Hacker News Reader

Comment by sitharus | Hacker News Reader

The METAR was 27028G35KT, or 28 gusting 35 from 270° magnetic

However the runway landing was 33, or 330° magnetic.

So this is 24-30kt crosswind component. The maximum landing crosswind on a dry runway is 32kt. The press conference reported the runway as dry, so if they’re correct then it’s within limits. At the reported -9°c if the runway has been de-iced it could be dry I guess?

The surveillance potato camera makes it look like a hard landing on the right main, which is mounted on the wing root. But it’s very low quality and we’re not going to get the first real answers for a month.

View on HN

> However the runway landing was 33, or 330° magnetic.

They were landing on runway 23.

> At the reported -9°c if the runway has been de-iced it could be dry I guess?

From the NOTAM, the runway condition codes for 23 were 5/5/5, so not dry, but "good".

[1] https://avherald.com/h?article=52439b47&opt=1

5/5/5 would still be good braking action and directional control (it’s out of 6).

I stand corrected.

5 is not "poor", but "good", with a wet runway or one with light snow or slush. [1]

[1] https://www.faa.gov/sites/faa.gov/files/about/initiatives/ta...

FYI: Canadian runways use true north, not magnetic.

Depends if you're in Canada's "northern domestic airspace" or "southern domestic airspace":

https://www.canada.ca/content/dam/dnd-mdn/images/technical-a...

Airports in the southern half of Canada still use magnetic for runways.

TIL!

... for now. Goal is to get everything on True within the next 5 years. https://www.navcanada.ca/en/magnetic%20north%20vs%20true%20n...

The global effort. https://www.icao.int/safety/OPS/OPS-Section/Pages/Truenorth....

I had to look this up, and I found the answer interesting because I used to develop software to accurately report magnetic declination at any point in time, for directional drilling oil wells in Canada. https://www.geomag.nrcan.gc.ca/mag_fld/magdec-en.php has some great information on why. For example, Yellowknife can experience declination changes over one degree every three years.

I haven't used a compass since I was a kid and at that time declination where I live was 21 degrees. Now it's down to 13 degrees. I had no idea it changed that much.

The rule of thumb I was taught for crosswind component based on difference between runway heading and wind direction was 60º = 6/6 of the crosswind, 30º = 1/2, 10º = 1/6. So if they're landing on runway 23, 270/28 would amount to (roughly) 4/6 of the wind as a crosswind component, or 19kt.

90º = 6/6, 60º = 5/6, 40º = 4/6, 30º = 3/6, 10º = 1/6 strikes me as pretty accurate.

Doesn't look like a severe crosswind to me, because there seems to be very little crabbing or rudder input, although the camera angles make it hard to tell for sure. You can also see snow blowing on the ground roughly parallel to the runway. I would guess either a downdraft or they forgot to flare or both.

Reply on news.ycombinator.com