Sunday, August 1, 2004
Mastering The Panel-Mounted GPS Part 1: VFR Use
Bendix/King, Garmin, Chelton? At first glance, they all seem so different, but are they really? It turns out they have a lot in common.
Learning to use even one of the modern IFR-approved GPS maps, let alone several of them, is challenging. Understanding the capabilities of a device requires as much class time as learning how to operate it. The how can be very different from unit to unit, but the what is surprisingly similar. And it’s hard to learn how to do something if you don’t know exactly what it does. In this two-part article, we’ll use the Bendix/King KLN94, Garmin Apollo CNX80, and 430 or 530 as representatives of the class of devices to help you figure them out.
Many of the things these units do are easily understood, even if they might be complicated to execute. You can make checklists, do flight-planning and fuel-planning, perform density-altitude calculations, set up Vnav operations, change map setup items, set timers, predict RAIM, etc. We’ll focus instead on capabilities that are understood in principle, but turn out to be more subtle or complex when you try to use them. For example, how many different ways can you use the Direct-To operation? What does it mean to activate an approach (there’s no Activate Approach option in the KLN94 or CNX80)? Where are arrivals and approaches added into your flight plan (after your destination in the 430 or 530, just before it in the CNX80 and KLN94), and what does Activate Leg mean? Let’s explore the major capabilities of these GPS devices in some depth.
Flight-plan operations are the meat and potatoes of these devices. For VFR use, a flight plan is just a list of waypoints you string together from your starting point to your destination. After you’ve activated it or made any changes, you should review it by scrolling through the active flight-plan list. The course between two adjacent waypoints defines one kind of flight leg (there are many kinds when procedures are added), and has a desired track and specific location on your map. The CNX80 has advanced features common to flight management systems and abilities to add airway segments to flight plans and, with its WAAS (Wide Area Augmentation System) capability, it’s certified for primary navigation under TSO-C146 (not secondary, like the TSO-C129 KLN94, and 430 or 530 systems).
The leg line is directional, always a Course-To (unlike To-From radials of a VOR). If you’re off course, the autopilot would take you to the active leg, then fly toward the next waypoint. The leg that is currently active is shown in magenta, with the others in white, and isn’t necessarily the one you’re on now (or near). You can choose to make any leg active (except in the KLN94), but by default, the one nearest to you will be selected when you activate the flight plan. If you’re within 5 nm of the departing airport, the CNX80 will automatically make the first leg active. Sometimes, however, it will declare “no active leg,” so you’ll have to choose one.
There are times (especially for IFR flight plans) when you want to activate a particular flight leg, not necessarily the one nearest to you. To “jump ahead” in the leg sequence choose Activate Leg in the 430 or 530s or Fly Leg in the CNX80. The KLN94 always selects the nearest leg when the flight plan is modified, so to jump ahead to a new waypoint in your list, you may have to use the Direct-To operation.
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Labels: Avionics, Buyer's Guide, Cockpit Gadgets, Handheld Avionics, Navigation, Pilot Supplies, User Guide