Worthless Freakin' Radar
For those of you new to airborne radar, here's how it works. Radio waves are sent out by an antenna in the aircraft's nose (or mounted in a wing pod). Some of these waves may hit a reflective object, such as rain or ground objects, and bounce back to the aircraft. The radar unit analyzes the reflected signal to determine distance and bearing to the objects, as well as how reflective the object is. The pilot looks at the radar returns and decides which are actual precipitation and which are simply ground clutter. Supposing the most intense returns - red and pink on color radar screens - to be thunderstorm activity, he keeps the aircraft clear of them.
That's how it's supposed to work, anyways. There are a few inherent limitations. The idea is to avoid turbulent air; but radar detects precip, not turbulence. We operate on the supposition that turbulence will accompany heavy precipitation - and it often does - but that doesn't protect us from developing storms where rain is not yet falling. Furthermore, sorting ground clutter from actual returns can be a full-time chore. You can try to minimize ground clutter by using the "tilt" control to tilt the radar beam upwards, but here's the catch: precip reflects radar waves best at and below the freezing level. At FL250, that involves aiming the radar beam downward.
It's not such a problem with a good radar unit that sends out a narrow, focused beam of radio waves. Such a narrow beam, however, is associated with large radar antennas. You'll find such antennas on airliners like the B757, but they will physically not fit in a light airplane's nose. My airplane also uses a small antenna - not because the nose is too small, but because somebody decided a large antenna would be too expensive. Thus, at altitude, cruising along with the tilt down results in massive amounts of ground clutter which prevent us from seeing returns until 15-20 miles away - only a few minutes' flying time. That's fine for a little tactical dodging and weaving, but makes navigating any large lines of storms a real treat.
Besides the problems associated with a small dish, this radar seems to either send out a weak signal or have a problem receiving the echoes. I've flown into heavy rain before with nary a peep of green on the screen. Other times, like yesterday, the screen seems to signal the coming apocalypse when actual conditions aren't that bad.
We had our first fit of winterlike weather in Seattle yesterday, with thick bunches of towering cumulus to 14,000 and heavy rain showers throughout the area. We went into the clouds while on the GLASR6 arrival and got our butt kicked with turbulence, but the radar painting no precip. As we got closer, our radar started painting some really heavy precip near HETHR intersection. The controller turned us before we got there, and vectored us onto the final approach for 16R. As we joined the localizer, we did a double-take at what the radar showed directly over the airport: large amounts of red and pink. I adjusted the tilt upwards, with the same results. It was not showing ground return.
I asked the tower if it was raining on the ground. They said yes, with aircraft reporting moderate precipitation on final approach, but no turbulence or windshear. As we broke out of the clouds over downtown, it looked dark near the approach end but nowhere as bad as the radar was saying. We chose to believe our eyes and the recent reports over the flaky radar, and sure enough: it really wasn't that bad.
The sad thing is that I've flown a Be58 Baron with a better radar than this one. Until somebody comes up with a solution, the best option is using visual avoidance whenever humanly possible, just like a non-radar equipped aircraft. Unlike light aircraft, however, I don't have the option of using VFR to stay low for visual avoidance.