Why Airplanes Can't Land In Fog in San José
The foul weather and lack of proper equipment at the Juan Santamaría (San José) international airport has caused a headache and financial loss for airlines and thousands of customers who saw their trip to Costa Rica extended for hours, to the next day in many cases.

Fog, a typical problem in the month of November, has been the cause of additional costs to the airlines and for travellers during the past week, as more than 20 flights have been diverted to other airports and a dozen or more cancelled.

The problem has been constant during the past week as fog sets in at night, instead of the usual rain, and the airport has had to be shut down, with no flights taking off or landing, on at least three nights, while on other nights delays have been for more than 2 hours.

The economic loss to the airlines and the inconvenience to passengers is incalculable.

Spent fuel to circle San José or land in an unscheduled airport - Nicaragua and Panama are the most common - add costs to airlines, not to mention the problems with staff and the cost of hotels rooms, meals to accommodate passengers and the loss of an airplane from the regular schedule.

A number of flights scheduled to arrive in San José have ended up in Liberia and then off to Panama or Nicaragua when it is definite that a San José landing is impossible.

In some cases, flights have had to turn around and head back to their point of destination.

Unfortunately there is no way of  telling ahead of time if the weather condition will permit a landing at  San José  or if the fog will clears before the flight is diverted.

The stories of passengers losing their connections and/or business meetings because of the delays or having to spend hours on end in an airplane while the pilot makes a final decision to divert are endless.

One passenger who contacted Insidecostarica.com told us of the tiring night of spending three hours sitting in the cramped airplane on the Liberia airport tarmac before the pilot made the decision of one last attempt at  San José, only to end up in Panama.

In Panama, one of the passengers, of Middle Easter descent, did not have a visa to enter Panama and the inconvenience for this person to endure for her trip to Costa Rica.

So why can't airplanes land in fog in San José?

The question is not simple to answer. It is a combination of a number of things, according to experts, which are partly due to the lack of proper equipment at the airport and weather that is so bad that it's "not safe" to rely on instruments alone to make the landing.

In one answer found on a website, the statement "do you completely trust a computer?" is the best answer that pilots, especially on landings, have to struggle with and end up preferring to divert a flight rather than put their completed trust in  their computer Instrument Landing System (ILS).

The ILS system as three categories: Category I - a precision instrument approach and landing with a decision height not lower than 60 m (200 ft) above touchdown zone elevation and with either a visibility not less than 800 m or a runway visual range not less than 550m; Category II - A precision instrument approach and landing with a decision height lower than 60 m (200 ft) above touchdown zone elevation but not lower than 30 m (100 ft), and a runway visual range not less than 350 m; and, Category III is further subdivided.

Decision Height is determined by a preset absolute altitude from within the Radio, or Radar Altimiter (RADALT) which is usually around 200 feet but can be adjusted to any altitude right down to the ground. When the plane reaches decision height above the ground, the light comes on, indicating as such, and if the pilot CANNOT see the runway, they will go around and try again or fly to another airport.

f a pilot does not go around at decision height, he is usually commited to land.

Simply, 200 feet may seem like a lot, but when you're flying at 135-140 knots just to keep your plane from falling out of the air, 200 feet is nothing.

Due to the complexity of ILS localizer and glideslope systems, there are some limitations.

 Localizer systems are sensitive to obstructions in the signal broadcast and are also limited by the terrain in front of the glideslope antennas. If terrain is sloping or uneven, reflections can create an uneven glidepath causing unwanted needle deflections. Additionally, since the ILS signals are pointed in one direction by the positioning of the arrays, ILS only supports straight in approaches. Installation of ILS can also be costly due to the complexity of the antenna system and siting criteria.

Though it has been difficult to ascertain exactly what instruments the Consejo Técnico de Aviación Civil (CETAC) in Costa Rica has installed that Juan Santamaría, it can only be concluded, by the number and frequency of flights diverted or cancelled due to bad weather, it is not enough.