Flare on a runway with significant upslope
 

Hello,

I’m approaching my first 500hrs on Airbus320 and all is working good. My flare technique is pretty consistent: at around 50’ I shift my view to the opposite runway threshold and this significantly help to judge my flare point depending on closure rate. Then it’s only a matter to keep the attitude and let it touch. Works perfectly. However I have some troubles with a few runways with a significant upslope. Because while the technique is the same I see I touches firmly and soon, this especially by night when the slope is not so appearant. Do you have some advices on how I can avoid this illusion and adjust my flare with those particular runways?

Personally I have never used the ‘look at the end of the runway’ technique. And indeed on certain upslope runways you will not see the end of the runway at all during the flare!

Having said that, uphill slopes can be tricky and only through experience I’ve learned to adjust my flare technique ever so slightly to adjust for upslope, downslope, glide slope angle. The first step is realizing that you will have to adjust your flare technique (ever so slightly, nothing drastic!!) to achieve the same result, it’s pure physics. You have opened this topic so, at least you are aware of the issue and others will reinforce this. The rest will come with experience.

(I’m no trainer as you probably can tell, consider this just the patient advice of your regular line captain)

As long as your g load is below 2,3g don't worry. And don't worry about cabin crews' comments neither, they drive their cart, you fly the plane.

You'll improve with time, just like I did. Yet, I still botch it from time to time!:}

Hello,
Very simple.
Everything is almost like if the upslope of the runway was added as a downslope on the approach.
For example if the runway climbs up 1°, it's almost equivalent as if you were on a 4° approach slope.

Then, increase flare height or force accordingly.
If you flare with the same force, the flare height should be increased by the square of the ratio of the slopes (for a stabilized approach).
Also if you flare with the same height, the flare force should be increased by the same ratio.
For example, if 4° instead of 3°, increase flare height by 77%.. Or increase both force and height by 30%.
I'm not asking you to compute this inflight, but keep in mind that you're going to have a significant effect due to this squared term.

Why overcomplicate matters?

You are approaching the runway with a certain sink rate dictated by the approach angle and Your ground speed. For touchdown, You will like to break this rate to put Your wheels on the runway at an appropriate, lower sink rate.

A sloping runway, be it up or down, will influence that sink rate. An upsloping runway will come up to meet You, a downsloping one will shy away from You. In the first case, Your effective sink rate is higher, in the second case, lower. So with an upsloping runway, flare a tad earlier and more; with a downsloping one, later and a little less. If done right, You will achieve roughly the same body angle on touchdown relative to the runway, whatever the slope may be.

Looking down the runway... this may help in some cases, in others, it will not. Not all runways show the same slope all along their length; some are a little wavy (Birmingham comes to mind), some may be U-shaped, others are mostly level but have a little upslope right in the touchdown area, they are all different. Consider judging the sink rate based on the runway edge, keeping in mind that different width runways look different - this seems to work for me quite nicely most of the time (the occasional solid arrival does happen) and also helps in case of variable slope runways.

Nice and easy explanation!

I would like to add the effect of increased (or reduced if the opposite) vertical speed: high temperature on RNAV approaches (high temp, steeper approach), high elevation airports (more altitude, for the same 3º glidleslope, more groundspeed and more vertical speed as well) or some tailwind of heavy weight; in those cases runway will be coming faster to meet you.

Think about those things and plan to make minor adjustments on your flaring technique. After a few hundred landings you'll get it.

Visually concentrate more on the near-field view and periferal vision; you cannot see the far end of the runway in reduced visibility.

There is anecdotal evidence that the 'human' control-law for flaring relates height against height-rate; dependant on aircraft type. This can be seen in the difference between a 3 deg approach and a steeper one - commencing flare at a higher altitude due to the higher vertical speed.

A similar effect might be encountered with sloping runways, but experience suggests that the variation in the quality of landing due to slope is within the variation of normal landings due to a range of airspeeds / ground speeds (changes ht rate and time of flare), and mass - the feel of the aircraft - pitch rate and time.

The basis of control depends on visual assessment of height - akin to 3D triangulation from the close-in visual scene, thence judgement of height rate.
Note the value of height call outs in larger aircraft during the flare.

This judgement, and the pitch rate and time relationship comes with experience on type. Try to capture the overall picture of what is seen, the control input, and progress, for a self debrief, ( experience is like having a large book of pictures )
.

Agree with all of the above. Just to put some numbers on there, at a GS of 140kts, 1% of slope is equivalent to ~150fpm RoD. This is noticeable but is not going to have a huge effect on the quality of the landing compared with some other factors.

On the contrary, the evolution with the square of the relative vertical speed will make it noticeable.
150 fpm will make around 45% difference. Call it what you like, it's 45%. I do not call it "a tad" personally.

To be honest, I do not advocate this technique in training. If you misjudge the higher flare only slightly it's an invitation for hard landings. On an upslope runway, you are tempted to pitch up even more which is very risky when you reduced thrust too soon as well.

It is much more important to focus on thrust control. Max 20ft above your normal flare moment, add a touch of thrust. Just push them 1-2cm forward to create the thrust required on a 2-2,5° slope glide and support the nose enough to allow the added thrust break the rate of descend every slightly. But don't let the nose "pitch up" too hard to avoid long landings. Then do a normal flare with normal thrust reduction. If the landing is slightly more positive, that is ok, it beats flying over the top of the uphill :-).

Just remember: we don't stall to land like Cessna's, we fly it on the runway to be able the land in full control.

Ps: B737 (added later on as I didn’t realise this was Airbus related).

My opinion is the only thing that matters is

Land on centerline
Land in touchdown zone

I stopped trying to "grease them" (and my disappointment when they did NOT get greased also stopped....). The FCOM says "begin flare at 30 feet." I do that also. I let it settle down and land. In most cases the first retard call is when I go to idle power.

Or…As I have heard a particular trainer say, the main aims are:

- land on the runway
- stop before the end

He's not wrong.

Indeed, he’s technically not wrong.

But there is a difference between a chef and a cook. Trainers should be able to help a cook on the road to chef, even if he’s never been a chef himself. Sounds cheasy, but training is all about getting the best out of people.