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Tuesday, April 1, 2014

GPS Approach: Need One? Get One!   

The digital electronic world has flooded the market with countless types of smart devices which rely on small GPS receivers to do an ever-increasing list of location-based tasks.

By Frank Lombardi, Technology Editor

Garmin booth at Heli-Expo 2014. Photo by Frank Lombardi
Peek into the cockpit of any aircraft on the ramp today, and you will be hard-pressed to find one whose panel does not contain a GPS, the common reference to global positioning system.

At a time seemingly not long ago, GPS was a new device that, to the pilots on the front end, was not much different than the terrestrial-based LORAN navigation systems they were replacing.

But as the sun rises on airports all over the globe these days, the digital electronic world has flooded the market with countless types of smart devices which rely on small GPS receivers to do an ever-increasing list of location-based tasks, such as “geo-tagging” the location at which you snapped some photos, finding the nearest coffee shop, helping you find your car, your spouse, or even just keeping really accurate time. Oh how far we’ve come.

With all the new uses that advances in GPS technology have given us, it’s easy to overlook the fact that we also have improved the ability to navigate from point A to point B in the safest most accurate manner ever possible.

 

What GPS Is

The Global Positioning System is a constellation of 24 satellites placed in orbit around the Earth at an altitude of approximately 12,000 miles, and a world-wide network of ground facilities that track the GPS satellites, monitor their transmissions, correct errors, and send commands and data to the constellation.

It was put in place by the U.S. Department of Defense in the 1980s for military purposes, but eventually was made available for public use. From their precise orbits, GPS satellites circle the globe twice a day and transmit signal information to Earth. The satellites contain very accurate atomic clocks.

Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. This time difference tells the GPS receiver how far away the satellite is. The GPS receiver needs to be locked onto at least three satellites to calculate the two-dimensional position of latitude and longitude, and track movement. Locking onto four or more satellites allows the receiver to calculate the third dimension of altitude.

In 2000, the government turned off what they termed “Selective Availability,” which was a Department of Defense intentional degradation of the GPS signal designed to thwart potential military adversaries. This greatly improved the accuracy of the GPS signal to its current average of about 15 meters.

What GPS is NOT

GPS receivers are passive. They do not transmit signals. While GPS receivers may contain a database of obstructions, they do not provide standalone ground proximity warning (GPWS) or terrain awareness (TAWS). These awareness systems use GPS location data along with their own database to look ahead of the aircraft and warn the pilot of impending impact with the ground.

Avoiding controlled flight into terrain (CFIT) is still the pilot’s job – and remains as such – regardless of any of these systems.

GPS and WAAS

As if the accuracy of standard GPS isn’t impressive enough, the advent of the Wide Area Augmentation System, or WAAS, improves on the current accuracy by about five-fold. Whereas basic GPS gets you within 15 meters of accuracy, WAAS brings that number to within 3-5 meters. It accomplishes this by doing even more error correction of atmospheric disturbances via multiple ground stations with very precise known locations. These corrections are sent via ground to a WAAS master station, where they are beamed to two geostationary satellites over the equator, which in turn send the more accurate position updates to GPS WAAS receivers.

So WAAS the Big Deal, You Say?

Ok, so that wasn’t very funny. But neither is the seriousness of flight in Instrument Meteorological Conditions (IMC). The ability to operate under instrument flight rules (IFR) is the mainstay of the U.S. National Airspace System. For years, the system has seemed to cater to aircraft of the fixed-wing variety. There are literally thousands of departure, enroute, and instrument approach procedures designed for airplanes that are flown by helicopters. Although this has continued to work as helicopters gain ground in the world of instrument flight, the true advantages of the helicopter as an IFR platform are only beginning to be realized. WAAS will surely change all that.

Instrument approaches are usually grouped into one of two categories: precision and non-precision.

The precision approach is one that incorporates vertical guidance as well as lateral. The traditional non-precision approach offers only lateral guidance via a VOR, NDB, or DME, and without the vertical portion, is accomplished with a step-down procedure, beginning from the Final Approach Fix, and halting at a Minimum Descent Altitude, flown to the Missed Approach Point. Pilots like to call this approach the “dive and drive” technique. Because of the inaccuracy and length of time exposed to low altitudes, the possibility of controlled flight into terrain is increased, and so the Minimum Descent Altitudes of non-precision approaches are decidedly higher than precision approaches. The lowest non-precision approaches terminate at about 500 feet AGL.

For years, the Instrument Landing System (ILS) has been the most recognized method of providing a precision approach procedure to an airport. Its sensitive electronics can bring an aircraft down a sloped path, providing obstacle clearance while tracking the localizer and glideslope, and terminate at a Decision Height (DH) of as low as 200 feet AGL.

A key point here is that these forms of instrument approaches all rely on ground-based equipment and infrastructure to operate. This makes them expensive, inconvenient, or impossible to incorporate at locations suited specifically for helicopter operation, such as hospitals, government facilities, or private helipads.

Enter the GPS WAAS Approach

GPS approaches have redefined what can be an acceptable location for the development of an approach procedure. With GPS being essentially space-based, there is no equipment or infrastructure to contend with at the intended site. And while standard GPS can be used only for supplemental navigation if used on a precision ILS approach or fly non-precision approaches down to basic non-precision minimums on a GPS (LNAV) approach, WAAS accuracy makes your GPS a primary navigational instrument – not just a supplemental source like approved non-WAAS GPS receivers.

WAAS approaches have “Localizer Performance with Vertical Guidance,” hence their acronym LPV. They have the ability to take an aircraft down to a DH of 200 feet AGL, along a sloping path as a typical ILS system can, but with essentially nothing more than a WAAS-enabled GPS in your aircraft.

The implications to helicopter operators are huge. No one knows this better than Steve Hickock, of Hickock and Associates. He has been developing IFR procedures for helicopters for over 20 years. Hickock reviewed some of his accomplishments, which include: initiating the first GPS approach to be approved by FAA, developing the first helicopter GPS airspace system, developing the first approved helicopter GPS departure, and developing the first WAAS LPV procedures. Not surprisingly, Hickock was the first FAA-approved non-federal developer.

Hickock said that “the primary impetus for developing helicopter instrument approach and departure procedures is to increase safety, especially in the enroute phase, with an emphasis on eliminating CFIT.” But an ancillary benefit is that having an approved LPV approach allows operators to recover some of the costs of their operation.

IFR helicopters are expensive to maintain, not to mention the cost of keeping their IFR pilots current. An operator who has to turn down flights because they have no instrument procedure at all, or just a non-precision LNAV procedure with higher minimums, is losing revenue.

So How Do You Get One?

There are many challenges to overcome if you’d like to have a custom-made approach set up at your location. By far the easiest route to take would be to contact a service provider such as Hickock and Associates, who would discuss the feasibility, all your options, and guide you through all the steps necessary. They confidently claim to be the only true sole-source 100 percent turnkey provider of helicopter instrument procedures.

No matter who you seek out to design your approach, it will most certainly have to begin with an on-site evaluation. Data collection on obstacles and heliport evaluation will affect the design of the approach and your options. Flight validation and flight inspections must be carried out, basic maintenance should be anticipated, and final approach charts and procedures are drawn up.

According to Hickock, plan on it taking an average overall of one year to develop and approve a GPS LPV approach to your private helipad or facility.

With the advent of NextGen and automatic dependent surveillance-broadcast (ADS-B) airspace system changes, a WAAS-enabled GPS will be part of the mandatory equipment required to provide “ADS-B out” information to ATC. Although WAAS only exists in North America at this point in time, it seems that with the widespread success and future implementation of WAAS in every cockpit, there is no better time than the present to take advantage and have a GPS LPV approach designed which you can call your own.

 

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