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You're flying into Durango, Colorado, and you're partial panel. Aside from your increased workload, you have a choice to make. You're west of the airport, and you've been cleared direct to the Durango VOR. You're planning to fly the ILS to runway 3, but you haven't decided what procedure you'll use to fly it.
Since you're below Center's minimum vectoring altitude, you need to fly the approach full procedure. And you can do it by flying the procedure turn, or flying the arc. So which one is the better option?
Option #1 is to fly outbound on the 207 radial from the DRO VOR, cross JUBEP, execute a procedure turn, and fly the ILS inbound to land.
There are a couple advantages, and an couple disadvantages to flying the procedure turn partial panel.
First, the advantages. If you fly the procedure turn, you're flying fewer, larger turns, which means you can time them more easily. That can be especially important if you're dealing with a heading failure.
You also set yourself up for a more shallow localizer intercept with a procedure turn, assuming you fly the procedure turn well. When you turn yourself inbound, you're on a 072 heading to intercept the 027 course inbound, which means you're flying a 45 degree intercept. And flying a 45 degree intercept to a localizer is easier to manage than flying a 90 degree intercept on the arc. (Yes, you have a lead radial on the arc, but it's one more thing to think about when you're partial panel).
But now, let's look at the disadvantages of the procedure turn. When you cross JUBEP outbound, you need to descend from 10,000' MSL to 9,300' MSL, then descend to 8,800' MSL when you're inbound on the procedure turn to set yourself up for a glideslope intercept. Managing a 1,200' descent during a procedure turn, in IMC, partial panel, can be quite a bit to handle. Especially if you're feeling a little rusty on your partial panel skills.
The procedure turn can also keep you closer to the airport, depending how fast you're flying, and how far outbound you fly the PT. That might seem like a good thing, but it means you have less time to descend and get yourself established inbound. And if you make any mistakes during your turns, like mis-timing them, you'll have less time to correct, which could send you missed and trying the approach again.
Option #2 is to fly outbound on the 120 radial from the DRO VOR, intercept SOVDE, and fly the arc to the ILS.
Just like the procedure turn, there advantages and an disadvantages to flying the arc partial panel.
The thought of flying a DME arc partial panel can sends shivers down and pilot's spine, but depending on the equipment you have on board, it can actually be pretty easy.
So let's look at the advantages of flying the arc. With the arc, you don't need to worry about combining turns and descents, because the arc minimum altitude is 10,000' MSL all the way around to the localizer intercept. Things also happen an a slower pace on the arc, because you're covering more distance on the arc than you are in the procedure turn. That means you have more time to fly the plane and prepare for your next turn and course intercept.
If you're flying with GPS, you don't need to worry about the "turn 10, twist 10" method of flying through radials, because the GPS navigates you along the arc, and gives you a heading leg to intercept the localizer too. And if you have an RMI, that makes flying an arc much easier too.
The disadvantage to the arc is that instead of a few large turns, you need to fly several small turns. That means it's difficult (and impractical) to time them. And if you're flying a true VOR/CDI arc (no GPS), flying the "turn 10, twist 10" method only adds to an already high workload situation.
So what's the best method of flying this approach partial panel? In many ways, it depends on the equipment you're flying. On this particular approach, there's a third option of the Rattlesnake VOR for a straight-in to the ILS. But on most ILS approaches at non-towered airports, that's not an option. So you're typically left with the options of an arc or procedure turn.
If you're in a GPS equipped airplane, or if you have an RMI, flying the arc means you don't need to combine turns and descents, and you'll have an overall slower, more paced approach.
If you're in a non-GPS equipped plane, arcing might be more of a challenge than you're interested in, and flying the procedure turn might be a better option.
If I had my choice in GPS equipped plane, I'd fly the arc. By slowing things down and making smaller turns, I'd have more time to prepare for the ILS intercept. And any time you're in a high workload situation in IMC, slowing things down is good.
So what do you think? Would you fly the procedure turn, or the arc? And what equipment would you by flying it in? Tell us about it in the comments.
Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at firstname.lastname@example.org.