"Memphis International information Golf; time one-seven-zero-five Zulu. Weather: five thousand broken, visibility eight miles. Winds two-one-zero at eight knots. Altimeter two-niner-point-seven-nine. ILS Runway One-Eight Right and One-Eight Center in use. Landing and departing Runway One-Eight Right and One-Eight Center. Remarks: cumulonimbus northwest. Advise on initial contact that you have information Golf."
A typical summer day in much of the country. By noon, warm, unstable air and abundant moisture from the Gulf of Mexico is transforming Chamber of Commerce cumulus into forbidding masses of thunderstorm fury. Looks like the arrival into Memphis will coincide with the maturity of several of these storehouses of water and energy.
As Memphis Center hands me off, my data block — showing N number, altitude, and airspeed — flashes on the Memphis approach controller's radar screen. He was already wondering how to shoehorn my Cessna 185 Skywagon into the steady stream of faster Northwest DC-9s, Airlink Saabs, and the Fedex Airbus and 727 arriving from the northwest. The controller alerts me to the rapidly changing weather. "November-Three-Zero-One-Mike-Charlie, roger, at four thousand. Squawk ident; information Hotel now current. Weather is two thousand five hundred broken with five miles visibility, thunderstorm and light rain. Winds are two-seven-zero at ten, gust to fifteen, altimeter two-niner-point-six-eight."
I can see the thunderstorm through my windscreen, puffed up like whipped cream. I am reminded that pireps and other information have a very short shelf life during these times.
But I've got a tool that will help. Memphis is one of the first airports in the nation to get TDWR, or terminal Doppler weather radar. The system augments the less capable LLWAS, low level wind shear alert system, and uses Doppler radar to detect shifts in air masses that indicate wind shear and microbursts; the simpler LLWAS used a network of anemometers to compare wind speed at various points around the airport.
With no weather radar or lightning detection equipment in my Skywagon, I must supplement the information from this new tool with old software: my eyes, ears, and headwork. I know, too, that I'll need to pay close attention to the frequency, creating a mental picture of where other aircraft and mine are in relation to the weather.
On the TDWR screen, which looks more like a computer than a radar display, the Gilmore Arrival is beginning to look colorful: areas of level 2, 3, and 4 precip are clustering near the Mississippi River. The cells are moving in an east-southeast direction — right toward Memphis International.
"Approach, Northwest Six-Ninety-Four, we need about thirty degrees right to heading of about one-five-zero for weather."
"Northwest Six-Ninety-Four, approved; descend and maintain six thousand."
"Approach, One-Mike-Charlie, we don't have weather radar on board, but it looks as though we need about forty right to avoid this weather; how's that look on your radar?" Controllers are not required to vector you around weather; their primary duty is to sequence and separate aircraft. They provide weather information only as time permits. If you want help, you have to ask for it. They won't normally assume that you need assistance — especially if they get busy.
"Roger, One-Mike-Charlie, my radar indicates a Level 4 cell in your twelve o'clock position, twelve miles. Suggest heading one-six- zero to avoid it."
That looks good visually and jibes with the Northwest DC-9's turn. It also allows me to remain in visual conditions for better decision making.
The weather is changing rapidly, as it always does in these situations; on the TDWR, a gust front is now visible ahead of the thunderstorms, causing concern and study by Approach Control shift supervisor Billy Rachul. Strangely, the TDWR display is located at the far corner of the approach control room near the supervisor's position; controllers working aircraft cannot see it at all unless they get up and walk across the room — which is not likely.
During busy times with a screenful of aircraft deviating around weather, TDWR wouldn't be very useful to the controllers anyhow — aircraft are not displayed on the TDWR screen, and controllers are strictly prohibited from using TDWR to vector aircraft around weather. The color weather display is used by supervisors like Rachul to make traffic and runway choices and to monitor closely the dynamic weather changes as they occur. It was obvious to Rachul that he would have to switch the traffic flow to runways 36L and 36C.
"Attention all aircraft: information India now current. Memphis landing runways three-six now, winds are beginning to pick up with the thunderstorms north of the airport, showing three-three-zero at fifteen, gusting to twenty-five. Expect vectors to Runway Three- Six-Left."
A controller's nightmare: "turning the airport around" during bad weather. Bumping down the Gilmore Arrival, I watch the sky darken and catch a glimpse of the billowy tops of the monster responsible, some 30,000 feet above me. The ride is woolly, and I try to keep my speed up for the Fedex Airbus behind me on the arrival — aware that, at 250 knots, it is flying at roughly twice my speed. Even though it is now 6,000 feet above me, we will eventually cross the outer marker at the same altitude. A controller's job of separating aircraft is largely a horizontal one.
Two other pilots choose to skirt the thunderstorm on the 302 radial, and one reports a bad ride at 6,000: "getting pretty choppy here; got...any...lower?" comes the copilot's disjointed voice, as he undoubtedly tugs his seat belt and checks to make sure the seat belt sign is on.
"One-Mike-Charlie, contact Final now on one-two-six-point- seven."
Checking in, I ask the controller, "How far northwest of the airport is that thunderstorm now?"
The controller, looking at his ASR-9 air traffic radar screen, sees a bright weather area on the northwest corner of the airport. His console has a row of six buttons indicating the six levels of precipitation that the traffic radar can detect; levels 1 to 4 are illuminated. He pushes two of the selector buttons to display levels 3 and 4 only, eliminating everything else. That's why you might fly through a fairly heavy rainshower (say, Level 2) that the controller can't even see on his screen. What he pushes is what he sees — not necessarily what you get.
"One-Mike-Charlie, I show a Level 4 thunderstorm just crossing the northwest airport boundary. The TDWR indicates a twenty-five-knot loss on the Three-Six-Left departure corridor at the present. The last two airplanes — both DC-9s — have landed with no problem. Turn left heading zero-nine-zero for base leg."
Turning the Skywagon east, I can once again see the weather that he described. There is a solid gray rain shaft below the bases now.
"One-Mike-Charlie, turn left heading zero-three-zero, intercept the Three-Six-Left localizer, maintain two thousand until established; cleared for the ILS approach Runway Three-Six-Left. Contact Tower now on one-one-niner-point-seven."
The view through the windshield is ugly as I track the localizer north, constantly mulling the quintessential pilot quandary: continue/don't continue. But the cloud bases are high; the storm, slow moving; and the aircraft ahead of me are not reporting anything other than light turbulence and moderate rain — maybe they're just too busy to give pireps. The tower controller will be the best source for current winds and radar information, and I'll be on his frequency in a moment.
There's a TDWR display in the tower, too, although controllers working local traffic cannot see it from their position. Another screen, called the ribbon display, located on the counter just below the local controller's primary D-Brite traffic radar display, shows information on each runway that the TDWR monitors. During my approach, an intermittent tone sounds and the ribbon display reads "36LA WSA 30K+ 2MF." Translated, that means that there is a wind shear alert, with a 30-knot gain, on a two-mile final to Runway 36L. The TDWR continuously looks three miles down the approach corridor and two miles off the departure end of each runway. It's a narrow view, too — only one-half mile on either side of the extended centerline.
When I contact Tower, the controller greets me with the bad news: "One-Mike-Charlie, winds at Memphis now three-four-zero at three-zero, gusting to four-five. It's raining heavily at the tower, and visibility has dropped to less than half a mile. We have a wind shear alert, thirty-knot gain on two-mile final to Runway Three- Six-Left. And a 727 just reported moderate turbulence and fifteen- knot airspeed fluctuations on short final."
"Roger, One-Mike-Charlie, we're going to divert to Charles Baker Airport while this stuff blows through. Request an immediate right turn to heading zero-nine-zero."
"Uh, One-Mike-Charlie, roger. Climb and maintain two thousand, turn right heading zero-nine-zero and contact departure on one-two- five-point-eight."
Even with all the newest hardware and oldest, most experienced software, sometimes the best approach is a missed approach.
Even Better Tools on the Way
You are not alone if you think terminal Doppler weather radar has a lot of potential but seems cumbersome to use; the excellent information offered by the system is just not as accessible to pilots and controllers as it could be. There is good news on the horizon, though: TDWR will soon be combined with information from the ASR- 9 traffic radar, the new Nexrad radar, and even wind information from aircraft through the Aircraft Communications Addressing and Reporting System (ACARS). This composite information will be available to controllers right at their consoles, a long overdue improvement in real-time weather information. At this writing, the new system, called ITWS, for Integrated Terminal Weather System, is already installed in a few test locations (including Memphis), but it will not be fully operational until the turn of the century.
Another private project that has promise might be available sooner, but it will cost pilots more. Currently being tested by AOPA, Arnav Systems, and MIT Lincoln Laboratories, the system will allow pilots in flight to download real-time radar, weather sequences, and other information into the cockpit. The test program uses a Mode S transponder as a datalink between the ground and the airplane. The final configuration may use a different form of datalink. In addition, the system uses a multifunction cockpit display that looks much like a small computer screen. Pilots will be able to view National Weather Service weather radar, sequences and forecasts, sigmets, pireps or other pertinent information for any area — even hundreds of miles away. That would be a giant stride in the right direction. Stay tuned. — MMC
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