In Episode 149 we discussed how to fly a 3-degree visual approach. In this episode we talk about how to fly a manual ILS approach, i.e., an approach flown without a flight director.
If you are planning to fly to an airport with an operable ILS, a little flight planning goes a long way. You can check weather forecasts for your destination and determine the probable runway that will be in use when you arrive, along with the forecast temperature and wind. You need this information to plan your approach.
To start, calculate the true airspeed of your aircraft at the anticipated landing weight when you arrive at your destination. Depending on your aircraft, this can vary considerably depending on weight. Now, consult your performance charts to determine your approach speed in indicated airspeed (IAS).
Use your IAS to calculate the true airspeed (TAS) for your approach. If you are operating into a sea level airport on a standard day, IAS an TAS are close to each other, but if you are flying your approach to a high-altitude airport there can be a considerable difference between IAS and TAS. The proper way to do this is to use your E6B computer, as explained in RFT 148. The fall-back method is to increase your IAS by 2 percent for each 1000 feet of altitude to determine TAS. For example, if you are flying 90 knots IAS at 5000 feet pressure altitude, your IAS would be 99 knots (90 knots plus 10 percent of 90).
You need this TAS to use the wind side of your E6B, as explained in RFT Episode 146. Perform a wind-side calculation to determine your groundspeed and wind correction angle for the approach.
Now, to stay on a nominal 3-degree ILS glide slope, descend at 1/2 your groundspeed times 10. If your groundspeed is 99 knots, descend at 500 feet per minute. When you intercept the localizer, apply the wind correction angle to the final approach course to get an initial approach heading.
ASSIGN yourself headings and descent rates, and you will find that it's relatively easy to fly an ILS with the needles centered, even without a flight director!
When you get to minimums and see the runway, don't change a thing!
