Ask the Captain: Do you have to see the runway to land in fog?
Question: When an airplane lands in fog on instruments, does the pilot have to be able to see the runway?
— Submitted by reader Carole Hayter, Monterey, Calif.
Answer: It depends on the type of airplane. There are some airplanes that are certified to land when the pilot cannot see the runway until a couple of seconds before touchdown. These highly automated airplanes use redundant computers to fly the approach, flare the airplane, land and track the center line.
The lowest visibility in which I landed was Seattle in thick fog — we did not see the runway until we were already flaring for touchdown. We had trained for this condition many times and it was good to see the training and sophisticated automation allow us to safely get our passengers to their destination in spite of the fog.
Q: Is visibility/dense fog a big problem for flights taking off?
— Krishna, San Francisco
A: All airports have visibility requirements for takeoff. The required visibility depends on the type of runway lighting and obstacles. The normal minimum visibility for takeoff at a major airport is 600 feet visibility on the runway. With very specialized equipment and training it can be reduced a bit below that, but it is rare. If the fog impairs visibility below the necessary requirement, operations are affected. Otherwise pilots train to fly in low-visibility conditions and mitigate the problems caused by fog.
Q: We were recently stuck at the airport in San Diego due to fog. Planes were unable to land due to the fog and diverted to Ontario to refuel and wait for conditions to clear. Why can planes take off in the fog (we watched quite a few leaving) but are unable to land?
— Cymberle, San Antonio
A: The visibility requirement for takeoff is less than for landing. In San Diego, the pilots must see the runway prior to landing. Some other airports have very low visibility requirements for landingm but San Diego requires approximately one mile of visibility.
Q: In your recent column about avoiding turbulence, I found one part misleading: If you’re out over the water on the track, you can only deviate so far before you impact the next track. Even with Captain’s emergency authority, you risk reduced separation or worse.
— Dave Jackson, AA international captain
A: A track is an “airway” over the ocean. They vary from day to day due to the winds. The Atlantic Tracks flow one way in the morning from Europe to the U.S., and reverse in the evenings. They are designated as Track A, Track B, Track C, etc., with coordinates provided in the flight plan.
If the turbulence is known or forecast, the tracks can be moved, or a re-filing of the track is possible. There are limits on the deviation in a track environment, but avoiding areas of thunderstorms is still done.
John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.