IFR-Capable GPS: Not Just for Approaches
June 16, 2011 1 Comment
Pilots often debate the value of adding an IFR-approved GPS to the avionics stack in their aircraft. Most of the arguments focus on the value of WAAS-capable units, which can be used as a primary means of navigation (see AIM 1-1-20) and allow you to fly Approaches with Vertical Guidance (APV), including procedures with LPV and LNAV/VNAV minimums. If the airports you use frequently have ILS procedures, the GPS skeptics assert, you really don’t need a WAAS-capable GPS box.
But the value of GPS (even non-WAAS) under IFR isn’t just in approaches. With an IFR-approved GPS, you can:
- Fly T-Routes, which will replace Victor airways as VORs are decommissioned, and which often offer lower MEAs that are often helpful when icing is forecast or reported. (For more information on decommissioning VORs and replacing Victor airways with T-Routes, see “Discontinuation of VOR Service and Associated Airways” in the minutes of the April 27-28, 2011 meeting of the Government / Industry Aeronautical Charting Forum [PDF]).
- Fly airways without hassle even when one of the navaids is OTS (as happened to me recently on a flight from the Southwest back to Seattle–the OED VOR went down while I was en route).
- Get GPSS steering on your autopilot.
- Eliminate the need for DME and ADF.
- File alternates that offer only GPS-based approaches.
- With suitable hardware, get real-time information about your fuel state without having to do calculations.
- View your position on a moving map, which greatly aids SA, especially when operating IFR as a single pilot.
- Fly RNAV SIDs from increasing numbers of small airports (e.g.,KTDO [PDF]), again increasing SA during a critical phase of flight and making departures easier to fly.
- Fly SIDs based on conventional navaids much more easily (e.g., the BRUTE 5 [PDF] procedure at KMFR and the NORTHTOWN TWO [PDF] SID at KVGT).
- Improve the accuracy and ease of descent planning with V-nav features.
Can you accomplish the above without GPS? Yes, mostly. But there’s real value in the additional capabilities that an IFR GPS brings, especially if you fly IFR single-pilot. Anything we can do to reduce mundane workload so that we can devote more brain cycles to SA and ADM makes flying safer.
For a good overview of some of these capabilities and features, see:
Advanced Avionics Handbook (FAA-H-8083-6) (PDF)
Instrument Procedures Handbook (FAA-H-8261-1A) (PDF)
Risk Management Handbook (FAA-H-8083-2) (PDF)