# Landing Distance

Does a 90° crosswind affect the landing distance of an airplane?
Yes  29%  [ 5 ]
No  52%  [ 9 ]
No idea  17%  [ 3 ]

Manuel Agustin Clausse (Agus0404) Chief Captain

This is a topic I was discussing in my pilot school with my classmates. Some say that a 90° crosswind does affect the landing distance. Some say it doesn't. I say it doesn't affect the landing distance. It will only affect the manoeuvrability of the airplane in the air, but not the landing distance.

What do you say?

Sean (SeanGa) Captain

I can't see why it would... so I voted no. Ask your instructor!

Manuel Agustin Clausse (Agus0404) Chief Captain

My Mass & Balance and Performance teacher agrees with me, but other classmates don't agree with that. I didn't ask my instructor, but maybe I will.

Crosswinds of more or less than 90 degrees to the runway DO affect the landing distance, because there is a headwind component or a tailwind component, but a 90 degree crosswind to the runway it doesn't affect the landing distance of an aircraft.

Jonathan (99jolegg) Chief Captain

In scientific theory, no, I don't think it would. The speed on approach would be the same, all other factors that affect landing distance, (aircraft weight, weather conditions, atmospheric conditions) are all irrelevant to a crosswind.

However, depending on the strength of the crosswind and the ability of the pilot, the aligning of the aircraft nose with the runway heading and / or floating when flaring may cause touchdown slightly further into the runway than would be done if conditions were calm.

If the pilot is suitably skilled to execute the landing in a crosswind, then no, there is no reason for the landing distance to be increased that I can see. Only pilot misjudgement / ineptness would affect the landing distance.

Maybe someone else has ideas as to why it would - I'd be interested in hearing them

CrashGordon Chief Captain

I am making a guess here, but since you have to compensate for the crosswind, you are using energy to do so (keeping the aircraft on the proper path by steering against the crosswind), and thereby shortening your landing distance.

Sean (SeanGa) Captain

of course, can't get more logical than that.

Can the person who voted yes please tell us why he voted yes? I am curious!

Jonathan (99jolegg) Chief Captain

CrashGordon wrote:

I am making a guess here, but since you have to compensate for the crosswind, you are using energy to do so (keeping the aircraft on the proper path by steering against the crosswind), and thereby shortening your landing distance.

I don't follow. If you are using more energy to maintain centerline, the forward momentum is still the same to maintain the same speed, despite possible cross-controlling in the process...

CRJCapt Chief Captain

A 90 degree crosswind causes a slight headwind component that is exaggerated by wind speed but at the usual speed of the wind for landing, it's considered zero. As you increase the speeds, it becomes more apparent. In reference to the picture below, you'll see that the GS line of the E6B flight computer is slightly curved. A 48 knot wind at a TAS of 140 knots would result in a GS of 130 knots even though it's at a 90 degree angle. Theres a +/- 1 knot margin of error(I didn't draw the dot or the box and had to estimate the wind value shown).

So the practical answer would be NO. A 20 knot, 90 degree wind would decrease GS of an aircraft flying at 130 knots by 1.6 knots, less for a lower wind value, too small to make a difference in landing performance. The scientific answer would be YES.

PS I didn't vote

Jonathan (99jolegg) Chief Captain

CRJCapt wrote:

A 90 degree crosswind causes a slight headwind component that is exaggerated by wind speed but at the usual speed of the wind for landing, it's considered zero. As you increase the speeds, it becomes more apparent. In reference to the picture below, you'll see that the GS line of the E6B flight computer is slightly curved. A 48 knot wind at a TAS of 140 knots would result in a GS of 130 knots even though it's at a 90 degree angle. Theres a +/- 1 knot margin of error(I didn't draw the dot or the box and had to estimate the wind value shown).

So the practical answer would be NO. A 20 knot, 90 degree wind would decrease GS of an aircraft flying at 130 knots by 1.6 knots, less for a lower wind value, too small to make a difference in landing performance. The scientific answer would be YES.

PS I didn't vote

Ah good thinking CRJCapt - I just had a look at my ARC-1 Flight Comp and yes that makes perfect sense. A small headwind component, nonetheless, its still a headwind.

Good job

Sean (SeanGa) Captain

sorry I don't get it... how can a 90 degree crosswind have a headwind/tailwind component? this goes against the rules and laws of physics!

CRJCapt Chief Captain

It's hard to give a good technical answer, in this format, but I'll try. It has to do with the crab angle, that's why it's exaggerated with wind speed. Some of the force of the vectors in the wind triangle solution have a slight rearward component the more the aircraft is angled. It's hard to teach in a class room so it's almost impossible to show you via chat.

In the below figure is a vector representation of a flight computers solution. Course 230, wind 315@40(90 degrees would be 320 but this is the best I could find). The line A-B represents the crab angle measured in reference to the North line and the TAS using the same unit and scale as the wind vector. The GS is measured from the North reference line to point B, measured in the same scale and unit as used to draw the wind vector. The course vector is slightly diminished because of the crab angle. I know that's not very clear but it's the best I can do, considering.

Here's an on-line E6B Flight computer that you can plug values into.
http://www.csgnetwork.com/e6bcalc.html

Sean (SeanGa) Captain

you're right, it is really hard for me to understand, but thanks a lot for at least trying your best CRJCapt.

Anyway, you're saying that if a plane was on a runway with zero friction between the tires and the runway surface, and there was a 90 degree crosswind, the plane would move backwards because of the headwind component of the crosswind?

and by the way, how come there's a headwind component but not a tailwind component? this is really weird.. T_T

CRJCapt Chief Captain

Your example, No it requires airspeed and crab angle also. At low wind speeds(which would cause low crab angle, it's practically zero. It deals with the relationship of crab angle, TAS and wind speed.

Think of it this way:
Mentally increase the wind vector in the vector diagram above, that will change the angle that line A-B intersects the course(shorter distance between ref line and point B) less GS because of the increased crab angle.

Sean (SeanGa) Captain

I think it's that crab angle thingie which is confusing me.. I mean, in my head I picture a plane landing on a runway and a wind blowing 90 degrees directly onto the side of the airplane. then I think to myself, how the h*** can this wind have a headwind component?? I mean, in physics its impossible to create a headwind/tailwind component of a force that is 90 degrees straight onto a surface... it's against the laws/rules of physics!! asmdpasdpasjd

anyway, what is actually this "crab" angle? the crab angle is something which decides the TAS, right? I mean, to me it seems that you consider it a force which has a headwind component or something.. or what is it? -_-,

EDIT: also, Agus, what do you think about all this? you must be shocked :p

Insight Chief Captain

I am no pilot (hope to be still) but here is what I think he means:

I guess the crab angle is the angle which the aircraft has to yaw into the wind to keep itself online with the runway

so - if you have a wind pushing you left of the run way from your right - you need to turn towards the wind on the approach with the rudders so you are powering yourself enough to the right to cancel out the sideways momentum...

Because of this you are now heading into the wind slightly - therefore your headwind element comes into play... ?

Sean (SeanGa) Captain

To me that doesn't make sense, because on approach, even if you have to face the wind, you still add more power to keep the approach speed. In other words the speed will be the same.. and as soon as you touch down you will align with the runway, and then the force will be 90 degrees to the surface..

so we're back to where we started

Jonathan (99jolegg) Chief Captain

I've thought about this a bit more, and I understand CRJCapt's explanation in that, you have your TAS (say 85) True Track (say 000) and Wind Variation (say 090/30), which allows you to work out the Drift (+19) and your True Heading (019), Magnetic Heading (019 - ignoring Variation) and thus GS (55). The GS is lower than the original TAS so constitutes a headwind, or they'd be the same. This makes perfect sense in cross-country navigation where you fly a different heading to the true track measured on the chart.

However, the original question involves the approach stage and yes, if you employ a crabbing technique then you will have a heading into the wind, whilst your track remains near runway heading. However, who says you need to crab into the wind on approach? The wing down method does not involve any yaw in order to maintain centerline thus the heading and ground track have little, if any difference, in which case, I would stand by my answer and my vote, that there is no headwind / tailwind on approach with a 90 degree crosswind. I understand that this method is less effective than crabbing, but for the relatively small crosswinds that are usually experienced, it is sufficient.

Feel free to correct me if I am wrong, anybody

Manuel Agustin Clausse (Agus0404) Chief Captain

You are not wrong, Jon. I agree with you 100%. That is also what I think.

SeanGa, I am not shocked. The answers given are what I expected.
However, when an airplane employs a crabbing technique there will be a slight headwing component, right? If an airplane is approaching the runway and it's maintaning the runway heading with zero wind there will not be any problem maintaining the runway heading. But, during the same conditions with a 90 degree crosswind, the wind will push the aircraft right or left. It doesn't matter if it is a 5 knots crosswing, because it will push a little the aircraft to one side. To compensate this drift, the pilot has to use the rudder to maintain the track. In my opinion, during the approach with a 90 degree crosswind the aircraft will have a slight headwind component. Just before touchdown the pilot aligns the aircraft to the runway and the landing distance is not affected. What it is affected it the manoeuvrability of the aircraft in the air.

Jonathan (99jolegg) Chief Captain

Agus0404 wrote:

But, during the same conditions with a 90 degree crosswind, the wind will push the aircraft right or left. It doesn't matter if it is a 5 knots crosswing, because it will push a little the aircraft to one side. To compensate this drift, the pilot has to use the rudder to maintain the track. In my opinion, during the approach with a 90 degree crosswind the aircraft will have a slight headwind component. Just before touchdown the pilot aligns the aircraft to the runway and the landing distance is not affected. What it is affected it the manoeuvrability of the aircraft in the air.

It sounds logical, but I think its slightly simplistic. When you align the aircraft with the runway heading, you are only 10ft above the runway - if you align any sooner than that and you'll be blown off centerline. If you kick the left / right rudder in all the way down to 10ft, then you still have the effects of the headwind - i.e. reduced GS relative to TAS so when you align with the runway, your GS will be the same as it was at 30ft with the yaw in place so in effect, causing you to shorten your landing distance. I know you aren't actually landing with a headwind, but aircraft inertia means that the effects of the headwind are still very much in effect if you use the rudder to such a low altitude.

I think that makes sense

Manuel Agustin Clausse (Agus0404) Chief Captain

It makes sense to me too. In my Perfomance manual it doesn't have much information about this. It just says that a 90 degree crosswind doesn't affect the landing distance and something more.

CRJCapt Chief Captain

The crab angle is the difference between the heading of the aircraft and it's course or ground track.

Think of it this way:
1. You're in a boat at the shore of a 10 nautical mile across river, your starting position is A and directly across the river is your destination B.

2. The river is moving left to right at a rate of 2 Knots(same effect as a 90 degree crosswind on an aircraft).

3. Your speed is 10 Knots thru the water(equivalent to TAS)

4. You keep the boat pointed at point B but the current causes your boat to drift 12 degrees to the right of the direct course(The crab angle).

5. At the end of 1 hour, you have traveled 10 nautical miles thru the water(TAS) but because you moved at an angle(12 degrees) from the direct course, you only traveled 9.8 nautical miles across the river(GS 9.8 knots). You're still .2 nautical miles from the shore at the end of 1 hour of travel, slowed by a direct cross current(crosswind).

PH First Officer

Landing distances are influenced by several factors as we all know...wind being one of them. Crabbing and crab angle has been mentioned but as Jo Legg correctly pointed out this can be binned. Well described though CRJ! If we want we can fly down the extended centreline without crabbing therefore wind is at 90 degrees to the runway and therefore at 90 degrees to the ac.

Original question being does 90 degree crosswing effect landing distance? No.

Canyon (NoWorries) Captain

A good discussion so far!

Here is how we solve it for sure...what if the 90* crosswind was 134 knots?

Then the landing distance would be 0 feet, because the crab angle would be so wild.

Using the concepts of Calculus, which I'm terrible at, we see that the distance will be from a no-wind distance ranging to zero feet, depending on wind speed.

Take for example this 734, which landed in zero feet:

Tailhook Chief Captain

You nailed it! Time to move on and close this thread.

CRJCapt Chief Captain

Here's a site about wind triangles that features a tiny program that you can download to you desktop (or anywhere else), that shows the changes to GS as you change the wind vector(interactive). Very simple and a one click delete when you want to remove it.

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