Aviation Theory

(Continued from part 2: The Glideslope)

The first thing to do before starting an ILS approach is to familiarize yourself with the relevant approach chart. Even though the chart is available during the approach, you should be familiar with the basic picture of the approach. This will improve your situational awareness and make things a lot easier during the approach. If you need to brush up on the charts, see thelessons on IAPs.

The minimums and the DH should be checked. The missed approach procedure should be reviewed. You should also check your fuel quantity to determine whether or not you have sufficient fuel to make one or more attempts before heading for your alternate. Make sure to allow for reserves.

These steps would be completed well before reaching the airport. This will allow you to concentrate on flying the approach and not having to worry about other details during that time.

For your trip, you will follow the normal procedures for enroute navigation. All clearances should be written down and read back to ATC as you proceed. All navaids should be identified before being used. If a holding pattern might be required, plan the correct entry based on your heading when you reach the holding point.

The closer you get to the airport, the heavier the workload. Besides flying the approach, you still have to attend to the normal procedures for landing, including the descent checklist, the pre landing checklist, configuration and airspeed changes, communications and navigation.

Once you have completed the enroute part of your flight, you will transition to the approach by using some combination of STARs, radar vectors, or other navigation techniques. Once you start the ILS approach, you will continue down the localizer and glideslope until reaching the DH. At the DH, if you are visual, you will complete the flight with a landing. If you do not break out of the clouds at or above the DH, or you do not have the required visibility, you will execute the missed approach procedure and then either make another attempt at landing or divert to an alternate.

It should be remembered that the missed approach is not an emergency procedure, but, a normal part of the approach which provides a safe path away from the airport if conditions are below minimums or you decide to execute the missed approach for other reasons. The missed approach should be commenced without delay and efficiently once it becomes necessary. If you decide to "go missed" before reaching the DH, you should continue on the localizer course until reaching the point where the missed approach procedure begins. Then follow the missed approach procedure or ATC instructions.

In finishing up the lesson, let's consider the various indications you may see as you fly the ILS approach. There are only nine basic indications during the approach. One is the correct glidepath. The other eight require a correction in either altitude, course, or both. All the combinations are shown in the following illustrations and include indications for the Cessna (top) and the Lear 45 HSI (bottom). The numbers in the illustration correspond to the numbered cells in the table below.

1 On GS, On Localizer	2 On GS, Left	3 On GS, Right
4 High, Left	5 High, On Localizer	6 High, Right
7 Low, Left	8 Low, On Localizer	9 Low, Right

This concludes the lessons on ILS Navigation.

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