Dead Reckoning and Your GPS

GPS is a fabulous tool. It is everywhere and I am hard-pressed to say when I last saw anyone utilize a map or aviation chart in their vehicle or aircraft. Ah, technology. In the past 20 years or so, GPS navigation has dominated how VFR (and IFR) airmen find their way around the National Airspace System (NAS). Because of that domination, VFR aviators have a tendency to set a Direct to (DTR) Route, press enter and then follow the course line indicated on their GPS navigation device.   

GPS is truly wonderful but as an active Certified Flight Instructor, I have observed a couple of things regarding how people use GPS in aircraft (VFR). First, in conducting flight reviews (FAR 61-56), I like to ask the pilots about their particular GPS navigation device that they utilize while flying. One question I ask is: what happens when their GPS goes into the DR mode (Dead Reckoning)?  Ninety-nine percent of the time I get the “Deer in the Headlights” stare.  I also ask them if they have ever seen their GPS enter that mode and the usual response is, “I do not know what the DR mode is and I have not seen it.”

Dead Reckoning Mode

Garmin states this: Dead Reckoning

Dead reckoning is the process of continuing navigation using your last known position and speed after a loss of GPS navigation while on an active flight plan, further Garmin states right next to the above sentence this: CAUTION: Navigation using dead reckoning is therefore only an estimate and should not be used as the sole means of navigation. Use other means of navigation, if possible.

The GPS unit goes into DR mode when input fails and there are many reasons why that might happen. But what I believe is more important is that most aviators do not research and study the manuals for their navigation device(s) installed in their aircraft. Thus when something happens the PIC is unable to make an excellent decision because they are not subject matter experts on that tool.

Again, the GPS navigation tool is spectacular in what it does, just amazing in fact, but if you do not know how to use the tool, or fix the tool (what if it is unfixable in the air – then what? You never really explain what to do if the unit goes into DR mode mid-flight.), then it may limit how you can respond in a critical situation.  May I suggest that you spend whatever time is necessary to become a subject matter expert on your GPS device….it just might allow you to fly with more confidence.

See and Avoid

Now another thing I have noticed when conducting flight reviews and we are cruising along (because I asked them to lay in a course to XYZ airport) – I observe that the PIC spends an inordinate amount of time looking at their flight panel and especially the GPS. Why is that a possible problem? Well let’s go back to the FAR’s, 91.113 specifically.  In the “General” statement of FAR 91.113 it says the following:

(b)General. When weather conditions permit, regardless of whether an operation is conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft.

SEE AND AVOID – That would imply that the PIC should be looking out the windows on a regular and continuous basis. But that is not what I observe (most of the time).  I believe there is some hope to change that behavior in PIC’s and what is and will cause that change is the new technology mandated by the FAA for aircraft flying in the NAS.  It is called ADSB (Automated Dependent Surveillance Broadcast System).  It generally will be on most aircraft by Jan 2020.  I have flown with a number of pilots who have that technology now, and it changes their behavior with regards to “SEE and AVOID”.  Why? Because inside the cockpit, they have a tablet or a built-in viewing screen that presents to them a pictorial representation of “known” aircraft also flying around them.  So what I see is when they view the screen, it shows that there are aircraft nearby (gives a relative position, a vector, and an altitude), the PIC then looks out the window to see where that other aircraft is.   FAR 91.113 is now fulfilled (on a regular and continuous basis).

See and Avoid, midair collision

So, technology is wonderful and it truly does aid us as aviators. I am encouraging you as the PIC of your aircraft to be the subject matter expert of your aircraft and all of the tools available to you. If you do, then you will be able to make excellent decisions while exercising the privileges of your Airmen’s certificate. 

Thank you

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