Low Visibility Operations (LVO) create a hazard to aircraft taxiing around an airport, especially when the tower can't see your location. Here's what you need to know for your next IFR flight...

Airline Disaster Narrowly Avoided

On December 6th, 1999, United 1448 made one wrong turn while taxiing in reduced visibility. It became the first link in a chain of mistaken assumptions by its crew and the tower controller. Before we get started with some learning topics, check out the following video to see just how dangerous taxiing in low visibility can be:

Take It Slow

The FAA says, "pilots and aircraft operators should be constantly aware that during certain low visibility conditions the movement of aircraft and vehicles on airports may not be visible to the tower controller. This may prevent visual confirmation of an aircraft's adherence to taxi instructions."

When in doubt, stop and ask a controller for clarification. If you're ever unsure about your position on the airport, you should stop immediately.

Heads UP... Always

If you taxi in dense fog, it's recommended to stop the airplane if you need to run checklists, adjust your flight plan, or do anything else that will focus your attention inside the airplane. While using a geo-referenced taxi chart on your EFB or MFD is a great resource, it shouldn't be your only source of location information.

This holds true for towered and non-towered airports. Be cautious when taxiing around non-towered airports. Without a ground controller aware of aircraft movement on the field, you could easily create a conflict. Give detailed CTAF radio reports of your location and progress during taxi.

Advanced Taxiway Lighting (SMGCS)

The FAA requires the commissioning of an FAA-approved Low Visibility Operations (LVO) Surface Movement Guidance Control System (SMGCS) operation for all new Category III ILS supported runways. This system provides pilots extra visual references to follow during taxi. When the visibility is below 1,200 RVR, pilots should comply with ATC ground instructions while referencing a SMGCS chart for lighting details and guidance.

The SMGCS low visibility taxi plan includes the enhancement of taxiway and runway signs, markings, and lighting, as well as the creation of SMGCS visual aid diagrams. Here are a few things thing installed at the airport under SMGCS:

• Controllable Stop Bar Lights
• Non-Controllable Stop Bar Lights
• Taxiway Centerline Lead-On Lights
• Runway Guard Lights
• Geographic Position Markings
• Clearance Bar Lights

To handle increasing demand at busy airports during LVO, "the FAA is implementing runway safety systems, such as Airport Surface Detection Equipment-Model X (ASDE-X) and Advanced Surface Movement Guidance and Control System (A-SMGCS) at various airports." You can find more about these systems in PHAK appendix 1 or in the AIM.

Pay Close Attention To Stop Bar Lighting

You might find stop bars located at an ILS critical area hold-short markings on illuminated taxiways. Pilots are not permitted to taxi past illuminated stop bars. When an aircraft is cleared for takeoff or to line up and wait, the stop bar lights are extinguished by ATC. As the red stop bar lights go off, a segment of the green centerline lights located beyond the stop bars illuminate. This confirms your clearance to taxi onto the runway.

As the aircraft taxis on the runway, a sensor is triggered with a time delay. The red stop bars are reactivated by this sensor, and the green centerline lights are extinguished in anticipation of the next aircraft. Aircraft and ground vehicles are never permitted to travel past an illuminated stop bar. If there's confusion or a discrepancy between illuminated lights and ATC instructions, query ATC to verify the clearance.

Have You Taxiied In Low Visbility?

What's your strategy for taxiing in low visibility? Have you ever encountered fog dense enough that the tower couldn't see your location? Tell us in the comments below.