Monday, January 25, 2016

Just follow the line...

As many of you know, I've been flying with a couple of guys that are either currently taking flight instruction, or who had started with a couple of lessons in the past but weren't able to keep going. When I fly with people in that kind of situation, I like to fly from the right seat and let them have the Captain's chair.  I also like to treat the flight as if it is actually a formal lesson - that's in furtherance of my long-term goal of obtaining an LSA Instructor Certification.

To rewind the clock a little bit, I have to share that I had always worried that I would not be particularly well suited to the role of instructor, my primary concern being that it would be hard for be to forget what I already know to a degree sufficient to allow me to explain relatively complex things that I personally do as a matter of routine, but that to an inexperienced pilot might be completely mind-boggling. Flying with low-time students has put that to the test, and I am pleased to announce that it isn't as big of a problem as I had thought it might be.

Then again....

I remember back in the day that I myself had difficulty understanding how to correctly enter the landing pattern at an untowered (more accurately referred to as "uncontrolled") airport. The FAA put out an advisory circular (the 'advisory' part is debatable if you're ever in an incident that was caused by ignoring the FAA's "suggestion" or "advice") in 1993 on the subject, but I found it to be somewhat less than illuminating.

You can read it yourself at this link.

 Here are a couple of the more salient passages:
a. Prior to entering the traffic pattern at an airport without an operating control tower, aircraft should avoid the flow of traffic until established on the entry leg. For example, wind and landing direction indicators can be checked while at an altitude above the traffic pattern. When the proper traffic pattern direction has been determined, the pilot should then proceed to a point well clear of the pattern before descending to the pattern altitude. 
b, Arriving aircraft should be at the appropriate traffic pattern altitude before entering the traffic pattern. Entry to the downwind leg should be at a 45-degree angle abeam the midpoint of the runway.
To be fair, while I find this image to be somewhat over-crowded and confusing, it does follow the descriptive paragraphs above, and those two concepts are pretty easy to understand anyway.


The problem for me always came down to figuring out what to do if I was approach from the "wrong" side of the runway.  If you look at point "1", it should be obvious that if I am approach the ostensibly east-west runway from the northeast, it is a trivial exercise to manage the FAA-preferred entry to the left downwind for the east-facing runway. But what if the prevailing wind direction happens to be from the west? I would need to be on the other side of the airport to make the required standard left turns to the westerly-facing runway - how do I get there?

The way that I was taught to address that scenario is to crossover the airport at midfield ("[airport name] traffic, experimental yada yada is six miles north, planning a midfield crosswind to left downwind runway 27") and turn left into the downwind.  Other variations include the very similar method of entering a true crosswind leg west of the departure end of runway 27 (in the diagram, that would be the 'base' leg shown between points "2" and "3", but it would continue south of the airport to enable a left turn onto the downwind leg), or if approaching from the east as shown in the diagram, flying an 'upwind' leg on the path labeled as 'downwind' in the diagram. Note that that choice would be particularly dangerous on a low-wind day, or if the wind is more or less perpendicular to the runway - in instances like that, it's a pilot's decision as to which direction to land. You could conceivably end up nose-to-nose with a pilot whose decision was opposite to yours.

This is an awful lot for an inexperience pilot to try to figure out 15-20 miles away from arriving at the airport to land. This turned out to be something that I could not adequately explain while in flight, so I spent quite a few hours noodling out a way to simply the process.

I eventually distilled the whole thing down to a pretty simple concept: ignoring straight-in approaches and approaches from directions perpendicular to the airport, there are only two ways the runway can present itself to an arriving airplane: it will either be diagonal with the approach end to the left, or diagonal with the approach end to the right.  The wind is also a variable, but it has no bearing (pun intentional) on how the runway looks to the pilot.

With that in mind, I was able to develop the Pattern Entry Assistant:



The usage of these is quite simple. These are printed two-sided, so one need only flip the card over to match the expected orientation on the runway. The idea is to remain at least 500 ft. above the published traffic pattern altitude (TPA) until well clear of the airport area, then descend to TPA. This can be seen in the change from green to red on the respective lines.  It does need to be drawn better; I am not in the least bit artistically inclined.

Determining what that expected orientation can be done through mental visualization ("we're approaching from due south and the runway in use is likely to be Rwy 32, so it the approach end will be to my right"), or one could simply zoom in on the airport as depicted on a decent moving map display such as the Dynon Skyview.

With a good moving map GPS, it would also be easy to create an applicable waypoint to match the correct starting point as depicted on the card, although this would require advance knowledge of what the prevailing winds will be upon arrival. Absent that, an overflight of the airport would be required.

Once the waypoint is reached and the landing direction determined, it's a simple matter to just follow the line and manage the descent as described above.

I had an opportunity to perform an inflight test with a neophyte to see how well it would work:


It seemed to work well enough on the first try, but obviously the "student" would improve rapidly over the next couple of flights,

So, what do you think?

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