Tuesday, March 11, 2014

Alternate missed approach holding? What is that?

Ever look at an approach chart and see TWO missed approach holding patterns depicted? How about this example from Seattle, Washington (KSEA) ILS OR LOC RWY 16L?  Or Norman, Oklahoma (KOUN) ILS OR LOC RWY 17? Maybe Moses Lake, Washington (KMWH) ILS OR LOC RWY 32R?

KSEA ILS OR LOC RWY 16L
 
KOUN ILS OR LOC RWY 17

KMWH ILS OR LOC RWY 32R

All of these have missed approach instructions (not shown in the excerpts above) that take you to the primary missed approach holding fix. But NONE of them tell you how to get to the alternate missed approach holding fix, or why you would use it, or when! So what are these for?

Imagine you're flying the ILS at SEA. The SEA VORTAC happens to be out of service, but that doesn't really matter for your ILS, does it? Not for final anyway. So you can fly the procedure just fine up until the missed approach point without needing the SEA VORTAC. However, if the SEA VORTAC is out of service, what then? You can't fly the missed approach procedure – after all, it depends on navigating via the SEA R-161 to MILLT intersection/DME fix. Since a clearance to fly the approach includes a clearance to fly the missed approach if necessary (unless ATC gives you different missed approach instructions), if the SEA VORTAC is out of service, you really couldn't fly the approach. So an alternate missed approach holding pattern is established, in this case at the TCM VORTAC.

Notice that while the alternate missed approach holding pattern is shown, how to get there is not! This is almost solely for chart clutter and readability reasons - you wouldn't want to follow the wrong missed approach by mistake. If you need to fly the alternate missed approach, ATC will tell you how to get there and at what altitude. The FAA evaluates these alternate missed approach procedures just like the primary ones, they just don’t put them on the chart.

Similarly, the OUN example above has holding based off the IRW VORTAC. If it's out of service, you hold at the OUN NDB. For MWH, instead of using a radial off the MWH VORTAC, you'd head to the EPH VORTAC.

You’ll see these most often on ILS procedures, since they usually have holding based off another NAVAID. Conversely, many VOR approaches use the same VOR for holding that they used for the final approach – so if it’s out of service, you’re not going to be able to fly the approach anyway. However, occasionally you do see alternate missed approach procedures on VOR approaches. You will never see them on GPS approaches, since if you don’t have GPS coverage, you’re not going to get that far to begin with!

Now, understand these are all backup plans. And not all of them are usable by all aircraft. For example, the alternate missed approach at OUN isn't usable if you only have VOR receivers on board. But if this is the case, just inform ATC and ask for something different.

However, as you look through various procedures, you will find some that look like they should have an alternate missed approach hold charted, but don’t.  This is often simply an issue of practicality. Sometimes ATC facilities request that there not be an alternate missed procedure for a certain airport, sometimes there is no alternate facility to use, sometimes the procedure has “RADAR REQUIRED” to enter the procedure anyway (so you know the missed would certainly be radar vectors), or some other considerations.

But if you see a missed approach holding pattern depicted out there all alone with no obvious way to get to it, now you know what it’s there for!


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