The Crab and the Grackle

About a week ago, we were finally seeing some nice weather here in Peterborough, but wow, was it windy there for a few days! I was driving south on Brealey Drive, on my way to do some grocery shopping when I noticed a small Grackle (a type of blackbird with a purplish head) also heading southbound off to my right at about 2 o'clock.

What caught my eye about this bird was that, despite the strong winds coming from our immediate right, it was flying in a direct line over the sidewalk - but its' body was askew to the right. The bird was crabbing! I followed that bird for about two blocks southbound watching it as it flew in a perfectly straight line, despite the efforts of the wind to blow it off course.

I openly laughed at myself, even though I was the only one in the truck. It was one of those moments that puts us humans in our place when we think we as a species have it all together and know more than other species. Here was a little bird doing what obviously came naturally to itself, but I had to pay thousands of dollars to learn - how to properly crab in a strong crosswind!

It had been awhile since I had read up on crabbing (it comes naturally to me now [wink] ), so I grabbed some of my old textbooks, grabbed a cup of coffee, saddled up in front of the internet and did a bit of reading. What I found was pretty surprising - apparently there are two methods of landing using the crabbing technique - the crab and the de-crab. The initial setup for each is identical, but the difference lies in the actual touchdown phase of landing.

The De-Crab

This is the form of crabbing on landing that I'm familiar with, and probably most people are, but didn't realize that it was called the De-Crab. During a crosswind, assuming no gusts, the nose of the aircraft is skewed into the wind to compensate for the crosswind component. In doing so, the illusion to the pilot is that they are flying sideways, although the aircraft is maintaining the center line of the runway. Just prior to the flare, the nose is brought back in line with the center line of the runway with opposite rudder and opposite aileron to maintain wings level. The aircraft lands in line with the center line of the runway. As the name implies, the crab is removed prior to touchdown.

The Crab

As with the De-Crab, the nose of the aircraft is skewed into the wind to compensate for the crosswind component on final. Wings are maintained level during decent. Now this is where the Crab differs from the De-Crab - during the flare, the nose is maintained off the center line of the runway through to touchdown. After touchdown, the aircraft automatically tracks to the upwind edge of the runway and the pilot has to apply rudder to bring the aircraft back tracking down the runway. If the crab is large due to a larger crosswind component, the greater the deviation to the upwind edge of the runway. It is for this reason that the Crab is not recommended on dry runways. On wet, slippery runways, the crab is a possibility as the tracking towards the upwind edge of the runways is reduced. From the reading I've done, the benefit of the crab is the fact that the pilot does not have to de-crab at a critical time of the landing sequence, effectively reducing additional risk by not having to remove the crab.

One thing to note regarding the above is that the information was obtained from reading about commercial operations and is likely why I hadn't heard about the different landing techniques involving the crab. I'm interested to hear from the commercial pilots in the community about these methods and whether they have anything further to add about the crab.