There are more than 13,000 light fixtures blinking and twinkling on the airfield at George Bush Intercontinental Airport (IAH), including a special set numbering from 9,000 to10,000, which are specifically designed to keep the airport running safely and smoothly during the foggiest days.

They are part of a procedure known as the Surface Movement Guidance Control System or SMGCS for short. The system is activated when visibility drops below 1,200 feet or about a fourth of a mile.

“The system monitors how far a pilot can see down the runway,” says Ken Whittakar, operations supervisor for Bush Airport. “When the technology is in use, it measures particles in the air, such as water then relays that information to the control tower, which relays it to the flight crews aboard the planes.”

Once the system is activated several procedures take effect.

Runway guard lights at so-called hold positions begin to flash, notifying pilots if they’re cleared to access the runway. Specific taxi routes are established for pilots to follow. Lighting inspections on the runways and taxiways increase from three times a day to once every two hours.

All non-essential personnel are required to leave the field and all fire station doors are required to remain open during the SMCGS activation.

Electronic monitoring devices are stationed at both ends of the runway and in the middle on each of the five runways that operate at IAH. Generally the foggiest periods during the year occur between November and February; however SMGCS has been activated several times already this year.

Pilots flying into Bush - which is the 7th largest airport in the US in terms of total passengers – must be instrument trained.

However, at an airport that routinely handles more than 1,800 flight operations a day cruising down the runway or taxiway can turn tricky in low visibility.