How common is a back-course approach? There are currently 69 back-course approaches in the United States.If there is a back-course published, the signal strength will be strong enough to fly the approach as required. What does back-course mean? It simply means you are flying on the opposite of the localizer signal.The problem comes in for the back-course is that the needle deflection is deflected the wrong way. The localizer needle doesn't know if you are on the front-course or the back-course and will show the same deflection for both situations. If you are flying the back-course, the blue lobe would be on the left. Now imagine flying the front-course, the blue lobe is on the right. Notice the top left of the picture shows the same lobes on the same side of the runway. See this figure from the Instrument Flying Handbook (2015) published by the FAA. The localizer needle in the airplane compares the relative strength it receives from both lobes and then shows a deflection. How a localizer works is it sends out two signal lobes: one at 90Hz and the other at 150Hz. That's an ILS BC approach.A localizer back course is simply flying on the back side of the localizer to the runway. Now you do the same thing, but you are on the opposite end, flying to the runway, and you descend to a certain altitude. That's basically how to track a ILS BC appch. Which brings me back to my first point, if you remember that the needle is the plane's position in relation to the centerline, which is the center of the Course Deviation Indication, CDI, then you are home free! If you are flying an ILS BC and the needle moves to the right, you would need to turn left, because the centerline is to your left. Now, which way should you turn to re-intercept the centerline? Accordingly, the VOR needle would move, you got it, to the right. It takes a bit of mental gymnastics, but your movement to the right of the line, facing away, is the same thing as moving to the left of the line if you were facing the station (you would be in the same position). You now move to the right of the line, keep in mind that the VOR receiver THINKS you are flying to the station, where would the VOR needle move this time? Now you are in the same spot, BUT you are facing away from the station. You are flying to a localizer (on a normal ILS), its transmitting a straight line down the runway, if you move to the right of that line, the VOR needle will move to the left, because the runway centerline is now to your left. So to the receiver, you are facing the transmitter, when actually you are turned around. Because the equipment is set up to transmit a signal to an aircraft flying to the station, a VOR receiver will process that signal accordingly. However, since on a normal VOR a BC appch causes reverse sensing, the needle is actually saying that you are right of course and need to turn left.Īnother way to look at it is if you were flying the localizer outbound. If the needle moves to the right, on an ILS and the usual reaction is to turn right. The way I fly it and I teach it is to think the VOR needle is the plane. But I think the final approach is a few miles longer with a BC approach, right? Our runway is 24, and this one DC9 was inbound from the east so he was vectored to a 330 heading until i guess he was cleared for the approach and made the turn to 240. I'm not sure I understand about tracking the approach from the other end. One of the posts above talks about why you can't just reverse the normal ILS. If it's not published, there is no backcourse approach. You just can't take a normal ILS and fly the backcourse. Just wanted to point out that in order to fly a LOC( BC), the procedure has to be published. GRB also has a published LOC( BC) for 24. The ILS is off the approach end of runway 6.so if you wanted to fly an instrument approach to 24 the only way you could do it is to back-course using the opposite of the ILS for 6.corrrect? The typical older rental training aircraft usually won't have a GPS receiver, but will have the standard nav/com.įor runway 6/24: there is an ILS/ DME approach published for runway 6 but not for 24. To fly an RNAV(GPS) you need to have an approach certified GPS receiver. Why would you use a BC instead of a RNAV GPS approach?Īnother reason is all you need to fly a LOC( BC) is the same equipment required to fly an ILS.
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