Page 10 - May 2019

Radar and Drift
by Joe Casey
PHOTO COURTESY OF GARMIN
Radar and drift. I bet you’ve never heard those words used in the same sentence. Fading, attenuat-
ing and even marching are interesting words occasionally used with the term “onboard radar” – but drift? Yes, drift has an important meaning when it comes to using onboard radar. However, my contention is not that the radar itself drifts, but that our use of onboard radar can drift. Let’s explore.
The Meaning Behind Drift
Drift is an interesting word. We use it frequently in aviation, but mostly in relation to a takeoff or landing as in “I drifted off centerline.” Or on a cross- country, I might “drift off course.” Or during an IFR flight, a pilot might “drift off altitude by 100 feet.” In each of those situations, there was a standard (center- line, course, altitude) and drift means an unintentional movement from that standard. Drift is an enemy to aviation and one that every pilot needs to keep a sharp lookout to avoid.
During refresher training, there’s an- other form of drift that I intentionally look for – drift from known standards and practices. You’ve probably heard this before: “I used to do it this way, but I started doing it that way.” I see it often when pilots of one particular airframe talk to a pilot (or well-meaning, but uninformed CFI) who operates a dif- ferent type of airplane. Practices that work well for one airframe may not work well for another. When these practices
are errantly transferred to the different airplane, drift occurs. I see it frequently in refresher training, and it’s one of the reasons that every twin and turbine pilot should pursue type-specific training, not just training from a local CFI. The CFI may be highly-competent yet does not know much about the specific airframe you operate.
So, how do drift and onboard radar fit in the same sentence? The connec- tion lies in defining the standard from which drift can occur. When it comes to thunderstorms, the standard is every pilot should remain 20 miles from thun- derstorms and should not drift closer. But here is an example of how drift can still happen.
Drifting Too Close
A few years ago, I flew in an MU2 Marquise with a veteran airline and commercial pilot. Our f light was from Montreal, Canada back to Texas, and after flipping a coin, it was deter- mined that I was to be the left-seater for this long flight. Draped across much of the United States on this summer af- ternoon were splotches of slow-moving thunderstorms, and inside some of the bigger splotches were some fairly intense cells. We climbed up to the smooth, clear skies at FL260, well on top of everything except for the convective stuff punching through the haze layer. We settled down to what appeared to be an easy flight.
About two hours in, we started receiv- ing the normal calls from ATC advising
of “scattered moderate to extreme cells from our 10 o’clock to 2 o’clock,” along with the usual “cleared to deviate right and left of course, advise when direct destination.” There were plenty of holes in the scattered cells, so my veteran pi- lot slipped off to the empty cabin for a short snooze (yes, the MU2 is a single- pilot airplane).
I then fired up the onboard radar, had downloadable radar on the GTN750, and contrasted everything against what my eyes were seeing through the front wind- screen. I remained in the clear, smooth air and weaved around scattered cells somewhere over Indiana. Picture a rather boring flight with the autopilot on HDG mode and my guiding the airplane along through the cumulous valleys. Nothing to it. We’ve all been there – 5 degrees right, 10 left, just a little touch of the heading bug back and forth.
After about 30 minutes or so, my bored friend woke up and stuck his head in the cockpit to “check in” and see our progress. He looked out the left window and said frightfully, “What are you doing? That’s a thunderstorm right there!”
Rather offended, I showed him the radar showing that we were in the clear, and I pointed to the blue sky that domi- nated the front windscreen. He merely pointed to the cell not too far out the left window and said, “You are crazy!”
He plopped down in the right seat, belted in, and told me my risk meter was broken. Of course, I took serious offense,
8 • TWIN & TURBINE / May 2019