# Calling all statisticians.. Airplanes and Meteors.

Does anyone know the probability of a meteor knocking an airplane out of the sky? Has it already happened? Have there been unexplained accidents where this has been given as a probable cause?

For starts, there are no meteors in orbit at the altitude that planes are flying. For that matter nothing is in orbit at that altitude for the same reason that planes are not in orbit - that altitude is within the Earth’s gravitational force. It would follow that any meteor that is present in the sky at that altitude is one that is falling to Earth. Therefore, the likelihood of a plane being hit by a meteor is the same as the likelihood of a given place on Earth being hit by a meteor. I couldn’t give a number, but it would have to be infinitesimally small.

That’s not quite true. Earth gravitational field extends something like 25,000 miles from the Earths surface. An object can’t be in orbit unless the Earths gravity is holding there like a tetherball cord.

Planes are not in orbit because they their engines require air to function.

Meteors are not in the atmosphere because atmospheric friction prevents them from maintaining orbital velocities. They either burn up or slow to the point where they fall from the sky.

Wow, earth’s gravity only extends 25,000 miles out huh? I hope nobody tells that to the moon or it might decide to wander off once it finds out that it is free to go

…i.e. chunks of space rock hitting a plane as they fall toward earth.

Airliner impact

I guess I was referring to a meteorite but I didnt think a meteor became a meteorITE until after it hit the ground.

IANAS, although IAAPilot, and I’m not aware of a meteor, or a meteorite, ever hitting a plane. (IIRC, a meteor is the chunk of rock out in space, meteorite is while it’s burning up in the atmosphere, and meteoroid is if it survives and impacts the earth.)

I’d say the odds are about the same as winning a few lotteries in a row.

Woops. Meteorite is, indeed, once it has fallen to earth. Meteoroid is the rock in outer space.

Sorry, I mis-spoke. I was thinking of being subject to enough gravity to bring it to Earth.

My impression is that if a plane’s engines fail the plane will come crashing to Earth, even at full altitude. Is this not true? If it is, than a meteor, lacking an engine will fall to Earth from this same altitude. Though I guess it would depend on the speed at which they are traveling (against gravity, that is).

At which point does the atmospheric friction burn them up? Is it after the point of a plane’s altitude?

Um, certainly with smallish planes, it’s possible to land them without the engine; the pilot keeps the plane in a dive to maintain airspeed, then levels out quite close to the ground (of course this does also rely on there being a suitable landing site reasonably close by).
Not sure if this would work with a commercial airliner as the stresses involved in levelling out after such a dive might be more than the plane’s structure could endure.

I would assume that most of them burn up well before it reaches the altitude of commercial airliners, but certainly a few of them keep burning at or below that altitude. Depending on their size and what they’re made of.

No, the “dive” part is misleading. Losing engine power does not mean you fall out of the sky like a meteorite to the ground. For smaller planes, you keep and airspeed of around 70 mph. This is maybe a couple degrees nose low, and isn’t a dive in any sense of the word. From the cockpit, it doesn’t look much different from flying with the engine. For airliners, it’d be the same way, although their nose may be a bit lower on the horizon. But it wouldn’t be in any sort of “dive,” at least, as I picture a “dive.” The real danger to losing your engines in an airliner is losing your hydraulic pressure along with them. The Sioux City, Iowa crash showed this. The guy could only control the direction of the plane using his engines, which, fortunately, still worked.

Um…Yeah, I guess I kind of pulled that number out of the air. But you get the idea.

The diference between an airplane and a meteor (or the space shuttle) is that an airplane uses the engines pushing the wings through the air to counter gravity with lift. The plane is sort of orbiting the earth but it isn’t stable. As soon as the lift goes away, gravity starts to pull it closer. An object in orbit uses its speed to create centrifugal (sp?) force to counter gravity (like swinging a bucket of water over your head). Like the bucket, if the object slows its orbital velocity, it falls to Earth (or the water lands on your head).

Depends on the speed, size and composition of the meteor/meteorid. Some obviously never burn up completely and hit the ground. Most burn up high above an airliners maximum altitude. The atmosphere still goes for many miles above the (30,000??) or so feet an airliner flys at.

At 10,000 mph, a rock hitting even the thinest atmosphere creates a lot of friction. That friction both burns up the meteor, and slows it, pulling it out of orbit.

I found a statement by someone claiming that: although the annual number of meteorites is usually estimated at 500, the real number is 50,000. I will use the 50,000 figure. Assume that an airplane has an average horizontal cross section of 200 feet by 200 feet = .04 miles by .04 miles = .0016 square miles. The surface of the earth is 4 pi r squared = 200,000,000 square miles. Assume that there’s an average of 5000 airplanes in the sky at a given moment. Then the expected annual number of meteorites hitting a plane = 500050,000.0016/200,000,000 =.002 = 1/500. That’s one hit every 500 years.

I have a feeling that this estimate may be on the high side. I could have used a much smaller number for the estimated number of meteroites. EVen if 50,000 is technically correct, many of them might be too small to bring down a plane. I also suspect that the assumed cross-sectional area of 40,000 square feet is unrealistically high. So, I would say that the chance of a meteor bringing down a plane in a given year is well under 1 in 500, perhaps as low as 1 in 50,000.

Your 30,000 figure is right on the money. That 25,000 figure seems a bit silly now, especially considering (and correct me if I’m wrong) that the Earth’s gravity (technically) affects all bodies on the planet and in space.

:rolleyes: No, airplanes do not “come crashing to Earth” with an engine failure. Way back in flight school I was told to think of it as moving from avgas power to gravity power. As long as the airplane is moving forward with sufficient speed it will remain controllable and can land safely, provided there is a suitable place to do so nearby. In fact, gliders and sailplanes do this on every landing.

No, no, no! Completely unnecessary to “dive”. In fact, a pilot is supposed to minimize altitude loss during this procedure, which is the opposite of what is implied by “dive”. In a no-power landing you try to maintain as normal an approach and landing as possible.

Yes, it can work. In fact, it has been done. Search on “Gimli Glider”. It was an Air Canada plane, a 747 or 757 or some such, that ran out of gas at 30,000 feet, result in complete loss of power. Lucky for those on board, one of the pilots was into competitive gliding as a hobby. No published “best glide” for the plane, so he had to guess at the value. Most everything on the panel was dead, but a significant difference betweent his and the Sioux City accident was that the crew still had full control of the flight controls. Since the pilot had no flaps available he had to land it in a forward slip, which is something I don’t had ever been seen in a plane that size. Landed safely with no injuries to any on board. Due to a lack of power the nose gear failed to properly extend and lock and collapsed after landing, causing the only damage in the incident. Air Canada had a crew of mechanics out to the landing site, fixed it, and had it flying again in a day or so. Last I heard (winter of 1999) the airplane is still in service today.

As further proof you don’t need an engine to land safely - the space shuttle lands as a glider. Yes, that’s right folks - it goes from Earth orbit to touchdown without using the engines. They use power to knock it out of orbit then rely on controlled use of gravity to get home. Yes, it glides like a brick, but it still works.

So now that several experts have chimed in, are my assertions in my first post true or not? Specifically

1. that the number of meteors that are to be found at plane altitude are the same (or at least roughly similar) to the amount that eventually land on Earth, and therefore

2. the likelihood of a plane being hit by a meteor is (roughly) similar to the likelihood of a same sized building being hit by one.

(Aside: several posters - pilots, no doubt - have focused on my statement that a plane without power will come “crashing” to the ground. What’s relevant here is whether it will land or orbit).

IzzyR, I’m no expert (but I did take a year’s worth of astophysics in college), but I think your assertions are pretty good.

1)Meteors that get down to 30,000 feet or less would have had to survive the ordeal of a hundred miles or so of atmosphere. This means lots of friction, robbing the meteoroid of speed, and trying to burn it up. I doubt that the last 5 miles would make any difference. And there’s no way it’s going to stay up there, or leave the earth after that.

1. pretty much follows