Monday, January 04, 2010
We did a trip to Quebec a few weeks ago, and I found the instrument approach here interesting from a pilot-geek perspective. Instrument approaches are what we use to line up with the runway even if we can't see outside due to clouds etc.
When I fly the jet, I mostly go to large airports that use ILS navigation technology which lets us get right down to the runway before having to look outside. However, not all airports have the capability to install ILS's, and a good rule of thumb is the more remote the airport, the more primitive the instrument approach.
The NDB approach certainly wins the 'most primitive' prize - it's old, not very accurate and has been almost completely replaced by more accurate forms of navigation. Basically you are following an arrow on an instrument which points to various radio stations on the ground, but the arrow tends to waver and wander and lag and point at thunderstorms instead of navigation aids etc, so it's not the most desirable way to find the airport, but it's legal (and presumably safe).
For those of you who don't do this sort of thing, this particular instrument approach goes roughly like this:
1. Dial the Thetford Mines beacon frequency (275) in on your navigation receiver.
2. Fly to the Thetford Mines beacon If you are coming from the west, you can descent to 3,500 feet once you are within 25 miles of the airport. If you are coming from the east, you can only descend to 6,000 feet - this tells us there is high terrain or maybe a radio tower in that area.
3. Once you cross the beacon, turn to a track of 235, which is heading southwest, and descend to 2,900'
4. Fly outbound on the 235 track for a while, maybe a minute. You have 10 miles of protected airspace, so make sure your timing leaves you within your 10 protected miles.
4. After your minute is up, turn left to a track of 190, fly for 30 seconds, then make a 180-degree turn to the right to a track of 010.
5. Hold the track of 010 to intercept the desired inbound track of 055.
6. Once you are established on your inbound track of 055, you can descend to your minimums of 2500'. The chart lists 3 miles as a visibility you'll likely need in order to see the runway, but in Canada visibility is an advisory value only.
7. Look outside for the airport. If you see it before you cross the Thetford Mines beacon then circle to the south, not descending below 2,500' until you are in a position to land. If you cross the beacon and don't see the airport, climb to 3,500' and make a left turn back to the beacon and hold.
First, let's follow along with me as I take a boo at the approach:
The minimums on this approach still keep us over 1,000' in the air, so I start to dimly realize there are other factors in play, like maybe the airport being in between a bunch of hills. Oh, also:
1. It's an NDB approach, which is a fairly old and inaccurate way of finding the runway.
2. It's to a relatively small 4,500' strip. The shortest field we will operate out of is 4,000', and that's only if the runway is clean and the airplane is light.
3. The NDB navigation aid is right at the airport, which can make the approach a little tight.
4. There is no circling north of the field, except;
5. If you miss the approach, you are expected to turn to the north.
6. The procedure turn is to the south, and if you see the field, you are expected to circle south, where a hilltop 89' below the airplane lurks.
7. There is no local altimeter setting, you are supposed to use a remote one.
8. There is a restricted area (open-pit blasting for an asbestos mine) just to the east, so straight-out departures are out of the question.
This is a clip of us circling to the south of the field. You can see the 2,411' tall hill looming in the fog at around 0:15 into the video. The rest of the video is kinda boring and my battery cut out just before we touched down, so skip it if you'd like.
Once we landed, we shut down and chased our passengers away for a few hours. The airport was closed the day we arrived, and we picked up a pile of ice on the way in. We tried using the credit-card scraper method, but the ice was really sticky and I broke my library card, so we went with plan B:
The middle part where we start the engine is a lot more boring than I had hoped, but check out near the end of the clip where the Captain deploys the thrust reverser. Thrust reversers are cool :)
The howling sound at the end is me singing along with the engine.