Considerations – How to Flare and Land a Big Jet

Question

Ricky recently asked me the following question on the QF32 web site:

Good evening Richard,

I read all your books and have been huge inspiration during my training to become a pilot. I read you have flown nearly all airplanes and in the book you also mention a technique used on Caribou airplane.

Now I’m flying PA28 and a problem I’ve had during my training is to start flaring quite high, basically I look to the aiming point (abeam the PAPI) then when over the threshold I start looking to the far end of the runway, and Immediately my perception is to start gradually pulling as I feel a high closure rate. The result is flaring high and running out of energy too high.

My instructor doesn’t give much help in this as the common answer is “you’ll develop with experience “. In your opinion how can I improve? Maybe before i posted on the wrong section of this website 

FLY! – the Elements of Resilience

Here is my Answer (for Big Jets)

Hi Riky,

Flying a stable approach to landing is one of the most difficult manoeuvres we do in aviation and poor-unstable approaches are almost inevitably contributing factors in most landing accidents. So it’s good to get a few basics correct about how to make an approach and land.

Please note: The following is written to suit Big (commercial airline) Jets.   Whilst your small aircraft is certified to standards that are different to the (part 25) standards for the Big Jets, many of the concepts remain relevant for your type.

The keys to a good approach and landing in big jets are:

1. Know your runway length (performance) and width (flare height perception)
2. Avoid Tailwinds if possible
3. Fly the correct approach-glidepath angle
4. Approach at the correct airspeed 1.3Vs / 1.23 Vs1g
5. Get the correct Flare Height
6. Focus on the aimpoint to the flare height
7. At the flare height lift your eyes to focus at the end of the runway
8. Touchdown in the correct area
9. Fly the aircraft onto the ground
10. Correct Rate of Descent at touchdown
11. Don’t float
12. Summary

1. Know your runway length and width.

Know your aircraft performance and the excess runways length for your landing.

Know the runway width. Pilots tend to flare high and float on runways that are wider than the runways they are (habitually) accustomed to.

2. Avoid Tailwinds if possible

Tailwinds increase your rate of descent:

• reducing approach thrust – increasing time to spool up the engines in a go-around – increasing height lost below the decision heights during aborted approaches
• increasing the risk for overstressing the landing gear
• increasing aircraft energy and stopping distance

3. Fly the correct approach-glidepath angle

The ideal approach angle is 3 degrees or 5%. This angle gives clearance from the Obstacle Free Zone (OFZ) that is carved by airport designers for your aircraft type and type of approach. The OFZ provides clearance from trees, obstacles and terrain. The three degree glidepath also gives a rate of descent (ROD) that can be calculated (using your GPS) as approximately “five times your groundspeed (GS) + 50” feet per minute. So if you are approaching in a big jet at 130 kts GS, your ROD should be 650 + 50 = 700 feet/min. When you do this calculation often enough, you can do it quickly in your head using a GS (NOT IAS) readout.

The PAPI / VASI should be aligned to your approach path.

It’s important to fly the correct approach path and airspeed because when you do this, you will also maintain the correct rate of descent as you approach the airfield to flare and land. If you come in to steep then your rate of descent is higher and you need to flare earlier-faster to arrest the rate of descent before touchdown.

Large aircraft are certified to sustain maximum RODs of 600 FPM (10 Feet Per Second (FPS) at touchdown. The shock absorbers are designed to take a ROD of 720 FPM / 12 FPS at touchdown.

4. Approach at the correct airspeed (IAS) 1.3Vs / 1.23 Vs1g

In 1943 the FAA designed landing performance with the aircraft at 50′ over the end of the runway at a speed equal to its stall speed + 30% (1.3 VS).

Because manufacturers test pilots fudged their flying techniques when calculating the VS speeds, the FAA in the late 1980s changed 1.3Vs to a more practicable and “unfudgeable” 1.23 VS1g. (VS1g is the speed where the lift equals the aircraft’s mass. It’s also called the “G Break” speed).

All aircraft certified after the mid 1990s are certified using Vs1g.

Be aware that tailwinds add significant risks to safe landings. For a constant IAS, not only does your groundspeed (GS) increase with tailwinds, but the kinetic energy to stop increases with the square of the GS.

Garuda Indonesia Flight 200‘s approach to Yogyakarta was at a classic example of excess energy.   The 737 touched down 860m beyond the runway threshold at a speed of 221 knots (409 km/h; 254 mph), 87 knots (161 km/h; 100 mph) faster than the normal landing speed.  That aircraft had an energy on touchdown 221^2/87^2 = 6.45 times the normal energy on a normal approach.

5. Get the correct Flare Height

It’s important to commence your flare at the correct height and develop a consistent flare to touchdown.

The ideal flare height depends upon many factors, but in ideal conditions (nil wind, flat runway, IAS, approach angle) will be at the same height. If your flight manual has no information or you are unsure about calculating this height then the Jacobson Flare website and software might be of help.

(Photo RDC)

6. Focus on the aimpoint to the flare height

It’s important to keep your eyes on your aimpoint all the way through to reaching your flare height. When you focus on the correct aimpoint, then you are guaranteeing setting up to reach 50 feet at the runway threshold, and so you are guaranteeing your aircraft performance.

DO NOT lift your eyes up to the end of the runway as you approach the flare height. If you do, you will unconsciously pull back on the controls, causing the aircraft to pitch up, float and land long.

As you approach the runway focussing on the aim point, you will “feel” the runway and the ground environment expands in your peripheral vision. It’s for this reason that you MUST know the width of your runway. It’s because of this altered peripheral perspectives that all (even experienced) pilots tend to (incorrectly) flare high and float on wider runways.

When your mind subconsciously matches its sensory inputs with pattern of sensors stored from ideal landings, then your mind subconsciously triggers a habitual response in your cerebellum to move the muscles to commence the flare.

The only ways to build the sensory memory of the correct flare point is to either follow the practices of the instructors that get it right, or study the Jacobson Flare above. Remember, practice builds habits.

7.  At the flare height lift your eyes to focus at the end of the runway.

When your peripheral vision gives you the sensory input that you have reached your flare height, this is the time when you should look up and focus towards the end of the runway and commence your flare.

When you look up, you now concentrate on the touchdown. Your peripheral sight provides your sense of your rate of descent, helping you arrest it and land at the correct rate of descent.

8.  Touchdown in the correct area

Vale Eric Melrose Winkle Brown (1919-2016)

The role of the approach is to position you at the runway threshold at 50 feet at a steady speed of 1.3VS / 1.23 VS1g. If you achieved this, then your approach was perfect. Now for the landing…

Landing performance is calculated using an air segment (commencing 50 feet over the runway threshold at the correct IAS) and a ground roll segment. The ideal air segment is about 7 seconds from 50 feet to touchdown.

The design rule of 7 seconds from 50′ to touchdown should be your guide. Anything quicker indicates a shorter and harder touchdown, anything longer should be a flag that you are probably outside your landing performance assumptions.

9.  Fly the aircraft onto the ground

At the flare height:

• Lift your eyes to focus on the end of the runway.
• Pitch the aircraft nose-up slightly to achieve a gradual reduction in the rate of descent (that your peripheral vision is sensing).
• When your rate of descent reduces to the rate of descent you wish to land with, then hold that attitude (by looking at the angle of the dashboard/cowling to the horizon)  until the aircraft settles on the ground.

Adarsh, Texas, USA (Photo: Vidhya)

10.  Correct Touchdown Rate of Descent

During the touchdown keep you eyes at the end of the runway as you fly your aircraft to the ground.

At touchdown, the designs have you flying at 5 knots slower than 1.3VS / 1.23VS1G (lose 5 kts in the flare) and so you have heaps of excess speed to lose. So if you pull the nose too high, then you will float!

The harshness of the touchdown should vary with conditions.

• If the runway is wet or slippery, then a harder touchdown is warranted to have the tyre push through and displace the viscous layers to the runway surface.
• If there is a strong crosswind then it’s good to get the wheels firmly on the ground quickly.
• If it’s a dry runway, then you can afford to finesse the touchdown.

Here’s guidance for the egotists who strive for a  smooth landing every time.  A smooth landing is only impressive or even acceptable when:

• you touch down within 7 seconds after passing the threshold at 50 feet.  A smooth touchdown in any other situation could be compromising performance margins and therefore increasing your risks of a float/overrun, and
• landing on a dry runway, or
• landing on an uncontaminated or wet runway at a speed that is below your aquaplaning speed. (Vaquaplane kts = 9 times the square root (tyre pressure psi)

11.  Don’t Float

Most people don’t realise why floating down the runway is dangerous. So here is the reason you should NOT float.

The Coefficient of Lift Induced Drag (Cdi) reduces exponentially as the aircraft approaches a few of its wing spans from the ground. The Prandtl’s Lifting Line Theory states that CDi (induced drag) reduces to ~ 50% at 10% of the wingspan ground clearance.

This reduction in Cdi is called “Ground Effect”. When the drag reduces, your deceleration reduces. So an aircraft flying in ground effect will decelerate at a slower rate than an aircraft outside ground effect. When arriving at 50 feet the correct speed of 1.3VS/1.23 VS1g, your aircraft has an excess speed of about 23%-30%, most of which must be lost during the landing. The aircraft in ground effect has significantly lower drag, so an aircraft in ground effect will lose its excess ground speed very slowly, and will be able to fly over and overrun the runway before touching down.

Here is Weiselberger’s theory (graph) for a 747-400 (213’ wingspan), increased by 12’ for the winglets. The graph shows the ground effect during an approach and Induced Drag. CDi is down to 50% in the flare!

InducedDrag_Vs_Alt

The reduction in CDi is why:

• Do not allow the airplane to float, fly the airplane (well above its stall speed) onto the runway.
• Do not attempt to extend the flare by increasing pitch attitude in an attempt to achieve a perfectly smooth touchdown.
• Do not attempt to hold the nose wheel off the runway (because you reduce the force on the wheels and their braking efficiency).

12.  Summary (for Big Jets)

• good landings only ever follow equally good approaches to 50 feet
• practice builds habits.   Practice your landings until the flare height and flare procedure becomes habitual
• know when to transition your focus from the aim point to the runway end
• fly the aircraft onto the ground – don’t float
• know your aquaplaning speed
• a smooth landing is only impressive when it’s within certification limits and safe