Variables That Affect a Smooth Landing

A perfect landing involves a stabilized approach, with precise alignment followed by a smooth flare.

You're seated at the window and about to land. You watch as the trees grow larger, cars appear closer, and roads grow wider. Your plane crosses over the airport perimeter fence, and the runway suddenly appears under the aircraft. You might reach for the armrest in preparation for landing, but the touchdown is nearly imperceptible. The landing was perfect. Behind the flight deck door, the flying pilot is silently (or overtly) pleased with their effort. What might have contributed to making this landing so buttery smooth? Well, a smooth aircraft landing, often called a "greaser," is a gentle touchdown, but a truly safe landing prioritizes accuracy and control over simple softness, involving precise timing of the flare (gentle nose-up to slow descent) and touchdown within the runway's target touchdown zone, using aerodynamic braking before wheel brakes, with experienced pilots knowing a firm landing is often safer than an overly slow, floating "greaser" that risks runway overrun. Key factors are controlling airspeed, maintaining the centerline, managing descent rate with power and pitch, and timing the flare perfectly as the runway appears to grow in size.

Severe crosswind landings will test a pilot's skill because they challenge fundamental flight control.

It’s not surprising that weather  has a strong affect on the quality of any landing. Gusty winds, especially those of a crosswind that blow across the runway, typically result in a firmer landing. Passengers seated in the rear of the aircraft will also feel a side-to-side yaw after landing as the pilots use the rudder to maintain the centerline. Aside from the wind, landing on a wet or icy runway requires pilots to establish firm contact between the tires and the runway surface to avoid hydroplaning or skidding. Pilots also want to initiate braking as soon as possible under these conditions, so less effort might be given to a graceful touchdown in exchange for enhanced stopping margins.

Icy runways reduce the friction necessary for effective tire braking and nose wheel steering.

If there is snow or other freezing precipitation at the airport, pilots have to adjust landing speeds in order to account for possible ice accumulation. Small amounts of ice on a plane can result in substantial aerodynamic penalties. Landing speeds are conservatively increased to maintain a healthy margin above the stall boundary to counter this. The tradeoff is that the pilots are handling a faster approach speed onto an already icy or wet runway. In the interest of safety, pilots will primarily focus on putting the plane on the runway. A smooth landing in these conditions is a bonus.

At 5,700 feet, the main commercial runway at the John Wayne Airport (SNA) is the shortest in the US.

An aircraft's approach speed, the runway length and the flap setting used for landing go hand-in-hand. A short runway requires special consideration. Most airlines identify "short runway airports" and use enhanced metrics to determine proper landing distances. One of the stipulations of landing at a short runway airport (usually less than 7,000 feet available for a narrow body aircraft) is using a higher degree flap setting. This reduces the approach speed pilots fly and consequently reduces the landing distance on the runway. An exceedingly short runway might require pilots to land on the runway’s first 1,000 feet. This generally means there won't be as much of a flare before landing, resulting in a firmer touchdown.

The B777 landing gear is a massive, robust system featuring two, 6-wheel mains and the nose gear.

An aircraft’s design characteristics also determine how easily pilots can consistently produce a smooth touchdown. All other factors being equal, the gear configuration and ground clearance dictate how pilots can fly their plane through the flare and landing. Take, for example, a Boeing 777. Reported by its pilots to handle nicely on landing, the 777 features complex multi-wheel assemblies that form each of the two main landing gear, designed to distribute the aircraft's massive weight, provide stability, and allow for smoother landings on runways by spreading the load over more tires. These assemblies are called bogies and they’re angled at a tilt when extended in the air so that the rear row meets the runway before the four remaining tires, thus absorbing and dispersing the vertical acceleration. This gear configuration more easily allows pilots to "roll it on" or produce a pleasant landing. Most widebody aircraft feature this type of landing gear.

The B737's design requires flatter landings with higher speed and less pitch to avoid tail strikes.

By comparison, Boeing 737 pilots report more difficulty in achieving soft landings. In particular, pilots of the stretched 737-900 variant operate a long aircraft and one that requires a relatively high approach speed. B737 pilots aim for a “flat flare” and controlled touchdown, managing energy by essentially squatting down to the runway rather than floating too high. The degree to which a 737-900 pilot can flare is more significantly limited by the maximum nose-up attitude before striking the tail. A comparable Airbus A321 has substantially more ground clearance and flies at a slower approach speed for a given weight. This means those pilots have less energy to manage and a greater flare margin with which to manage this energy. The takeaway here is that flying some planes are more challenging to land softly than others. 

Cockpit view of a KLM Royal Dutch Airlines B747 coming in for a lading at Schiphol Airport (AMS).

The best conditions for a smooth landing are a constant, non-gusting headwind straight down the runway. Preferably, the runway is long and dry, and there are no buildings nearby to disrupt the wind as the aircraft approaches. Ideally, the plane is not in icing conditions, a standard flap configuration is being used and the aircraft is at an average landing weight—not too heavy, but not too light. The approach speed should be within the standard range that the pilots are accustomed to flying. The pilots should also be experienced with the aircraft and familiar with the runway elevation at which they are landing. 

Even if every condition for landing is perfect, the human factor is always at play. Every pilot will agree that landings combine skill and adjusting to environmental factors. Humble pilots will admit that the perfect landing requires not just skill, but also a touch of luck. 

Until next time…safe travels.with