airways or route segments is unusable, then the Victor airway or route segments that those radials establish are also unusable. An airway or segment might also be rendered unusable for other reasons, including new obstacles.

In other words, even if you fly an RNAV-capable airplane and routinely fly Victor airways using GPS, according to the chart below, you can’t legally file or fly V292 between SAGES and WIGEN. ATC should not even issue a clearance that includes “V292” for that part of the route.

In this case, there’s an easy way around the dilemma. The unusable segment coincides with a T-route, T295. T-routes are designated for use by aircraft with an IFR-approved GPS. And a note below the unusable segment of the airway states: ONLY V292 UNUSABLE.

So you could fly along the black line beneath the zigzag on this segment, provided ATC cleared you via T295.

Another option, point-to-point RNAV navigation, is also legal. ATC could clear you to fly (for example, west-to-east) along this segment via SAGES -> WIGAN.

Sometimes a segment marked as unusable does not have a charted MEA, or the only MEA is a GPS minimum altitude (in blue) associated with a coincident T-route. But ATC can still clear you by using its normal off-route or point-to-point procedures, including the minimum IFR altitudes (MIA) or minimum vectoring altitudes (MVA) established for that area.

This discussion may seem moot in the RNAV era. Most IFR pilots routinely fly victor airways using only GPS. As a practical matter, if you have a navigator that supports airways (for example, a GTN or newer G1000 system) and ATC clears you to fly the “unusable” segment via SAGES -> WIGAN, you would probably still load V292 into the box.

Or you could enter and fly that portion of T295. Either option saves you from having to enter the fixes individually.

As we’ve seen, the preceding example offers a couple of choices, because a T-route coincides with the Victor airway. But that’s not always the case if a Victor airway has been rendered unusable because a VOR has been decommissioned.

Consider this segment of V469:

The chart shows a GPS-based MEA (6900) for one segment marked unusable, but there is no coincident T-route. According to the AIM reference cited above, you can’t file or accept a clearance to fly V469 south of BRUCY. In this situation, legally, if you want to fly the course defined by the black line on the chart (and if the lack of a VOR signal is the only reason for the unusable segment), you must file, and ATC must clear you, via the fixes along that route: BRUCY -> EXRAS -> IFAVU -> BOOME

Again, you could save time and avoid potential errors by loading the airway into a navigator like a GTN. But technically, your clearance would be direct between the fixes at an altitude assigned by ATC for that portion of the route.

VOR Decommissioning: October 2020 Update

FAA continues its program to decommission about 307 (34%) of the VORs in the continental U.S. Some 589 VORs (with enhanced service volumes) will remain operational when the minimum operational network (MON) program is complete, now scheduled for FY2030.

At the October 2020 session of the Aeronautical Charting Meeting, Ernesto Etienne, VOR MON Lead Engineer at FAA, provided an update on the program to date.

For more information about the MON program, see: Updated VOR Retention List, Next Round of VOR Shutdowns, VOR Status–Another Update, Minimum Operational Network (MON) Airports.

As of September 20, 2020, FAA had shut down 82 VORs. In Phase 2 of the program, which runs through FY2030, another 225 navaids will be decommissioned.

The 82 VORs discontinued as of September 30, 2020 are in this list (PDF).

Through the end of calendar year 2020, the following navaids are scheduled to be shut down (to see these VORs on a chart at SkyVector, click the links).

Five (5) VORs planned for discontinuance – November 5, 2020:

  • (FAH) Falls, in Sheboygan, WI
  • (LNR) Lone Rock, in Lone Rock, WI
  • (MKG) Muskegon, in Muskegon, MI
  • (RBA) Robinson, in Robinson, KS
  • (UKN) Waukon, in Waukon, IA

Three (3) VORs planned for discontinuance – December 31, 2020:

  • (EWO) New Hope, in New Hope, KY
  • (ITH) Ithaca, in Ithaca, NY
  • (URH) Texoma, in Durant, OK

Arrival Holding Patterns

Some instrument approaches include arrival holding patterns, described in a note in AIM 5−4−9. Procedure Turn and Hold−in−lieu of Procedure Turn:

Note: Some approach charts have an arrival holding pattern depicted at the IAF using a “thin line” holding symbol. It is charted where holding is frequently required prior to starting the approach procedure so that detailed holding instructions are not required. The arrival holding pattern is not authorized unless assigned by Air Traffic Control. Holding at the same fix may also be depicted on the en route chart…. (AIM 5−4−9. Procedure Turn and Hold−in−lieu of Procedure Turn)

For example, see the RNAV (GPS) RWY 15 approach at Kingston-Ulster-Airport, NY (20N), described in detail at A Challenging Approach. The hold shown at ILGEZ is an arrival hold, not to be confused with the missed-approach hold shown at JOEYL or with a holding pattern used as a course reversal (i.e., a HILPT).

As the AIM notes, flying an arrival hold requires ATC clearance. Unlike a HILPT, the hold at ILGEZ isn’t shown when you load the procedure in a GPS navigator such as a GTN 750. If ATC clears you fly the hold, probably to descend from cruising altitude before you begin the approach or to allow another aircraft to land or depart, you must build the hold in the box or use OBS mode.

Arrival holds aren’t common, but FAA Order 8260.19I, updated June 2020, includes updated guidance to procedure designers for incorporating arrival holds.

An arrival holding pattern now may be added, at ATC request, when a procedure includes notes that limit joining an approach if you navigate to an IAF via specific range of VOR radials or airways. For example, see the plan view note on the RNAV (GPS) Z RWY 16 chart at Bend, OR (KBDN).

Order 8260.19I now reads:

8-2-5.e(2) An arrival holding pattern may be established at the beginning of a feeder route when requested by ATC to support local operational needs. An arrival holding pattern may also be established to provide an alternative to denying use when arriving from a specified direction that does not meet alignment criteria. When an arrival holding pattern is established and arrival from one or more directions does not meet alignment criteria, annotate the procedure to indicate the option to hold, and annotate the requirement to obtain ATC clearance.

Example: “Chart planview note: Procedure NA via V343 northeast bound without holding at JOXIT. ATC clearance required.”

But it’s still important to understand a couple of limitations of arrival holds.

First, the FAA order also says:

An arrival holding pattern may be established at the beginning of an initial segment when requested by ATC to support local operational needs. An arrival holding pattern must not be used to function as a “hold-in-lieu of procedure turn” in order to accommodate descent gradient requirements and/or used to mandate a course reversal.

Note: A hold-in-lieu-of-PT is only permitted at a FAF (non-RNAV procedure) or at the beginning of the intermediate segment [see Order 8260.3, paragraph 2-4-5.e].

Second, you should understand that arrival holds are not included in the databases for procedures. For example, if you use a GTN 750 to fly the RNAV approach at 20N, the map doesn’t show the arrival hold at ILGEZ. If ATC clears you to fly that hold, you must set it up in your navigator. If you’re prepared, that’s easy to do in newer GPS avionics, such as the Garmin GTN series. If you have an older GPS, you may have to use OBS mode to fly the arrival hold.

If you do fly the arrival hold, remember that when you create a hold, you must unsuspend (or switch out of OBS mode) when you are ready to continue the approach after passing the arrival hold fix.

A Challenging Approach

The RNAV (GPS) RWY 15 approach at Kingston-Ulster-Airport, NY (20N) is a great exercise for IFR pilots to practice in an ATD or flight simulation. And it’s a terrific starting point for scenarios that instrument instructors and evaluators can review with students and IFR candidates. (Thanks to Doug Stewart, one my colleagues in the IFR Mastery series at Pilot Workshops, for pointing me to this procedure.)

Flying this procedure requires preparation. It’s not a basic ILS or straight-in RNAV approach where the only significant deviations from “standard” are the altitudes and tracks along the final approach course. In fact, flying this approach in IMC or at night also requires study of the Chart Supplement, not just the procedure chart. Comparing the approach chart with the sectional and low-altitude IFR charts for the area also helps you understand some of the challenges associated with this procedure.

Planning for and flying an approach like this highlights an advantage of using EFB app like ForeFlight, Garmin Pilot, or FlyQ. Those tools make it easy to switch between IFR and VFR charts, review the Chart Supplement, and look up other important information, but only if you study those resources before takeoff.

For more information about planning for and flying IFR procedures, see Annotating IFR Charts, Briefing IFR Procedures, and An IFR Scenario for Practice in an ATD.

This RNAV approach has a bit everything to challenge an IFR pilot, including:

  • A series of (sometimes short) segments from the IAF to the missed approach point, each with a change of track.
  • LP and LNAV minimums to MDAs (and LP+V advisory vertical guidance if you have a WAAS navigator with the appropriate system software).
  • A steeper-than-normal (3.45 degrees) descent angle from the FAF to the MAP, if you follow advisory vertical guidance. That descent path is shown on Jeppesen charts, but not on the FAA chart.
  • Two crossing restrictions inside the FAF that you must observe even if you do follow advisory guidance.
  • Obstacles in the visual segment.
  • A 29.15-degree offset from the final approach to the threshold (barely inside the 30-degree limit for straight-in minimums).
  • A short runway at 3100 ft., but with a displaced threshold that leaves only 2775 ft. available for landing.
  • An arrival holding pattern anchored at ILGEZ , not to be confused with the missed-approach hold shown at JOEYL (see AIM 5-4-9, cited in part below) or with a holding pattern used as a course reversal (i.e., a HILPT).
  • Other subtleties such as an off-airport altimeter source (no AWOS) and one frequency for the CTAF, another for activating the runway lights and PAPIs.
  • Important information related to this approach that is available in the Chart Supplement entry for N20, but which isn’t published on the chart.

Kingston-Ulster-Airport lies along the Hudson River in upstate New York, with rising terrain west of the runway. The sectional chart shows why bends are required to get you to the runway from the north and why the final approach segment isn’t lined up with the pavement.

The low-altitude IFR en route chart for the area also offers puzzles to ponder, such as an airway segment that is unusable, but only if you’re flying V292 using VORs, not T295, the overlapping T-route that runs east-west, north of the airport. In fact, the area around 20N is crisscrossed by T-routes, which in many cases have replaced or supplanted VOR-based airways, especially where VORs have been decommissioned.

A Detailed Review

Let’s take a closer at this interesting approach, preferably during preflight planning, not while descending from cruise.

The procedure title indicates that this approach offers straight-in minimums (the title includes the runway number; it isn’t RNAV (GPS) – A or – B). But as we’ve seen, this approach barely meets the alignment criterion for straight-in minimums.

The notes at the top of the chart, which often include information that isn’t relevant to pilots of light, piston-powered airplanes, warrant special attention here. For example, the runway length available for landing–2775 ft.–doesn’t match the the 3100 ft. shown on the inset airport diagram, a detail that’s easy to miss if you don’t notice the displaced threshold symbols.

You need to consider how that short runway might affect the speed you’ll fly on final. For example, I fly most approaches in my A36 Bonanza at 110 KIAS, but when approaching a runway less than 4000-5000 feet long, I plan to fly final at 90 KIAS, which is just 10 knots above the 80 knot minimum speed for engaging the GFC 600 autopilot in my panel, should I choose to use it.

The minimum runway lengths associated with various approach types are described in AC 150/5300; more information at Update on WAAS Approaches from FAA.

The notes also reveal that the airport has non-standard takeoff minimums, often a hint about nearby terrain, and that 20N can’t be filed as an alternate, probably because it doesn’t have on-site weather reporting.

Another important note specifies that the primary source for setting the altimeter is Hudson (KPOU), 22 nm south. That detail requires additional attention when you set up and then brief the approach.

The frequency blocks include an oddity: 122.8 for the CTAF, but a different frequency, 123.3, to activate the pilot controlled lighting at this nontowered airport.

The plan view shows an arrival hold at ILGEZ, depicted with thin lines. Arrival holds aren’t common. When reviewing holds on charts, it’s important to distinguish between arrival holds and their cousins: holds in lieu of a procedure turn (HILPT), missed approach holds, and holds shown at alternate missed approach holding points.

Note: Some approach charts have an arrival holding pattern depicted at the IAF using a “thin line” holding symbol. It is charted where holding is frequently required prior to starting the approach procedure so that detailed holding instructions are not required. The arrival holding pattern is not authorized unless assigned by Air Traffic Control. Holding at the same fix may also be depicted on the en route chart…. (AIM 5−4−9. Procedure Turn and Hold−in−lieu of Procedure Turn)

As the AIM notes, flying an arrival hold requires ATC clearance. Unlike a HILPT, the hold at ILGEZ isn’t shown when you load the procedure in a GPS navigator such as a GTN 750. If ATC clears you fly the hold, perhaps to lose altitude before you begin the approach, you must build the hold in the box or use OBS mode.

The plan view shows four segments from the IAF at ILGEZ to the MAP at NEWMN, which is 0.7 nm from the threshold. The last segment, from FRLDI to NEWMN, is just 1.8 nm long. Flying these “final” segments involves 3 course changes. Landing requires another turn of almost 30 degrees at NEWMN to align with the runway centerline.

The profile view hints at more challenges, including a steep descent angle from IMIBE to FRLDI, which you must cross at or above 1080 ft. The FAA chart for this approach doesn’t show a visual descent angle (VDA), because, as a note points out, the visual segment isn’t clear of obstacles.

If there are obstacles in the visual segment that could cause an aircraft to destabilize the approach between MDA and touchdown, the profile will not show a VDA and will instead show a note that states “Visual Segment-Obstacles”. (Aeronautical Chart Users Guide)

Notice also that the heavy black line levels off before NEWMN, and that this approach does not include a visual descent point (VDP). These details are more clues that obstacles loom close to the runway. Fortunately, a check of the inset airport diagram reveals a PAPI available on the left side of the runway, definitely something to look for when (if) you break out.

For more information about VDP, see “Arrival Procedures” in the AIM:

The Visual Descent Point (VDP), identified by the symbol (V), is a defined point on the final approach course of a nonprecision straight−in approach procedure from which a stabilized visual descent from the MDA to the runway touchdown point may be commenced. The pilot should not descend below the MDA prior to reaching the VDP. The VDP will be identified by DME or RNAV along−track distance to the MAP. The VDP distance is based on the lowest MDA published on the IAP and harmonized with the angle of the visual glide slope indicator (VGSI) (if installed) or the procedure VDA (if no VGSI is installed). A VDP may not be published under certain circumstances which may result in a destabilized descent between the MDA and the runway touchdown point. Such circumstances include an obstacle penetrating the visual surface between the MDA and runway threshold, lack of distance measuring capability, or the procedure design prevents a VDP to be identified. (AIM

The leg from WOBVU to IMIBE is 7.5 nm long, allowing a comfortable descent from 3200 ft. to 1600 ft. But if you continue from IMIBE and level off at 1080 ft. to observe the restriction at FRLDI (which applies even if you’re following advisory vertical guidance), you have another 360 ft. to descend to the LP MDA of 720 ft. (280 ft. if you use the LNAV MDA of 800 ft.). And you have just 1.8 nm to make that last step-down descent.

As we’ve seen, the MAP is at NEWMN, located 0.7 nm from the threshold. That offset may be a surprise if you’re accustomed to RNAV approaches where the MAP coincides with the threshold. Moreover, the minimum visibility required for this approach is 1 sm. The runway doesn’t have approach lights, just the PAPI noted earlier, so you need to pick up the required visual references (see 14 CFR 91.175) before you reach NEWMN.

The PAPI is set at a 4.5 degree descent angle to cross the threshold at 50 ft. That important detail, by the way, is in the Chart Supplement entry for 20N, not on the approach chart.

The Chart Supplement also reveals that the PCL on 123.3 activates the PAPIs at both runway ends, and the runway lights, which are available from dusk to dawn. In addition, the PAPI serving runway 15 is unusable more than 5 degrees left and 8 degrees right of the final approach course. In other words, you won’t see–or shouldn’t follow–the PAPI visual guidance until you turn toward the runway at NEWMN. And another note–on the procedure chart–prohibits night landings on runway 15. Again, those close-in obstacles, probably unlit, loom.

All of the preceding details should make you consider carefully how you’ll configure the airplane and use an autopilot and flight director when you fly this approach. When will you extend the landing gear and flaps? What power settings will you use as the approach progresses through the various segments?

An autopilot could be a great help as you track all the course changes, but managing the descent, even if the autopilot offers VNAV and can follow glidepaths, requires a plan and close monitoring.

An approach like this also highlights the advantages of an electronic PFD and moving map. The following images, captured with the free Garmin PC Trainer Suite, show some of the key details discussed above.

When you load the approach in a WAAS navigator, LP+V minimums may be available. Note that LP+V indicates LP minimums to an MDA with advisory vertical guidance. LP+V is not the same as LPV, which provides approved vertical guidance to a DA. For more information, see Handy WAAS and RNAV (GPS) Approach Fact Sheets.

Note that the GTN 750 map doesn’t show the arrival hold at ILGEZ. If ATC clears you to fly that hold, you must set it up in your navigator. If you’re prepared, that’s easy to do in a GTN navigator. If you have an older GPS, you may have to use OBS mode to fly the arrival hold.

If you fly the arrival hold, you must manually resume sequencing (unsuspend/cancel OBS mode) to continue flying the approach.

At this point, your PFD should show LP+V if advisory vertical guidance is available.

As you continue inbound, you (or the autopilot) can follow the advisory vertical guidance to the MDA. But make sure you observe the crossing restrictions as you continue toward the missed approach point.

A PFD with a map also helps you anticipate the last turn to align with the runway.

I hope this approach helps you appreciate the need for thorough preflight planning, even if you use an EFB and have a panel that features advanced avionics. Those tools are terrific aids, especially when flying single-pilot IFR. But using them effectively requires preparation.

For more information about planning for and flying IFR procedures, see Annotating IFR Charts, Briefing IFR Procedures, and An IFR Scenario for Practice in an ATD.

Briefing IFR Procedures

Charts for instrument procedures include a lot of information, and IFR pilots learn to brief departures, arrivals, and approaches as part of the preparation for takeoff, descent, and landing.

Often, however, those briefings aren’t especially effective, because the pilot or crew just recites data on the chart and doesn’t actually prepare to fly the procedure.

For example, a traditional approach briefing usually goes something like this:

“We’re flying the ILS runway 17 at Tacoma. The chart date is October 8, and it’s amendment 8C. The inbound course is 167, and the runway is 5000 feet long…”

In other words, the pilot reads courses, altitudes, and other details off the chart.

But reading a chart aloud doesn’t truly prepare you to fly a procedure. It’s like trying to sight-read a piece of music instead of practicing before a recital.

In other words, a traditional briefing often doesn’t describe how you’ll navigate the segments of an approach. And too often, a briefing is also rushed or juggled with other tasks, especially in an aircraft equipped with modern avionics.

Today most IFR pilots fly with at least some electronic displays and GPS navigators, and we use electronic flight bags—tablets and apps—to plan our flights on the ground and to display charts and related information in the air.

Given the way we fly IFR today, it’s time to update the briefing process to reflect modern avionics and the tools we bring into the cockpit.

So how can you develop an efficient, effective IFR briefing so that both you and the airplane are in the groove and the runway appears ahead through the mist? Follow this link to view a presentation at my YouTube channel that can help you create effective briefings that reflect how we fly in the 21st century.

Approach Briefing: Key Elements

Procedure titleIs the correct procedure displayed and loaded?
Procedure entry: Transition/VectorsDirect to an initial fix or activate leg (vectors)? Course reversal?
Use of RNAV / Ground-based navigationGPS for feeder routes, course reversal, and missed approach? LOC/VOR for final approach course?
Avionics flow checkCom and nav frequencies, active and standby.
Vertical guidance / Missed approach pointApproved or advisory vertical guidance? How to ID the MAP location. Use of VDP?
CDIs / Bearing pointersConfirm if/when you’ll change the primary CDI.
Key altitudes / Bugs setFAF crossing /GS/GP intercept. DA or MDA minimums. Initial MAP altitude.
Autopilot/FD or
Coupled or FD or raw data and AP modes?
Approach configurationTarget power setting, configuration, and speed.
CTAF and PCLCTAF calls and PCL activation at nontowered airport.
Runway exit planPlanned intersection; left or right; intersecting/crossing runways; hotspots?
Cancel IFRHow will you cancel IFR if landing at a nontowered airport?

To watch presentations on other topics, including Annotating IFR Charts and An IFR Scenario for an ATD, visit the Presentations for Pilots playlist at my YouTube Channel.

Draft AC 91-92: Pilot’s Guide to a Preflight Briefing

FAA has published draft AC 91-92: Pilot’s Guide to a Preflight Briefing, which:

…[P]rovides an educational roadmap for the development and implementation of preflight self-briefings, including planning, weather interpretation, and risk identification/mitigation skills. Pilots adopting these guidelines will be better prepared to interpret and utilize real-time weather information before departure and en route, in the cockpit, via technology like Automatic Dependent Surveillance-Broadcast (ADS-B) and via third-party providers. This AC provides guidance for required preflight actions under Title 14 of the Code of Federal Regulations (14 CFR) part 91, § 91.103, which states, “Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight.” This AC will also encourage pilots to utilize Flight Service in a consultative capacity, when needed.

The draft AC is open for comment through November 3, 2020 via an email link from the FAA website. It appears to supplant the General Aviation Pilot’s Guide to Preflight Weather Planning, Weather Self-Briefings, and Weather Decision Making (PDF) published in 2006.

The draft includes checklists to help you collect and use weather reports and forecasts, NOTAMs, and other information required by 14 CFR § 91.103, and the AC updates references to sources such as FSS (via Leidos), ADS-B, and websites that provide supplemental information about special-use airspace, charts, and other data.

The first two background paragraphs of the draft AC include language that encourages pilots to use FSS as “a consultative resource that can be utilized when needed.”

6.1 Flight Service ( provides service and value to users of the National Airspace System (NAS), leveraging advanced technologies to safely and efficiently deliver Flight Services in the continental United States (CONUS), Hawaii, Puerto Rico, and Alaska. Flight Service provides continuous assessment of Flight Services based on feedback and continued research and development of new aviation technology to enhance efficiency and add value for pilots. Flight Service increases aviation safety by making aeronautical and meteorological information accessible where and when you need it with the evolution of pilot weather briefings conducted using automated resources.

6.2 The FAA encourages innovation in the delivery of services to pilots. User preferences for automation and new distribution methods make communication with pilots easier and faster. Pilots are encouraged to utilize online automated weather resources to conduct self-briefings prior to contacting Flight Service. Pilots who have preflight weather/risk assessment and risk mitigation skills are better prepared to make in-flight decisions as real-time weather information is consumed. This allows Flight Service to become a consultative resource that can be utilized when needed.

In section 7 GENERAL OPERATING PRACTICES, paragraph 7.1 Preflight Actions also notes that:

However, most pilots have become more accustomed to performing a self-briefing than calling an FSS. The FAA considers that a self-briefing may be compliant with current Federal aviation regulations. By self-briefing, pilots can often improve their knowledge of weather and aeronautical information. Flight Service personnel are available should a pilot need assistance.

These statements align with the FAA Plans for FSS Modernization:

The FAA’s Future Flight Services Program (FFSP) vision is to transform and modernize the delivery of flight services over a 15-year period. The FAA believes that costs can be reduced by focusing on changing user behavior and migrating to automated, self-assisted service delivery models, while still maintaining quality of service and safety.

However, the draft AC does not explicitly answer a question that continues to puzzle pilots: “What constitutes an official/approved preflight briefing?” (The short answer is that FAA has never clearly laid out what must be included in a preflight briefing.) But section 7.3 Briefing Sources includes descriptions of and links to many sources of information that “are suggested aids to help pilots conduct a thorough self-briefing and ensure they do not miss any area of preflight preparation.”

Unfortunately, the draft document also does not directly address how popular apps such as ForeFlight, Garmin Pilot, FlyQ, and WingX fit into the preflight paradigm. In fact, those apps offer connections to user accounts at the Leidos (FSS) portal, and through the Leidos Service Provider Authorization and Integration program, they use current data from the FAA, NWS, and other sources described in 7.3 to create preflight briefings that comply with the intent of 14 CFR § 91.103.