Heads Down

I went flying with Frank yesterday. We went down to Sarnia to fly some ILS approaches. It was quite the challenge, and its going to be refreshing to get back into some training that is constantly pushing my limits. Practicing ILS's involves flying the localizer/glideslope down to our decision height, pretending we don't see the airport, then flying the missed approach procedure, back to the NDB, doing a procedure turn to reverse our direction, and then intercepting the localizer and glideslope to try again. That last sentence I'm sure made no sense to any of my readers, and up to a little while ago, it would have made no sense to me either. So I will proceed to decipher what I just said.

The diagram in the top left illustrates the systems we have available to find and align ourselves with the runway. The Non-Directional Beacon, or NDB transmits a low frequency radio wave in all directions that the aircraft's ADF (Automatic Direction Finder) can sense. It actually transmits in the AM band, meaning if we wanted to we could tune to an AM radio station, home in to where they are transmitting from, and at the same time listen to a low budget talk show. The aviation NDB stations however are generally a lot more powerful so they have a greater range, and the only audio they transmit is a series of dots and dashes so we can quickly identify that we have the right station tuned. The ADF indicator in the cockpit has an arrow that will point to the NDB, so all we have to do is follow the arrow to find the NDB station.

The green beam in the diagram illustrates our localizer and glideslope. The localizer will give us horizontal guidance, meaning it will line us up with the runway centerline, where the glideslope will give us vertical guidance, meaning it will help establish us on the correct angle of descent to safely land. The ILS can only sense the localizer signal within 30° either side of centerline. The indicator in the cockpit, shown below on the left, has two needles, that show where we need to be. The horizontal needle gives us glideslope information. If we are below the proper glideslope, the needle will be deflected up, showing us the proper glideslope is above us. Naturally if the needle is deflected down, we are above the proper glideslope, and if the needle is in the center, we are on the glideslope. The localizer needle, the vertical one, works on the same principal. If it is deflected left, we are left of the runway centerline, and visa versa. The indicator shown here is both on the runway centerline, and on the correct glideslope.

Assuming we are in actual IMC (instrument meterological conditions), as in we can't see jack out the windows, and we're flying the ILS down the runway, there has to be a point somewhere that if we still don't see the runway, we have to call it off. That is called our decision height. At Sarnia the decision height for the ILS approach (there are other types of approaches which I'm sure I'll learn eventually) is 200 ft above airport elevation. So as we're descending down along the glideslope, when we reach an altitude of 794 ft ASL (200 ft above the ground), we look up. If we can see the runway in front of us, we land the airplane. If we still can't see anything, we have to execute a missed approach. A missed approach is a procedure to climb out, return to the beacon, and set up for another try. In Sarnia the procedure is a climbing right turn back to the NDB. Now as we're homing back to the NDB, we're going to be traveling in the opposite direction we want to be to set up for another landing attempt. This means we have to do a procedure turn to turn us around. This involves flying away from the NDB on the reciprocal runway heading (rwy 32 at Sarnia is 324°, so we fly a heading of 144°) for 60 seconds, turning left to a heading of 099° for 45 seconds, and then making a 180 back around until we intercept the localizer.

All of this may seem overly complicated and unnecessary when if we have a GPS all we have to is use it to fly where we need to be, but these system of doing things was established long before GPS's existed. Without a GPS, and with no visual reference of where we are, we need some sort of standard practice to ensure that we will be able to find and align ourselves with the runway. Its easy to know where we are when we are looking at a little map with a picture of an airplane on it showing us where we are, but visualizing our position becomes much more difficult when we don't have that birds-eye picture, and we can't see outside. We have to be able to find our way around using only our ADF and ILS.

Understanding how the approach works is one thing, actually being able to fly it is another. Learning to track a localizer and glideslope down to the runway accurately is going to take a little practice. Yesterday I had three attempts. I'm sure on my first attempt if someone was watching us on radar they might have thought I was drunk. I was swinging wildly back and forth across both the localizer centerline, and the glideslope. Its difficult to find the sweet spot that will keep the needles centered - it takes anticipation. We use power to control our glidepath, meaning if we're below the proper glideslope we add power, if we're above, we take some away. It'd be below so I'd add a little bit of power to get back to where I should be, then I'd overshoot the glidepath and be too high, which would require a reduction in power. It took a little bit of practice to learn to anticipate when I needed to reduce or add power to end up stabilizing the descent rate with the needle centered. Each attempt was better then the last. It was some of the most intense flying I've done in a while.

Its really cool to be learning new things and pushing my flying skills into new levels. IFR flying has always seemed like such a daunting thing to me, as it does to many other VFR only pilots. I love the fact that I'm starting to dive into it. It requires so much more precise control of the airplane then VFR flying has ever required, and there's also new concepts, and new things I have to learn. Its so exciting to think about.