WHEN WILL WE START THE FLARE - Three Case Studies

ENGLISH	PORTUGUÊS
The above gif was taken when for a minute of simulation from the 900 seconds to the 960 seconds. It shows tracks identified as safe in cyan and tracks identified as anomalous in yellow. This identification is done at every simulation step as can be seen for track 3661.	O gif acima foi tomado quando para um minuto de simulação a partir de 900 segundos até os 960 segundos. El mostra trajetórias identificadas como seguras em ciano e trilhas identificadas como anômalas em amarelo. Esta identificação é feita em cada etapa de simulação, como pode ser visto para a faixa 3661.

WHEN WILL WE START THE FLARE

·         Source: Airbus Safety

Contributors:

-    Raimund GEUTER Expert Pilot Flight Operations Support

-    Sundeep GUPTA Accident/Incident Investigator Product Safety

-    Thomas LEPAGNOT Accident/Incident Investigator Product Safety

-    Marc LE-LOUER A300/A310 Flight Operations Support Engineer Customer Support

-    Xavier LESCEU,  Andris LITAVNIKS and Christian PAQUIN-LAVIGNE

-    Airbus Canada.

Source: National Aviation University, Kyiv, Ukraine.

PROCEEDINGS, THE SIXTH WORLD CONGRESS, "AVIATION IN THE XXI CENTURY", “Safety in Aviation and Space Technologies”.

E. O. Kovalevskiy, candidate of engineering

V.V. Konin, Doctor of Engineering

T.I. Olevinska, post-graduate student

Source: James Albright, retired U.S. Air Force pilot with time in the T-37B, T-38A, KC-135A, EC-135J (Boeing 707), E-4B (Boeing 747) and C-20A/B/C (Gulfstream III).

Source: Math Works, MATLAB for Artificial Intelligence.

Source: Vernier, Airliner Takeoffs and Landing with Graphical Analysis

 Two methods of aircraft flare are considered:

a) fixation of touchdown point and altitude exponential step     change.

b)     step change of trajectory slope.

In both cases gradual descending of height and vertical speed was achieved.

 Landing is divided into linear decrease on the glide slope and maneuver of flare, in which aircraft is moving by the exponential trajectory.

 For a trajectory coming to land at Boston Logan International airport (KBOS) on runway 22L to be safe, the trajectory must satisfy the following rules:

•   The trajectory must be closely aligned with the runway          direction.
•   The glide slope must be between 2.5 and 4 degrees in the last 20963 meters. At distances above 20963 meters, the altitude must be at least 3000 ft.
•   The speed must be between 120 knots and 180 knots at the landing point. The upper speed bound can increase linearly with distance from the landing point.

 Below a graph illustration for Boeing 737’s takeoff and landing.

FIRST CASE STUDY: Airbus

BOUNCED LANDING

NOSE LANDING GEAR IMPACT AND

A TAIL STRIKE ON GO-AROUND

 An A320 was on the final approach segment of its ILS approach, configured for landing (CONF FULL).

The Pilot Flying (PF) disconnected the autopilot at 370 ft Radio Altitude (RA) and kept autothrust ON. At 200 ft, tailwind variations caused the airspeed to drop below approach speed (Vapp).

Operational Considerations

 Role of the Pilot Monitoring (PM)

The FCOM SOP for landing requests a SPEED callout by the PM in the case of speed deviation of 5 kt below the target speed. The PF should initiate a go-around unless they consider that a stabilized condition can be recovered by small corrections to the aircraft and within sufficient time prior to landing.

The FCTM states that the risk of tail strike is increased due to the high angle of attack and high pitch attitude if the speed of the aircraft is allowed to decrease too far below Vapp before the flare.

Looking at step ① in the event described above, it shows the speed went below Vapp -5 kt from 100 ft and below. If the PM had made a “SPEED” callout then the PF may have noticed the speed decay and attempted to correct it or initiate a go-around if it was not likely to stabilize in time.

Flare Height

The FCOM states that in a stabilized approach, the flare should be initiated at 30 ft for A320 family aircraft (the values for other Airbus aircraft are provided later in this article).

The FCTM recommends initiating the flare earlier if there is a tailwind. This is because a tailwind will contribute to a higher ground speed with an associated increase in vertical speed to maintain the approach slope.

Initiating the flare earlier would have reduced the high vertical speed of the aircraft in the event described above.

Thrust Lever Management

The A320 FCTM explains that the flight crew can rapidly retard all thrust levers to IDLE either earlier or later than the 20 ft “RETARD” auto callout reminder depending on the conditions. However, the thrust levers should be at IDLE by touchdown to ensure that the ground spoilers will extend and keep the aircraft on the ground.

In step ② of the event, the PF pushed the thrust levers above the CLB detent during flare. This increased thrust and inhibited the ground spoiler extension during the initial touchdown, which contributed to the aircraft bounce.

Bounce Management

For a high bounce, as was the case in the incident described above, the FCTM recommends maintaining the aircraft’s pitch attitude and performing a go-around.

The hard impact of the nose landing gear with the runway described in step ④ of the event was caused by extension of the ground spoilers when the thrust levers were retarded to IDLE during the bounce combined with a full forward stick input after the bounce.

 Go-Around Close to the Ground

The FCTM recommends avoiding an excessive rotation rate during a go-around close to the ground and to counteract any pitch-up effect due to the thrust increase.

In step ⑤ of the event, it was the full back stick input combined with the nose landing gear bounce and thrust increase that contributed to the tail strike.

RECIPE FOR A SAFE LANDING

The recommendations below summarize the procedures and techniques provided in the FCOM and FCTM.

Be stabilized

A safe flare can only be achieved when the aircraft is stabilized, meaning that all of the flight parameters areas expected, including:

- the aircraft is on its expected final flight path (lateral and vertical)

- speed is close to Vapp, and

- wings are level.

If the aircraft reaches the flare height at the correct speed and it is on the expected flight path, then a normal flare technique will lead to a safe landing.

PM must call out any flight parameter deviation

Careful monitoring of the flight parameters including speed, pitch, bank and vertical speed, enables the PM to raise the attention of the PF to any deviation during the final approach. This will enable the PF to respond accordingly and initiate a go-around, if required.

Refer to the FCOM SOP for Approach for more information about the PM callout related to the flight parameter deviation threshold.

Flare at the right time

Flare should be initiated at around:

·         30 ft RA (A220/A300/A310/A320) or

·         40 ft RA (A330/A340/A350/A380) in stabilized conditions.

 Factors that may require an earlier initiation of the flare:

- Steeper approach slope (more than the nominal 3º)

- Increasing runway slope or rising terrain before the runway threshold

- Tailwind

- High airport elevation.

SECOND CASE STUDY: National Aviation University, Ukraine

The bottom line is fixation of flare beginning point coordinates (x_f, h_f) and touchdown point coordinates (x_td, h_td).

(x_g, h_g) – glide slope beginning point, (x_g0, h_g0) – is a fictitious point on the ground on which glide path is projected, (x_∞, h_c) – is a final point of flare which is chosen in such way, that the exponent of flare trajectory intersects the ground at the touchdown point.

Two stages for reaching desired horizontal and vertical speed at touchdown point (x_td).

First stage

Decreasing horizontal speed W up to desired value W_z from point x_g to point x_f while height is on level h_f = h_z.

Second stage

Fixing the horizontal speed and begin to change the height by the exponential law from the value h_z – h_с to the value h_с in such a way, that the exponent line crosses the point x_td with the vertical speed of h_p.

The input data for Math modeling is:

Horizontal speed: Wz=40 m/s;

Desired vertical speed in touchdown point (point where h=0): phz=0.5 m/s;

Initial trajectory slope angle in radians: γ₀ =0.097;

Flare beginning height: hz=15 m.

Flare begins at the moment: t=655 s.

The trajectory slope angle change from the flare beginning by the height change law, the vertical speed change law and the flare period equation.

FROM INPUT DATA

Height and vertical speed calculation

The first method provides more accurate touchdown.

It is the fixation of touchdown point and altitude exponential step change.

THIRD CASE STUDY: James Albright

A G450’s flight path vector at 10 ft. on a short runway (KBED Runway 23). By James Albright.

“I find that raising my eyes to the end of the runway, but below the horizon, does the trick. The photo shows the flight path vector (symbology that shows the aircraft’s trajectory) slightly below the end of the runway because I was looking at the runway’s end, not the horizon. If I sense the airplane has leveled off, I’ll nudge the stick forward with the thought, “Keep it coming down.” This assures the aircraft continues to descend. Even without flight path vector technology, the pilot needs only to shift his or her eyes to the end of the runway to keep the descent rate going. But there is a little more to it than that, and for that we need to look at some timing.”

G650’s flare path starting at 25 ft

When we begin the flare, the MLG will be at 25 ft. and the pilot’s eyes 14.5 ft. higher. The aimpoint will be 39.5 ft. / tan(3deg.) = 754 ft. away. Since the MLG have to travel an additional 42 ft., we know the distance of the flare will be a total of 796 ft. If we assume a ground speed of 120 kt., the flare will take:

The flare can be learned scientifically by instilling the need to begin at a consistent height, pulling back at a consistent rate, and with your eyes pointed at the end of the runway. Each event should be graded looking for a 4-sec. rotation to flare, ending with the wheels touching at the desired aimpoint.

How to Land an Airplane, in Summary

(1) Fly a stable approach, on speed, on the proper glidepath.

(2) Cross the runway threshold at 50 ft. visually or electronically. Remember that if flying visually or on an ILS glideslope, your wheels will be lower than 50 ft. (In our example, that was 35.5 ft. when flying visually.)

(3) Determine the proper flare height based on any flight manual data or on what you have determined by experience. This height can be made evident by electronic means, such as a radio altimeter, but should always be backed up with a point on the runway that you expect to just disappear under the nose. (In our example, a point 600 ft. short of the aimpoint.)

(4) At the proper flare height, shift your eyes to the end of the runway (not the horizon), and using one smooth and continuous motion, pull back to your flare rotation pitch. The pull should take 4 sec. and should end as the wheels touch with the aircraft still in a 100- to 200-fpm descent rate.

Notice that we have not mentioned thrust at all, which will be handled in accordance with aircraft-specific procedures. My technique is to allow the autothrottle “retard” function, if available, to function as designed. This further reduces the number of variables. If operating without autothrottles, I attempt to initiate the reduction at the same time I initiate the pitch rotation, reaching idle as the wheels touch. This has worked on every aircraft I have flown, but I recognize it will not work for others.

One last note for those flying aircraft with unpublished eye-to-wheel and flare heights. The math shown here is for a Gulfstream G650, an aircraft in the 100,000-lb. range that is nearly 100 ft. long. Using a 25-ft. flare height will probably be conservative for smaller aircraft but will give you a starting point. (Remember larger aircraft may have flare heights around 30 ft.) I recommend trying these out in the simulator or seeing what you have been doing in the airplane as a comparison. The first step in any scientific endeavor is observation. I believe you can improve your landings if you approach the landing flare as science, not art.

Factors that may require an earlier flare

Flare should be initiated at around:

30 ft RA (A220/A300/A310/A320) or

40 ft (A330/A340/A350/A380) in stabilized conditions.

“The PF must avoid forward stick inputs once flare is initiated.”

Any forward stick input after flare is initiated will increase the risk of landing on NLG with hard impact.

The PF must start the flare with a positive and prompt back pressure on the control column to break the descent rate. The PF must then maintain a constant and positive back input on the control column until touchdown.

Retard! Retard! Retard! Retard!

For A320/A330/A340/A350/A380 aircraft

The 20 ft “RETARD” auto callout is a reminder, not an order. The PF can retard the thrust levers earlier or later depending on the conditions.

“The PF must ensure that the thrust levers are at idle in any case, by touchdown at the latest, to enable automatic extension of the ground spoilers.”

In the case of a bounce - Maintain the aircraft pitch

HIGH BOUNCE

·         Maintain pitch

·         Apply go-around thrust

·         Counteract any pitch-up tendency (because of THRUST INCRESE. That will avoid TAILSTRIKE).