Professional Pilot, May 2018

know the wind situation before taking off or landing In most cases current winds are broadcast over ATIS or ASOS AWOS frequencies or in some cases from navaid frequencies They can also be requested from ATC At untowered fields or when the tower is closed other pilots or the FBO may be able to provide winds via the CTAF Similarly helicopters or aircraft landing at off airport sites may seek wind guidance from someone on the ground at the site before they land Estimating winds In the absence of an unambiguous reporting of wind speed and direction from a source on the ground pilots might estimate the wind in one of several ways The first is to reference any wind sock or similar indicator on the airport grounds Many are even lighted for nighttime use If possible pay particular attention to any movement of the indicator In gusty winds a wind sock may rise and fall with each gust as long as the sustained winds are not stronger than the maximum for the sock while most indicators will move from side to side in shifting winds Other potential wind indicators include nearby flags or smoke from a smokestack Even the ripples in a nearby water body may help a pilot estimate the wind condition Pilots can also try to dial in the weather information from neighboring airports that have an automated system If a pilot is using visual reference information to estimate winds it is best to do avoid doing so after starting the approach A fly by of the airport will give time to process the information and plan the approach Similarly if no other visual cues are available overflying the approach at altitude to identify any crosswind drift before returning to execute the approach can 82 PROFESSIONAL PILOT May 2018 help to keep crosswind landing surprises to a minimum Crosswind components should not be taken lightly Underestimated crosswinds have contributed to thousands of runway accidents Aircraft are tested to determine the maximum crosswind the aircraft flown by an average pilot not necessarily a tough as nails test pilot can reasonably handle For most aircraft that works out to a 90 º crosswind of 20 VSO Calculating the crosswind component involves using a crosswind chart or calculator The angle between the runway and wind headings and the reported wind speed will provide the breakdown of headwind versus crosswind In the absence of a chart or calculator a rule of thumb is that at an offset of 15 º the crosswind is 25 of the wind speed at 30 º it is 50 75 at 45 º and at more than 60 º pilots should just assume that the full wind speed is the crosswind component Be aware of gusts While in gusty winds most pilots will add a gust factor to their approach speeds most dont add one into their crosswind calculations In fact gusts during crosswind landings have been a factor in many accidents especially where gusts are more than 15 kts or so above the sustained wind speed Getting hit by a strong gust at a low altitude and slow speed may result in a wingtip strike a lateral touchdown or at least make it impossible to regain the centerline in time to land safely Similarly a gust on takeoff can easily cause loss of lift or control As soon as the mains are off orienting into the wind to maximize a strong headwind for climbout is advised whenever possible The key is to get as much stability and lift as quickly as possible to get away from the ground so you have time to recover from any gust induced upset The gust factor for adding speed to an approach is gust speed minus sustained wind You are then suggested to add half of that to final approach speed In gusty conditions it is also worthwhile to add at least half the gust factor to your sustained wind in your crosswind calculation So if you were facing a 25 kt wind with gusts to 35 kts using 30 kts will give you a better measure of the possible crosswind conditions you might face This doesnt mean you shouldnt attempt the landing if that places your crosswind outside of the envelope but it does mean youd want to exercise extra caution as you neared the ground While pilot reports are very important to inform controllers and your fellow pilots of the conditions you faced as you landed or departed an active runway these reports may not be the best source of information to a pilot on final approach in gusty winds Many wind related landing accidents were preceded by aircraft that landed safely and reported no problem That is the nature of gusty winds and the variable skill or tolerance of those flying If at any time in an approach you feel that the wind is behaving beyond your or your aircrafts capabilities a go around is the safest course of action Gusts often only last a few seconds and the next approach may be far smoother Karsten Shein is a climatologist with NOAA in Asheville NC He formerly served as an assistant professor at Shippensburg University Shein holds a commercial license with instrument rating Despite advances in wind shear alerting technology thunderstorm downbursts remain a significant danger to aircraft that are already flying slowly and close to the ground Outflow Outflow Increasing Tailwind