Is a smooth airplane touchdown always the safest landing?

Have you ever wondered why one flight lands with a thud while another feels like it’s landing on a cloud?

A soft, smooth landing is undoubtedly the best way to end a long flight, but it might come as a surprise that a “butter soft” landing is not the pilot’s objective. The ultimate goal is a safe landing. It’s also one of the most challenging aspects of learning how to fly.

Boom engineer and certified flight instructor Mike Tuccio says, “You can think of flying an aircraft like riding a bicycle. It’s easy to maintain stability and direction when you have a constant speed. But when you slow down, it’s more difficult to stay upright; it’s harder to control. As an aircraft approaches landing and slows down, even small variables make a huge difference. It’s when training kicks in.”

If you’ve ever wondered what goes into a safe landing, here’s a quick look at the factors pilots weigh when landing large, commercial aircraft at major airports.

Runway Length: Not all runways are the same.

The distance an aircraft has available for landing and coming to a full stop varies by runway. How much, exactly? Take, for example, two major American airports. At Denver International, runways are about 12,000 ft., while at Chicago’s Midway Airport they are between 5,000 and 6,000 ft.

Touchdown Zone: Landing in the correct area of the runway.

At commercial airports, a typical aircraft landing threshold is one-third of the runway or 3,000 ft. (whichever is shortest). Aircraft should touchdown in this optimal zone. (Even with a long runway, policies limit what portion of the runway is actually available for landing.) Most landings on a very short runway are firm because there is a shorter touchdown zone. If an aircraft misses its touchdown window, the pilot will likely do a go around (abort the landing and climb back up to try again).

Environmental Factors: It’s all about the weather.

Have you ever been on a plane that seems to be landing sideways? Your pilot might be “crabbing” or “slipping,” which we’ll discuss below. It’s just one of the factors that could make your landing a little bumpier than expected. Your pilot might be dealing with:

Gusty winds

As the name suggests, gusty winds are unpredictable, sudden increases and decreases in wind. Often, pilots will fly at a higher speed to compensate for the increases and decreases of the gusts.

Excessive crosswinds

Defined as a 90-degree crosswind from the runway heading. Every aircraft has a maximum demonstrated crosswind limit that’s designated by its manufacturer. Commercial airline pilots likely won’t attempt landing if crosswinds exceed that number (also, an airport might close one or all of its runways when winds get this strong). If it’s deemed safe to land, pilots might use “crabbing” and “slipping.”

A) Crab (aka weathervaning or crabbing), which gets its name from how crabs walk sideways. The aircraft’s nose turns into the wind. (It’s not pointing down the centerline of the runway.) This counteracts the crosswind while preventing the aircraft from drifting off centerline of the runway (hopefully putting it in the touchdown zone). Watch a Turkish Airlines Airbus A330 Drift land in extreme crosswinds in Düsseldorf, Germany.

B) Side-slip (aka wing low or slipping), which is when an aircraft’s nose is pointing down the center of the runway, but one of the wings is lower to counteract the crosswind. The upwind wheel may touch down first. The downwind wheel will touch down further along the runway. A pilot in a large aircraft is unlikely to use an excessive amount of side-slip because of the risk of the wing tip or engine hitting the runway. For another look at aircraft landing in crosswinds, watch a TUI Airways Boeing 757–200 land during a storm in Bristol, England.

Wet runways (aka contaminated runways)

Water, snow and ice can reduce the braking action of an aircraft — thereby increasing its stopping distance (how much runway needed to slow down).

Grooved or ungrooved: Not all runways are created equal, and ungrooved runways require firm landings because surface water can result in hydroplaning. Most major runways are grooved in the U.S. for this reason. If an ungrooved runway is dry, this isn’t a factor.

CAVOK

Are the Ceiling and Visibility OK? This acronym sums up two weather-related terms you may have heard on the news. When visibility is reduced significantly due to weather conditions such as fog, a manual landing will be more challenging.

Type of Aircraft: Size, load and model matter.

Every aircraft has a different approach speed, with the Boeing 737–900 having one of the highest among commercial aircraft. Generally speaking, heavier aircraft require greater speeds at landing to avoid stalls.

Glide Path (Slope)

A pilot’s goal is to always have the correct glide path for the runway — and they’re all different. Runways with approaches over steep, mountainous terrain might have a different glide path than those over water or fields. However, the majority of runways have a 3 degree glide path.

For Tuccio, weather conditions often determine what a student will practice on any given day. If you’re learning to fly and there’s a chance of wind, it’s a no-go kind of day. As students gain experience in winds, they will fly in different conditions; it’s a gradual learning process.

“Some airports are notoriously challenging and others less so,” explained Tuccio. “The Telluride Airport in Colorado is known for its winds, and it’s built on a cliff. Winds blow over the edge of the cliff and swirl across the runway. It’s like the wind is trying to roll your plane. But when you have the correct experience and knowledge, you can execute a good, safe landing. When it comes to landing, experience matters.”