You’ve probably wondered how high planes can fly, but at some point you might have also wondered just how far you can see from a plane when you’re tens of thousands of feet up in the air too.
While the exact distance you can see from a plane is impossible to calculate, if we assume that the earth was perfectly spherical with a smooth surface, we can deduce that you can see between 200 and 250 miles from a passenger plane at cruising altitude.
Theoretically, you can calculate how far you can see from any height using the following formula:
D≈1.22√h
D = visible distance
h =height above sea level
According to the formula:
At 30,000 Feet: You can see 211 miles from a height of 30,000 feet.
At 35,000 Feet: You can see 228 miles from a height of 35,000 feet.
At 40,000 Feet: You can see 244 miles from a height of 40,000 feet.
This formula uses trigonometry to calculate visible distance. It calculates this distance from the observer to the line at which the earth’s surface and the sky appear to meet – i.e. the horizon.
In actuality, the visible distance will be lower than this estimate for several reasons.
Factors That Determine How Far You Can See From a Plane
Shape of the Earth
The above equation assumes a uniformly spherical earth.
In actuality, the earth is not perfectly spherical since it bulges near the equator, and this bulge is not even either.
Further distortions are caused by the uneven distribution of the earth’s continents.
As a result, how far you can see into the horizon also depends on which direction you’re looking from.
If you face east or west, the horizon will look much further away than if you looked north or south.
The mathematical model above also assumes a smooth earth with no surface distortions.
This assumption is also inaccurate, since the earth’s surface contains mountains and valleys that give the earth a rough surface.
The distance you can see from a plane is also affected by the presence of any tall objects.
For example, a 10,000 foot-tall mountain may be visible above the horizon’s edge when seen from 30,000 feet in altitude.
Even the Ocean’s surface is not perfectly smooth, as the tide can create bulges on the earth’s ocean surface.
Behavior of Light
Light does not always travel linearly, especially at large distances.
Atmospheric conditions, like refraction, can reduce or increase the visible distance from a plane.
Refraction occurs when denser cold air forms above less-dense warm air.
This usually occurs over oceans since the warm water currents keep surface temperatures high.
When light passes from warm air to cold air, it gets slightly bent.
This slight bending of light rays is known as ‘atmospheric refraction’ and increases a light ray’s distance when reaching the eye.
Atmospheric refraction makes light appear to curve over the horizon, which could permit you to see slightly further than the horizon, especially if you see a tall object.
The overall effect of atmospheric refraction is to make tall objects appear further away because light travels a greater distance to reach your eye.
Atmospheric Conditions
Other atmospheric phenomena, like clouds and thunderstorms, also affect visibility.
If a plane is flying over clouds, it’s almost impossible to calculate visible distance – you might not be able to see outside the plane at all.
The equation we used above uses a constant 1.22.
This constant is obtained through approximating the earth’s radius. The entire equation would have to change if we include cloud altitude.
For simplicity’s sake, assume the distance you see is shortened because your plane is too close to the cloud’s top layer.
Other aerial phenomena, like dust storms, high humidity and artificial pollutants, can also impact visibility from a plane.
How Far Pilots Can See (Pilots vs. Passengers)
Pilots can see further than passengers can from their windows.
The narrow size and height of a passenger window prevents passengers from seeing further than a few miles horizontally.
Unless the weather is completely clear and the passenger is standing up, they cannot see land from one of the side passenger windows.
It’s even more difficult for passengers to see at night because pilots can view beacons from afar, but passengers are usually not able to from their seating viewpoint.
While at cruising altitude, depending on atmospheric conditions, a pilot can see as far as 200-250 miles.
How Far You Can See a Plane From the Ground
How far you can spot a plane from the ground depends on several factors, primarily weather conditions.
On a perfectly clear day, you can spot a plane as far as 374km or 232 miles away.
But, this figure is entirely theoretical; it assumes that there is no air pollution, no effect of refraction or any other atmospheric effects that can impact visibility.
Practically, it is normally too difficult for people to spot planes at cruising altitude, but you can realistically spot contrails with the naked eye.
Can You See Farther From a Plane or Helicopter?
Since planes fly much higher than helicopters on average, you can see much further from a plane than a helicopter.
As the average helicopter flies at only 12,000 to 15,000 feet; the theoretical viewing distance at this altitude would be between 133 miles.
But, since helicopters are closer to the ground, you can spot more visible features on the ground when in a helicopter than when in a plane.
The speed of planes also makes it more difficult to spot an object on land from a plane than on a helicopter.
Helen Krasner holds a PPL(A), with 15 years experience flying fixed-wing aircraft; a PPL(H), with 13 years experience flying helicopters; and a CPL(H), Helicopter Instructor Rating, with 12 years working as a helicopter instructor.
Helen is an accomplished aviation writer with 12 years of experience, having authored several books and published numerous articles while also serving as the Editor of the BWPA (British Women Pilots Association) newsletter, with her excellent work having been recognized with her nomination of the “Aviation Journalist of the Year” award.
Helen has won the “Dawn to Dusk” International Flying Competition, along with the best all-female competitors, three times with her copilot.
