Atmospheric Moisture and Clouds

What are the effects and hazards of fog in aviation? How did a low visibility day lead to two planes colliding on the runway?

Fog is a cloud that rests low on the ground and it causes reduced visibility conditions. Fog is formed either by air being cooled below its saturation point or by water vapor being added to the air by evaporation resulting in moist air mixing with dry air. Radiation fog forms mostly on clear nights when there is a thin moist layer near the ground that has a layer of drier air above it. The moist layer of air does not absorb much of the Earth's infrared radiation and this "causes a surface inversion with cool air at the surface and warmer air above it..."(Ahrens & Henson, 2018). The lower moist layer of air becomes saturated and fog is produced.

Radiation fog puts aircraft at bigger risk during ground operations because of the low visibility conditions that are produced. Pilots must be extra cautious while taxiing, taking off, and landing in radiation fog because they may become disoriented or even become lost in the fog. Taxiing becomes more dangerous because, in reduced visibility, it becomes harder to identify your surroundings. Taking off becomes more dangerous because, if the radiation fog is dense enough, the pilot may not be able to see more than a couple of hundred feet down the runway that they are taking off of. Landing becomes more dangerous because again if the radiation fog is dense enough, the pilot may not be able to see how high or how low they are in relation to the runway and they may land too early or too late. Luckily, thanks to modern technology, more advanced aircraft have an autopilot that aids in the operation during poor weather conditions.

On December 3, 1990, two aircraft collided on a runway after one aircraft got lost in heavy fog, taxied onto a runway, and taxied into the takeoff path of another aircraft. "Official Edward McNamara said the fog was so thick at the time of the crash that firefighters failed to see the damaged plane after reaching the spot where the 727 rolled to a halt after aborting its takeoff. He said he was told by officials that visibility was about 100 feet... Jerry Linton, who oversees air traffic controllers at the airport, said he thought weather played a role in the crash. "It was very, very foggy," he said. "Both planes were not observable from the control tower."..." (Robinson, 2018).

References

Ahrens, C. D., & Henson, R. (2018). Meteorology today: Introductory weather climate & environment, 12th Edition. Mason, OH: Cengage Learning.

Robinson, L. (2018, October 26). 8 killed, 22 hurt as 2 jets collide on Detroit runway. https://www.baltimoresun.com/news/bs-xpm-1990-12-04-1990338076-story.html

Smithsonian Channel Aviation Nation (Director). (2020, December 17). Two planes collide on a foggy Detroit runway. https://youtu.be/AEFowmslWAk