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Slam Dunk

After the Asiana crash, some speculated that the pilots were attempting a slam dunk–style landing. In pilot jargon, this refers to approaching the airport at a higher-than-normal altitude and then quickly descending to get into a stable position prior to landing.

"It largely depends on what airport you're going into and what the airspace is looking like, but sometimes [air traffic control] will ask you to do a higher or short approach," says former airline captain Greg Zahornacky, an assistant professor at Embry-Riddle Aeronautical University. "It's a higher descent rate from a higher altitude."

The procedures followed during a slam dunk are the same as any other approach, Zahornacky says. Pilots select a good rate of descent that allows them time to deploy landing gear and flaps, and be stable at around 1000 feet of altitude. Pilots do not consider a slam dunk to be dangerous, though it is a bit more difficult than a standard arrival.

"Ideally, if it were up to you, it would be a more gradual descent," says Patrick Smith, an airline pilot for more than 20 years and author of Cockpit Confidential: Everything You Need to Know About Air Travel: Questions, Answers, and Reflections. "So it's tricky in the sense that you've got to manage the plane's momentum during descent to make sure you can get down per [air traffic control's] instructions and be stabilized at the bottom of the descent to go ahead and finish the approach."

Slam dunk or not, pilots look at the same metrics to ensure a safe landing. "Your final approach to the runway always has to be stable, and there's certain criteria that all pilots have to maintain," Smith says. "If you're not in those parameters you break off and go around," or abort the landing and regain altitude ahead of a second attempt.

Gusty Crosswinds

Landing through crosswinds, or winds not aligned with the runway, make any approach a little harder. Smith says certain airports are notorious for their crosswinds. Those include Keflavik International Airport in Iceland, LAX in Los Angeles, and Logan in Boston.

A bit of extra speed during the approach helps cut through the wind. To gauge the appropriate amount of additional oomph, pilots refer to what's called a crosswind component chart. "We use a formula for how much speed we have to add to the approach," Smith says. In general, commercial aircraft come in at an approach speed of 130 to 150 knots. Smith says they might add 10 to 15 knots (12 to 17 miles per hour) on top of that on very windy days. As wind speeds change, pilots also adjust the plane's thrust up or down to keep pace.

"Very strong winds always make a landing more challenging, and if the winds are crosswinds that makes it more challenging still," Smith says. "But every plane has a maximum crosswind component. If the crosswind gusts exceed a certain amount, you can't land."

Since a crosswind wants to push a plane away from the center of the runway, pilots steer into the crosswind to offset the drift. To compensate for the wind, the pilot manipulates the ailerons, usually on the wings' trailing edges, to control the plane's roll, as well as the rudder, which controls the yaw. As a result, a plane landing in a gusty crosswind might not be perfectly level when it touches down on the runway.

"You put one set of landing gears down first—you're landing crooked," Smith says. "People might feel the plane hitting on one side before the other and think it's a mistake, but it's not." Smith says the technique itself is "a little tricky to master, but you get used to it." What's more, he says, windy situations produce turbulence that can make things very bumpy for all involved. "The landings can be a little squirrelly."

Sharp differences in wind speed over a small area—known as wind shear or microbursts—used to be a major problem for airplanes, and were implicated in disasters such as Eastern Airlines Flight 66, which crashed as it headed into John F. Kennedy International Airport in 1975. Nowadays detection technologies at airports and on planes themselves, as well as better avoidance of heavy storms, have vastly lessened the threat of windshear. "Those kinds of accidents for the most part have disappeared," Smith says. "Wind shear can be seen and predicted, and crews warned accordingly."

Short Runway

Another landing scenario that requires some additional pilot awareness is a short runway. "You do tend to concentrate a little more on short runway approaches," says Smith. "There's less margin for error." At LaGuardia airport in New York, for example, the runways are only 7000 feet long because the airport is pressed against the water. Ronald Reagan Washington National Airport's longest is 6869 feet. Runways at other airports typically run a few thousand feet longer.

Smith says that pilots try to land at the slowest possible speed to compensate for less runway real estate. These speeds are not decided arbitrarily but are based on the aircraft's weight, flap-setting options, and other variables. Ultimately, the approach plan will guarantee that a plane will have ample stopping distance even on a truncated runway. Zahornacky adds that pilots also brake the plane harder and rely on reverse thrusting more when runways are short.

Steep Bank

In rare situations an aircraft must execute a rather sharp turn as part of entering the approach and landing phase of the flight.

A famous example, Smith says, is known as the expressway visual approach to runway 31 at LaGuardia. Pilots follow the Long Island Expressway heading east until they reach the New York Mets' baseball park, Citi Field, whereupon the plane operators' bank their craft to the left about 90 degrees to align with the runway.

"It's not typical to be making that big of a turn that close to the ground," Smith says, "but you're still at 1000 feet or so, which is plenty of altitude."

Pilots have gushed about catching a bird's-eye view of baseball games when pulling this maneuver. Passengers' reactions, however, can be mixed. "In the minds of some people, it seems like the wing is scraping the ground, that you're doing this steep bank," Smith says. "But those turns are never as steep as people think they are." Even when making a big left or right-hand turn, commercial jetliners rarely bank beyond 25 degrees of wing angle, he says.

While some approaches and landings keep pilots on their toes, traveling by air remains extremely safe from a statistical standpoint. "There's no such thing as an unsafe commercial airport. If there were, no airline would fly there," Smith says. "By extension, there's no such thing as an unsafe landing."

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