APPROACH OPERATIONS IN REDUCED VISIBILITY

 

HUD With a Velocity (Flight-Path)

Vector Reduces Lateral Error During

Landing in Restricted Visibility

Örjan Goteman

Scandinavian Airlines

Stockholm, Sweden

Kip Smith and Sidney Dekker

Department of Industrial Ergonomics

Linköping Institute of Technology

The majority of approaches (the segment of flight immediately before touchdown) performed in U.S. and European civil air transport operation are conducted as Category I instrument landing system (ILS) approaches. For a Category I approach 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 approach lights will then guide the pilot to the runway.

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.

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.

EXPERIMENT 1

Method

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. Experience on the B–737–700 varied from 50 hr to more than 1,000 hr. There is every reason to believe that these participants are representative of the population of commercial pilots to whom regulators need the data to generalize. Apparatus. We 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 head-down instrumentation was a B–737–700 instrument panel in primary flight display (PFD) configuration with flight director guidance. This instrumentation was available in both the with-HUD and the no-HUD conditions.

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 meterological conditions (IMC) mode used when conducting Category I ILS and non-precision approaches (see Figure 6). This mode was deliberately chosen to improve the external validity on the form of operational usability of the study. In normal operations, the vast majority of ILSs are only approved for Category I operations. 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.

The radio navigation facilities simulated in the study conformed to the ICAO (1996) standard for ILS radio navigation aids for Category I approaches transmitting a radio beam for both vertical and lateral reference. The integrity of the transmitted beam is guaranteed to keep the aircraft within allowable airspace, safe from

Gulfstream GVII-G500 in level flight at 40,000 feet, Mach 0.90. 

obstacles down to 200 ft height, corresponding to lowest allowable decision height. Approaches in Experiment 1 were flown to a simulated runway with a system of approach lights 900 m in length. This length falls within the full facilities system category of European aviation regulation (JAA, 2004b).

Procedure. 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 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.

All approaches were recorded to determine approach success. Approach and landing plots for approaches ending with a landing were printed using the aircraft’s center of gravity as the reference to determine the size of the touchdown footprint.

Results

Approach success rate. Each of the 48 pilots attempted two approaches.

Thirty-seven made two successful landings, one with HUD and one without. Three made go-arounds in both conditions. Two pilots landed with the HUD and made go-arounds without the HUD; six landed without the HUD and made go-arounds with the HUD.

The McNemar change test is the appropriate statistical procedure for testing the null hypothesis that pilots were equally likely to (a) land with the HUD and go-around without it, and (b) land without the HUD and go-around with it (Siegel & Castellan, 1988). Because the observed test statistic, calculated from the values given earlier (2 and 6), is 1.125 and is less than the criterion, x² (.05, 1) = 3.84, we cannot reject the null hypothesis. Accordingly we infer that HUD use had no impact on approach success rate.

Touchdown performance. As noted previously, 11 of the 48 pilots conducted 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. The data for the main effect of HUD use are shown in Figure 7. Landings were closer to the centerline when pilots used the HUD. The two-factors repeated-measures analysis of variance (ANOVA) revealed a strong effect for HUD use on the lateral component of the touchdown footprint, F(1, 28) = 9.05, p < .006,   n² = .12 indicating a power of .80 at α = .05.

The main effects for RVR and order of HUD condition were not significant. There was, however, a marginally significant interaction between HUD use and the order

EXPERIMENT 2

Method

The method, procedure, and design used in the second experiment were identical to those used in the first experiment with the few exceptions discussed here. The different criteria for standard RVR across facility types preclude collapsing and analyzing the data as a single experiment.

Participants. Forty-five 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 theirHUDtraining for the operator. Experience on the B–737–700 varied from more than 50 hr to more than 1,000 hr.

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

 

Results

Approach success rate. Each of the 45 pilots attempted two approaches.

Thirty-two made two successful landings, one with HUD and one without. Four pilots 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. Once again we used the McNemar change test to test the null hypothesis that pilots were equally likely to (a) land with the HUD and go-around without it, and (b) land without the HUD and go-around with it. Because the observed test statistic, calculated from the values given previously (3 and 6) is 0.44 and is less than the criterion, x² (.05, 1) = 3.84, we infer that HUD use had no impact on approach success rate.

 Touchdown performance. As noted earlier, 13 of the 45 pilots conducted one or two go-arounds. The simulator failed to capture the location of the landing footprint for another 4 pilots. 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. The opportunistic nature of data collection precluded balancing the order of HUD use.

The main effect for HUD use, shown in Figure 9, is the only factor in the two-factor repeated-measures ANOVA to achieve statistical significance. As in Experiment 1, the effect for HUD use on the lateral component of the touchdown footprint is strong, F(1, 26) = 14.9, p < .001, n² = .10, indicating a power greater than .70. Once again, landings were closer to the centerline when pilots used the HUD. Because participant order was not fully counterbalanced, it is not possible to assess the potential for asymmetric transfer effects. As in Experiment 1, there was no significant effect for HUD use or RVR on the longitudinal component of the touchdown footprint. Once again, the difference in the observed variances across conditions of HUD use would be significant at  α = .10 if the data sets were independent.

There are three findings. First, 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. Second, HUD use significantly reduced the size of the lateral component of the touchdown footprint for all RVR conditions.

 Arguably it can be said that 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. Third, 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 first two findings conform to our hypotheses. Here we reexamine our hypotheses about the impact of HUD use on the touchdown footprint and offer an explanation for its differential impact on the lateral and longitudinal components.

 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. So, if the pilots are relying more on timing of a flare maneuver than on velocity cues from the HUD to initiate the flare, it is easy to understand why we failed to detect any effect of the tested HUD with a flight-path symbol on longitudinal touchdown performance. It remains to be seen whether similar results are found for HUD modes with flare guidance, and which visual representations are actually most effective in prompting pilots to reduce sink rate at the optimal height above the runway.

 

CONCLUSIONS

Data from the experiments reported here show that HUD with a conformal velocity symbol (flight path) improved lateral touchdown performance, likely because the conformal flight-path vector in conjunction with the visual ground segment makes it easier for pilots to determine and correct for aircraft drift. We did not find an effect of HUD use on longitudinal touchdown performance, probably because the pilots flared the aircraft using a time-to-contact strategy, rather than using the flight-path vector available in the HUD modes studied here. The beneficial effects of HUD use on landing performance were seen in both in standard and lower than standard RVR conditions in both experiments, which implies that the minimum RVR for approaches using an HUD could be set lower than for approaches without an HUD.

BACKGROUND

 “Where is the nose of the aircraft?” 

It is shown as a flat vee with wings and is called a boresight.

 “Where is the horizon?”

It is below you, as shown by the synthetically drawn terrain.

The pilot’s primary focus is no longer where the aircraft is pointed, but where it is going. That is represented by the Flight Path Vector (FPV) and is drawn as a circle with small wings and a tail. The white horizontal line can be thought of as a horizon that has been adjusted to consider the altitude of the aircraft, as if the earth’s diameter has been increased. In some HUDs it is called a Zero Pitch Reference Line. You maintain level flight by placing the FPV on the Zero Pitch Reference Line.

The U.S. rules are given in 14 CFR 91.176 and are further explained in Advisory Circular 90-106A. If you meet the requirements of section (b) of that FAR, you can operate using EFVS to 100 feet above the touchdown zone elevation, at which point you must take over what the regulations call “natural vision” to complete the approach and landing. If you are operating under part 91K, 121, 129, or 135, you will need a management or operations specification. If you meet the requirements of section (a) of that FAR, you can operate using EFVS to touchdown and rollout. You will need a letter of authorization, management specification, or operations specification. AC 90-106A lists 1000 RVR as an adequate flight visibility and authorizations are normally written with this as a minimum.

Recent flight experience: EFVS. Except as provided in paragraphs (f) and (h) of this section, no person may manipulate the controls of an aircraft during an EFVS operation or act as pilot in command of an aircraft during an EFVS operation unless, within 6 calendar months preceding the month of the flight, that person performs and logs six instrument approaches as the sole manipulator of the controls using an EFVS under any weather conditions in the category of aircraft for which the person seeks the EFVS privilege. The instrument approaches may be performed in day or night conditions; and

(1) One approach must terminate in a full stop landing; and

(2) For persons authorized to exercise the privileges of § 91.176(a), the full stop landing must be conducted using the EFVS.

Source: 14 CFR 61, ¶61.66 (d)

comparison of flight director symbology

Click on image below to download it for visualization on large TV (magnification 9 times)

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.

FPV - Flight Path Vector - It Is Sensible You Include It in Your Scanflow

ENGLISH                                                                             PORTUGUÊS

If you have a heads up display and/or synthetic vision, the flight path vector is your best friend. What follows are some explanations on how we do the following tasks without the flight path vector and how we can do things better with it.

Se você tiver um heads-up display e/ou visão sintética, o vetor de trajetória de voo (FPV) é seu melhor amigo. O que segue são algumas explicações sobre como fazer as tarefas seguintes sem o vetor de trajetória de voo e como podemos fazer as coisas melhor com ele.

Flight Path Vector (FPV) and Flight Path Angle (FPA)

Vetor de Trajetória de Voo (FPV) e Ângulo de Trajetória de Voo (FPA)

Bibliografia

Davies, D. P., Handling the Big Jets, Civil Aviation Authority, Kingsway, London.
Instrument Procedure Handbook FAA-H-8083-16

Using the 60 to 1 concept, you know that a three degree glide path should keep you 300 feet in the air for every nautical mile from the runway. At 2 nm you should be at 600', 3 nm at 900', and so on. If there is a VOR near the runway, you can figure the DME at the touchdown zone and subtract that. In the example drawing, for example, the VOR is a mile from the end of the runway.	Usando o conceito 60 para 1, você sabe que uma trajetória de planeio de 3° (três graus) deve manter você no ar menos 300 pés a cada milha náutica da cabeceira da pista. A 2 NM, você deverá estar a 600', 3 NM a 900' e assim por diante. Se houver um VOR perto da pista, você pode estimar o DME na touchdown zone e subtrair isso. No exemplo do desenho, o VOR está distante uma milha do final da pista.
Your FMS should also have the runway end programmed, giving you another excellent countdown of the miles to go. Just multiply the miles to go by 300'.	Seu FMS também deve ter o fim de pista programado, dando a você uma outra excelente contagem regressiva das milhas a voar. Basta multiplicar as milhas a serem voadas por 300 pés.

The FPV is a small circular symbol (1) which, when the FPV button on the EFIS is depressed, superimposes over the Attitude Indicator (AI) part of the Primary Flight Display (PFD). The circular symbol represents the aircraft's axis in relation to the vertical and lateral movement referenced to the Earth's surface.  If you were stationary on the ground, the circle would be on the horizon line and centered in the display.

O FPV é um pequeno símbolo circular (1) que, quando o botão FPV no painel do EFIS é pressionado, superpõe sobre a parte do Indicador de Atitude (AI) do PFD – Primary Flight Display. O símbolo circular representa o eixo da aeronave em relação ao movimento vertical e lateral em referência à superfície da Terra.  Se você estivesse parado no solo, o círculo estaria na linha do horizonte e centrado na tela.

The data received by the FPV is derived mostly from the Internal Reference System (IRS) of the aircraft; therefore, the Flight Path Vector provides an almost instantaneous display of flight path angle and drift information.

Os dados recebidos pelo FPV são derivados principalmente do Sistema de Referência (IRS) da aeronave. Portanto, o FPV fornece uma exibição quase instantânea de informações da deriva e do Ângulo da Trajetória de Voo (FPV).

When the aircraft changes from climb phase to level flight, the FD bar is commensurate with the configuration of the aircraft (speed, weight, flap, etc.) and the FPV would be on the horizon line, indicating level flight.	Quando a aeronave muda de fase de subida para voo nivelado, a bar do FD fica proporcional com a configuração da aeronave (velocidade, peso, flaps, etc.) e o FPV estaria na linha do horizonte, indicando o nível de voo.
Decending in approach phase on a 3 degree glidepath, the position of the FD and Horizon Heading Scale (aircraft symbol bar/pitch bar) is  dependent upon the speed, flap and gear extension, but the position of the FPV will stay at 3 degrees, unless the flight controls are used to alter the aircraft's pitch.	Descendo na fase de aproximação em uma trajetória de planeio de  3 graus, a posição da Escala de Proa no Horizonte (símbolo da aeronave/símbolo de “pitch”) e FD é dependente da velocidade, posição dos Flaps, extensão do trem de pouso, mas a posição do FPV ficará em 3 graus, a menos que os controles de voo sejam usados para alterar o ângulo de inclinação longitudinal da aeronave.
The FPV will provide greater accuracy than the Horizon Heading Scale as it does not 'lag' behind real time as other instruments can do; therefore, it is sensible for flight crews to include this tool in their routine scan.	O FPV proporcionará maior precisão do que a Escala de Proa no Horizonte, visto que ele não 'se move' lentamente em tempo real como outros instrumentos pode fazer. Portanto, é SENSATO para as tripulações de voo incluir esta ferramenta na rotina de scanflow.

FPV - Flight Path Vector Operation click on this link to watch the operation

Flight Path Vector (FPV)

The flight path vector shows where the airplane is headed. On the HUD, it shows the pilot the airplane's vector in relation to all the weather, to the runway's database position, and to terrain as infrared characteristics permit. With synthetic vision, it will shown the airplane's vector in relation to the terrain and the runway's database position. With just a few exceptions, your primary focus is on the flight path vector.

Vetor de Trajetória de Voo (Flight Path Vector - FPV) mostra onde o avião está aproado. No HUD, mostra ao piloto o vetor do avião em relação a tudo: formação meteorológica, posição da pista baseado nos dados da pista e terreno quando  características infravermelho  permitirem. Com visão sintética, será mostrado o vetor do avião em relação ao terreno e a posição em relação à pista de pouso. Com apenas umas poucas exceções, seu foco primário está no Flight Path Vector.

Bore Sight

The bore sight is the nose of the aircraft, which is where the airplane is headed adjusted for Deck Angle, and drift. It is where the pointy end of the aircraft symbol appears on a conventional attitude indicator. You will need to focus exclusively on this in the event of a wind shear recovery maneuver; the flight path vector will be greatly impacted by the wind and aircraft performance during the recovery. During a CFIT escape maneuver you will also focus on the boresight, but the flight path vector will be of use on your synthetic vision.

A Visão de Mira (Bore Sight – BS) é o nariz da aeronave, o qual é onde o avião está aproado e ajustado pelo   ângulo do Flightdeck e deriva. É onde a ponta do ponteiro do símbolo do avião aparece em um indicador convencional de atitude. Você precisará focar exclusivamente sobre isto no caso de uma manobra de recuperação de WINDSHEAR; o Vetor de Trajetória de Voo (FPV) será grandemente afetado pelo vento e desempenho da aeronave durante a recuperação. Durante uma manobra de fuga CFIT você também focará no Bore Sight (Visão de Mira), mas o FPV será de melhor utilidade para você no visor sintético.

Reference Flight Path Angle (FPA)

Ângulo de Referência da Trajetória de Voo (FPA)

The reference flight path angle (FPA) draws a line at a selected angle from the airplane to the ground or the air above. It is independent of aircraft attitude.

O Ângulo de Referência da Trajetória de Voo (FPA) traça uma linha em um ângulo selecionado a partir do avião até o solo, ou até um ponto no espaço aéreo acima. Ele é independente da atitude da aeronave.

Reference Flight Path Angle (FPA) Line and flight path vector

Ângulo de Referência de Trajetória de Voo (FPA) e Vetor de Trajetória de Voo (FPV)

The HUD draws a line from the airplane to the ground at whatever angle you command. This angle comes from the airplane to the ground. The line it draws on the ground shows where your airplane will end up if you follow that angle.	O HUD traça uma linha do avião até o solo em qualquer ângulo que você comandar. Este ângulo vai do avião ao chão. A linha que ele desenha no chão mostra onde seu avião terminará o voo se você seguir esse ângulo.
Understanding that the line comes from the aircraft and not the ground is vital to using the line to your advantage. In each of the three examples, the flight path vector is right on the touchdown zone of the runway.	Entendendo que a linha vem da aeronave e não do chão é vital para usar a linha em seu benefício. Em cada um dos três exemplos, o Vetor de Trajetória de Voo (FPV) vai direto na zona de toque da pista.

If the line is short of the runway, you need to “walk the line up” by reducing your angle of descent. In the drawing you have raised your pitch to the touchdown zone but your flight path angle is still short of the runway. This means you will indeed land in the touchdown zone, but at too shallow an angle. You should further reduce your angle to "return to glide path."

Se a linha terminar antes da cabeceira da pista, você precisa "deslocar a linha para frente", ao reduzir seu ângulo de descida. No desenho você teve seu “pitch” levantado para a zona de toque, mas seu Ângulo da Trajetória de Voo (FPA) está ainda aquém da pista. Isto significa que você realmente pousará na zona de toque, mas em um ângulo muito raso. Você deve reduzir ainda mais o seu ângulo para "voltar à trajetória de planeio”.

If the line is beyond the touchdown zone of the runway, you need to “walk the line back” by increasing your angle of descent. In the drawing you have decreased your pitch so that the flight path vector is on the touchdown zone. This means you will land in the touchdown zone, but at too steep an angle. If time permits and you are above Stabilized Approach height, you should further increase your descent angle to "return to glide path."

Se a linha terminar além da zona de toque na pista, você precisa "trazer a linha para  trás", aumentando seu ângulo de descida. No desenho você diminuiu seu “pitch” tal que o Vetor da Trajetória de Voo (FPV)  está sobre a zona de toque. Isto significa que você pousará na zona de toque, mas em um ângulo muito acentuado. Se o tempo permitir e você estiver acima da altura de Aproximação Estabilizada, você deve aumentar ainda mais o seu ângulo de descida para "voltar à trajetória de planeio".

If the line is on top of the touchdown zone of the runway, that is where you will end up if you don't flare. A proper flare consumes less than 500'.

Se a linha estiver no topo da zona de toque da pista, que é onde você terminará se você não flutuar no pouso. Uma flutuação em si, consome menos de 150 metros de pista.

With a flight path vector and HUD all the guessing is history; simply place the flight path vector on the touchdown zone and keep it there until it is time to flare.

Com um Vetor de Trajetória de Voo (FPV) e Head-Up Display todos os palpites são estórias; simplesmente coloque o FPV sobre a touchdown zone e o manteha lá até a hora de flare.

If you are performing an honest to goodness PULL UP response to a GPWS warning on rising terrain, by all means perform the AFM maneuver, such as the G-450 CFIT escape maneuver. But if you have synthetic vision it really pays to have the flight path vector up, especially when IMC.

Se você estiver executando uma resposta  autêntica à mensagem PULL UP do alerta do GPWS sobre terreno acidentado, sem dúvidas realize a manobra do AFM, a manobra de fuga. Mas se você tem visão sintética, realmente vale a pena ter o FPV em cima, especialmente quando em IMC.

Remember to perform the maneuver while looking at the aircraft boresight, that shows where the nose is and gives you the best idea about how to max-perform the aircraft's vertical escape. But try to take a look at the flight path vector while you are at it. It will tell you if you are going to clear the terrain or not, but it also gives you a view several degrees left or right. Maybe you can make life a lot easier, and livable, by sneaking in a few degrees of bank one way or another.

Lembre-se de executar a manobra enquanto observa na Visão de Mira (Bore Sight) da aeronave,  que mostra onde o nariz está e dá a você a melhor ideia acerca de como efetuar a máxima fuga vertical da aeronave. Mas tente dar uma olhada no FPV enquanto você está nisso. Ele dirá a se você  está indo livrar-se do terreno ou não, mas também dá a você uma visão de vários graus a esquerda ou direita. Talvez você possa fazer a vida muito mais fácil e vivível, ao mover furtivamente  uns poucos graus de inclinação lateral em um rumo ou no outro.

You fly the BORE SIGHT to steer the FLIGHT PATH VECTOR away from MOUNTAIN TOPS

Flight Path Vector (FPV) Advantages

Vantagens do Vetor de Trajetória de Voo (FPV)

It allows you, at a glance, to assess the performance of the aircraft. If the FPV is in the blue part of the Primary Flight Display, you are definitely ascending. Vice-versa when you are 'in the brown'. If you are unlucky enough to have a windshear encounter, the first instrument to warn you other than the  aural warning will be the FPV as it assumes an unusual position (drops away or rushes up). The other instruments (altitude, vertical speed and airspeed) have significant lag before they accurately show the true picture of what is occurring, but the FPV provides an almost immediate indication (live-time).  It is an ideal tool to use during non-precision approaches as it provides the flight crew with additional situational awareness, especially during night operations. The FPV is an ideal tool to gauge the accuracy with which the aircraft is flying a glideslope and can be used to cross check against other information. The FPV is an ideal tool to monitor non-automation phases of the flight (manual flying) as the flight crew need only to keep the FPV on the horizon to maintain level flight. The FPV registers the smallest trend almost immediately, while the flight director (FD) will only correct an issue after a deviation has occurred.  The FPV can be used to provide additional information during crosswind landings. If you look at the FPV as part of your usual instrument scan, the FPV will provide visual display to whether you are correctly aligned with the centerline of the runway (the FPV will display the drift). ·         The last point requires expanding upon, as the FPV can be used to determine the correct rudder deviation to use when using the sideslip method for a crosswind approach and landing. A crosswind will push the FPV circle in the direction that the wind is blowing TO. Rudder inputs will cause the FPV symbol to move towards the the center of the Altitude Indicator.  Once the the FPV is centred in the Altitude Indicator, the aircraft is aligned correctly (no drift).

• Ele permite a você, de relance, avaliar o desempenho da aeronave. Se o FPV estiver na parte azul do PFD, você definitivamente está subindo. Você estará descendo quando ele estiver na parte ' marrom' do PFD. • Se você estiver azarado o suficiente para ter um encontro com windshear, o primeiro instrumento a avisar você, não sendo o aviso aural, será o FPV quando ele assume uma posição incomum (cai fora ou apressa-se para acima). Os outros instrumentos (altitude, velocidade vertical e velocidade do aerodinâmica) tem atraso significativo antes que eles mostrem com precisão oa verdadeiro quadro do que está ocorrendo, mas o FPV fornece uma indicação quase imediata (tempo real). • É uma ferramenta ideal para usar durante aproximações de não-precisão uma vez que ele fornece à tripulação de voo consciência situacional adicional, especialmente durante as operações à noite. • O FPV é uma ferramenta ideal para medir a precisão com a qual a aeronave está voando uma RAMPA DE PLANEIO e pode ser usada para verificação cruzada contra outras informações. • O FPV é uma ferramenta ideal para monitorar as fases do voo de não-automação (voo manual) como quando a tripulação de voo necessita de só manter o FPV no horizonte para manter o voo nivelado.  • O FPV registra a menor tendência quase que imediatamente, enquanto o diretor de voo (FD) somente corrigirá um problema após um desvio ter ocorrido. • O FPV pode ser usado para fornecer informação adicional durante os pousos com vento cruzado. Se você olhar no FPV como parte de seu scanflow usual de instrumentos, o FPV fornecerá apresentação visual se você está corretamente alinhado com a linha central da pista (o FPV exibirá a deriva). • O último ponto requer expandir, como o FPV pode ser usado para  determinar a deflexão correta do leme a usar, quando usando o método de derrapagem para uma aproximação e pouso com vento cruzado. Um vento cruzado empurrará o círculo do FPV na direção para qual o vento estiver soprando. Ajustes do leme causarão ao símbolo do FPV mover-se em direção ao centro do Indicador de Altitude.  Uma vez que o FPV estiver centrado no Indicador de Altitude, a aeronave estará alinhada corretamente (sem deriva).