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I live in the UK, and as such frequently have flight plans cancelled in Microlights (Ikarus C42). Anyway, one of the reasons is it has a low crosswind limit (15 kts). When I look at the weather, I ensure the gusts do not exceed this.

But sometimes the windspeed is under this, say 12 kts, whilst the gusts are much higher, say 30kts. I keep missing flights as I decide not to fly based on gust speeds. Can I just ignore these and focus on the average speed?

wind speed example

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    $\begingroup$ Are you a student? I ask because the capabilities of a student are generally less than that of someone with a licence. $\endgroup$
    – Ben
    Oct 21, 2022 at 7:53
  • $\begingroup$ @Ben The crosswind limit is set based on the maximum speed a test pilot achieved a reasonably controlled landing at. I don't wish to presume my skills would out-do those of a professional test pilot! $\endgroup$
    – Cloud
    Oct 21, 2022 at 8:49
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    $\begingroup$ @Cloud “Max demo” doesn’t mean a test pilot couldn’t do more, merely that the mfr didn’t pay them to try anything beyond the design goal. $\endgroup$
    – StephenS
    Oct 21, 2022 at 19:11

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Gusts are wind bursts of up to 20 seconds, they may be short lived but you should take these into account, so you should use the gust speed, not the steady wind speed. If you are on short final close to your crosswind limit and a gust comes that's higher than your control surfaces can compensate for it doesn't matter how good a pilot you are, the airplane is going to go sideways and there's nothing you can do to prevent it. A brief burst may not sound like a lot but it only takes 2-3 seconds to blow you off the runway.

As painful as it may be you have to take the gust values and your own personal capabilities as a pilot into account. That doesn't necessarily mean that having gusts over the limit is an automatic no-go, there are mitigating factors to consider, especially if it's very close to the limit. Shelter helps, the airfield I fly from has some woods which shelter the landing end of one of the runways, which is the one that's most frequently in use. These woods moderate the wind and gusts from the west, which is prevailing, so I often can fly in higher winds.

The OP is probably well aware of this, but a well rounded answer needs to mention wind direction and calculating the crosswind component. Wind direction is also a consideration, the calculation is V x Sine degrees of crosswind. 30 degrees is 50%, 45 degrees is 70% and 60 degrees is %85. This is hard to calculate in the air, it's easier to say that 45 degrees is 75% and 60 degrees is 100%, and gives a bit of 'fudge factor' for safety. So, if you have a 45 degree crosswind at 20kt gusts you are within limits.

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  • $\begingroup$ When you say degrees, are you talking about wind heading, or relative to the aircraft? $\endgroup$
    – Cloud
    Oct 25, 2022 at 8:14
  • $\begingroup$ I mean degrees of crosswind, which is calculated from the difference between the wind angle and runway heading. If your runway is 90 and the winds are from 45 or 135 you have 45 degrees of crosswind. $\endgroup$
    – GdD
    Oct 25, 2022 at 8:23
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You've mentioned gust speeds, and you've mentioned crosswind limits of the aircraft (and by extension, your own limitations). But you have not specified the runway direction.

If the gusts are straight down the runway, you may be ok to fly. You will want to increase your final approach speed by (at least) half of the gust speed. If the gusts are directly perpendicular to the runway then you need to check your aircraft limit. Somewhere in between, then you'll want to know what component is a headwind and what is a crosswind and adjust the above accordingly.

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