Circling Approaches

Question:  I recently heard this conversation:  Navy VF103, you are 23 miles southeast, turn left heading 255. Expect vectors ILS runway 7L approach, circle to land Runway 1.
If Runway 7L is assigned, what is the reason for the circle to land  Runway 1?

John Fischbeck, Melbourne, FL

Answer:  A circle-to-land maneuver consists of either a visual or instrument approach to one runway, terminating in a visual landing on another.  There is more than one reason air traffic control would clear an airplane to make an approach to one runway, but land on another.  Let me give you a likely scenario.

Let's say the prevailing winds at a particular airport are from the west.  It makes sense that an instrument approach, such as an Instrument Landing System (ILS), would be available, then, for aircraft landing to the west.  An ILS guides aircraft down to an altitude low enough for pilots to visually land the aircraft.  In some cases, when the airplane, pilots and runway are all certified, the plane may even be brought all the way to a landing without the pilots ever having outside reference.  

Other runways may be oriented in different directions to handle landings when the winds are from less common directions, but they may not be equipped with an instrument approach.  This may be due to terrain obstacles, traffic flow considerations or it might be because the runway just isn't used that often in typical weather conditions at that airport.

Let's say we're coming in for a landing and the winds are blustery but not from the prevailing direction for the airport.   We're going to need to land into the wind, but there is no published approach procedure for the only runway aligned closely enough with the wind to use.  Even though it seems we would just fly a visual approach to this runway,   this is not always possible due to other traffic flow in the area, or possibly obstructions on what would be considered a normal approach to the runway.  It's also possible there is a cloud deck through which we must first descend before finding ourselves in visual conditions.

So how do we get lined up for the runway we want to land on if weather or obstacles prevent us from doing so in what would be considered a normal pattern?  The solution may be for air traffic control to get us relatively close to the airport, and even have us descend through a cloud deck if necessary by flying down the glide slope (electronic vertical guidance) of a runway equipped with an ILS, but which is not the runway of intended landing.  After we break out under the cloud deck we can visually maneuver ourselves into position to land on the runway oriented with the wind, but which has no instrument approach.

There are more and more runways equipped with ILS approaches these days, especially at large airports, but this is still a maneuver pilots might find themselves flying on occasion.  The last one I remember flying was in a DC-10 in the late eighties, which I'll describe in a moment. I did, however, practice them not long ago in a simulator during training.

Let me illustrate the concept and its purpose a little further:  Consider an airport such as LAX; there are two sets of two runways, each of which has an ILS approach.  That's four runways, each of which has an ILS for both directions of landing. There is no reason a circling approach would ever be flown there during normal operations.

 By contrast, let's have a look at an approach procedure for Newark Airport (courtesy of http://flightaware.com)   The following link will take you to the ILS 22L approach at Newark:   http://flightaware.com/resources/airport/EWR/IAP/ILS+RWY+22L/pdf

You'll see two main runways (look at the small airport diagram in the lower right-hand corner) each end of which is equipped with an ILS.  (You can't tell by looking at this particular plate which runways have ILS's.)  However, there is a less-used cross runway with an ILS on one end (Runway 29) but no instrument approach at the other end (Runway 11).  I landed on Runway 29 once years ago when flying a DC-10.  There was no cloud cover but there were very high winds out of the west, blowing around 30-35 knots or so.
 
Planes arriving from the north were instructed to fly inbound on the ILS to Runway 22L until five miles out, then circle-to-land to the west on Runway 29.  This means we were headed in a mostly southerly direction toward Runway 22 Left.  Five miles from the approach end (which we can read on cockpit displays), we turned left (downwind leg), then right (base leg), then right again onto final to land in a westerly direction on Runway 29.  This procedure kept an orderly and precise flow of traffic, all of which needed to land on Runway 29 due to the strong wind that day.  (Add a "0" to these runway numbers for the closest magnetic heading.  For instance, Runway 29 is closest to a magnetic heading of 290 degrees).

Notice the circling minimums at the very bottom of the approach plate for different categories of aircraft.  Many airlines use more conservative minimums than those published by the F.A.A., however, for an extra margin of safety since pilots don't get the opportunity to fly them much outside a simulator.  The circle-to-land approach is a visual maneuver.  That is, pilots fly it only with outside visual reference.

There is an instrument version which is similar, where the pilot sets up for an "arc" approach by keeping the mileage from a navigational aid constant while flying a curve until intersecting a point at which a straight- in approach to the runway can be made. The minimum altitude pilots may descend to without gaining outside visual reference is higher than that allowed on a "precision approach" such as an ILS, but lower than that on a circling approach, which is strictly visual. 

That's a fairly technical discussion, but the main gist is that sometimes it's necessary for us to be guided toward a runway which has an instrument approach, but land on another runway when the wind or other conditions (such as an unusable runway for some reason) dictate.

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