Before instrument landing systems, military pilots relied on controllers to steer them right to the runway.
- By Robert P. Mark
- Air & Space magazine, March 2012
Courtesy Robert P. Mark; USAF; Photo-illustration By Théo
Long before anyone dreamed up the Next-Generation Air Transportation System—using signals from satellites some 12,000 miles above Earth to keep airplanes from running into one another—the job of returning military aircraft from murky skies required pilots to do something they loathed: let other folks, like air traffic controllers, boss them around. But in the decades following World War II, when weather took away all other options, pilots put themselves in the hands of military air traffic controllers skilled in the use of Ground Controlled Approach radar systems. Many came to think of a GCA controller’s calming voice as that of another pilot who had happened along at just the right time.
The people talking the jet jockeys down were often enlisted kids like me, a student pilot and a recent graduate of the U.S. Air Force Air Traffic Control School at Keesler Air Force Base in Biloxi, Mississippi. I was stunned when, with the Vietnam War raging, my first duty station turned out to be a Royal Air Force station in a sleepy English hamlet, Wethersfield, just a few miles east of what is now London Stansted Airport.
Wethersfield, along with a dozen other British military bases, was loaned to the Air Force to support NATO’s cold war commitment in Europe. I learned that the Air Force seasoned new controllers for a few years in low-key sites like Wethersfield before sending them to Southeast Asia to help battle-damaged F-100s, F-4s, and F-105s stagger home.
The idea of using radar to guide pilots to the runway in virtually any weather was a radical concept when GCA—sometimes called PAR for Precision Approach Radar—emerged in England during World War II. But it caught on quickly, and with help from the Brits, Gilfillan Brothers, a Los Angeles radio manufacturer, adopted, improved, and built it for the U.S. Army Air Forces and the Navy. One name associated with the early days of GCA development was Royal Air Force Flying Officer A. Clarke, a radar specialist who the world would later come to know as Arthur C. Clarke, author of 2001: A Space Odyssey and hundreds of other books, short stories, and essays. His 1963 novel, Glide Path, explored the lives of the scientists, pilots, and other service people who helped perfect the ground-controlled approach system. Clarke dedicated it to Luis Alvarez, who in 1945 was awarded the Collier Trophy for developing the microwave phased-array antenna, used in GCA.
In the late 1940s, GCA proved to be the only reliable method of safely landing tens of thousands of Allied military transports at West Germany’s Templehof Airport during the Berlin airlift. For the Allies, the ground-controlled approach became the primary method of guiding landing aircraft, far more precise than Automatic Direction Finder systems.
On my first day at Wethersfield, I was given a tour of the red-and-white GCA facility. The shacks usually sat just 100 feet from the runway for radar accuracy; when the weather was clear, the checkerboard paint scheme warned pilots to steer clear. When an aircraft did stray too close, a klaxon on the nearby control tower sounded, signaling “Run like hell.”
We were housed in two 20-foot semi-trailers joined end to end, and the facilities were cramped. One entire trailer alone housed the massive air conditioning units necessary to cool the magnetron tube, a GCA’s radio wave life force. In the other unit, our operations trailer, the aisle was just wide enough to seat four controllers in the dark for hours on end. (Slim waistlines were a plus.) Ordinarily, three GCA controllers handled basic air traffic control duties: One vectored aircraft to a 10-mile approach, at which point either of the other two controllers used a two-view (horizontal and vertical scans) radarscope that provided precise heading and altitude information. On a telephone, a fourth controller coordinated arrivals and departures with other air traffic control facilities.
Think of GCA as a sort of instrument landing system, only the needles are watched by the controller on the ground instead of the pilot. All a pilot needed to land were two snippets of guidance information—altitude and heading. The challenge for the controller was updating pilots rapidly and frequently enough to keep them on a smooth path to a landing. We focused on the radar blip, trying to stay 10 seconds ahead of an airplane headed toward the runway—and us—at 2.5 miles a minute.
Every controller-in-training had a hero. At Wethersfield, mine was Senior Master Sergeant John Mahoney, a man of some heft who had flown Northrop P-61 night fighters in World War II and served GCA tours in Vietnam. One morning, in fog so thick I could barely find my way from the standby shack to the GCA trailer, Mahoney offered a demonstration. For some reason, only three of us were on duty. With just a month’s experience, all I could do was don a headset and stay out of the way.
The arrival controller had split up a flight of three F-100s returning from a training mission. “Give them to me about seven miles apart,” Mahoney told the arrival controller.
“Pop 21, this is your Wethersfield final controller,” Mahoney said as the first aircraft neared the glideslope intercept point. “How do you hear me?” The pilot acknowledged, and Mahoney told him that for a few minutes, he’d be doing all the talking. He’d provide headings and altitudes, and the pilot had just one task: Fly them precisely.
“Six miles from touchdown, begin descent now, maintain present heading.” The pilot lowered flaps and landing gear and squeezed some power off to begin a 500-feet-per-minute descent. “On glidepath, turn right three degrees. Four miles from touchdown, now dropping 100 feet low on the glidepath. Check gear down, you are cleared to land.”
The radar blip flew level for a few seconds and intercepted the glidepath, which only we could see (instrument landing system displays in fighter cockpits were well in the future). “Now on course, on glidepath, two miles from touchdown. Drifting slightly right of course, turn left two degrees, on glidepath.” Mahoney barely took a breath. “Approaching decision height, on course. You should see the approach lights. Take over visually and land.” Two seconds later the pilot reported in: “Pop 21’s on the ground.”
With barely time for a “Roger,” Mahoney made radio contact with Pop 22, seven miles out, and guided him back home safely, followed by Pop 23. We—Mahoney mostly—kept this up, bringing in more aircraft for nearly an hour until a relief controller finally showed up. He’d been delayed on the road trying to find the GCA shack in the dense fog.
After all three of the F-100s were down, one of the pilots came back on the radio: “Thanks, GCA. You’re my hero.” At age 18 I was hooked. I wanted to be like Sergeant Mahoney and talk airplanes down like he did: effortlessly—or so it seemed. During my training I watched GCA controllers bring down airplanes in zero ceilings and zero horizontal visibility. Under those conditions, a pilot’s only other option was punching out over the North Sea.
Ground-controlled approach duty taught me many now-extinct terms: I learned about the “main bang” (the center of the radar display), and how to get a pilot to “squawk his parrot” (turn his transponder radar beacon to a discrete code). Aligning the GCA’s precision radar in a darkened trailer by just feeling the controls that I’d learned the locations of in my sleep, I was able to pass my final exam.
I never forgot what Sergeant Mahoney and the other senior controllers taught me at Wethersfield. By the time my orders to leave England came in 1970, I had even managed to win a few thanks from pilots myself.