Chicago gets first RNP approach

Chicago’s O’Hare airport recently implemented its first RNP (required navigation performance) instrument approach. The satellite-based precision approach is part of the new generation of GPS approaches popping up at airports around the nation and the world. Chris Baur, president and CEO of Hughes Aerospace, the company that developed the approach, told Examiner on Wednesday that the new approach is an environmentally friendly alternative to current land-based approaches.

Instrument approaches are the procedures used by pilots to locate the landing runway when the weather precludes a visual approach. At large airports like O’Hare (KORD), the typical method of tracking to the runway involves an ILS (instrument landing system) approach. ILS approaches use land-based transmitters to send signals to the pilots that bring the airplanes to the touchdown point on the runway both laterally (with a localizer) and vertically (with a glideslope). This requires two separate transmitter facilities for each runway that utilizes an ILS. This can be cost-prohibitive for small airports.

RNP approaches utilize satellite navigation technology instead of ground-based navigational facilities. The aircraft’s flight management computer is programmed to fly a predetermined course along a series of waypoints, locations on a map that do not have to coincide with any geographic feature, toward the runway. Because the airplane is following GPS waypoints, approaches can easily be planned to avoid terrain features or noise sensitive areas. They can also be developed over water where land-based facilities are impractical. At some airports, RNP approaches even follow a curved path to the runway using RF (radius to fix) segments, such as this approach at Atlanta’s Peachtree-DeKalb airport (KPDK).

The RNP, required navigation performance of the approach, determines the accuracy of the approach and has an effect on the minimums, how low the pilot can go without seeing the runway. The required navigation performance for approaches can be as low as 0.1. This means that an airplane’s navigational system must be accurate to with 0.1 nautical mile radius 95 percent of the time. This is referred to as performance-based navigation (PBN).

Baur says the new approach has several advantages over traditional ILS approaches. The RNP approach uses GPS satellites so there are no “costly ground based Infrastructure, architectural weakness and repetitive flight inspections” that are required of traditional ILS facilities. This can reduce costs for maintaining the approach.

Ground-based facilities are also subject to interference from local weather conditions. Baur notes that snow from the infamous Chicago winters can accumulate on antennas and cause a degradation of the navigation signals just when accuracy is needed most. “In the event of the loss or degradation of the ILS, traffic flows and arrival rates can be maintained” with RNP approaches, Baur says. This can translate into fewer delayed or canceled flights for airline passengers. Baur also points out that, because RNP approaches are designed with the stabilized approach concept in mind, they will likely result in fewer missed approaches or “go-arounds.”

“Collectively this reduces the overall environmental impact to the airport and surrounding community,” Baur says.

There are some disadvantages to RNP approaches as well. RNP approaches require special pilot and aircraft certification. Baur notes that many, but not all, modern airliners are equipped with avionics that are capable of RNP approaches. Many airlines have already incorporated RNP approaches into their training programs. Many, if not most, private airplanes are not equipped to fly RNP approaches. This means that smaller aircraft flying into smaller, rural airports cannot benefit from RNP approaches where their value could be greatest.

Further, RNP approaches are nearly, but not quite, as accurate as an ILS. An ILS typically has minimums of 200 feet and ½ mile visibility, but can go even lower in some cases. This means that the airplane can descend as low as 200 feet above the ground without making visual contact with the runway. The RNP approach at O’Hare has minimums of 330 feet and ¾ mile visibility. In most cases, the higher minimum will not make a difference, but in a snowstorm or fog, the extra 130 feet might make the difference between landing and going around.

In spite of the drawbacks, Baur feels that RNP and PBN are the future of aviation. “Today most of the major US Airlines and many of the foreign airlines have received authorization for RNP AR [arrival] procedures, as well as many corporate operators,” he says. “I feel RNAV (RNP) as well as RNP AR will continue to grow and provide benefits.  The number of participating operators will also increase with improved access through avionics.”

Hughes Aerospace has already developed RNP approaches in numerous countries around the world. Baur notes that the approaches would be valuable to airports that are concerned with terrain, noise abatement, airspace restrictions or maintaining arrival rates in the event of a disruption of ground-based facilities. They are also an alternative to the high cost of traditional ground-based approach facilities. As technology improves as entry costs for RNP-capable avionics improve, RNP approaches will become more and more common around the world.

Read the full article on Aviation Examiner

Ga Ga for Geocaching

Sneaking a peak at something in his hand, the stranger walks up to the bus stop and sits on the bench. He casually looks around and, when he sees no one is watching him, reaches under the bench. He pulls a small object from under the bench. He examines the object, opens it, and pulls out a piece of paper. He unrolls the paper, makes a note on it, and replaces it in the object. He then replaces the object under the bench, and strolls away.

The stranger is not a spy or drug dealer engaging in nefarious deeds. He is a geocacher, who has just logged another find.

I became aware of geocaching several years ago through coworkers and acquaintances that were involved in the sport. I recently received a GPS for Father’s Day and decided to try searching for a cache. My frequent business trips give me the opportunity to geocacher around the country, although at this point, I am still a novice.

Geocaching (pronounced “cashing”) is a relatively new sport that revolves around the availability of handheld GPS (global positioning system) units. Geocaching is essentially a high-tech scavenger hunt in which cachers look up the coordinates of caches on the internet, and then use their GPS units to find them. When they find a cache, they log their find on the internet. Some caches are only large enough to hold a piece of paper for cachers to sign. Others are large enough for cachers to swap small trinkets and coins. Still others are virtual caches that are simply logged on the internet.

GPS is a satellite navigation system that first became operational in the early 1990s. In the early days, it was primarily a military system. Civilian GPS receivers had only a limited ability to decode the GPS signals, and so were not as accurate as military units. That changed on May 1, 2000 when the Department of Defense turned off selective-availability, which greatly improved the accuracy of civilian units. Geocaching got its start a few days later on when Dave Ulmer of Oregon placed a cache, which was found twice in the next few days.

Today, GPS accuracy is much improved by the addition of more satellites to the GPS constellation. However, a civilian GPS still does not have pinpoint accuracy. Most GPS units can find a position within 30-40 feet. When searching for a cache, this means that your GPS will get you close, but you still have to do some looking.

To start geocaching, visit www.geocaching.com. The site is the grand central station of the geocaching world. It includes a section on how to get started and has links to websites that will help you select a GPS unit. You can purchase a GPS for approximately $150. Registration on geocaching.com is free for basic services. You can become a premium member for $30 per year.

Once you have your GPS, the next step is to find a cache. On geocaching.com, you can search for a cache in several different ways, including near an address and by ZIP code. On my trips, I usually search for caches using the address of my hotel. In most areas, there are a multitude of caches within one mile of the hotel.

Caches are listed with a name, code, and distance. There is also a rating on how difficult the cache is to find and how difficult the terrain around the cache is. A novice geocacher would probably want to look for 1s in both areas. Icons tell the type of cache as well as identifying caches that contain special items such as travel bugs and geocoins.

A travel bug is a tag that is attached to an item. You then place the bug in a cache and track it as cachers move it from cache to cache. Geocoins are promotional coins with unique IDs that are tracked like travel bugs.

An important item to note about the cache page is its size. Caches range from micro, about the size of a film canister, to large ammunition cans and watertight plastic containers. Micro caches are more common in urban areas because they are easier to conceal. Larger caches may require camouflage to prevent passersby from finding them.

People not in on the geocaching game are referred to as mugglers. Mugglers sometimes muggle, or remove, caches. Geocachers should try to avoid mugglers to ensure that caches are not muggled.

An assortment of tricks and camouflage are used to prevent muggling. Micro caches can be concealed in nooks and crannies. Magnetic key holders could hold a micro cache. Larger caches can be hidden under leaves, rocks, bricks or other debris. Fake rocks can also camouflage a larger cache. Cache creators can be very creative.

Geocaching has become a popular family activity. Adults and kids alike enjoy getting out and searching for a cache. Kids enjoy swapping items, such as small toys, from the “treasure chest.” Kids sometimes seem to have an easier time finding caches than the adults.

Geocaching can be whatever you want it to be. Whether you want to drive directly to the cache site or go on a hike, you can find caches to suit your preference. Many of the caches that I have found were in urban areas where my feet never left the pavement. With 620,132 caches currently listed on geocaching.com, the odds are that you can find a suitable cache near you, no matter where in the world you are.