9 degrees from true north
27 degrees from true north
If you’re a pilot, or even just an aviation enthusiast, you know that the numbers 9 and 27 on a runway indicate that the runway is oriented approximately 9 and 27 degrees from true north, respectively. But have you ever wondered why runways are numbered this way?
The answer has to do with the way magnetic fields work. The earth’s magnetic field is created by the earth’s molten outer core, which is made up of iron and other metals. This molten core creates a magnetic field that extends from the earth’s surface into space.
The earth’s magnetic field is not perfectly aligned with the earth’s rotation axis, however. It is tilted at an angle of about 11 degrees. This tilt is what causes the north and south magnetic poles.
Because the earth’s magnetic field is tilted, a compass will not point directly at the north pole. Instead, it will point to a location that is offset from the true north pole by an angle that is equal to the tilt of the earth’s magnetic field. This angle is called the magnetic declination.
The magnetic declination varies from place to place on the earth’s surface. It is zero at the magnetic equator (which is located about halfway between the north and south magnetic poles) and increases to about 23 degrees at the magnetic poles.
In the northern hemisphere, the magnetic declination is positive (that is, the compass needle points to the right of true north) if you are west of the magnetic meridian and negative (the compass needle points to the left of true north) if you are east of the magnetic meridian. The magnetic meridian is the line on the earth’s surface that runs from the north magnetic pole to the south magnetic pole.
In the southern hemisphere, the situation is reversed: the magnetic declination is positive if you are east of the magnetic meridian and negative if you are west of the magnetic meridian.
The runway numbering system is based on the magnetic declination at the location of the runway. For example, runway 9 at an airport in the northern hemisphere is oriented towards the east, and runway 27 is oriented towards the west. This is because the magnetic declination is positive in the east and negative in the west.
In the southern hemisphere, the situation is reversed: runway 9 is oriented towards the west and runway 27 is oriented towards the east. This is because the magnetic declination is negative in the west and positive in the east.
The runway numbering system is a simple and effective way to ensure that pilots can take off and land safely in all parts of the world, regardless of the local magnetic conditions.
Other related questions:
Q: Why is there a 27 on the runway?
A: There is a 27 on the runway because it is the designation for the runway.
Q: What do the numbers on the runway mean?
A: The numbers on the runway indicate the runway length available for takeoffs and landings. The first number is the length of the runway available for takeoffs, and the second number is the length of the runway available for landings. For example, a runway with a length of 8,000 feet would have a takeoff length of 8,000 feet and a landing length of 8,000 feet.
Q: How do you determine runway orientation?
A: The runway orientation is determined by the approach path of the aircraft.
Q: What is the slope of runway 9?
A: The slope of runway 9 is 2.5%.