The Dark Side of the Visual Landing

 

The Dark Side of the Visual Landing

 The visual approach, intended to benefit everyone, frequently results in pilots experiencing exactly the opposite effect. Visual approach incidents reported to the ASRS frequently cite confusion, with resultant stress on the flight crews. There are a variety of performance errors revealed in ASRS reports.

 How do Visual Illusions Affect the Pilot's Perception?

Visual illusions result from the absence of or the alteration of visual references that modifies the pilot perception of his / her position relative to the runway threshold.

Visual illusions affect perception of heights, distances and/or intercept angles.

 

Visual illusions are most critical when transitioning from IMC and instrument references to VMC and visual references.

Visual illusions (such as the black-hole effect) affect the flight crew vertical and horizontal situational awareness, particularly during the base leg and when turning final (as applicable) and during the final approach.

Visual illusions usually induce crew inputs (corrections) that cause the aircraft to deviate from the original and intended vertical or lateral flight path.

 “Black hole” along the final approach flight path:

In case of approach over water or with an unlighted area on the approach path, the absence of visible ground features reduces the crew ability to perceive the aircraft lateral and vertical position relative to the intended flight path.

 

Low intensity lights create the impression of being farther away (hence on a shallower glide path).

 Decrease in Speed (Well Below Vapp) Before the Flare

Flight at too low a speed results in a high Angle-of-Attack and a high pitch attitude, and therefore, reduced ground clearance. When the aircraft reaches the flare height, the flight crew must significantly increase the pitch to reduce the sink rate. This will further reduce the ground clearance.

 Sink Rate Too High Just Prior to Reaching the Flare Height

If the sink rate is too high when the aircraft is close to the ground, the flight crew may attempt to avoid a firm touchdown by commanding a high pitch rate. This action will significantly increase the pitch attitude. However, if the resulting lift increase is not sufficient to significantly reduce the sink rate, a firm touchdown may occur. In addition, the high pitch rate may be difficult to control after touchdown, particularly in the case of a bounce.

 

Bounce at Touchdown

In the case of a bounce at touchdown, the flight crew may decide to increase the pitch attitude, to ensure a smooth second touchdown. If the bounce results from a firm touchdown associated with a high pitch rate, it is important for the flight crew to control the pitch, so that it does not continue to increase.

Crosswinds Not Handled Correctly

When the aircraft is close to the ground, the wind velocity tends to decrease, and the wind direction tends to turn (direction in degrees decreasing in northern latitudes). The flight crew must be aware that during the approach phase, and especially during the flare, a crosswind effect could suddenly increase the pitch of the aircraft, and result in tailstrike.

 HGST - Head-UP Guidance System Technology

 Most importantly, HGST provides real-time display of the aircraft Flight Path Vector and acceleration conformal with the real world scene and allows the pilot access to other critical information such as airspeed, altitude, etc. while viewing the outside scene.

 

Seventeen distinct safety properties of the HGST were defined

 The study concludes that in modern jet aircraft (glass cockpit) the HGST might have prevented or positively influenced 38% of the accidents overall.

 Of these accidents where the pilot was directly involved, such as takeoff and landing and loss-of-control accidents, the likehood of accident prevention due to HGST safety properties becomes much greater, 69% and 57%, respectively.

HGS SAFETY PROPERTIES

1. Flight Path Vector

The Flight Path Vector is inertially derived and provides instantaneous indication of where the aircraft is going relatively to the outside world on a conformal display.

2. Flight Path Acceleration

The acceleration (or deceleration) of the aircraft along the flight path is indicated by the Flight Path Acceleration symbol. The flight path acceleration is made up of the total acceleration forces acting on the aircraft, including acceleration generated by both the aircraft in the form of thrust and acceleration generated by the air mass the aircraft is moving through. To avoid confusion in the control of aircraft thrust, the Flight Path Acceleration symbol is removed from the display when the HGS detects a low-level decreasing performance windshear.

3. Guidance Cue

The guidance cue provides lateral/vertical guidance from the Flight Control Computers (FCC) and provides lateral/vertical guidance to touchdown through rollout from the HGS computer. It also provides takeoff guidance from the HGST computer for lower-than-standard takeoff minimums.

 4. Speed Error Tape

The speed error tape provides a positive or a negative presentation of airspeed difference between actual and selected airspeed with an intuitive tape presentation. It also provides the pilot very precise control of speed in conjunction with the inertia caret.

 5. Runway Remaining

The Runway Remaining symbology provides a digital readout in 500 feet increments during the takeoff ground roll and Category III Mode Rollout. The symbol simulates the runway markings such that the display will show a decrement by 500 feet as each marker is passed.

 6. Deceleration Rate Index

The deceleration rate index presented using the inertia caret indicates deceleration with respect to the airplane autobrake algorithms or other deceleration references familiar to the crew. The inertia caret algorithms run independently in the HGS computer and present an inertially derived deceleration indexed on the combiner. The index on the combiner is presented with indices that represent their values that correlate to the airplane autobrake settings or other deceleration performance references useful to the crew.

 

7. Unusual Attitude Display

During unusual attitudes, the HGS display automatically switches to a format designed for recognition of and recovery from the conditions. When the airplane attitude is restored to a stable condition, the display format is returned to the selected operating mode.

The HGS Unusual Attitude mode main display feature is a large attitude sphere in the center of the display with a distinct sky/ground indication. The basic airspeed and altitude scales from the Primary mode are also displayed, and the rest of the display is de-cluttered for concentration on the basic flight information. The Unusual Attitude mode is automatically entered and exited, overriding the currently selected normal operational mode on the display.

 8. Autonomous Flare Guidance

The Flight Path Canards will appear attached to the sides of the Flight Path. They appear at approximately 105 feet altitude AGL. The serve as reference points that position them in line with the Autonomous Flare Cue when the flare maneuver is being correctly executed.

 The Autonomous Flare Cue provides flare symbology in PRI, IMC AND VMC modes. The symbol is both a flare anticipation and flare symbology cue. To distinguish between these two functions the dashed lines will become solid lines when the symbol is to be used as a flare symbology cue.

The No Flare Annunciation provides an indication that Autonomous Flare symbology cannot be provided. The symbol displayed in the upper left area of the display.

 9. Tailstrike Limit and Tailstrike Advisory

On takeoff the HGS provides a Tailstrike Limit symbol that is displayed when the pitch attitude indicates that the airplane is rotating at a rate or to an extent that will cause a tailstrike. The symbol looks like a bar bell: O----O.  In order to avoid a tailstrike, the pilot must not allow the boresight symbol to pass through the Tailstrike Limit symbol.

 On landing, a Tailstrike Advisory is displayed in text on the combiner when the airplane is in an attitude or flares et a rate that would cause the airplane to strike the tail. This is caused by improper configuration, significant negative speed deviation or pilot induced oscillation from over-rotating during the flare.

10. TCAS Guidance

When a Resolution Advisory 9RA) is received from the TCAS Computer, a TCAS Resolution Advisory Symbol is displayed on the HGS display. TCAS Resolution Advisories are either corrective or preventive. Corrective advisories are issued when the aircraft vertical flight path must be altered to avoid collision, while preventive advisories are as issued when an intruder is within range, but the current vertical flight path of the aircraft is safe and the pilot only needs to monitor vertical speed.

When a Corrective Up or Corrective Down TCAS Resolution Advisory is received by the HGS, the Corrective Resolution Advisory symbol is displayed indicating  the "fly" region for the Flight Path symbol to avoid a collision with the other traffic.

11. Windshear Avoidance/Recovery Guidance/Performance Margin Awareness

Early recognition of wind shear is identified by observing the erratic wind direction and wind velocity on the direction symbol and velocity symbol. The HGS/HUD will provide an intuitive and immediate identification of performance margin available to the pilot during a wind shear recovery by displaying the AoA limit symbol. The pilot maintains the flight path vector over the solid guidance cue and between the zero degree pitch line and the AoA limit symbol. The pilot is able to monitor the energy of the airplane via the inertia caret, which combined with the Speed Error Tape, can also provide indications of windshear conditions. To avoid confusion in the control of aircraft thrust, the Flight Path Acceleration symbol is removed from the display when the HGS detects a low-level decreasing performance windshear.

 12. Improved Pilot Performance during Engine Failure on Takeoff Operations

The following symbols provide the pilot with a more intuitive method to quickly ascertain airplane plate, stability, performance and performance margin.

Flight path vector

Inertia caret

Speed error tape

Slip skid

Zero degree pitch line

Angle of Attack Limit (AoA)

 This set of symbols allows the pilot to quickly and intuitively determine the inputs required to stabilize the airplane for engine-inoperative flight. The flight path displays the airplane's path referenced to the zero degree pitch line to establish a positive rate of climb, The AoA limit symbol provides the pilot a  visual reference establishing the maximum ascent capability. The area displayed between the glideslope reference line and the AoA limit determines the performance margin available. The flight path also presents lateral position and when referenced to the slip/skid indicator intuitively provides guidance to the pilot to apply the appropriate rudder forces to stabilize the airplane laterally. The speed error tape presents precise speed control to maintain the designated speed or the engine-out condition. Since the speed the pilot must maintain can vary with when the engine failure occurred during the profile, the speed error tape can be a significant benefit to the pilot in establishing and maintains the desired speed.

13. Surface Movement Guidance

Surface Movement Guidance is a  system that will help pilots navigate better on airport taxiways and runways. The Surface Guidance System (SGS) uses an airport database to identify the centerline and edges of the current runway or taxiway the aircraft is operating on, and display virtual centerline, edges lines, signs and other symbols that overlay the actual airport taxiways, runways and signage will be able to maneuver on the ground with confidence and minimize runway incursions. This capability will utilize multiple technologies to provide accurate position information to ATC and other aircraft.

 14. Weather Avoidance

The zero degree pitch line can be used to determine whether the airplane has the ability to safely fly over low-level thunderstorm in the airplane's path, or the flight path vector can be used to determine a safe and efficient route to circumnavigating thunderstorms.

 15. Selectable Descent Path - Glideslope Reference Line

The reference setting for glideslope is indicated by the position of the Glideslope Reference Line relative to the Horizon Line. The Reference Glideslope value is also displayed digitally at both ends of the Glideslope Reference Line. The Glideslope Reference Line is a conformal display representing the glideslope value selected on the HCP or MCDU or received from the FMC, meaning that the Glideslope Reference Line overlaying a pointy on the ground indicates that the airplane position is at an angle equal to the glideslope reference point.

Maneuvering the aircraft so that the Flight Path symbol overlies any point along the symbol's dashed line results in a descent angle equal to the glideslope value selected. Initiating a descent when the Glideslope Reference Line overlays the runway touchdown zone allows a constant descent angle approach to be flown with pure visual information.

 16. Energy Management during RTO

The inertia caret and deceleration index are used to monitor the Rejected Takeoff (RTO) function. The inertia caret and deceleration index presentation display to the pilot the stopping efficiency and capability of the airplane. The pilot knows the stopping value associated with indexed points of the display and the inertia caret represents the level of braking effect the system is experiencing.

17. Angle of Attack (AoA)

The Angle of Attack Scale and Indicator is displayed in the upper right of the display. It consists of a round dial with pointer and a digital readout that indicate the aircraft's current angle of attack.

 The angle of attack approach reference band is displayed on the Angle of Attack Scale. It indicates the normal approach angles of attack when the flaps are in a landing position.

The angle of attack stick shaker trip point is displayed to provide a visual indication of the aircraft's stick shaker angle of attack.

 Approach

A stabilized approach (i.e. pitch, thrust, flight path, VAPP) is essential for achieving a successful landing.

Auto thrust and the Flight Path Vector (FPV), if available, are effective flight crew aids.

For the approach phase, the flight crew should:

 • Not chase the glide slope close to the ground: Progressively and carefully monitor the pitch attitude and sink rate.

• Avoid high sink rate when close to the ground.

PNF callouts during the final approach are essential to alert the PF of any excessive deviation of flight parameters, and/or excessive pitch attitude at landing. Following a PNF flight parameter exceedance callout, the suitable PF response will be to:

 • Acknowledge the PNF callout, for proper crew coordination purposes

• Take immediate corrective action to control the exceeded parameter back into the defined stabilized conditions

• Assess whether stabilized conditions will be recovered early enough prior to landing, otherwise initiate a go-around.

 Landing

The flight crew should avoid “holding off the aircraft” in an attempt to make an excessively smooth landing.

Immediately after main landing gear touchdown, the PF should release the back pressure on the sidestick (or control column, as applicable) and fly the nose wheel smoothly, but without delay, on to the runway.

The PNF should continue to monitor the attitude.

“PITCH, PITCH” auto callout (synthetic voice, if installed) triggers when pitch becomes excessive during flare and landing.

The Pitch Limit Indication on the PFD (if installed) can also help flight crew awareness, because it indicates the pitch limit before a tailstrike.

Bouncing at Touchdown

In case of a light bounce, the flight crew can apply the following typical recovery technique:

• Maintain a normal landing pitch attitude:

- Do not increase pitch attitude, as this could cause a tailstrike

- Do not allow the pitch attitude to increase, particularly following a firm touchdown with a high pitch rate.

Note: Spoiler extension may induce a pitch-up effect.

 • Continue the landing

• Keep thrust at idle

• Be aware of the increased landing distance.

In case of a more severe bounce, the flight crew should not attempt to land, because the remaining runway length might not be sufficient to stop the aircraft.

For more information, refer to the Flight Operations Briefing Note Bounce Recovery – Rejected Landing.