Glide Path

by Arthur C. Clarke

  ***

  It was a subdued and thoughtful little group that gathered at the trucks the next morning. Only Howard was fitfully cheerful; Sergeant McGregor appeared to have a slight hangover and clearly resented being dragged out to the airfield on a Saturday morning, while Alan had a somewhat anxious expression and kept glancing apprehensively at his NCO. He had not slept at all well, and his dreams had been highly frustrating.

  Mac tramped morosely into the transmitter truck, from which bad language emerged in an unbroken stream for a good five minutes before the diesel coughed into life. The petrol-driven starter engine was on strike, and Mac was compelled to swing the massive motor by hand. This was not an easy job at the best of times, and was certainly not recommended immediately after a hectic night. Then the regulator began to misbehave, the voltage swinging wildly between 90 and 140 until Mac hammered the recalcitrant unit into submission. When the lights had stopped flickering and the generator had accepted the fact that it, too, had to work on a weekend, Alan switched on the electronic circuits and waited for them to warm up. His own warming-up period still showed no signs of coming to an end.

  After an hour’s work with hack saws, soldering irons, screw drivers and electric drills, the new circuit was tucked into an out-of-the-way corner of the van, and its wiring added to the maze that already existed. The actual test was a considerable anticlimax; when Howard threw the switch, all that happened was that a faint dotted line appeared simultaneously on all the radar indicators. He turned the control knob, and the line glided smoothly across the screens, a movable signpost that could be set on any target at the touch of a finger. Now, no matter how many aircraft there were on the screens, the trackers would know which to start following, and which to ignore.

  “Well, that’s that,” said Howard, in a rather self-satisfied voice. “What shall we call it?”

  “Oh, what about—er—identification marker?”

  “Too much of a mouthful. You want something short and snappy. I have it-target indicator!”

  “Well, that’s a bit better,” admitted Alan, who was sending the dotted line scurrying back and forth across the azimuth display. Filey Station’s little group of four tightly bunched echoes made a good target; he could place the indicator on each in turn without confusing it with its neighbors. Which of these echoes, Alan wondered, was the tower he had climbed with Geoffrey?

  He was still amusing himself with the new control when a faint, luminous mist appeared at the extreme edge of the tube, ten miles away. A heavy rainstorm was approaching, and with surprising speed. The rain was moving forward in parallel bands, quite sharply defined, so that the radar screens looked as if they had been smeared with streaks of luminous paint.

  “I’d hate to be up in that,” said Alan thoughtfully. “Let’s get back to our billets before it hits us.”

  “I agree,” answered Howard. “Looks like a regular cloudburst. I’ll tell Mac to close down.” He was about to call the transmitter truck when the field telephone to Flying Control startled them by its sudden urgency.

  “What the heck!” said Howard. “We’re not supposed to be here. Someone must have got the wrong number; I shouldn’t answer.”

  “It may be important,” Alan reprimanded him as he lifted the receiver. “GCD truck here; who’s calling?”

  The next few minutes were highly frustrating to Howard, who could hear only one end of the conversation. It consisted mostly of, “I see… Yes, of course… I’m afraid that’s impossible… But there are only three of us here… No, they all have the weekend off—there’s probably not one on the station… Well, you can try… Of course we close down on weekends—this is a training unit, not an operational one… It’s no good blaming me… Oh… I see… Well, in that case… How long did you say?… Let me talk it over…”

  He put down the phone and turned to the exasperated Rawlings.

  “Flying Control has an emergency on their hands. There’s an aircraft trying to land over at Davistowe—it’s been caught by this storm—seems it was on its way there from somewhere else. They want to know if we can bring it in.”

  “Can’t it use Standard Beam Approach?”

  “No. It’s an experimental prototype and only carries VHF radio.”

  “Then someone ought to be shot.”

  “It was making a delivery flight and the weather forecast was good, so I guess it seemed safe enough. But what are we going to do?”

  “There’s damn all we can do. We’ve no trackers and no controllers.”

  “Flying Control is trying to round some up, but I doubt if they’ll find any on the station. And the pilot only has fifteen minutes of fuel left.”

  “Then he’ll just have to bail out. I presume he has a parachute?”

  “I didn’t ask,” Alan replied, too worried to notice the sarcasm. “But it’s a very valuable aircraft, and they don’t want to lose it. Besides, what a boost it would be for us if…”

  “I know what you’re thinking, and it’s impossible. There are only three of us here—just enough to do the tracking, though I don’t suppose Mac has ever tried his hand at it. That leaves no one to do the talking down, even if we knew how to.”

  Alan was perfectly well aware of this, but it did not affect his belief that something could be done. A few minutes ago he had felt a sense of helpless frustration—the Flying Control Officer had been quite unnecessarily rude—yet now he was swinging to the opposite extreme. He had been presented with an exciting challenge and had already seen one way of answering it. There was no time to analyze the motives behind his actions, but his two recent, though totally different, debacles undoubtedly spurred him on. Now was an opportunity to redeem himself, and GCD, at one swoop.

  He picked up the telephone and spoke to the impatient Flying Control Officer.

  “We’ll do our best,” he said. “Try to locate one of our controllers while we get lined up. While you rush him out here, we’ll contact the aircraft and vector him into position. What’s his call sign and frequency?”

  “Z Zebra; he’s using your Channel D.”

  Thank God for that, thought Alan. If their press-button radio transmitters had not been set up on the right frequency, they would have been completely helpless. It would have involved too great a time lag to relay all instructions via Flying Control; at least they could talk to Z Zebra directly.

  Once he had made up his mind, he moved swiftly. “Howard,” he snapped, “get the precision system calibrated as quickly as you can; it won’t have drifted much since last time. Mac”—this into the intercom—“see that your side’s OK and come over here. The transmitter truck will have to run itself—we want you as a tracker. I’ll explain when you get here. Just make sure that everything’s tuned up and hope for the best. Check the search system first—we’ve got to locate an aircraft.”

  That was not going to be easy with all this rain cluttering up the screens. As Alan peered into the hundred-mile-wide plan-position-indicator display, he was faced with a hopeless confusion of echoes from ground and sky. To find a lost aircraft among them seemed impossible; luckily a now-less-acidulous Flying Control Officer was able to give him an approximate fix, so he knew which area of the tube to examine.

  Twenty miles away to the northeast, on bearing 040, he found the faint, solitary echo whose comet tail betrayed its movement. Was it the right aircraft? Well, there was probably no one else in the sky at the moment, and he’d soon know.

  He pressed button D on the channel-selector switch. In a few seconds, he’d find out if there was any hope.

  “Hello, Z Zebra,” he said. “This is Ranger. We are going to vector you toward St. Erryn. Can you hear me? Over.” One was not supposed to mention the name of the airfield (as if the Germans did not know it was there!), but this was no time to worry about correct radio procedure and the feelings of the Station Signals Officer.

  The ether was silent, apart from the louder-than-usual background caused by the static of the approaching storm. Perhaps Z Z
ebra had been transmitting and hadn’t heard the message. Alan tried again.

  He had wasted thirty precious seconds, and worked himself into quite a state, when he realized he’d pushed the transmit-receive key in the wrong direction. Well, he’d known experienced controllers to do the same thing, and he’d never handled this job before. No need to panic, F/O Bishop, he told himself firmly, But no more mistakes, please.

  It was just as well for his morale—not to mention Z Zebra’s—that contact was established immediately. The delay might even have been useful, for it had given him extra time to size up the situation on the radar display, and to decide the best course to give the aircraft. If he could get it roughly lined up by the time a controller arrived, that would be half the battle.

  “Hearing you loud and clear,” said Z Zebra. “Awaiting your instructions. Over.”

  The pilot sounded remarkably calm, considering the circumstances. But then, test pilots had to be calm in emergencies, and perhaps this one had an exaggerated impression of the help that was now being offered to him.

  Alan’s problem was to get the aircraft orbiting in a convenient spot from which it could be whistled down to the approach with the minimum of delay—when the still-hypothetical controller turned up to do the job. Mac, who had just arrived from the other truck, said that the station P.A. system was bawling its head off in an attempt to locate any GCD controllers, trained or untrained, who hadn’t taken a weekend pass. He also remarked that it was a filthy day outside, that he’d got soaked crossing the forty feet between trucks, and what the hell was all the flap about?

  Howard told him while he checked the calibration of the precision system. Mac, who would try his hand at anything, was quite confident that he could follow a radar echo at least as well as the girls who had been practicing for weeks. Though it had never been attempted, it was theoretically possible for two people to do the work of the three trackers. Mac could handle azimuth while Howard coped with range and—most critical of all—elevation.

  There were only ten minutes left when Alan, with as much luck as judgment, got Z Zebra approximately lined up on the runway, some fifteen miles out. The aircraft was orbiting in tight circles at three thousand feet, its pilot doubtless very conscious of his fuel gauge and wondering what was happening on the ground.

  In between reassuring messages, Alan was watching the clock and waiting desperately for the news that a controller had been located. As soon as one was found, it would take at least two minutes to rush him out to the GCD site, and he would have only a single opportunity. Z Zebra would not have enough fuel to go around again if the first approach failed.

  Up there in the stormy sky, fuel was dripping inexorably from almost-empty tanks. Soon the engine—or engines, no one had told him which—would cough into silence, and then would follow the long, whistling dive to the ground. The pilot would probably get out in safety, but how much of the taxpayers’ money would go up in smoke, and how big would be the setback to the country’s research-and-development program?

  It was too dangerous to wait any longer; the half-hoped-for, half-feared decision that had been hovering in Alan’s mind from the very beginning must now be made. And after that, there could be no going back—either for himself or for Z Zebra.

  He had never talked down an aircraft, even on a practice run. Well, now was the time to learn.

  17

  Ranger to Z Zebra,” said Alan into the mike. “I am now bringing you on to the approach. Cease orbiting and change course to zero two zero; I say again, zero two zero.”

  “Wilco,” acknowledged Z Zebra. Perhaps it was imagination on Alan’s part, but he thought he could sense the relief in the pilot’s voice. He only hoped it was justified.

  Almost at once, the distant echo on the search screen broke away from the circle in which it had been wheeling for the last few minutes. Now it was heading for the airfield, flying on the same bearing as the runway in use. It seemed an impossibly tiny target to hit from such a distance—a strip of concrete fifty yards wide, more than ten miles away…

  The problem, of course, was not really quite as bad as that. As long as he funneled the aircraft into the twenty-degree-wide field of view of the precision system, the first part of the job was done. Admittedly it was the easier part, but unless it was successfully accomplished, there was no hope of proceeding any further.

  “He’s twelve miles out,” Alan warned the waiting trackers. “You should pick him up in a minute.”

  “Are you going to try to land him?” said Howard in a shocked voice.

  “Have you any other suggestions?” asked Alan. “He has about five minutes’ gas left.”

  There was no reply from the back room. For a moment Alan wondered if Howard would volunteer to take over the job, and relegate him to the humble role of tracker. But Howard had never landed an aircraft either, and wisely stayed where he was.

  Alan gave Z Zebra one more course correction when he appeared to be drifting to the left, and rather belatedly told him to reduce height to fifteen hundred feet. A few seconds later there were simultaneous shouts from Mac and Howard.

  “We’ve got him! Too high, and well off to the left.”

  “OK. Start feeding me information.”

  As reluctantly as a man lowering himself into an electric chair, Alan moved the short distance from the director’s position to the approach controller’s seat. He swiveled around until he faced the meter panel; scores of times he had sat here, checking the readings on the handmade scales while one of his mechanics adjusted the calibration. But he had never dreamed that the time would come when he would have to use these meter readings and convert them into instructions to a pilot. It was not his job, he had never learned it, and it seemed highly unfair that he should have to do it. He did not even know the precise meaning of some of the controller’s patter: “Check gyro,” for example, was a mystic incantation whose exact purpose he had never bothered to ascertain. As to allowing for drift and suchlike navigational minutiae—well, he might be able to do it with paper and pencil; but certainly not in his head.

  This spasm of annoyance lasted no longer than the moment it took Alan to settle himself comfortably before the controller’s panel. By the time he had checked the readings on the range, elevation, and azimuth meters he had already arrived at a less egocentric view; the person he should be sorry for, he told himself, was the unfortunate pilot wandering around up there in the clouds.

  “Z Zebra,” he said, his voice as full of confidence as he could make it, “I have you on approach control. Change course ten degrees right; I say again, ten degrees right. Maintain height at fifteen hundred feet. How do you receive me? Over.”

  “Receiving you loud and clear,” answered the pilot. “Changing course ten degrees right. Over.”

  Somewhat late in the day, it occurred to Alan that he should have warned the pilot what to expect. He must be completely mystified, unless he had already heard of GCD. But there had been no time for any explanations, and perhaps it was just as well.

  That ten degrees right was not sufficient, Alan saw at once. He gave an extra five, then told Z Zebra to leave his receiver on and not to acknowledge further instructions. From now on, Alan would be doing all the talking.

  He was no longer aware of time or space, except as seen through the three meters that occupied his entire field of consciousness. Even his own identity had ceased to exist; he had merged himself into all the controllers he had ever seen sitting in front of this panel, and was using all the skills he had unwittingly absorbed as he watched them work. He had almost forgotten that these moving pointers wrote the fate of a valuable aircraft and a still more valuable man. It was better to think of this purely as a kind of game, like getting a dart into the bull’s-eye. But perhaps golf was a closer analogy—and he had to hole in one…

  In the back room, Howard and Mac had also submerged their personalities into the machine. Mac’s task was relatively simple, since he was tracking only in azimuth, but Howar
d had become a veritable one-man band. Not only was he tracking simultaneously in range and elevation, using one hand for each control, but he was also monitoring the whole approach, prepared to warn Alan if anything went seriously wrong. He had the gravest doubts about the entire proceedings, and thought that Alan was a fool to attempt such a feat. Yet at the same time he could see no alternative, and wondered if he lacked guts because he hadn’t volunteered for the job.

  The echo was six miles away when Alan got it reasonably lined up with the runway, though it was still much too high. A few seconds later it flew into one of the bands of rain that had been the cause of all the trouble, and they caught only glimpses of it through the sparkling fog. They were tracking by guess for half a mile, but Howard thought it as well not to let Alan know. If he realized that his information was dubious, it might ruin his confidence. Luckily, when the aircraft emerged from the obscuring haze, it had drifted less than a hundred feet from the assumed position, and the back room corrected the error so smoothly that even an experienced controller would never have known.

  It seemed to Alan that the plane was coming in unusually fast, even for a fighter; the range meter was clocking off the miles at a startling rate. Five miles from touchdown, the aircraft entered the glide path; at this speed of approach, the normal five-hundred-feet-a-minute rate of descent would be nothing like enough. With a silent prayer, Alan radioed: “Reduce height at a thousand feet a minute.”

  That would bring him down to the ground in ninety seconds. It was a horrifying thought, but little more time was available. Z Zebra was no leisurely Anson or Oxford, stooging gently down the sky at a modest two miles a minute.

  “You are four miles from touchdown,” said Alan. “Check wheels and flaps.”

  Perhaps he’d said that before, but it was a good idea to play safe.

  “You are getting a little low. Reduce rate of descent to fife hundred feet a minute.”