Wednesday, July 25, 2007

The Art of Going Missed - Updated

The missed approach may be thought of as a Plan B maneuver. It is normal to anticipate and expect that an instrument approach will result in a beautiful runway emerging from the mist and clag. That’s what we expect to see and our mindset tends to be “It is going to be there.” But sometimes it isn’t – and that’s when we need a Plan B.

DH or MAP point is not the time to be looking down at your approach plate, trying to find the missed approach instructions, during which time the plane will most likely continue to descend. The first part of the missed approach procedure should be firmly fixed in your mind, right alongside DH or the MAP point. You are low to the ground at that point, and you need to start reversing that situation immediately. So pitch up and power up right away. Get started climbing away from what is all-too-firm terra firma. Once you have a positive rate of climb established, then you can attend to other duties – cleaning the plane up and reporting your missed approach.

Many missed approach procedures involve climbing straight ahead to a certain altitude, then executing a turn to go to the waypoint for the hold. With more and more planes being equipped with IFR approved GPS units, it is increasingly common to have the instrument approach loaded in FPL 0, even if it is not a GPS approach. The GPS will automatically sequence through the waypoints in the approach until the missed approach point is reached. At that point automatic sequencing is suspended, and the GPS will wait for input from the pilot.

What happens next is specific to the model of GPS. The Garmin 400/500 series wait for the pilot to press the OBS button, which will bring up the published missed approach waypoint and provide guidance to it. The KLN89B and KLN94 units expect the pilot to press the DIRECT-TO button, which will bring up the waypoint for the published hold. By the way, this works on the Garmin unit too, and has some advantages. More on this later. The trick here is to know when to press either the OBS button or the DIRECT-TO button. The ILS-30 into Air Lake (KLVN) offers a good example.

The missed approach instructions are to climb straight ahead to 1500 feet, then climbing left turn to 2800 feet, to hold at the Farmington (FGT) VOR. The GPS will stop sequencing at the runway threshold. If OBS (or DIRECT-TO) is pressed at this point, the GPS gives guidance from that point to the VOR. But this is not what you want. The secret here is to delay pressing the OBS button until you have completed the climb to 1500 feet. When you press the OBS button after completing the straight-ahead climb, the Garmin 430 will display the magenta track that will take you to the holding fix, as shown below. Notice that the magenta track is offset by the distance required for you to make a standard rate turn to the desired heading.

Sometimes there may be an intermediate waypoint between the missed approach waypoint and the fix for the published hold. My best guess is that this is done to prevent the possibility of a plane hitting an obstacle while executing the missed approach. The GPS-13 at Rochester (KRST) provides an example of this.

The waypoints in FPL 0 for this approach in the Garmin 430W, look like this:

The Garmin 430 will stop automatic sequencing when RW13 is reached. If you press OBS at this point, it brings up the next waypoint in FPL 0, which is POKYI. Since there is no turn involved here, it is okay to press OBS as soon as you start the missed approach. This approach, by the way, is an LPV (precision GPS approach). I have had a Garmin 430W installed in my plane. I received the Garmin 430W/530W trainer CD from Garmin, and it does contain this approach. I will be writing future entries on the Garmin 430W unit.

I mentioned earlier that when the GPS stops sequencing through the waypoints, pressing the DIRECT-TO button is another way of bringing up the waypoint for the hold. Sometimes there is a distinct advantage to doing it this way.

  • Press OBS at the MAP point and the Garmin 400/500 series will immediately make the next waypoint in FPL 0 the active waypoint
  • Press DIRECT-TO at the MAP point and both the KLN and Garmin units will present the next waypoint in FPL 0 in a dialog box with the cursor turned on, so that it can be changed to another waypoint if so desired

So when would you ever want to utilize another waypoint for the hold. The ILS-27 into Anoka (KANE) provides a good example. This is the Jeppesen plate for the ILS-27.

Gopher VOR (GEP) is the waypoint for the published hold. However note in the upper left-hand corner of the plan view there is an alternate holding waypoint at the Princeton NDB (PNM). If you had been told to proceed to the alternate holding point, utilizing the DIRECT-TO method of bringing the waypoint for the hold would definitely be the preferred method.

Interestingly enough, the NOS version of the ILS-27/ANE shows the PNM holding point but gives the pilot no clue as to why it is on the approach plate.

To wrap this up, when you are briefing an approach, there are four items that you need to commit to memory.

  • The FAF
  • DH or MDA
  • How to identify the MAP point
  • The first part of the missed approach instructions

My experience in being a CFII for many years is that it is the last one that most people forget to do.


Almost a CFI said...

Great information. Thanks for taking your time to put it up. I will be coming back to read your various write-ups more than once.

starganz said...

Will this also work with FS2004? I usually just climb straight ahead and wait for vectors from the sim - but this owuld be very useful on the VATSIM network with controllers who might expect the pilot to fly the full published missed approach procedure.