Rudolph the red-nosed reindeer had a very shiny nose, and if you ever saw it, you would even say it glows. Late one foggy Christmas Eve, Santa came to say, “Rudolph, with your nose so bright, won’t you guide my sleigh tonight?” Rudolph declined, noting that when flying around in foggy conditions, a bright red light for a nose wouldn’t do a thing.
We’ve all been in Santa’s position that fateful Christmas Eve, and can probably understand his desperation. Holiday travel is as inevitable for us as it is for the jolly old elf. Occasionally, dense fog rolls in, delaying our flights. “Why don’t the planes just put a big light on the front so we can get moving?” you might ask. But when visibility drops, taking off isn’t the main problem--it’s landing. Radio signals, not excessive lighting, solve that problem.
Rudolph didn’t have a radio beam transmitter in his nose, as far as we know.
By definition, a dense cloud of water droplets that reduces visibility to less than a kilometer is considered fog. When it blankets a tarmac, flight delays result from the safety protocols we have put in place for our planes. When taking off or landing, the space between planes has to be nearly doubled to make sure no one hits each other. Think of it like driving in bad weather—you wouldn’t ride the tail of a car in "pea soup" fog conditions.
Thanks to technology, it’s easy to fly when pilots can’t see. They call it IFR—or Instrument Flight Rules. Sophisticated knobs and buttons and computers direct the soaring aluminum tube towards its destination. And those instruments are even more crucial during landing. If the pilots can’t see, the instruments on board substitute as eyes. Everything gets trickier when fog is involved.
When pilots are coming in for a landing under IFR, airports guide them onto the runway with Instrument Landing Systems, or ILSs. These systems are basically radio transmitters that send beams of different frequencies out vertically and horizontally. When a plane's computer picks them up, it can determine its location relative to the ground by calculating the difference between these two frequencies. The airport modulates the beams to give the pilots the best approach, and the pilots (or autopilots) can land the plane like hitting a target in cross-hairs. (You can watch a nice little animation of how this system works here.)
Airports of different sizes have different ILSs. Larger airports have higher resolution systems, meaning that pilots can more or less land blindly on a runway. At smaller airports, they have a window to decide if they can make the runway or not—given the resolution they can see from their ILS—and have to turn around for another pass if it looks too dangerous.
What this all means for Rudolph the nasal abnormality is that Santa had no use for him. Without instruments to guide all aspects of his flight, Santa could neither take-off or land safely in fog. In fact, considering that Kringle would be traveling at hundreds of miles per second, he would need an absolutely state-of-the-art ILS, unlikely to fit in the snout of an arctic caribou.
Though it made all the other reindeer love him, a bright red light would make no real difference in the fog—as anyone who has tried to turn on his or her car's high beams to shoot through the stuff knows. And in most countries, the use of so called "fog lights" is entirely cosmetic, and there is no legal requirement to own them. So, a bright light in a dense Christmas Eve fog would have likely reduced Santa’s visibility even more, making the jolly man that much more reliant on airline instrumentation.
If we must keep around the fable of the little reindeer who found his place at the front of a flying sleigh, I propose a change to the song: “Rudolph the Red-Nosed Reindeer had an Instrument Landing System Category III B…”
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