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Request about touchdown analysis

Started by acannata, Tue, 17 Jul 2018 22:25


Dear Hardy,

Could you add aircraft track (degrees) to touchdown analysis page?
Thank you


Hardy Heinlin

Dear Aldo,

the page displays the crab angle. Isn't this sufficient?



Touchdown may be right on the centerline, no crab. Nevertheless the aircraft could be not correctly aligned to the runway axis. Knowing the track just before touchdown could be useful in order to judge the landing performance.


Jeroen Hoppenbrouwers

But crab is an angle, not a lateral shift? Right on centerline with 5 degrees right crab = track is runway heading plus 5.

Markus Vitzethum

I think I understand Aldo's question. Crab angle can be defined as angle between the airplane's ground track (direction of movement) and the heading of the airplane (direction of the nose) at the moment of touchdown.

But the ground track might not agree with the runway heading.


To be honest ... usually ground track and runway heading will agree to within maybe, say, +/- 3-5°. Otherwise it will be a really bad landing.  ;D

One of the cases where it does matter:
Edit: got it wrong ... the famous Kai Tak crosswind landing is this one:

Hardy Heinlin

Yes, crab is not track and not heading. But crab says something about lateral gear strain. The crab parameter is important as there are limitations.

Other lateral parameters are centerline offset and threshold distance. These are important too as they have limitations.

Touchdown is a point, not a line. If the above parameters are fine, the lateral touchdown is fine.

Track is not a point, and a track snapshot says nothing about the track before and after the touchdown.

For tracking there is the map which shows the track line before and after the touchdown.

I could add hundreds of further parameters to the touchdown page, but I don't want to do this.


P.S.: Some may say track is an angle just like heading is an angle. I say you first need a line before you can name a track angle. When your heading is 360 and your groundspeed is 0, what is your track angle? The track won't be 360; it just won't exist. The computer will say: Error.