Airport Operations 101


Please use the quick links below to navigate to a specific topic:

O'Hare Airport Runways​
O'Hare Aircraft Operations
Prevailing Winds
Air Traffic Control
Glide Slope Procedures and Standard Approach Profile
White Papers​

Daily operations at an airport are divided into two groups: airside operations and landside operations. This webpage concentrates on airside operations, meaning airport operat​ions that take place within the airport security fence and on the airfield.

O'Hare Airport Runways

Chicago O’Hare International Airport (O’Hare) has eight runways which are listed below. The runway numbers are magnetic compass headings that an aircraft landing or taking off would use, so a runway numbered 9-27 faces east to west (compass headings​ of 90° and 270°).

  • 4L-22R​
  • 4R-22L
  • 9L-27R
  • 9C-27C
  • 9R-27L
  • 10L-28R
  • 10C-28C
  • 10R-28L

Current O’Hare Airfield Layout

O'Hare Aircraft Operations

Click h​e​re​​ to see an exhibit depicting annual aircraft operations at O’Hare.

Prevailing Winds

Aircraft take off and land into the prevailing winds. Federal Aviation Administration (FAA) Air Traffic Control determines which runway will be used based on wind and other weather conditions as well as ground conditions, such as runway closures due to periodic maintenance. At O’Hare, the primary runways face east to west. In east flow, aircraft depart the primary runways to the east; arriving aircraft approach from the west. Generally, east flow conditions occur during periods of inclement weather. Conversely, in west flow, aircraft depart the primary runways to the west and arrivals come from the east.

Due to prevailing winds, the FAA Air Traffic Control Tower can sometimes use the same runways for an extended period of time. At times one may notice a shift in the way airplanes fly over an area, and this is usually because the “flow” has changed and different runways are in use.

Runway usage is primarily dictated by the prevailing winds, although it is important to note that winds aloft can vary in speed and​ direction from winds at ground​ level. During calm wind conditions and air traffic permitting, it is not uncommon for FAA Air Traffic Control to approve a pilot's request to depart in the opposite direction. This is done in accordance with the latest version of FAA Order JO 7110.65.

Air Traffic Control

The FAA and the pilot-in-command of each aircraft have sole jurisdiction and responsibility for flight paths. Accordingly, only the FAA has enforcement capability over these issues. The Chicago Department of Aviation has no authority or control over aircraft in flight.

According to the FAA, helicopters have no minimum altitude requirements when weather, safety, and other air traffic permit. See Federal Aviation Regulations (FAR) Par​t 91.119​.

Glideslope Procedures and Standard Approach Profile

The glideslope is the proper imaginary path for an airplane approaching a runway that shows the vertical path a landing airplane would follow if it made a textbook descent. While aircraft can intercept the glideslope at various locations due to traffic flow, the aircraft is typically on the glideslope before reaching the Final Approach Fix (FAF). The FAF is typically located between four and six nautical miles from the end of the runway. The 3.0 degree glideslope has been determined by the FAA to be the optimal approach glideslope angle for all aircraft from an operational safety perspective.

For O’Hare the 3.0 degrees could only be increased to the maximum allowable (3.1 degrees) in order to clear obstacles. There are no obstacles in the runway approaches at O’Hare, therefore given this fact, and the types/sizes of aircraft serving O’Hare, all O’Hare approaches operate with a 3.0 degree glideslope angle, and are required to operate in that manner.


The below table lists standard arrival altitudes for Runways 9R and 27L at 2, 3, and 4 nautical miles from the runway threshold for a typical day on a 3.0 degree glideslope.

White Papers

White Paper – Air Traffic B​asics
White Paper – Parallel Runways​
White Paper – Converging Runway Operations​

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