Does Length Really Matter?

For me, the first thing to establish (even before looking at the aircraft performance charts) is an answer to one simple question: Is your required landing distance longer than your take-off distance?

If it is, then there is most likely room for improvement in your landing technique.

This question first arose when I was waiting at the holding point one sunny Saturday morning. A typical training aircraft should require more distance for the take-off than for the landing, if you believe the charts in the POH. But while watching pilots practicing touch and goes at my favourite airport, more often than not I found the opposite to be true.

From the theory and everything that we are taught, that should not be correct. All the performance charts that I have completed over the years suggest that the landing distance should be (often much) less than the take-off distance. Yet every week I sit and watch pilots taking much further to land their aircraft than take off.

Question 1

Is your required landing distance longer than your take-off distance?

According to the POH (see the Cessna 172 examples following) it should not be.

Question 2

How do you score in relation to the performance chart from the POH for your aircraft?

Have you ever tried to work this out? We may fill out the performance chart before every flight, but what use is it if we don’t even know how we score in relation to the manufacturer’s standards?

Assessing your abilities

Let’s talk about pilot ability and skills. Firstly, it is not your fault if, until now, you have not been aware of your own capabilities, or even those of the airplane you fly. But by reading this article you just ran out of excuses. So, how can you do better?

I know that it is easy to land halfway down the runway when the runway is long enough for fighter jets. But the problem with this approach is that the pilot never works on getting the landing distance under control. What’s the point?

Then one day, suddenly the runway is only just long enough for the aircraft. The pilot discovers the hard way that stopping before the fence at the far end of the farmer’s landing strip is not as easy as the POH says. The pilot discovers that the fence is there to stop the cattle from entering the strip. It is not really intended as a catch fence to allow for below-par landing skills.

Personal benchmarking

Landing performance charts are compiled from data generated by the aircraft manufacturer’s test pilot. They provide a good starting point to allow comparison of the pilot’s abilities to a known reference point. From the landing distance chart sample below, you can see that they take into account all of the factors listed under ‘conditions’ above the main tables.

Three scenarios are possible. The first is that you can consistently perform exactly as per the performance chart numbers. That is very good.

In the second case, you do not do as well, which is likely to be the case for most pilots. The critical question is: By how much? 10 per cent, 20 per cent, 30 per cent or even more? Knowing this value allows you to add your performance factors to the performance charts and therefore calculate a more accurate landing distance based on the circumstances of the day.

The third option is that you consistently do better than the test pilot most of the time. Now you can reduce your own numbers compared to the POH. The performance chart can have a negative factor for you. For example, you may apply minus 10 per cent to the performance chart. However, you would probably want to be very consistent and reliable in your personal performance before reducing these distances when space is tight.

Remember, this exercise is about evaluating and benchmarking your performance. You should never reduce these distances for flight planning purposes, although it may be prudent to increase them if your results consistently fall into the second category.

Measuring the take-off roll & climb

This is usually quite easy to measure. Your starting point is straightforward as you can choose somewhere easily identifiable. You can observe your lift-off point and 50-foot AGL point in relation to various airport features such as taxiways, nearby buildings or even trees, airfield signs and markers, windsocks, etc.

You can then use Google Maps to determine (with reasonable accuracy) your take-off distances for the conditions on the day (wind, temperature, runway surface, aircraft weight, etc). Voila! You now have a reasonably accurate way to benchmark your abilities against the performance charts, as well as a method of measuring whether your own skills are improving, static or declining.

Even better, you now have a method of calibrating your (possibly ageing) aircraft’s take-off ground roll to the performance chart figures which were based on a brand-new aircraft. Just make sure to use the POH short-field take-off procedure. It might be interesting to see just how much the worn engine, dirty paintwork and the odd ‘wing ding’ really makes.

Once you know your take-off roll, you can compare it to the performance chart. At the Aero Circus home airfield, the POH suggests that when commencing our take-off roll from the threshold (A), our Cessna 172 should be airborne by the middle of the wide touchdown markers (B) shown in the photo below. However, due to old age (of the aircraft, not the pilot) we usually find the lift-off point is closer to the first taxiway (C). This is about 30 per cent more than ‘the book’ would suggest. Factors such as decreased engine output, propeller efficiency and airframe ‘slipperiness’ may contribute to these results. We also don’t generally use the short field take-off method for reasons that we will cover another time.

Measuring the landing roll

Before we begin, the only way to accurately determine the end of the landing roll is to bring the aircraft to a complete stop without the use of heavy braking. Heavy braking will lead to flat spots on tyres and the need to replace them before their normal life expectancy.

So, either request a ‘Stop and Go’ from ATC or announce that during your CTAF calls (assuming you don’t have a jet following you in to land).

To gather the required data, we need three things. First, to cross the threshold (or another easily identifiable point) at 50 ft AGL (if possible, using the Jacobson Flare for consistency). Second, we need to note the point when the main wheels first contact the runaway (or taxiway if you are a certain Hollywood actor). Thirdly we must note the point at which the aircraft comes to a complete halt.

Again, this should be relatively easy if there are some handy features available on or around the runway. It should be pretty easy to spot whether your landing roll ended before or after the point where you reached the 50ft AGL mark a few minutes earlier. However, you cannot blame the aircraft for poor performance for the same reasons given above for take-offs. For example, a reduction in airframe slipperiness should shorten your landing distance rather than increase it.

Be aware that this process is not about using an advanced short field landing technique (e.g. back of the power curve/reverse command) on every landing. Use the technique outlined in the POH. Follow the performance chart details and compare your performance against the actual conditions listed in the charts. These may include aircraft weight, density altitude, approach speed, flap settings, etc.

For better or worse

Keeping track of your own performance using actual data means that you will have an objective method of evaluating whether your skills are getting sharper or are eroding. For best results keep detailed written records of every measured take-off and landing. Obviously, the best way to compare apples with apples is in the circuit where conditions will usually be fairly consistent during each session.

Be aware that your performance variations from day to day may be environmental rather than your own failings, hence recording these factors along with your take-off and landing distances will provide more useful data in the long term. It may even uncover a particular weakness that needs more work to rectify. You might even discover how much tailwind is too much for your ability level and aircraft (only try this on a long runway).

Meanwhile, back in the real world

All this theory is well and good. But what actually happens in the real world?

Cameron Marchant is part-owner and CEO of air charter organisation Kakadu Air Services in the Northern Territory. He advises that when flying a route that involves a number of stops, the key is to identify the ‘limiting event’. This is the segment of the flight where the runway length, aircraft weight and prevailing environmental conditions will be the closest to marginal. If the take-off or landing distance for the limiting event is within the aircraft’s capabilities according to the Performance Chart, then the whole flight can proceed.

“The process used by Kakadu Air when visiting a new or unfamiliar airstrip begins in the flight briefing office. Firstly, if information about the intended airstrip is not available in ERSA or the Country Airstrip Guide, Google Maps is used to measure the runway length with a fair degree of accuracy,” says Marchant.

“Next, the normal factors (distances available, weight, wind, slope, surface and airfield elevation) are used along with meteorological conditions (usually based on declared conditions) to calculate LDR and TODR. In most (but not all) circumstances, the landing distance will be shorter than the take-off distance. Therefore, if the take-off distance available is more than the take-off distance required, the flight can proceed.”

The calculations must also take into account any obstructions on approach or departure. For example, with a clear approach path the touchdown point might be assumed at the threshold or shortly thereafter. The Ground Roll value from the Performance Chart is therefore the relevant comparison. However, if there are trees or other obstructions on the approach path, the Distance to Clear 50ft Obstacle, or a variation of that, would be the appropriate distance to use.

Improving long landings

There are a few things that might be the cause of the aircraft not wanting to settle on the runway.

Approach speed: I guess from my observations if the floating distance is too long, maybe the approach speed is not being maintained accurately. Ten knots faster in approach speed can make the airplane not want to land. There is too much kinetic energy to get rid of. To fix this, fly accurately, fly the numbers. If the aircraft is trimmed accurately, it is a relatively easy thing to achieve. Trim to achieve stable speed on the approach.

If the wind is gusting and you do need to increase the approach speed to allow for this, then make sure the data you capture from the landing distance is noted under those specific conditions. It is not valid to compare a higher-speed gusting approach to a stable wind situation. But it is useful to know how it does affect your landing distance should that situation ever arise ‘in the wild’.

Aiming point: There is no doubt that choosing an aiming point halfway down the runway will not be conducive to a relatively short landing distance. The aiming point should be just in front of the piano keys giving you the 50ft above the threshold ready for the flare.

The flare: Maybe you are flaring too high. In this case it will take longer to transit from a descent attitude to the flare. Using the Jacobson Flare might help you fix that problem by giving you a point at which to start the flare. This technique works regardless of your sitting height in relation to the ground (I am thinking of a A380 versus C152 situation) and therefore transfers painlessly between different aircraft.

Attitude: Maybe you have been taught to raise the nose very high above the horizon to protect the nosewheel. We do need to protect the nosewheel but it doesn’t mean stalling the aircraft in the process by being too nose-high. One might then need power to recover from the oncoming stall, which increases the landing distance even further. Save that technique for night landings if you are NVFR rated.

Tailwind: This will increase landing and taking off distance. It is not a good way to evaluate your landing skills. Use the headwind/tailwind adjustment factors in the tables if they are present. High idle speed: On landing, not reducing the power to idle will increase the distance necessary for landing. This may also occur if your trusty LAME has set the idle speed too high.

Some general advice

Keep back pressure on the control column at the point where the main wheels make contact with the ground. As the vessel transforms from a flying machine to a ground-based vehicle, the centre of pressure moves forward. This can be very hard to counteract on some aircraft, so be ready for it. When the aircraft is ready, it will land without your help. So, the secret of a good landing is in the approach.

The brakes should not be over-used to make the landing distance shorter. On many occasions during pre-flight inspections, I have noticed flat spots on main wheels which have been caused by pilots trying to shorten the landing distance by locking the brakes after touch-down. The solution? With plenty of back pressure on the stick, apply the brakes firmly – but not firmly enough to lock them up. If a wheel does lock, release the brake pressure slightly and reapply a bit less firmly until you get a feel for where the lockup point is for that particular aircraft and runway conditions.

How much back pressure on the stick? Enough to unload the nosewheel but not enough to put the aircraft back into the air. This will usually involve progressively increasing the back pressure as the airspeed drops away. During the ground roll the control column will need to be pulled back so that the weight of the aircraft is concentrated on the main wheels, and application of the brakes does not put more pressure on the nose wheel than is necessary.

And don’t forget go-arounds. If you are not certain that you will stop in the remaining runway distance, go-around and try again (or go somewhere more suitable to your skill level). All this might seem academic until you need it. One day you might need to land on the Caribbean island of Saba. The runway is only 400 metres total length! If you are not up to scratch, take a snorkel. Hopefully, that will give you some good reasons to get out and analyse your landing performance, and if there are problems, you should now be able to work on those (with the help of your instructor).

Aero Circus has recently published a book called ‘Refine Your Flying Skills’. This article is an extract from the book, which explores a range of techniques pilots can use to enhance their professionalism when ‘behind the yoke’. See aerocircus.com.au for more details. Aero Circus is run by a small group of pilots who are independent of airlines, employers, flying schools or other industry associations. They attempt to write unbiased articles with the aim of helping pilots of any experience level get more out of aviation.