Flying IFR, Lesson 6
Non-Precision Approaches
Well, we've navigated our way through the system and it's time for us to make our approach into the airport. There are many types of approaches we can execute into airports across the country and they're generally classified as Precision and Non-Precision approaches. The first set of lessons is ``Non-Precision Approaches", so I'll first start by telling you what the difference between precision and non-precision approaches is. Quite simply, a precision approach is one that provides an electronic glideslope. Since we don't receive any glideslope information from a VOR, NDB, or localizer, they are categorized as non-precision approaches. Current GPS approaches are also non-precision, but we'll discuss those in their own lesson. There are also other types of approaches which we won't discuss such as Precision Approach Radar and Surveillance Radar approaches. These are completely ATC-controlled, so they're not applicable to X-Plane's technology. There are some rules which we must follow when making approaches, so let's look at those now. As we discussed in the ``Arrivals" section, ATC will give us descent clearances until we're cleared for the approach. So, we must maintain whatever altitude we've been cleared to until we actually here ATC say ``...cleared for the approach...". Once we hear that, we are free to navigate and descend at our discretion per the approach chart procedure. Keep in mind that ATC may instruct you to proceed along a portion of the approach course before they actually ``clear" you for the approach. So, in real life, it's very important to be sure of what ATC has asked you to do. ATC instructions take precedence over charted procedure. Now back into the FARs for a look at 91.175-Takeoff and landing under IFR, specifically (c)operation below DH or MDA. We know that we're going to be descending to a certain altitude at which we hope to make visual contact with the runway and land. Now, there are a few items we have to be aware of when making the decision to proceed below the MDA/DH and land. If you don't follow the rules, the FAA might be waiting for you on the ramp after your beautiful approach. The first rule says that we have to continually be in a position to make a normal landing. So, we can't pop out of the clouds right over the threshold at 400ft and decide we're going to chop and drop the airplane in. Second, the FLIGHT visibility must not be lower than the minimum visibility prescribed for the approach(located on the approach plate). Notice I say FLIGHT, not ground visibility. If the tower is reporting less than mimimuns and you've got at least the minimums from the air, you can go ahead and land. Just be prepared to justify it(I could see the threshold from the outer marker, etc...). Lastly, you must have one of the following in sight(distinctly visible and identifiable) for the runway of intended landing: the threshold, threshold markings, threshold lights, runway end identifier lights(REILs), visual approach slope indicator(VASI), touchdown zone or markings, touchdown zone lights, runway markings, runway lights. There's also one last thing. If you have the approach lighting system in sight, you may descend to 100 above the touchdown zone elevation. However, if the approach lighting system is of the type ALSF-I/II(the kind with the red side row or terminating bars), you may descend to the runway if you have the red lights in sight. So, what all of this means if that, if you're making your approach and you pass over the McDonald's that you know is a mile from the runway, you still can't descend. Visual checkpoints don't count, only the items listed in the FARs. Believe me, it's tempting to do this. I flew the ILS 7 into Santa Barbara(SBA) once and the visibility was awful. I caught sight of the ground just as I was passing over K-Mart at about 350ft and I was thinking ``Oh yeah, I'm almost there, no problem". But, I kept on cruising along and I didn't actually spot the runway area for about another 7-8 seconds right at the DH. So, the moral of the story is, keep it safe. Don't stop flying the approach just because you're starting to catch glimpses of the ground. Take short glances up and then come back and keep flying the instruments. Once you've established visual contact positively with one of the proper items, then make your transition. It's an interesting part of the flight. You go from airline pilot to fighter pilot in just a couple of hundred feet. You want to be frozen on the interments until it's time to make the landing and then you've got to fly the plane like it was meant to be flown to get it on the runway in a normal manner. Now, of course, I'm not saying to fly wildly because the FARs say we have to be able to make a normal approach at all times. I'm just saying, do what you have to do. Popping out of the clouds at minimums is no time to be light on the controls. Finally, let's talk about the aircraft procedures we'll be following. The way we teach here at FlightSafety is to configure the first flap setting when on the initial approach segment. We don't normally fly approaches with full flaps because we want to be able to go around easily if we have to execute a missed approach. Since we're not using full flaps, we're also going to be flying at a faster speed. I'll use an approach speed of 90kts for the 172RG. Finally, the gear is brought down when passing the final approach fix. So, that's how we'll be operating the aircraft. For our demonstrations, we won't be doing arrivals, we'll just depart the local airport and start right into the approach. We'll be flying in weather that is pretty close to minimums so there won't be any cheating. OK, let's get started..
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1999 - AVSIM Online and Andrew Ayers |
