Glide Path

by Arthur C. Clarke

  “Longstop to Ranger. Your aircraft S Sugar will be landing in twenty minutes. Requests your assistance. Can you provide it? Over.”

  As it was a cold but brilliant morning with unlimited visibility, this appeal was hardly a serious one. However, it was received with great satisfaction by the entire team, and Deveraux answered at once:

  “Ranger to Longstop. Wilco. Please inform S Sugar that we will be watching for him and listening on this frequency. Out.”

  In the trucks, there was a flurry of well-coordinated activity. While Sgt. McGregor and Benny Schwartz tuned the transmitters, Howard Rawlings and Pat Connor checked the radar line-up; it would never do to tell the Professor that he was bang on the center of the runway when he could look down and see that he was a hundred feet off. The three WAAF operators were already in position, fingers resting lightly on their tracking wheels—though it would be at least fifteen minutes before they would have anything on their screens.

  The first person to see S Sugar would be Dr. Hatton, who was crouching over the search display that showed everything within fifty miles of the airfield. The GCD trucks, Alan had been surprised and impressed to discover, contained two quite separate radars. The fantastically accurate landing system had only a short range and a very narrow field of view; it was blind around ninety-five per cent of the sky. It therefore had to be backed up by a search radar that could sweep right around the horizon, to locate and direct aircraft that might approach from any point of the compass.

  This preliminary shepherding—known as traffic direction—was as important and as specialized as the talk-down itself; for unless the Traffic Director could steer the aircraft into the landing system’s restricted field of view, there would be no talk-down. At the moment, Dr. Hatton was trying his hand at the game, while Alan stood and watched over his shoulder.

  Hatton’s display was the conventional circular map, painted by a line of light spinning around like the hand of a clock. Scattered here and there over the face of the disk were glowing patches of light—the reflection of hills, buildings, and other ground objects. Also superimposed upon it were concentric circles at ten-mile intervals, and an illuminated compass grid. The operator could thus not only read the range of an aircraft and observe the course on which it was flying, but could also see instantly how well it responded to his orders.

  “I have him,” said Hatton suddenly. “Bearing zero eight zero, range fifty miles.”

  Yes, there was S Sugar—a tiny blip at the very edge of the screen. The luminous brush of the scan repainted it every two seconds, as the big antenna on top of the transmitter truck swept around the sky. After three or four reappearances, one could see that it had moved, crawling slowly in toward the center of the picture. The pilot was, obviously, on a course that would bring him to St. Erryn without any assistance from GCD, and there was little for Hatton to do except make radio contact.

  “Hello, S Sugar,” said Hatton. “This is Ranger. I have you in contact. Are you receiving me? Over.”

  There was a brief pause; then a deep, slow American voice came from the speaker.

  “Hello, Ted. This is S Sugar. Receiving you loud and clear. Awaiting your instructions. Over.”

  “Continue on present course, and remain listening on this channel.”

  “Wilco,” acknowledged S Sugar, and for a moment there was silence on the air, save for the inevitable background of distant static.

  Alan, peering into the search display, watched the little glowworm crawl in toward the forty-mile-range circle. It was not the only aircraft on the screen, for a much fatter one was heading straight out from the center. Somebody had just taken off; Alan had heard the roar of engines only a few seconds ago.

  “Calling S Sugar,” said Hatton again. “Change course to two fife zero and reduce height to fifteen hundred feet.”

  That “fife,” thought Alan, sounded very affected; but it had a good survival value in a noisy background. He would soon grow so used to it that it would require a distinct effort of will to say “five” in normal conversation.

  “This isn’t as easy as it looks,” Deveraux whispered in Alan’s ear. “Although he’s already almost lined up, Ted has to allow for wind—and that often changes at different altitudes.”

  Alan didn’t think it looked at all easy, as he tried to visualize what was happening up there in the sky. Perhaps one day he would have a compass card in his mind, with 0 at north, 180 at south, and so on. Then all these figures and courses would be instantly transformed into actual movements through the heavens: but for the moment he had to stop and draw a little mental picture every time he heard Hatton call a new number.

  Slowly the echo crawled in toward the center of the map, while from time to time Dr. Hatton gave it a slight course correction. At fifteen miles, as far as Alan could tell, S Sugar was exactly lined up with the runway; but he knew that the scale of this hundred-mile-wide picture was much too small to judge that accurately.

  Suddenly, one of the WAAFs gave an excited squeak.

  “I’ve got him on elevation!” Almost at once another said, “I have him on azimuth!”

  Alan looked up from the search display, its work now done, and glanced at Dr. Wendt, who was preparing to do the talk-down. The scientist was studying the meters intently, as the trackers fed their information to him, mentally judging the position and behavior of the still far-off S Sugar. Then the cigarette holder lifted to a jaunty angle, and he said to Hatton: “Not bad, Ted. I’ll take him.”

  Alan was looking forward eagerly to seeing a controller in action for the first time, but Deveraux had other ideas.

  “I want to watch this from the runway,” he said. “Come along, Bishop—will you bring the Hallicrafter?”

  The portable short-wave radio was no light weight, but Alan was outranked. As he emerged from the gloom of the control van and stood blinking in the sunlight, he felt a momentary surprise that there was no sight or sound of S Sugar, but, of course, the aircraft was still many miles away.

  It was fifty yards from the trucks to the edge of the runway—Alan sometimes wondered if this safety margin was sufficient—and when they had reached the edge of the great concrete strip, they paused to tune in the radio. Deveraux pulled out the whip aerial, fiddled with the controls, and at once the peaceful airfield was assaulted by an adenoidal humorist telling vapid jokes to an audience of what appeared to be fifty thousand hysterical factory girls.

  “‘Worker’s Playtime,’” Deveraux muttered in disgust. “Sometimes makes me wonder if we deserve to win. Still, I suppose it keeps them happy.” Having expressed these democratic sentiments, he rejected the program with a scornful twist of the waveband switch, and tuned the receiver with great care to an ink mark on the ten-meter band. At once, faint but clear, came the voice of S Sugar acknowledging the controller’s first instructions. They were just in time to hear, blastingly powerful at this short range, a sonorous American voice say: “Hello, S Sugar. I have you in contact, seven miles from the airfield. Maintain present altitude and change course to two seven zero. How are you reading me? Over.”

  It was the beginning of a litany that Alan was soon to know by heart, though on this first hearing he could grasp only a part of its meaning. He hardly recognized Dr. Wendt’s voice; it seemed to have become an octave lower as he talked to the oncoming S Sugar in his best bedside manner.

  “Receiving you loud and clear,” replied S Sugar. “Changing course to two seven zero. Over.”

  “Remain on receive,” ordered Wendt, who would have to talk almost continuously for the next few minutes and so did not want any back-chat from the pilot. “Now change course fife degrees right; I say again, fife degrees right.”

  (“We repeat instructions,” commented Deveraux, “to reduce the chance of errors. Dr. Wendt shouldn’t have much difficulty bringing him in; there’s practically no cross wind today.”)

  “I have you lined up, six miles from touchdown. Change course fife degrees right; I say again, fife degree
s right.”

  (“Hmm—that’s ten degrees he’s given altogether. There must be more wind up there than I thought.”)

  “You are now fife miles from touchdown,” continued that omniscient voice. “Start descending at fife hundred feet a minute. Change course three degrees left; I say again, three degrees left. You are nicely on the glide path.”

  “There he is!” said Alan suddenly. For the last couple of minutes he had been searching the heavens with such lack of success that he had realized very vividly the advantages of radar over ordinary vision, even on a clear day like this. But now a tiny spot had appeared low in the eastern sky; it was still so far away that it was quite impossible to tell how accurately it was headed toward the runway. Yet Dr. Wendt, sitting in semidarkness in front of his three meters, knew exactly what that remote speck was doing…

  “Increase rate of descent slightly. You are a hundred feet above the glide path. Four miles to go. Now fly three degrees left; I say again, three degrees left. Three and a half miles to go. Resume normal rate of descent. You are now on the glide path. Check wheels down.”

  The descending plane was now near enough to be identified as an Anson, but it was still difficult for the eye to judge how accurately it was following the invisible line that led to the end of the runway. One had to take Wendt’s word for it that it was coming along nicely.

  “Two and a half miles to go. Reduce rate of descent slightly. You are a hundred and fifty feet low; a hundred feet low; fifty feet; on the glide path. Now back to normal rate of descent. Two miles to go. You are cleared to land on this approach. Fly three degrees right; I say again, three degrees right.”

  The plane was now dropping swiftly toward them, the roar of its twin engines beginning to fill the sky. Deveraux turned up the gain of the receiver.

  “One and a half miles to go. Getting a little low again. Reduce rate of descent slightly. You’re lined up with the runway. One mile to go. Hold present rate of descent. Three quarters of a mile; half a mile; one thousand feet—go ahead and land visually.”

  With a roar, the aircraft swept in over the far end of the runway, made a perfect touchdown, and came hurtling toward them with an intermittent squealing of brakes. Long before it had drawn level with the trucks, its tail had come down and it was taxiing with engines throttled back; Alan was not surprised when it came to a halt a few yards away and disgorged one of its passengers.

  He was a shorter-than-average man, about thirty years old, wearing an unbuttoned raincoat and walking with the aid of a stick. Apart from his limp, which did not seem to slow him down greatly, and his unruly shock of hair, there was nothing that would make one look twice at Professor Schuster. He might have been a schoolmaster or a bank clerk, rather than one of the finest scientific brains of the Western world. Alan had not known what to expect, yet he was somehow disappointed.

  “Nice to have you back, Prof,” said Deveraux, with obvious warmth and sincerity. “This is Alan Bishop, who’s just joined us.” They shook hands, and Deveraux continued. “That was a good approach—Doc had you right on the center line.”

  “Well, let’s say about twenty feet to the left, but because we’re both out of practice, we can’t grumble at that.”

  It was then that Alan realized, a little belatedly, that Schuster had been flying the aircraft himself. Alan had a great (though well-concealed) admiration for anyone who could fly, and he looked at the Professor with increased respect.

  “Have you got all the spares we wanted?” asked Deveraux as S Sugar’s copilot taxied the Anson away down the runway.

  “Most of them,” answered Schuster. “With luck, we’ll keep the gear running now—well enough, at any rate, to prove our point. But it was a close thing; you got the equipment serviceable just in time.”

  Deveraux made a face.

  “As bad as that, eh?”

  “I’m afraid so. There’s some tough opposition, especially among the pilots. You know the argument—‘I’m damned if I’ll let anyone on the ground tell me what to do!’ Well, we have to convince them by good salesmanship and actual demonstration. So from now on we’ll be having a continual string of VIPs descending on us. If we deliver the goods, the news will get around soon enough. But if we don’t, then we might just as well pack up and go home.”

  “We’ll deliver,” said Deveraux confidently. “Won’t we, Bishop?”

  Both touched and surprised, for a moment Alan could only nod his head in agreement. Then he said, with all the determination he could muster: “We certainly will.”

  He was not much use yet, but he had been accepted as one of the team; and that was a fine, heart-warming experience.

  8

  Now that the Mark I had recovered from its ocean voyage and its brush with the British climate, the unit began to grow rapidly. Sergeant McGregor and the three WAAF operators were only the beginning; soon they were joined by two Flying Control officers to be trained in the talk-down technique, four radar mechanics, three more operators, and a complete flying unit.

  “D” Flight—GCD’s private air force—would not have scared the Luftwaffe, but it was enough for the job in hand. It consisted of two yellow-painted trainers—an Oxford and an Anson—together with the necessary pilots, navigators, fitters, and mechanics. The flying personnel were all experienced with instrument-approach and blind-landing systems, and looked upon GCD with interested skepticism.

  In an experimental unit operating with a single complex and temperamental piece of equipment there was no such thing as a normal working day. There were uneventful days and there were catastrophic days, but no two were ever quite the same. It all depended on the gremlins.

  Like Abominable Snowmen, gremlins have never actually been seen; but nobody who has worked with electronic gear doubts the existence of these mischievous and elusive entities. There are too many malfunctions and failures that can have no other explanation.

  On mornings when the gods smiled and the gremlins hibernated, the GCD trucks would drive out to the runway in use at 8:00 A.M. There Alan and his radar mechs would set up the equipment under the watchful (and often anxious) eyes of its American inventors, and report back when all was satisfactory. The WAAF operators would put away their knitting and climb on their bicycles—except when the weather was really bad; then a bus would be grudgingly provided by the station’s hard-pressed Motor Transport Section. At the same time, “D” Flight would warm up its aircraft, check their radios, and send them off into the sky. By 9:00 A.M., if all went well, the operators would be tracking the radar echoes across their screens, and the controllers would be calling S Sugar and F Fox down from the clouds like homing pigeons.

  On the whole, it was a happy family, despite the mingling of nationalities and occupations. Scientists, pilots, controllers, mechanics, operators—all were united by the importance of their work, and the privilege of being in at the beginning of a new and vital project. The pilots’ initial skepticism had quickly vanished, and the fact that all the officers and civilians shared the same hut added to the family feeling. They could discuss their problems and difficulties, suggest new procedures, hold post-mortems on bad approaches—and, occasionally, blow off steam. The biggest blowup occurred one miserable afternoon when the aircraft had been grounded by bad weather and there was nothing to do but sit in the hut and talk.

  Though there were some good talkers in the unit, the best was undoubtedly Pat Connor. Not only did he have a ready wit, but he was an excellent mimic. Like many Americans, he was fascinated by the English and could not altogether believe that they were true.

  “Look at Dennis Collins,” he would say. “Is he real, or am I imagining him?”

  F/Lt. Collins, DFC, was the twenty-four-year-old commanding officer of “D” Flight. A veteran of the Battle of Britain, with an impressive row of medal ribbons, he was waiting with some impatience for his return to operational flying. Although enthusiastic about GCD, he was not too happy about his present status, maintaining that he was a fighter pilo
t, not a blasted bus driver.

  With his handlebar mustache, carefully unbuttoned tunic, wilting cap, and knotted scarf, he was almost a caricature of his species. To make matters worse, he had a public-school drawl that sounded peculiar even to most of his compatriots, and often baffled the Americans. Even the gentle and good-natured Benny Schwartz, who normally spoke pure Bostonian, made a point of relapsing into deep Brooklynese when Dennis was around. This delighted Alan, for reasons that he would not admit even to himself. His own accent—especially under stress—was a long way from the playing fields of Eton; and he was secretly jealous of those ribbons and that Distinguished Flying Cross.

  The cause of the trouble was Pat’s latest limerick; on the average, he produced one a day. Though few could be repeated in polite society, this one, by a miracle, was both amusing and clean. Putting on an accent hardly distinguishable from Dennis Collins’s, he declaimed:

  I sat next to the Duchess at tea;

  It was just as I feared it would be.

  Her rumblings abdominal

  Were simply phenomenal—

  And everyone thought it was me.

  Even Dennis, who had little sense of humor, would have enjoyed this had it not been for two unfortunate coincidences. In the first place, it was teatime, and everyone was drinking from the usual battered RAF mugs. And secondly, he was sitting next to Pat.

  “I don’t think that’s at all funny,” said Dennis belligerently. This only focused attention on him and made everybody laugh harder.

  “And indaid, ’tis sorry I am to hear it,” replied Pat, switching accents quickly to the other side of the Irish Sea. “But my poor muither, just before they shot her in the Troubles, always said the English couldn’t see a joke.”

  “My mother,” said Dennis, with more wit than Alan would have given him credit for, “always said that the Yanks couldn’t see a war, until it was nearly over and they knew which side would win.”