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Collins ANS-31A) used existing VORs and “electronically moved” the ground- based transmitters to align them into the desired course. In 2000, there were about 3,000 VORs around the world, including 1,033 in the U.S. By 2013, they had been reduced to 967 and by 2020, to just under 900. Even though reliance on the above ground-based systems limits both the availability and accuracy of routes, the FAA and aviation alphabet groups recognize the necessity of maintaining multiple forms of navigation as a backup, and a Minimum Operational Network (MON) of VORs will remain operation- al indefinitely. The minimum number of VORs is expected to be 589 stations.
Necessity is the
mother of invention. – Plato
A historic increase in airline travel has been the major impetus for a new (and overdue) approach to air naviga- tion. The advent of Flight Management Systems and computers that use mul- tiple navigation sensors, like VOR and DME, allowed the electronic calcula- tion of routes between points with- out flying over them. Computers also removed the need for pilots to calcu- late fixes and program RNAV units in order to “electronically move” ground stations. Position and route accuracy then increased geometrically with the advent of a satellite-based global posi- tioning system.
As GPS was added to existing navi- gation units or as a stand-alone capabil- ity, Required Navigation Performance (RNP) was initiated. RNP describes how aircraft may fly an RNAV route or procedure using either ground- based or satellite-based navigation, as long as the required performance (RNP) specified in the procedure can be achieved. A required navigational performance is specified when posi- tion accuracy is essential for navi- gation accuracy, separation, and in many cases, obstacle clearance. RNP requires navigation systems to not only monitor performance compli- ance but to alert us if the aircraft flies outside of those parameters – it’s at the heart of PBN. GA has not only ridden
on the coattails of the resulting capa- bility, utility and safety but very often has led the way.
You’re right...we didn’t have those things when we were young. We invented them.
– Ronald Reagan
Over the years we’ve all seen
changes in our airspace system: TCA’s
(terminal control areas – now class
B), TFR’s (that aren’t so temporary
after all), RVSM (Reduced Vertical
Separation Minimums), LAHSO (Land
And Hold Short), PRM (Precision
Runway Monitoring), and now with
PBN, enroute RNAV, descend via and
climb via RNAV arrivals and RNAV
instrument approaches. These pro-
cedures have been developed for a
variety of reasons, some of them to
increase the efficiency of our airspace
system and airports, and others to
allow more aircraft to use the same
airspace and airports simultaneously.
There is no doubt the procedures are AOPA more stable, predictable and accurate
than ever before.
And for general aviation, GPS/
WAAS has opened thousands of “little” airports to us through the use of GPS approaches, especially when they have LPV minimums. GA continues to dom- inate the U.S. airspace and airport sys- tem, with three out of four takeoffs and landings conducted by GA. And out of some 19,000 GA airports, 4,074 have a GPS/WAAS augmented LPV approach with 2,876 of those to runways with no ILS – and over 1,050 of those have minimums to 200’ HAT. The signifi- cance of this capability is astonishing to anyone who grew up flying ADF, VOR and circling approaches.
Except It’s Your Butt
Single-pilot IMC in high-perfor- mance aircraft is a safe endeavor because of our training, equipment, and the reliability of avionics, pow- erplants and airframes. And because of the decreased workload these new technologies and reliability provide, including GPS, WAAS, LNAV, VNAV, ADS-B and real-time weather, our
April 2021 / TWIN & TURBINE • 23