Old 11th Dec 2013, 15:58
  #78 (permalink)  
Join Date: Apr 2005
Location: Southeast USA
Posts: 802
Hi Screwballs - I'd be happy to describe how a circle-to-land maneuver should be conducted at the "theoretical" airport you have described ... but, in that you're describing a theoretical, not a real, airport, I doubt there is an approach plate available. As you would certainly recognize, having the information available on that plate is crucial to the performance of any such instrument approach - regardless of whether or not a circle-to-land is planned. While the information you provided is relatively comprehensive - there is substantial information that is not available in your description: the layout of the airport, including the locations of runways, taxiways, tower, hangars, fire departments, airport locator beacon, and other buildings, the location and elevation of any obstacles, the ceiling and visibility required for the approach, the ceiling and visibility required for conducting the circle maneuver, minimum altitude to maintain during the circle, other restrictions to any circle authorizations, limitations to and locations of appropriate reference points for the ILS to be flown (OM, MM, IM, FAF, MAP and the means used to identify those points), any instrument procedures and similar reference points for authorized instrument procedures for the runway of intended landing (if any), and, unfortunately, the list could go on rather extensively. In fact, a picture is worth 10,000 words. However, and I think importantly, before we get to whatever potential solution might be appropriate to answer your request of me … I think there may be a larger question to resolve first.

In your opening post you said…
Originally Posted by Screwballs
The reason I am wondering about is to do with the protected area and the tightness of the turn to final. Cat C aircraft will have 4.2nm to manouevre inside safely. And this is based on a max speed of 180 knots with a 25 wind plus correction for TAS gives a speed of 215 knots for the circling area. (Jepp Text pg. 233 Table I-4-7-2) However, with that speed and timing based on 1,000ft AAL circle to land, you would end up approximately 2.7nm from the threshold.* Plus a turn inbound would still give you a margin on the 4.2nm. And that's at 215 knots! The normal reality would be closer to approximately 160 knots or so.
I’m not sure what it is you are saying here. Why would you presume that you would have to circle at 215 knots? I think that if you check the approach plate for an ILS at any airport/runway you know well, you’ll find the distance from the OM to the runway threshold is on the order of 4.5 to 5.0 miles. You’re describing a “safe maneuvering radius” of 4.2 nautical miles, which is over 25,500 feet – more than twice the distance of some of the longest runways in the world. Additionally, the safe circling distance from the end of the runway you are describing would be just inside of that OM/FAF location. Given the fact that most ILS OM/FAFs are at 1500 feet AGL, and you’re describing a circling altitude of 1,000 feet AGL, it would seem to me that you should find yourself quite comfortable with those circumstances. The circling distances are calculated for the various categories of airplanes in accordance with their maximum gross landing weight and the airspeed they would have to maintain to be safe at those weights – plus whatever margin above that distance the airport/approach planners allow. Of course, we all recognize that a circle-to-land authorization does not guarantee that everything will work out well and that the landing is guaranteed. That’s why they have missed approach procedures. However, IF the airplane is flown carefully and within the parameters prescribed, and there are no unusual “winds aloft,” there is little reason that the approach and landing could not be safely accomplished – and they are – regularly. Again, my interest was initiated strictly due to what appeared to be the attempted structure of a “set of numbers” solution to a set of specific circumstances that inexperienced pilots might want to apply to a different circumstance that could easily get them into trouble. And, I continue to think there is more to learn about the Asiana landing accident at SFO along these specific lines.

However, given all these issues, if you desire that I describe how a specific circle-to-land should be flown, I can still do that for you, IF the information that is typically available on an approach plate is available for that description.

Last edited by AirRabbit; 11th Dec 2013 at 16:57.
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