Sunday, September 27, 2015

What if?

It wasn't too very long ago that I said, and I quote, "The interesting dichotomy of the autopilot is that it makes me both a better pilot (tons of information at my finger tips and time to read it) and a worse pilot (I don't hand fly nearly as much as I used to)."

It's a somewhat glib statement, but it carries more than a germ of truth, at least in the category of my modern avionics making me a better pilot. That should not be confused with the idea that modern avionics can automate the process of becoming a better pilot; they are more of an enabler than a mentor.

Something a pilot should always be doing is thinking about "What if?"  This will take different forms depending on the phase of flight, of course.

Before I even go out to fly, I'm looking at the forecast and asking myself "What if the winds are stronger than forecast?" I asked myself this very question just before the flight to Wheeling, WV last week. I had enough gas to get there and back with the forecast winds, but what if there was a stronger than forecast headwind on the way back? I decided to put in another five gallons, and sure enough I had a 26 knot headwind on the way back, much higher than the anticipated 9 knots.

Had I not added that extra gas, I still would have made it back but I might have dipped into my 30 minute reserve, something I consider to be something of a planning failure and thus to be avoided.

More in the realm of the hypothetical, let's consider the question of "What if it's legal VFR visibility and ceilings, but marginal on the visibility due to haze. Further, what if I'm landing to the west and the setting sun has combined with the haze to create a reduced visibility situation so severe that it becomes difficult to find the airport?"

This happened recently too, although it was really more the case that the visibility itself was fairly poor (around 4 miles - legal, but marginal) and I was having a hard time finding the always-elusive Jackson / Rhodes airport (I43).  It is true that the GPS would have taken be directly to it and I could have figured it out from there, but there is a more elegant approach, especially if we throw in a hypothetically just-barely-legal VFR ceiling.  How does the lower ceiling change things? Well, it means I would come barging in over the airport at pretty much pattern altitude, and that is not a good way to make new friends.

I grant that a case like this would reflect pretty poorly on my preflight planning, but for the sake of argument let's assume that the low ceiling was not forecast.  That actually does happen quite a bit, so it's not a huge stretch of the imagination.

With the Dynon Skyview and the optional Seattle Avionics FAA Charts package, I can simply bring up the instrument approach plate for the airport on the map segment of the screen. It does cover the map view when a chart is open, making me periodically wish for a 2nd Skyview screen, but things don't change all that rapidly on the map anyway.

While I cannot legally fly under instrument conditions (although I have the required rating, I let it lapse years ago), I know of no FAA regulation that would prohibit me from using the approach charts for VFR navigation.

As an aside, this is the internet and we live in interesting times*. I would be remiss if I didn't say that the following does not constitute flight instruction, and what you do or don't do in your own airplane is entirely up to you.

That having been bleated....

While I was still at my cruising altitude of 3,500', I engaged the autopilot and pulled up the approach chart to study it. As the winds, such as they were, were favoring runway 19, I selected the GPS approach to that runway. You can see the most salient aspects of said chart below.

There are two major components to the chart. The top is a top-down view that provides lateral direction, while the bottom shows a side view to be used for vertical navigation.

The chart (they are actually called 'approach plates') shown below is the GPS approach to runway 19 at I43.  The five letter ALL CAPS names sprinkled around in it are called 'fixes', and their purpose is simply to assign a unique name to a spot in the sky. Just as with airport identifiers (I43 is the identifier for Jackson / Rhodes), these fixes are included in the Skyview database and thus can be used for GPS navigation. It then follows that I can use the autopilot's NAV setting to get to them.

There are three (by my count - I might be missing one or more) places that I could use to start the approach. They are HUPIX, FEDIK, and SIPOY. The fact that they can be used as starting points is indicated by the parenthetical (IAF) next to them, which is an acronym for Initial Approach Fix.

After having flown to an IAF, you need then only to follow the black lines/arrows to the runway.

That's all well and good, but how do you descend?

That's what the vertical nav section on the bottom shows.  A number with an underline means "fly no lower than," and as you cam see, the progression in the descent would be:

Fly no lower than 2,800' from HUPIX or SIPOY (or if you skip down two pictures, within 30nm of FEDIK as shown next to the big red '1') to FEDIK, fly towards KOYEK at no lower than 2,500', then fly no lower than 1,460' from KOYEK to PECID.  PECID is the Final Approach Fix (FAF) - after passing it, the next thing you're looking for is the runway.

There are conditions that would allow a descent to a lower altitude once past PECID, but those are not germane to this scenario. The VFR pattern altitude at I43 is right around 1,460', so under our VFR conditions we would not need to (or want to) go any lower than that. I generally use 1,500'.

Here's what it looks like in the airplane:

As I was coming from the northwest, I was heading southeast and the most viable IAF looked to me to be FEDIK. I was on a Direct-To to I43, but in the Skyview even a Direct-To creates a flight plan. It was a simple matter to add FEDIK, KOYEK, and PECID to the flight plan as waypoints before I43. 

I then used the Flight Plan Menu to select FEDIK as the active leg.

I set the desired altitude to 2,800' and adjusted the vertical speed to a setting that would have me reach 2,800' right around the same time I would reach FEDIK.  As you can see, the answer was -200 feet-per-minute. (the blue -200 next to the selected altitude of 2800FT)

But how did I figure that out? If you look at the Skyview picture below, just past FEDIK is a small, light blue segment of a circle located between the numbers '1' and '2'. That arc represents the spot in space at which the Slyview calculates I will reach 2,800'.  I just used the UP / DOWN buttons on the autopilot switch panel to find a setting that was close to the goal. Obviously the arc moves back and forth up the purple course line as variations in airspeed and wind occur, but it serves well as a rough guide.

Because KOYEK was the next fix / waypoint in the flight plan, and I still had the autopilot configured to follow the GPS in NAV mode, it automatically made the turn required to follow the final approach course through KOYEK and PECID to the runway.

I could have continued to use the autopilot for the descent to 1,500' inside of KOYEK and before PECID, but the descent rate was such that I felt more comfortable doing it by hand. 

Ta-da!! There's the runway, all lined up right where I needed it to be.

Had the visibility been low enough, I could have cruised along at pattern altitude until I got to the runway.  If I needed to, I could then have entered and flown a normal landing traffic pattern.

* Understatement alert!! 

1 comment:

Unknown said...

I would like to practce that once or twice with you before I head to Florida.

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