Monday, November 06, 2006

If it's Baroque, Fix it!

Reading an instrument approach chart is much like reading music. And as in a musical performance, flying an approach involves executing a sequence of tasks, at the right time, in order to arrive at the airport or runway. And like music, reading an instrument approach chart and setting up the navigational equipment is easier if you have flown the approach before because you already know the tune. In spite of recent advances that are making single-pilot instrument flying more manageable, there are many procedures out there that may still involve a dangerously high workload for the average GA pilot to manage single-handedly.

If you are flying an approach you've never seen before, reading the approach chart is very much like what musicians call sight reading: Translating squiggles on a page into music you've never heard before, in real time, often in concert with other musicians. To maintain sight reading skills, whether from a piece of music or an approach chart, you have to practice. If you don't practice flying unfamiliar approaches from time to time, your sight reading skills will deteriorate. Playing wrong notes during a musical performance can be embarrassing, but the results of a mistake on an instrument approach chart can be far, far worse.

The Oroville NDB RWY 1 approach has a very simple layout and the sad fact is that there seem to be fewer and fewer approaches like it. The disadvantages of this type of approach are that accurately flying an ADF indicator is admittedly a bit harder than a VOR and definitely harder than flying to a GPS waypoint. The approach requires a procedure turn and the minimum descent altitude is not terribly low. This sort of approach works well in relatively flat, obstruction-free areas, but doesn't work as well in mountainous areas. And of course there all the vagaries to which NDB transmissions are heir. The advantages of this approach are that it is clean, easy to read, and flying to the missed approach point involves just one navigational aid. Ah, the good old days ...

At first blush, the Tracy VOR or GPS A approach seems simple, which is why I like to assign it to instrument rating candidates and pilots during a proficiency check. I've witnessed pilots fly this approach, oh, at least 80 times in aircraft with equipment of varying sophistication. Even though I know this approach pretty well, I'd prefer flying it in instrument conditions as either a GPS approach or in an aircraft with DME. Here's why.

The intermediate and final approach segments are based on the Manteca 220˚radial and if you have DME, identifying the step-down fix, final approach fix, and missed approach point is easy. To navigate to the MAP, you only need to do a minimum of three tasks: Set a VOR receiver to the Manteca VOR, set the DME to Manteca, and set the correct radial on the OBS. To be ready to fly the missed approach, you'll accomplish two more tasks: Get the Sacramento VOR tuned in on the number two VOR receiver and set the 157˚ radial on the number two OBS, though you could identify TRACY intersection with just one VOR receiver and DME. So with VOR and DME, you have a grand total of five tasks (six, if you count resetting the OBS to the Manteca 229˚radial on the missed approach).

If you have two VOR receivers and no DME, you'll have five more tasks to accomplish. On the number two VOR, you'll need to tune and identify the Modesto VOR, set the OBS to identify MANCO intersection, and passing MANCO, you'll need to set the OBS to identify the final approach fix. If you have a flip-flop frequency feature, put Sacramento in the backup frequency so you'll be ready for the missed approach. Passing MANCO, make the Sacramento VOR frequency active in the number two receiver and set the 157˚ radial (this requires you to twist the OBS nearly 180˚). And if your aircraft has an ADF and you want to be really thorough, the designers of this approach have even thrown in the Livermore REIGA LOM into the mix, though I'm not sure what this buys you. So if you don't have DME, you'll have at least 11 tasks to accomplish to fly this approach all the way to the missed approach.

What might not be obvious is that this approach starts with a relaxed tempo: The descent profile is very gradual all the way to the missed approach point. But things unfold very quickly when flying the missed approach: You only have to climb to 2000 feet and TRACY intersection (where you hold) is not at all far away. The devil is in the details, as they say.

Flying this approach with GPS involves loading the approach, then (depending on the model of GPS) possibly activating the approach, and setting the course (unless the plane is equipped with an electronic HSI). Throw RAIM prediction and this brings you to a grand total of two to four tasks. Flying the missed approach involves just one or two tasks (depending on the GPS equipment being used). What's not to like?

The Tracy approach I've cited is not the worst of 'em in terms of complexity. Consider the Roanoke LDA RWY 6 approach, which is one of the more complex approach charts I recall seeing. Aside from all the restrictions, walk through the missed approach procedure and imagine what sorts of knob twisting and button pushing you'd need to do. And you want to make sure you get it right because there is plenty of cumulus granitus around Roanoke.

As the specifications for developing instrument approaches gradually became more complicated, it was inevitable that some instrument approaches would, themselves, become complicated as well. Pilots usually don't have much say in the matter. We just want a procedure we can safely fly in bad weather.

So how can the average GA pilot go about handling complexity in instrument approaches when flying single-pilot IFR? I'll offer some strategies in the next installment. In the meantime, if you have a favorite procedure that is particularly arcane, please feel free to share it.


Ron said...

I don't know that it's particularly arcane, per se, but the Santa Monica VOR-A approach is interesting. It's aligned with runway 21, yet it is not named VOR 21. It's VOR-A.

If you look at the location of the VOR (which is also the missed approach point), you'll see why it's got a letter suffix.

The approach requires a fairly significant descent rate to reach minimums, look up, see the field, and still be able to land. I teach students to use a 1000 fpm descent rate on non-precision approaches, but there are quite a few out there for which that descent rate is barely adequate.

I'd be interested in seeing you do a piece on GPS and RNAV approaches. Many -- perhaps most -- people are not aware of the difference between VNAV, LNAV/VNAV, RNP, and other such GPS related minima. Just selecting the proper minimums can be a head scratcher if you haven't see those terms before.


Jack said...

Hey, I remember the business of that approch at TCY when I was an instrument student! Hmmm, nice reminder that it's time to go there and fly those approaches again.

On a similar note, I remember doing the SAC ILS 02 and being amazed at how fast things went on the missed. Did that one on my checkride and was *very* glad I'd had the opportunity to practice.

Anonymous said...

The Martin State (KMTN) VOR/DME 15 ( arcs to the runway - no turning inbound from the arc to a final approach course.


John said...


Funny you should mention it, I've been thinking about writing about RNAV and GPS approaches. I'll see if I can get something posted next week.

And Anonymous, thanks for pointing me to the Martin State VOR/DME RWY 15 approach. I'll put that in my bag of tricks for simulator training. It's a great example of when you might need to fly a DME arc within +/-0.1nm (while descending, no less).

Aviatrix said...

Castlegar NDB C is kinda tricky. You're tracking inbound to the first NDB, then have to change and track to the second, but if you're not able to complete the landing you have to continue tracking outbound for the missed approach and then turn, retune the original NDB and intercept a track of 349 to that, all after you are dizzy and disoriented from the the shuttle decent.

And you have to nail the ADF track on the instrument, because you know how scary the errors will be in the mountains.

The Nanaimo NDB RWY 16 (it's after the GPS in the PDF) is fun, because at the beacon you have to turn and reintercept a different outbound track than the one you tracked inbound, and then when the time expires very shortly afterwards, there's a hard left on the missed approach. This one has a neat trick because there's a pulp mill right on the shoreline. You can literally smell the fact that you're about to reach the NDB!

Dano from MA said...

The approach is fun, but the departure procedure will cost you your life if you're not sharp as a razor on your DPs. Check out the Berlin, NH (KBML) DP.

It would be a hardy fool who tried to sight-read this one at the hold short line, first in sequence.