Silky Slips and Crabby Pilots

The debate over crosswind landing technique isn’t as intense or polarizing as arguments over the wisdom of turning back to the runway after an engine failure or the proper way to enter a non-towered pattern.  However, it can still spark a pretty brisk hangar discussion.  It’s not that there’s a vast range of options or that many are incontrovertibly wrong, but people naturally become invested in whichever method works for them in the airplane(s) they usually fly.

For the benefit of any readers who’ve either forgotten there are alternatives or haven’t yet taken their pre-solo written exams, we’ll quickly review the four (yes, four) most prevalent ways of coping with significant crosswinds during approach and landing. A time, if you recall, when the necessity of reducing airspeed to get the machine on the ground results in progressively decreasing control authority just as the earth gets close enough to bite.

1.  The Crab:  Keep the wings level and the nose pointed into the wind to maintain a ground track straight down the extended centerline.  Just before touchdown, kick the downwind rudder enough to align the nose with the runway.

2.  The Sideslip:  Bank into the wind, then use opposite rudder to keep the airplane’s longitudinal axis aligned with the extended centerline.  Touch down with the upwind wing low, settling onto the other main and nose or tail gear as airspeed dissipates.

3.  The Combination:  Hold the crab until short final, then transition into a sideslip after entering ground effect.

4.  Do Nothing:  We have yet to meet the instructor who admits to recommending this, but there’s no question it’s in widespread use.  Presumably it works until it doesn’t – and it doesn’t dozens of times every year, resulting in airplanes getting blown off runways, ground-looping, or collapsing their main gear, outcomes that aren’t mutually exclusive.

The crosswind landing problem is a relatively recent development, at least if you consider the 1930s “recent.”  No less an authority than General Billy Mitchell advocated “airfields” that were actually fields: mowed grass, a mile on each side, with a windsock in the middle.  This has the virtue of eliminating crosswinds: just land directly into the wind, whatever its direction.  But by the time the U.S. entered World War II, paved runways were becoming more the rule than the exception, and the flight characteristics of that era’s airplanes – taildraggers with ample adverse yaw – made positive control during crosswind touchdowns a significant concern.

One response was in airport design.  Hundreds around the country were laid out with three runways defining roughly equilateral triangles.  By assuring there’s a runway within 30 degrees of the wind direction, this limits the maximum crosswind component to half the wind speed – still ample to pose a challenge during a gale on the Carolina coast or a windy West Texas spring.

Aeronautical engineers also responded, first with better-harmonized flight controls, then more significantly by introducing tricycle landing gear.  Moving the center of gravity ahead of the mains curtailed weathervaning tendencies, while lowering taildraggers’ characteristic nose-high attitude on the ground reduced the risk of wind lifting a wingtip.  (Tailwheel pilots have made a virtue of adversity ever since by boasting of the superior airmanship required to manage their jittery mounts.)  While technically not a post-war innovation – the first mass-produced consumer aircraft with tricycle gear, Fred Weick’s Ercoupe 415, entered the market in 1940, and the tricycle-gear Consolidated B-24 Liberator was the most-produced heavy bomber in military history – it wasn’t until Cessna’s 1956 introduction of the 172 and 182 that nose wheels began their march to dominance of the light-airplane market.

But just as automobile anti-lock brakes encourage tailgating, more tractable ground handling also provides cover for lazy feet and sloppy airmanship.  (Yes, guilty as charged…)  Bungled landings remain far and away aviation’s most common type of unhappy ending, consistently accounting for about one-third of all reportable accidents on non-commercial fixed-wing flights.  Unfortunately, the limitations of the NTSB’s data collection make it difficult to tease out how many can be pinned on poor crosswind control – and impossible to marshal hard numbers proving that one technique outperforms its rivals.

About half of all landing accidents involve losses of directional control not attributed to mechanical problems (blown tires or stuck brakes), but crosswinds aren’t necessarily to blame – and pilots’ attempts to blame crosswinds aren’t always credible.  Fewer than half cited crosswinds or gusts as contributory factors.  Others did despite reported crosswind components of five knots or less.  Worse yet, some were blamed on the lack of an expected crosswind: a Wisconsin Cessna 172 pilot ran off the left side of the runway after he “established a crab angle to compensate for the wind” … which was straight down the runway at, yes, five knots.

As for the crab-vs.-slip argument, not only do accident reports rarely record the pilot’s technique; there’s no general information on which is tried more often or under what circumstances.  So, what’s a confused but conscientious aviator to do?

We could start by remembering the wise words of our judo coach: “It’s all physics.”  Since kicking out of a crab requires precise timing, it’s easiest to pull off in airplanes with slow approach speeds.  (Airliners also use the crab-and-kick method to avoid discomfiting passengers with prolonged banks on final, but their gear trucks are built to withstand side loads measured in tons.)  Dialing in a sideslip on final is the simplest method to learn and helps reinforce the concept of the stabilized approach:  Only incremental aileron and rudder inputs are required from any final flap deployment to touchdown.  Holding cross-controlled inputs is a bit more fatiguing, particularly during a prolonged pattern session of crosswind practice; transitioning from a crab to a slip eases that workload.  (If it also impresses passengers with your expertise, well, that’s beside the point.)

If you haven’t determined which works best for you, find an instructor and thrash it out.  If you’ve got a preferred technique for a specific aircraft, keep in mind that these skills are perishable and flight-plan accordingly.  If it’s been six months since you faced breezes more than 10 degrees off the runway heading, you can probably still handle that dreaded five-knot crosswind … but might think twice about trying your luck with 15.

The crucial point is that positive aircraft control becomes ever more important the closer you get to solid objects, terra firma prominently included.  The crab, the slip, and the transition can all be made to work consistently.  Mastering at least one makes flying more fun and less expensive – while repair costs and premium increases await those who rely on Option Number Four.

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David Jack Kenny is an aviation writer and recovering statistician in Frederick, Maryland. He has been a statistician twice as long as he’s been a pilot but enjoys flying more than twice as much as analyzing data – particularly flying long cross-countries IFR, rescuing dogs as a volunteer for Pilots N Paws, and taking friends and neighbors up for introductory flights. He ascribes his helicopter certification to a characteristic lack of impulse control.