Question: How does a pilot land a plane during heavy rain and low visibility?
— Submitted by reader Samuel, Jakarta
Answer: Pilots use precise navigation equipment, usually the Instrument Landing System (ILS), to maneuver the airplane laterally and vertically to land on the runway. If an ILS is not available, GPS or other navigation aids are used.
A high-quality ILS combined with special equipment onboard can allow pilots to safely land when the visibility is very limited.
Q: We were recently departing from Fort Myers (RSW) and flights were delayed from landing due to fog. This delay created a cascade of problems such as diversions for refueling, flight crews “timing out,” gate changes, flight changes, etc. With modern avionics, radar, GPS, etc., why can't aircraft land in the fog?
— John Kersh, no location given
A: Low-visibility landings depend on many things. The runway navigation facilities (the ILS), runway lighting and approach path must be specially certified for low-visibility landing. Pilots are required to visually see the runway at 200 feet and ½ mile out unless there are special Category I, II or III procedures available. Airports such as RSW do not have this capability.
The landing visibility requirements are ½ mile or 1,800 feet runway visual range (a special visibility monitor). If the pilot cannot see the runway when they descend to 200 feet, then they may not land.
Large airports such as ATL, SEA, ORD, JFK and others have Category III equipment available. Airplanes that are specially equipped and certified with certified crews may land with as little as 300 feet visibility.
We landed in SEA very late one night when the visibility was 300 feet. The airplane was flown by the autopilot/autothrottle system during the approach all the way to touchdown and roll-out. We did not see runway until we were over it at less than 50 feet. It is very impressive technology.
Airplanes can land in the fog, but not all airports and airplanes are equally capable.
Q: Hello, Captain Cox. On a perfectly clear day, would an airline pilot landing his/her plane prefer to do a visual approach or an ILS landing? Or is it up to air traffic control?
— Fang, Massachusetts
A: Pilots prefer a visual approach backed up by the ILS to ensure proper lateral and vertical guidance. Air traffic control uses visual when possible to expedite the traffic flow.
Q: What are the advantages and disadvantages of RNav over ILS?
— Merrill, Miami
A: RNav, or Area Navigation, approaches provide more lateral freedom and do not require ground navigation aids. Almost any runway can have an RNav approach. The visibility requirement for RNav approaches is higher than for an ILS.
The Instrument Landing System (ILS) is a ground-based, very accurate means to align the airplane with the proper lateral and vertical paths. It is more expensive than RNav, but is more accurate.
John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.
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