Strong Gusty Crosswinds - When Do You Say No?

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Strong Gusty Crosswinds – When Do You Say No?

“Robert Novell’s Third Dimension Blog”

Good Morning—This week I want to showcase another article from the Flight Safety Foundation that will help each of us rationalize how to deal with the decision making process when confronted with strong, and gusty, winds/crosswinds at your destination. The basics apply to all airplanes so take a few minutes to see if the information has value for you.


Strong Gusty Crosswinds

(By Wayne Rosenkrans – AeroSafety World)

Challenging encounters with strong gusty crosswinds during the approach and landing phase in commercial air transport — never routine for flight crews and sometimes underestimated by air traffic control (ATC) — involve some risk because of systemic gaps, mismatches and misconceptions, says Gerard van Es, senior consultant for flight operations and flight safety, National Aerospace Laboratory Netherlands (NLR).

He explained the impetus for further study of the factors involved and a few of NLR’s recently developed recommendations during Flight Safety Foundation’s International Air Safety Seminar in Santiago, Chile, in October 2012. In April, van Es updated AeroSafety World about industry responses to the complete report that he and a colleague, Emmanuel Isambert, prepared as advisers to the European Aviation Safety Agency (EASA).1

Difficult surface wind conditions2 have confronted pilots since the flights of Wilbur and Orville Wright, and one of the many recent examples was a serious incident in Germany in 2008 (see “Serious Incident in 2008 Prompted German and EASA Analyses,” p. 41) that motivated German accident investigators, and subsequently EASA, to dig deeper into the causal factors and to update mitigations. A German recommendation — calling for assessment of all measuring systems that detect the presence of near-surface gusts and how pilots integrate various wind data into landing/go-around decisions — led to the NLR study for EASA, van Es said.

Crosswind-related regulations originated in a period from a few years after World War II to 1978, when demonstrated crosswind in airworthiness-certification regulations became fixed for industry use, van Es said.3

NLR’s scope included querying operators about understanding of aircraft certification for crosswind and relevant policies and procedures; a brief review of factors in crosswind-related occurrences; a review of measurement technologies; and the salience of wind instrument precision.

“First of all, we noticed that the way of arriving at and presenting the [crosswind] information varies between the manufacturers and even between the aircraft models,” van Es said. “Most [manufacturers] don’t mention any kind of gusts, but also the way they’ve derived the [demonstrated crosswind value] during the flight test can be very different, giving different results. And they are allowed to, and the regulations on the means of compliance [allow them] this opportunity. Limits, real hard limits, are very rare, nor are they required to be established. Typically, it’s up to the operators to decide if they transfer a demonstrated value into a hard limit. … This all can result in a possible mismatch [between] what the operator is using and what the data from the manufacturer is telling [us].”

The NLR survey was sent to 115 operators from Asia, Europe and North America, and yielded 36 operator responses. “Basically they were telling a story that we were expecting, to some extent,” van Es said, especially regarding the variability in practices. “They were very keen to see what others were doing and what the issues were,” given their anecdotal knowledge of many crosswind-related occurrences.4

Wind Data Sources
Operators and pilots have several disadvantages as they integrate complex factors. “First of all, there is no common interpretation of the manufacturer’s crosswind,” he said. “[Respondents] operate similar models, and they have a different view of what was told to them or what was written in the manuals provided to them. When it came to reported gust values in their operation — the wind reports, how to deal with gusts — some operators said, ‘We don’t take into account the gusts when we look at the reported wind values.’ Others said, ‘Yes, we do, and we do it this way.’ Others said, ‘We do, but we don’t specify how to deal with the gusts.’”

Each type of wind information has advantages and limitations. “FMS [flight management system–derived] wind is something that you have to be very careful in using, especially during the approach,” van Es said. “[Yet] some operators … said use of FMS wind is encouraged and [indicates] good airmanship. Others said, ‘It’s strictly prohibited because we had incidents where we nearly lost the aircraft by using FMS winds.’” Problems in relying on this source in this context include lack of system correction for side slip, its use of an average value and its applicability to winds at altitude — not at the surface.

Some respondents’ pilots request from ATC a series of instantaneous wind reports during approach. “These are snapshots — the actual [real-time] wind that is available as measured at the airport,” he said. “Typically, you get an average [two-minute] wind, but some airports allow you to ask for an instantaneous wind [report].” Some respondents promote the use of instantaneous winds; overall, there was no common way of determining the components either in tailwind or in crosswind.
The survey also found that 75 percent of respondents use a combination of demonstrated and advised crosswinds, and a number of these set maximum crosswind values lower than the manufacturer’s demonstrated/advised crosswinds; 82.9 percent use the crosswind values as hard limits; 67 percent have procedures for how their pilots should calculate the crosswind component, with 58 percent of these specifying how the pilots should take gusts into account; and 33 percent do not include gusts in their crosswind values. “A small number of the respondents left the decision — to include gusts or not — up to the captain,” the report said.

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Have a good week and thanks for letting the 3DB be a part of your routine. Fly safe/be safe.

Robert Novell

May 5, 2014