WAS IT A FLARE ACCIDENT OR LANDING ACCIDENT?

 

INVESTIGATION MUST REPORT IF THE ACCIDENT WAS A LANDING ACCIDENT OR A FLARE ACCIDENT

Mastering the Landing Flare/Round out

Pilot Perception

Analysis of 6,676 aircraft accident reports published by the National Transportation Safety Board

134 pilots with varying experience levels

Sources:

•           THE INTERNATIONAL JOURNAL OF AVIATION PSYCHOLOGY, 12(2), 137–152
•      Oklahoma State University
•      Department of Psychology
•      Laboratory of Comparative and  Behavioral Biology

           Danny Benbassat and Charles I. Abramson

•  Razia Rashid - founder of Psychology To Safety
•  ATSB RESEARCH AND ANALYSIS REPORT
• Aviation Safety Research Grant – B2005/0119

Aerial perspective is a monocular cue which is used for depth perception [the atmosphere causes distant objects to look hazy or blurry], which is used to judge how far away objects are. Monocular cues are named because they can occur only using one eye (as opposed to binocular cues which only occur with the use of both eyes).

Critical perceived time to contact (TTC)

Time remaining until the aircraft’s wheels make contact with the runway if no further action is taken (Mulder et al 2000).

TTC must be estimated directly, without first estimating speed and distance, based on the following ratio (known as tau):

TTC ≈ θ/(dθ/dt)

Where θ is the visual angle between the aimpoint and any other point on the ground plane at time one (see Figure above); and dθ/dt is the rate of change of this angle over time (Hoyle F 1957; Kaiser & Mowafy 1993; Lee, DN 1976).

Tau is a monocular cue to time-to-contact. During a landing, tau can be defined as the ratio of the angular distance between any two points on the ground (which happen to lie along the aiming line) divided by how fast this angular distance is increasing. Several other versions of tau have been proposed (see Regan & Gray 2000).

In more recent aviation research, Mulder and colleagues (2000) found mixed support for the proposals that flare timing is based on perceived runway angle (ψ) and perceived TTC (based on tau).

Study

The effects of pilot’s critical flare operation on long and hard landing events based on real flight Quick Access Recorder (QAR) data.

Flare accident rates

Causes for improper flares

The flare is the transition from a controlled descent to actual contact with the landing surface (Federal Aviation Administration [FAA], 1999; Grosz et al., 1995) and is also known as the flare out, round out, or level off (Jeppesen, 1985).

The task of determining the aircraft altitude above ground is crucial to a successful flare (Green, Muir, James, Gradwell, & Green, 1996) and is accomplished by the use of vision more than any other sense (FAA, 1999; Jeppesen, 1985; Menon, 1996; Nagel, 1988; Thom, 1992).

Depth Perception

Depth perception deals with the ability to see the environment in three dimensions and estimate distances of objects from us and from each other.

Aerial Perspective, objects at larger distances from us are affected by natural scattering of light and form less of a contrast with their background; making it harder to gauge a distance between the two and us.

Monocular cues operate when a person is looking with only one eye

 Pilots rely on monocular depth perception cues rather than binocular depth perception cues (Benson, 1999; Bond, Bryan, Rigney, & Warren, 1962; Langewiesche, 1972; Nagel, 1988).

Monocular depth perception is learned or dependent on experience (Benson, 1999; Bramson, 1982; Langewiesche, 1972; Love, 1995; Marieb, 1995; Tredici, 1996).

-          It is used by artists to induce depth in their two dimensional paintings. Thus, they are also called as the pictorial cues.

The monocular cues that help us in judging the depth and distance in two-dimensional surfaces:

·         Linear perspective: Imagine you are standing between the rail tracks and looking in the distance. You would see that the rail track become smaller and smaller, until there is a point where they meet each other. Linear perspective reflects this phenomena. It says that the distant between two objects far away appear to be smaller than what the distance actually is.

·         Interposition or overlapping:  This monocular cue occurs when one object covers the other. The object that is completely visible seems to be nearer and the object that is partially visible seems to be farther away.

·         Clearness: The more clear the object the nearer it seems. For example, on a hazy day a distant mountain would appear far away than on a clear day, because haze blurs the fine details. Therefore, if we see details of an object we perceive it closer.

·         Relative height: We perceive large objects to be closer to us and smaller objects to be farther away.

·         Motion parallax/ Movement: This cue occurs when the objects are in motion. The distant object appears to move slowly than the objects that are close.

Binocular cues operate when both our eyes are working together

Binocular depth perception is innate or acquired very early in life (Fox, Aslin, Shea, & Dumais, 1980; Kalat, 1998; Reading, 1983; Reinecke & Simons, 1974).

The cues that are provided by both the eyes working together:

·         Retinal or binocular disparity: Humans have two eyes which are horizontally separated by a distance of 6.5 centimeters. Because of this distance between two eyes the images formed on retina of a same object is slightly different. This difference in the images of two eyes is retinal disparity.

·         Convergence: when we see a closer object our eyes turn inward or converge, so that the image is formed on the fovea. Some muscles in our eyes send signal to the brain regarding the degree of convergence and our brain interprets it as a cue for depth perception. The more your eyes turn inward or converge the nearer the objects appear in the space.

·         Accommodation: The process by which ciliary muscles change the focal length of the eyes so that the image is clearly formed on the retina is called the accommodation of the eye. The accommodation varies for near and distant objects and also for objects moving away or towards the eye.

Failure to accurately determine aircraft altitude may result in flaring the aircraft too high (Gleim, 1998; King, 1999; Quinlan, 1999) or too low above the runway (Christy, 1991; Kershner, 1981; Love, 1995).

Improper flares also increase brake, nosewheel tire, and nosewheel shimmy dampener wear (on Cessnas; Christy, 1991; Jorgensen & Schley, 1990).

Improper flares may affect pilot self-esteem and selfefficacy.

The flare maneuver was defined as the ability to determine 10 to 20 ft from the ground and initiate the leveloff.

Three groups of pilots (novice, intermediate, and expert) were surveyed with purposive sampling.

Participants were 134 pilots (novice = 55, intermediate = 45, expert = 34) from three Part 141-approved flight schools in the state of Oklahoma.

Pilot perceptions were assessed with a 21-item questionnaire.

Pilots were asked to rate the flare maneuver and nine other randomly selected standard flight maneuvers for the level of difficulty on a scale ranging from 1 (extremely easy) to 7 (extremely difficult) under optimal conditions (i.e., no wind, 10 miles visibility).

After rating the 10 items, pilots turned the page and learned that the study was specific to the landing flare.

In Item 11

Pilots were provided with the number of total annual U.S. landing accidents and were asked to estimate the number of annual flare accident frequencies.

In Item 12

Pilots were asked to indicate how confident they were in their estimates of annual flare accident frequencies on a scale ranging from 1 (low confident) to 7 (high confidence).

The next items were not only specific to the landing flare but also to their ability to determine when to initiate the flare, that is, estimate 10 to 20 ft from the ground.

In Item 13

Pilots imagined that they were transitioning from descent attitude to flare attitude and indicated how confident they were that their aircraft was 10 to 20 ft from the ground on a scale ranging from 1 (low confidence) to 7 (high confidence).

In Item 14

Pilots recalled their first solo flare attempts and rated factors that assisted them in determining the aircraft altitude before initiating the flare (CFI instruction, instrument readings, practice, pilot manual, ground-school training, other) on a 7-point-scale ranging from 1 (not at all) to 7 (to great extent).

In Item 15

After a reminder that pilots flare the aircraft 10 to 20 ft from the ground, ascertained how pilots rated the task of judging altitude when initiating the flare on a scale ranging from 1 (very easy) to 7 (very difficult).

In Item 16

Pilots imagined that they were on approach for landing and were asked to choose how they determine when to initiate the flare. how did they know they were 10 to 20 ft from the ground (instrument readings, gut reaction, I don’t, sense of sight, sense of balance, other).

In Item 17

Pilots were asked to indicate if there was a need for improved flare-training methods, on a scale ranging from 1 (definitely yes) to 7 (definitely no).

In Item 18

To what factors (pattern practice, natural ability, sheer luck, aviation books, my instructor, other) did they attribute their current successful landing flares, on a scale ranging from 1 (not at all) to 7 (to great extent).

Items 19 and 20 (reiterated Items 16 and 18)

Required pilots to elaborate and explain their responses. Pilots were instructed to think carefully before they answered and be as specific as possible.

In Item 21

Pilots were asked to indicate what type of visual information assisted them in determining when to initiate the flare.

CONCLUSION

 Overall, 6,676 accident reports produced by the NTSB were analyzed for flare accident rates.

Flare accidents

Proper flares depend on monocular cues, and monocular cues depend on experience (Hawkins, 1993; Rinalducci, Patterson, Forren, & Andes, 1985).

On average, the flare only lasts approximately 6 sec and a pilot with a total time of 5,000 hr only has approximately 8 hr of flare time (King, 1998).

In more recent aviation research, Mulder and colleagues (2000) found mixed support for the proposals that flare timing is based on perceived runway angle (ψ) and perceived TTC (based on tau).

Critical perceived runway angle (ψ)

Pilots could initiate the landing flare when the visual angle (ψ) formed between the left and right edges of the runway at the aiming line reaches a critical value (Mulder et al, 2000).

In fact, pilots use different cues or combinations of monocular cues. For example, overall, the horizon and end of runway, shape of runway or runway markings, and familiar objects were the most frequent visual cues that pilots used to estimate their altitude during the flare.

However, University of Oklahoma pilots most frequently used the horizon or end of runway, whereas Oklahoma State University pilots used the shape of runway or runway markings.

Softer throttle reduction is helpful for a better flare performance. Not immediately IDLE. 

The force of the engines and of gravity are driving the airplane down and forward. When you rotate the nose up for the flare, some of the energy that was used to propel the airplane forward is now used to further arrest the force of gravity. You have less force available for forward motion, your speed necessarily decreases.

Flare energy

The rotation-to-flare requires energy to arrest downward momentum; the amount of energy required depends on the glide path angle, any differences in aircraft speed from target speed, and any acceleration/deceleration. It will be to your advantage to make the angle and speed differences the same for every landing.

The rotation-to-flare may or may not bleed airspeed, depending on aircraft flight idle and ground effect characteristics. Here are three examples:

 B747 — The combination of a very large wing span induced ground effect perfectly compensates for energy needed to arrest the descent. Once the descent has been arrested, the flight idle and ground effect result in no airspeed loss at all under most conditions. The airplane has to be flown onto the runway, it will not run out of speed and sit itself down.

GV — The GV also has a very large wing span and high flight idle engines. The descent can be arrested with very little loss of speed, but the airplane does lose speed gradually if held inches off the runway. But, once again, it should be flown onto the runway to avoid a long landing.

G450 — The G450 will lose about 5 knots in the rotation to flare, which is precisely the minimum speed increment to VREF. Once the rotation to flare is made, speed decay continues as flight idle and ground effect are not enough to maintain speed. Any exaggerated flare for the sake of touchdown will result in a significant loss of speed. Once again, the airplane should be flown onto the runway.

VERY SOFT LANDING

The FLARE curve it has two breaking points: The first, it is on (Xf, Hf) [Glide Slope breaking point] and the second one it is on Xtd flare breaking point [Flare breaking point it is at the touchdown point]. Ideally, from this point on the flare curve must be tangent to runway surface to make a soft landing.

Very soft landing, it is that the Pilot Flying does not let the green curve flare segment [beyond Xtd point] to descend below X axis.

That green curve segment after the touchdown point it can NOT descend below the X axis. 

It does tangent on the runway surface plane for smoothing landing.

When to flare

What "the book" says:

"Very few manufacturers specify a flare height. Gulfstream, for example, leaves you off at 50 feet and the next thing you know, you are in the touchdown zone. Some Bombardier manuals say, "at or below 50 feet." About the only manufacturer that does print a height is Boeing. In their Boeing 777 Flight Crew Training Manual, they say this: "Initiate the flare when the main gear is approximately 20 to 30 feet above the runway by increasing pitch attitude approximately 2° - 3°. This slows the rate of descent." That pretty much agrees with what we did in the Boeing 747." 

You should consult your manufacturer's books.

HINT

Pilot after crossing over threshold at the height 50 ft for landing MUST NOT LET his/her eye corners to capture any lateral vision, mainly Pilot Flying, because of lateral vision illusion which induces pilot to see a relative movement speeding up the plane. That false relative speed up produces a sensation of runway length it would be shortening very quickly. Runway excursion.

LATERAL ERROR DURING LANDING

 

Conventional head-down display X Head-up display (HUD)

Source:

Örjan Goteman

Scandinavian Airlines Stockholm, Sweden

 

Kip Smith and Sidney Dekker

Department of Industrial Ergonomics Linköping Institute of Technology

References

Refer to FAA Advisory Circular 90-106A, issued 3/2/17

Nichol, Ryan J., “Airline Head-up Display Systems: Human Factors Considerations”. International Journal of Economics and Management Sciences, 4:248, May 3, 2015. https://www.omicsonline.org/open-access/airline-headup-display-systems-human-factors-considerations-2162-6359-1000248.php?aid=54170

 

AC No: 90-106A 2017

AC No: 20-167A 2016

AC No: 25-118 2014

AC No: 90-106A 2017

Third-generation aviation HUDs use optical waveguides that produce images directly in the combiner, without the need for a projection system. Some of the latest HUD systems use a scanning laser, which can display images and video on a clear transparent medium, such as a windshield.

It is possible that, during approach and landing, the HUD might affect the pilot’s ability to assimilate outside cues at the decision height, thereby reducing the success ratio for landings using an HUD.

HUD use reduced the width of the touchdown footprint in all tested visibility and lighting conditions, including visibility below the minimum allowed.

HUD use had no effect on the length of the touchdown footprint.

How ambient RVR affects approach and landing operations.

HUD USE IN COMMERCIAL FLIGHT OPERATIONS

A computer-generated aircraft flight-path and energy symbols presented onto a transparent screen in the pilot’s primary view.

HUDs replicate the information on the pilot’s conventional flight instruments, showing aircraft attitude, speed, altitude, and heading, and containing a flight-path symbol showing the aircraft velocity.

Conformal HUDs

A conformal HUD with a flight-path symbol can explicitly show the pilot where the aircraft is going relative to the surrounding world.

A pilot flying with conventional flight instruments must infer the aircraft’s flight path from a synthesis of the H-angle (Lintern & Liu, 1991), optical flow (Gibson, 1986), and possibly also the relative perspective gradient (Lintern, 2000).

Comparisons between HUDs and head-down displays in manual flight have found that conformal HUDs use improved track, speed, and altitude maintenance (Lauber, Bray, Harrison, Hemingway, & Scott, 1982; Martin-Emerson & Wickens, 1997).

The civil aviation community assumed that these HUD performance advantages over conventional head-down instrumentation could reduce the number of approach and landing incidents and accidents (Flight Safety Foundation, 1991).

Two well-documented problems associated with approach and landing: visual approaches to runways without radio navigation aids or with unreliable navigation aids, and the transition from instrument to external visual cues for landing in low visibility (e.g., Newman, 1995).

Pilot performance during landing in low-RVR conditions where transitioning from instrument to external cues for maneuvering is an issue.

The presumed sources for the advantage in flight-tracking performance for the HUD are that it eliminates the need for the pilot to move his or her gaze from head-down instruments to the outside world to look for maneuvering cues (Stuart, McAnally, & Meehan, 2003) and it minimizes scanning requirements (Mar[1]tin-Emerson & Wickens, 1997). The transition from head down to the outside world requires a change in visual accommodation (e.g., the visual depth of field changes from less than 1 m to infinity). Because conformal HUD symbology is focused at infinity, HUD use eliminates the need for and time demand of visual accommodation, simplifying the pilot’s task.

Cognitive tunneling

One possible negative effect of HUD in the landing situation is that inserting a glass plate with symbols in front of a pilot may affect his or her ability to visually acquire the approach lights, which is necessary to continue the approach below the decision height.

The light transmission through the HUD is not 100%. A commercial HUD will let about 85% to 90% of the incoming light pass through the glass plate. A detrimental effect of HUD use during the landing would then show up as a lower success ratio for HUD than for a conventional flight deck without HUD.

The segment of flight immediately before touch[1]down performed in U.S. and European civil air transport operation are conducted as Category I instrument landing system (ILS) approaches.

The two critical factors when making the decision of whether to land are the decision height and the RVR. Decision height refers to the aircraft’s vertical distance above the runway threshold where the pilot must make the decision to land or make a go-around.

The pilot must be able to see at least some of the approach or runway lights at the decision height.

The RVR is a measure of horizontal visibility defined by the length of visible approach and runway lights in the ambient atmospheric conditions. If the RVR is too low the pilot will not be able to see any of the approach lights at the decision height and must make a go-around.

Missed approach

It  is part of normal operations (and formal procedures), it adds an undesired additional risk(International Civil Aviation Organization [ICAO], 1993).

The approach light lengths differ from runway to runway. Geographical constraints sometimes make the standard full length of 720 m (Full Facilities) impossible to achieve. Fewer approach lights means less guidance and later contact with the approach lights during the approach.

For example, to commence a Category I ILS approach to a runway equipped with a 720 m length of approach lights, the RVR measured at the runway must not be less than 550 m (Federal Aviation Administration [FAA], 2002; Joint Aviation Authorities [JAA], 2004b). This RVR is expected to allow the pilot to see a visual segment of the ground that contains enough of the runway approach lights to judge the aircraft’s lateral position, cross-track velocity, and position in roll when the aircraft is at decision height.

Apart from the obvious effect that the approach lights will come in view later with lower RVR, other effects of shorter approach lights lengths could also come into play. If runway length has been shown to influence the perceived descent path (Lintern & Walker, 1991) it is also possible that a reduced length of approach lights can have similar effects, adding a source of uncertainty to the vertical control of the aircraft.

During landing the pilots have to concurrently process both outside cues and HUD cues to get any benefit from the HUD. The operational benefit from a reduction in touchdown variability could be that regulations would allow approach operations using HUD in lower than standard RVR conditions. The current operating minima were not set bearing HUD operations in mind and may be too restrictive for operations using HUD, a fact that the existing legislative text acknowledges (JAA, 2004b).

Setting RVR for approach too low will ultimately reduce approach success rate. In low RVR with very few external cues available at decision height, there is a risk that the pilots will focus their attention on the HUD symbology to the extent that they might not perceive the few visible approach lights at decision height. Pilots who do not pick up the out[1]side cues may thereby initiate a go-around when the approach actually could have been continued, an outcome that is not desirable from an operational stand[1]point.

The effect of HUD on touchdown performance for two different approach lights conditions as defined in the European regulations:

F     Full Approach Light facilities (≥ 720 m) and

b     Intermediate Approach Light facilities (420 to 719 m; JAA, 2004b).

EXPERIMENT 1

Experience on the B–737–700 varied from 50 hr to more than 1,000 hr.

It was used a CAE B–737–700 training simulator with aircraft aerodynamics and visual angles valid for B–737–700 to collect data. This six-axis full-motion simulator is approved for low-visibility operations down to an RVR of 200 m. The simulator’s visual system had a field of vision of 180°/40° with a focal distance greater than 10 m.

The HUD installed in the simulator was a Rockwell-Collins Flight Dynamics HGS–4000® (Head-up Guidance System), certified for low-visibility operations down to and including an RVR of 200 m. The HUD symbology and functionality used in the experiment met the production-line standard specification for the instrument meteorological conditions (IMC) mode used when conducting Cate[1]gory I ILS and non-precision approaches.

Forty-eight pilots from a major European airline volunteered to participate. All were qualified to fly the B–737–700 aircraft and had completed their HUD training for the operator. The HUD training sessions consisted of 1 day of theory and two simulator sessions of 4 hr duration each.

The HUD provided conformal display of flight path (velocity) and flight-path guidance. The flight path was displayed as a circle with slanted wings. Flight-path guidance was displayed in the form of a ring inside the flight-path symbol.

Flight-path guidance was not available in the conventional head-down instrumentation.

Each pilot manually flew two approaches using standard operating procedures of the airline. The scenarios started as a 6 nm final to the runway in lower than standard or standard RVR in a simulated 10 kt left crosswind. In the with-HUD condition, the pilots kept the aircraft on lateral and vertical by following the flight-path guidance ring with the flight-path symbol on the HUD. At 50 ft above the runway threshold, the guidance cue was automatically removed and the pilots performed the landing flare using external visual cues in conjunction with the HUD flight-path symbol. The HGS–4000® IMC mode incorporating automatic removal[1]of the guidance cue was deliberately chosen to ensure that the pilots could not attend solely to the HUD symbology in the with-HUD conditions.

In the no-HUD condition the pilots kept the aircraft on lateral and vertical track by following the flight director bar guidance. At decision height they continued the approach and landing using the external cues only.

Touchdown performance

11 of the 48 pilots con[1]ducted one or two go-arounds. The simulator failed to capture the location of the landing footprint for another 7 pilots. As a result the data set for comparing the touchdown footprints across the HUD and no-HUD conditions consists of 30 pairs of approaches. Of these 30, 15 were flown using the HUD in the first approach and 15 using the conventional head-down instruments (no-HUD) in the first approach;

15 were flown in standard RVR (550 m) conditions and 15 in lower than standard RVR conditions (450 m).

Lateral touchdown performance was measured as the absolute lateral deviation from the runway centerline at touchdown.

EXPERIMENT 2

Approaches in Experiment 2 were flown to simulations of a runway with 420 m of approach lights. This length falls within the intermediate facilities category of approach lights as defined by European aviation regulations (JAA, 2004b).

Each participant flew one approach with HUD and one approach without HUD to a runway with a system of approach lights of 420 m length. The between-subject variable was RVR at two levels, a standard minimum RVR (700 m) for intermediate facilities and a lower than standard minimum RVR (550 m to 600 m).

Forty-five [45] pilots from the same major European airline volunteered to participate. None of the volunteers had participated in Experiment 1. All were qualified to fly the B–737–700 aircraft and had completed their HUD training for the operator. Experience on the B–737–700 varied from more than 50 hr to more than 1,000 hr.

Each of the 45 pilots attempted two approaches.

Thirty-two made two successful landings, one with HUD and one without. Four pi[1]lots made go-arounds in both conditions. Three pilots landed with the HUD and made go-arounds without the HUD; six pilots landed without the HUD and made go-arounds with the HUD.

Touchdown performance

As a result, the data set for comparing the touchdown footprints across the HUD and no-HUD conditions consists of 28 pairs of approaches. Of these 28 pairs of approaches, 9 were flown using the HUD in the first approach and 19 using the conventional head-down instruments (no-HUD) in the first approach; 14 were flown in standard RVR (700 m) conditions and 14 in lower than standard RVR conditions.

As in Experiment 1, the effect for HUD use on the lateral component of the touch[1]down footprint is strong, F(1, 26) = 14.9, p < .001, η2 = .10, indicating a power greater than .70. Once again, landings were closer to the centerline when pilots used the HUD.

Three findings:

111. HUD use per se did not influence the pilots’ decision to land or go-around at the decision height.

The lack of an effect of HUD suggests that the additional information in the HUD did not distract the pilots’ attention or interfere with their decision making during the most critical portion of the approach and landing sequence.

2.2.HUD use significantly reduced the size of the lateral component of the touchdown footprint for all RVR conditions.

The difference between the HUD and the no-HUD conditions lay in the presence of a conformal flight-path vector in the pilots’ primary field of view during the landing.

3.3.In contrast to its effect on the lateral component of the touchdown footprint, it appears that the HUD did not influence the size of the longitudinal footprint.

The ubiquitous and ever-varying direction and velocity of wind is likely to preclude the development of true automaticity at touch[1]down. Crosswinds introduce an element of uncertainty regarding drift (the shift in lateral location of the aircraft relative to the runway’s centerline). For the pilot to detect drift the visual ground segment needs to be long enough to determine the aircraft’s movement over the ground. That means that to detect drift at all, a notice able lateral displacement must take place and not all of this displacement can be corrected before touchdown.

The HUD largely eliminates uncertainty about drift.

The addition of a conformal flight-path vector projected over the runway provides instantaneous feedback about aircraft drift and actual flight path. The additional information enables precise control of the flight path during approach and landing and reduces the variance in lateral displacement practically to nil.

Control of the longitudinal component of the touchdown footprint is largely an effect of how pilots handle the aircraft’s energy (operationally manifested as sink rate) in the final seconds before landing. The pilot uses information provided by the optic flow from the looming runway to control the aircraft’s energy (Lee, 1974). It is important to note that pilots of large commercial air transport aircraft are also aided by radio altimeter callouts that count down from 50 ft to 0 ft (runway contact) in 10-ft decrements.

The initiation of the landing flare has been shown to be a function of time to contact (Mulder, Pleijsant, van der Vaart, & van Wieringen, 2000). A small change in the timing of a landing flare at the nominal glide slope of 3° results in large longitudinal differences. The HUD mode used in the experiments provided no flare guidance and no additional information that could be used to guide the pilots when to initiate the landing flare.

HARD LANDINGS - Helping pilots better handle the airplane during landing

 

SOURCE: NTSB and FAA

Advisory Circular 120-71 "Standard Operating Procedures for Flight Deck Crew Members" and Flight Standards Information Bulletins for Air Transport (FSATs) 00-08 and 00-12.

 

World Intellectual Property Organization (WIPO)

HARD LANDING REPORT BASED ON SINK RATE ALGORITHM

Issue: High sink rate awareness during landing.

Foresight bounce recognition and recovery

Hard or heavy landings are significant high load events that may adversely impact airframe structural integrity. Such landings may result in damage that affects the ability of the aircraft to fly safely. When this happens, repairs must be performed prior to flying the aircraft again.

The inspection process that is required to assess the potential for damage due to a suspected hard landing event is undesirably time consuming.

Studies showed that up to 90% of pilot-initiated hard landing inspections resulted in no finding of damage.

The results of performing unnecessary inspections include undesirably increased labor costs and lost revenues due to the down time of the aircraft.

Study case

Strong pitch up after the second hard touch-down and strong nose-down pitch forces.

Boeing defines hard landings that exceed 12.3 feet per second [fps] or that involve rapid derotation [lowering the nose wheel to the runway after the main gear touches down after the initial touchdown as severe.

1. ·         Pilot monitoring for high sink rates.
2. ·         Appropriate timing of the landing flare.
3. ·         The flare is based on gross weight, temperature and pressure.
4. ·         Airspeed trend vector is useful tool in determining when to begin to flare.
5. ·         Aural altitude calls and the radar altimeter.

You don't want that accident investigation final report writes down "the cause of the accident it was the pilot-flying inability to arrest the high rate of descent existing at 50 feet [ft] radio altitude."

"SINK RATE" aural alert from EGPWS [Enhanced Ground Proximity Warning System] it is your first and foremost calling for your attention.

The load factor provided by an air data inertial reference unit AD RU), which is not reliable due to the body-bending response in the fuselage at touchdown.

The ADIRU is located at the forward section of the fuselage and the load factor is mathematically translated to the airplane's center of gravity to determine the load factor value. Data analyses of actual landings from operators have shown that the load factor is an unreliable indicator of a hard landing event.

A false report of a hard landing can result in an unnecessary costly structural inspection and has the potential to delay dispatch of the airplane.

The indication of a hard landing as reported within an airplane condition monitoring function (ACIV1F) is based on data recorded from nose[1]mounted accelerometers, combined and recalculated to correct for the true location of the aircraft's center of gravity.

The sink rate algorithm comprises a second-order complementary filter

followed by a lag time noise reduction (i.e., smoothing) filter. The output main gear vertical sink rate takes into account the landing gear position with respect to the runway surface.

Activation of the sink rate computation occurs at some preset elevation (e.g., 200 feet) above ground level of the wheel carriage as determined by the radio or radar altimeter.

Monitoring continues until a predetermined time (e.g., 2 second) after the point of touchdown.

The sink rate algorithm disclosed herein has application for reporting hard

landings by aircraft of different types. The sink rate algorithm disclosed herein has been adapted for use with models 200 and 300 of the Boeing 777 aircraft.

The sink rate algorithm disclosed herein is based on a design that has been widely used in autopilots.

FIG. 1 shows the main components of a hard landing detection system in accordance with one embodiment of the invention. The ACMF 10 comprises a logic unit for performing the steps of a sink rate algorithm, such as the algorithm depicted in FIGS. 2A[1]2D. The sink rate algorithm outputs a main gear sink rate in response to the inputting of the following parameters: (1) radio altitude (in feet; + is up); (2) pitch attitude (in degrees; + is nose up); (3) body pitch rate (in deg/sec; + is nose up); (4) vertical speed (feet/min; + is up); and (5) vertical acceleration (g; + is up). The ACMF 10 receives radio altitude data from a radio altimeter 14, which is mounted on the airplane. The ACMF 10 receives data representing values of the other four parameters from an ADIRU 12. As will be explained in more detail later, the ACMF also receives data representing the current gross weight of the airplane from a flight management function (FMF) 16.

The sink rate output is smoothed with a quarter-second time constant lag filter to provide a clean, well-behaved estimate of the sink rate during flare and touchdown. This algorithm is currently being used within Flight Controls on the 777 because of its accuracy.

Using the vertical acceleration parameter to calculate sink rate has an advantage over using the vertical speed in that the vertical acceleration is not corrupted by ground effects as the airplane nears the ground.

Ground Proximity Warning System (GPWS)

Mode 4 – Terrain Clearance Not Sufficient (while in landing configuration). Mode 4A and 4B are active during cruise and approach, and Mode 4C is active during go-around. Mode 4A triggers “Too Low Terrain, Too Low Gear” when the landing gear is up, Mode 4B triggers “Too Low Terrain, Too Low Flaps” with flaps not in landing configuration (but landing gear down) and Mode 4C triggers with flaps not in landing configuration OR gear up: “Too Low Terrain”.

Mode 5 – Excessive Descent Below Glide Slope – triggered when the aircraft descends below the glideslope and the aural alert “Glideslope” is triggered.

Note: the above warnings, cautions and callouts differ depending on the aircraft type (and can even differ on the same type of aircraft when different systems are installed).

Enhanced GPWS

Enhanced GPWS (EGPWS) supplements Basic GPWS with a database of terrain and airports, and correlates this with the known position of the aircraft.

EGPWS (or “Predictive GPWS”) has a computer model of the aircraft performance and uses this to create a caution and warning envelope in front of the aircraft, including the ability of the aircraft to climb.

When the Predictive GPWS is operating normally the Basic GPWS Mode 2 (Excessive Terrain Closure Rate) is inhibited. If a failure is detected in the Predictive GPWS, or there is a significant discrepancy between detected rad alt height and the T2CAS altitude, Basic Mode 2 is re-enabled.

On Basic GPWS

Mode 2 – Excessive Terrain Closure Rate: Mode 2 takes into account gear and flap configuration. There are two types of Mode 2 alerts: Mode 2A (active during climb, cruise and initial approach) and Mode 2B (active during approach and 60 secs after takeoff). With landing gear up the warnings are “Terrain”, “Terrain Terrain” and “Pull Up”. With landing gear down, the “Terrain” caution is triggered.

Airbus A320/A330/A340 Predictive GPWS – Warnings and Cautions

The Airbus A320/330/340 aircraft utilize a Terrain Awareness Display (TAD) function which develops a caution and warning envelope in front of the aircraft. The TAD takes into consideration the aircraft’s altitude, nearby runways and the altitude of the runway, together with the aircraft’s speed and turn radius.

When the system detects a threat in the projected envelope it will trigger the relevant GPWS caution and warning callouts (aural alerts).

Adam B733 at Surabaya on Feb 21st 2007, hard landing.

Adam Air Boeing 737-300, registration PK-KKV performing flight KI-172 from Jakarta to Surabaya (Indonesia) with 148 passengers and 7 crew, was approaching Surabaya's runway 28 in thunderstorm rain, visibility 8000 meters. When the aircraft descended through 200 feet AGL the captain called the aircraft was too high and took control, subsequently the Ground Proximity System issued alerts "Pull Up!" and "Sink Rate!" The right hand main gear touched down outside the runway, about 4 meters off the right edge of the runway. The captain steered the aircraft back to the center line of the runway and brought it to a stop about 100 meters short of taxiway N3. Two passengers received minor injuries (backbone pain), the aircraft received substantial damage including a fractured/bent fuselage.