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1. (WO2004036328) APPROACH MONITORING AND ADVISORY SYSTEM AND METHOD
Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

APPROACH MONITORING AND ADVISORY SYSTEM AND METHOD
INVENTOR
John H. Glover
PRIORITY CLAIM
This patent application claims priority from U.S. Provisional Patent Application Serial No. 60/418,906 filed October 15, 2002, and entitled "Approach Monitoring and Advisory System," the entire contents of which are hereby incorporated by reference.
FIELD OF THE INVENTION
This invention relates generally to hazard alert systems for aircraft and, more specifically, to cockpit landing aids.
BACKGROUND OF THE INVENTION
Landing an aircraft is the most demanding task in flying. During the landing process, the aircraft must transition from operating in three dimensions of motion to operating in only two dimensions of motion and must be brought to a safe and complete stop. To perform the landing properly, the aircraft must approach the runway within certain attitude, track, speed, and rate of descent limits. An approach outside of these limits can result in the aircraft making a "hard" landing, overrunning the runway end, or otherwise contacting the runway surface in an uncontrolled manner. Any one of these events has the potential to cause severe damage to the aircraft and may additionally result in passenger injuries or fatalities.
In the past, a "too-low" approach was the most hazardous type of approach. However, the Ground Proximity Warning System/Enhanced Ground Proximity Warning System (GPWS/EGPWS) developed by Honeywell International, Inc. has reduced this risk significantly.
A "high energy" approach is now the highest risk, and a significant number of aircraft accidents and incidents are caused by high energy approaches. A high energy approach is an approach that is too fast and/or too high - that is, speed and/or altitude during the landing approach is excessive. The result of these "high energy" landing approaches may be a hard landing, over-running the runway, or departing the runway. For example, for each knot of airspeed in excess of a reference airspeed (unique to that aircraft and landing configuration on landing approach), the aircraft rollout distance may increase by approximately two percent. As a further example, aircraft approaching the runway at too steep an angle (that is, in excess of a nominal glidepath of around three degrees or so) have an excess amount of energy that must be dissipated during landing flare and touchdown. This condition not only places the aircraft at risk for undercarriage damage, but also may result in the aircraft floating down the runway during the flare in order to bleed off the excess energy. The runway distance consumed during the float is no longer available to stop the aircraft after touchdown and a runway overrun condition is possible.
Nonetheless, many successful landing approaches are made outside defined "stable approach" criteria. For example, successful approaches are made when air traffic control requirements cause conditions, such as a late turn to final approach or a late descent. Further, schedule pressure may cause conditions outside stable approach criteria, such as excessive airspeed.

As a result, it would be desirable to improve flight crew awareness of an impending problem with an approach - such as a high energy approach; to provide an advisory when probability of an unsuccessful approach is significant; to allow a margin from stable approach criteria; and to avoid increasing aural and visual clutter in the flight deck. However, there is an unmet need in the art for a system and method for monitoring and advising a flight crew of high energy landing approaches.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide a system, method, and computer program product for monitoring for high energy landing approaches and advising a flight crew of an aircraft. Advantageously, the present invention improves flight crew awareness of an impending problem with a landing approach, such as a high energy approach. The present invention provides an advisory when probability of an unsuccessful approach is significant and allows a margin from stable approach criteria while avoiding increased aural and visual clutter in the flight deck.
According to an exemplary embodiment of the present invention, specific aircraft energy is predicted at a touchdown zone of a runway. The predicted specific energy is compared with predetermined threshold specific energy. An alert is generated when the predicted specific energy is at least the predetermined threshold specific energy.
According to an aspect of the present invention, the specific energy may include specific potential energy, specific kinetic energy, and specific total energy.
The alert may include a message that is indicative of an aircraft altitude that is higher than a predetermined glide slope when the predicted specific potential energy is at least the predetermined threshold specific potential energy. Also, the alert may include a message that is indicative of an aircraft speed that is faster than a predetermined ground speed when the predicted specific kinetic energy is at least the predetermined threshold specific kinetic energy. Further, the alert may include a message that is indicative of an aircraft altitude that is higher than the predetermined glide slope and an aircraft speed that is faster than the predetermined ground speed when the predicted specific total kinetic energy is at least the predetermined threshold specific total energy.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings.
FIGURE 1 is a block diagram of an exemplary system according to an embodiment of the present invention;
FIGURE 2 is a detailed block diagram of a portion of the system of FIGURE 1;
FIGURE 3 A illustrates enabling criteria;
FIGURE 3B is a logic diagram of exemplary enabling logic;
FIGURE 4 is an illustration of exemplary alert thresholds; and
FIGURES 5-7 illustrate safety margins associated with the alert thresholds of FIGURE 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
By way of overview and referring to FIGURE 1, an exemplary system 10 according to an embodiment of the present invention alerts a flight crew of an aircraft (not shown) of a potentially hazardous condition, such as an impending high energy landing. Embodiments of the present invention provide an advisory when probability of an unsuccessful approach is significant and allows a margin from stable approach criteria while avoiding increased aural and visual clutter in a flight deck (not shown) of the aircraft. According to an exemplary embodiment of the present invention, specific aircraft energy is predicted at a touchdown zone of a runway (not shown). The predicted specific energy is compared with predetermined threshold specific energy. The specific energy may include specific potential energy, specific kmetic energy, and specific total energy. An alert is generated and provided to the flight crew via a display device 11 and/or an aural alerting device 13 when the predicted specific energy is at least the predetermined threshold specific energy. Details of an exemplary embodiment of the present invention will be set forth below.
A processor 12 is configured to predict specific energy of the aircraft at the touchdown zone of the runway. The processor 12 suitably is any microprocessor, firmware, executable code, general purpose processor, existing aircraft subsystem having a general purpose processor, flight computer known in the art that is capable of performing mathematical calculations, or any combination thereof. Examples of existing aircraft subsystems having a general purpose processor include without limitation a Traffic Collision and Avoidance System (TCAS) and a Flight Management System (FMS).
In a presently preferred embodiment, the processor 12 is an Enhanced Ground Proximity Warning System (EGPWS) Computer, available from Honeywell International, Inc. Advantageously, use of an EGPWS computer provides within the processor 12 a terrain database 14 (including natural and/or man-made terrain features such as geographic data and/or runway data), an obstacle database 16, terrain and obstacle alerting algorithms 18, a terrain display driver 20, and an alert message generator 22. The terrain database 14 may be useful for determining runway heading, available runway length, runway slope, and nominal glide slope angle. The obstacle database 16 may be useful for identifying any obstacles along an approach course and runway ends.
The processor 12 receives various inputs useful for predicting components of specific energy of the aircraft (described in detail below). In one exemplary embodiment of the present invention, the processor 12 receives position and groundspeed signals 24 from a Global Positioning System (GPS) receiver 26. The processor 12 also receives altitude and airspeed signals 28 from any acceptable air data sensor system 30. Finally, the processor 12 receives heading, pitch, and roll signals 32 from any acceptable altitude and heading reference system 34.

Advantageously, according to the present invention, the processor 12 includes approach energy algorithms 36 that predict specific energy of the aircraft during a landing approach. Exemplary calculations that implement the approach energy algorithms will be discussed below, followed by a discussion of an exemplary logic implementation of the approach energy algorithms 36.
The approach energy algorithms 36 predict specific energy of the aircraft at touchdown as follows. As is known, total energy E0 is the sum of potential energy Ep and kinetic energy ER. For an aircraft, total energy E0 may be given as
E0 = Ep + Eκ = ghAT
(!) where
m = mass of the aircraft;
g = acceleration due to gravity;
IIAT -= height of the aircraft above the touchdown zone of the runway; and
VG = groundspeed of the aircraft.
Total specific energy e0 is therefore a sum of specific potential energy ep and specific potential energy e- , and may be given as
E V2
eo =ep +eK =- = hAT +-f- (2)
mg 2g

Predicting a predicted total specific energy GE at the touchdown zone entails adding to the total specific energy e0 a differential total specific energy predicted to arise during the landing approach:
dX)
eE ~ &0 X AZ
\ dt TDZ (3)

where
eε = predicted specific total energy;
de
— = rate of change of specific energy; and
dt ATTDZ = estimated time to touchdown.
de
The rate of change of specific energy — is given as
dt
de ; VG VG
(4)
dt g
where
h = rate of change of height; and
VG = rate of change of groundspeed; and
the estimated time to touchdown ATTDZ is given as
D„
AT = - (5)

where
DTDZ = distance to touchdown; and
VG = average groundspeed.
It will be appreciated that a target, or threshold, specific potential energy at the touchdown zone eτp,τDz is zero, because the height above the touchdown zone IIAT is zero. A target, or threshold, specific kinetic energy at the touchdown zone eχκ,τDz is given by
V2
eτκ = — (6)

where
VcRef = Vχ.Ref - Vπeadwind = desired reference ground speed; and
τ.Ref is Vref (reference or desired approach indicated airspeed) converted to true airspeed.
According to an embodiment of the present invention, predicted excess specific total energy Δeχ,τDZ is predicted as follows:
Ae 'τTDZ = Ae -pOZ +Ae Λk,roz
where Aep = predicted excess specific potential energy; and
Aeκ = predicted excess specific kinetic energy.
Predicted excess specific potential energy Aep is predicted as follows:



where
γ = flight path angle.
Thus, the predicted excess specific potential energy Δe is the amount of specific potential

energy above what the aircraft would have if the aircraft arrived at the runway on a nominal flight path angle γ.
Predicted excess specific kinetic energy Δe^. is predicted as follows:

AeκTDZ =~(Va ~ V f + 2E Va) ^

Thus, the predicted execess specific kinetic energy ΔeA, is the amount of specific kinetic

energy above what the aircraft would have if the aircraft arrived at the runway with a ground speed of VGRef- As a result, according to an embodiment of the present invention the predicted excess specific total energy Δeχ,χDz, the predicted excess specific potential energy Δe , and the predicted execess specific kinetic energy Δe^. are the quantities of specific

energy that are compared to alert thresholds to determine if an alert is to be generated.
It will be appreciated that the predicted excess specific potential energy Δe and the predicted execess specific kinetic energy Δe^ are "predicted" because they are

estimated based upon what will happen at the runway based on the present state (that is, speed and altitude) and based upon rate of change of state (that is, VG and γ).
Referring now to FIGURES 1 and 2, exemplary logic 38 determines the predicted excess specific potential energy Δe , the predicted excess specific kinetic energy Δe^ ,

and the predicted excess specific total energy Δeχ,χDZ- The predicted excess specific potential energy ΔeA. is determined as follows. Height

above mean sea level IIMSL is applied to an input of a summing junction 40 and elevation above mean sea level of the nearest runway end hχoz is applied to an inverting input of the junction 40. The height above the touchdown zone IIAX is calculated by subtracting the elevation above mean sea level of the nearest runway end hχoz from the h eight above mean

sea level IIMSL- The rate of change of height h is divided by the groundspeed VG at a block

42, thereby yielding the flight path angle γ. The flight path angle γ is in turn multiplied by the distance to the touchdown zone DχDZ at a block 44. This is added to the height above the touchdown zone IIAX by a summing junction 46. This yields the predicted excess specific potential energy Aeκ as set forth in Equation (8).
The predicted excess specific kinetic energy Aeκ is determined as follows. The square of the groundspeed VG is provided to an input of a summing junction and the square of the reference approach speed VG Ref is provided to an inverting input of the junction 48.

The junction 48 thus subtracts the square of the reference approach speed VG Ref from the square of the groundspeed VG . This difference is provided to an input of a summing junction

50. The rate of change of groundspeed VG is multiplied by twice the distance to the touchdown zone Dχoz at a block 52. The product from the block 52 is provided to another input of the junction 50 and added to the difference from the junction 48. The sum from the block 50 is divided by twice the acceleration due to gravity (that is, 2g) at a block 53, thereby yielding the predicted excess specific kinetic energy ΔeΛ, as set forth in Equation (9).
The predicted excess specific potential energy Δe^. is provided to an input of a summing junction 54 and the predicted excess specific kinetic energy Δe^ is provided to

another input of the junction 54. The junction 54 adds together the predicted excess specific potential energy Δe^. and the predicted excess specific kinetic energy Δe^ , thereby

yielding the predicted excess specific total energy Δeτ>TDz as set forth in Equation (7). The predicted excess specific potential energy Aep , the predicted excess specific kinetic energy Δe^ , and the predicted excess specific total energy Δeχ;TDz are provided to comparators for

comparison against predetermined thresholds for generation of alert messages as discussed further below.
Referring now to FIGURES 3A and 3B, exemplary enabling logic 56 enables the system 10 (FIGURE 1) to determine the predicted excess specific potential energy Δe^ , the predicted excess specific kinetic energy Aeκ , and the predicted excess specific total energy

Δe oz during a landing approach. As will be discussed in detail below, the system 10 (FIGURE 1) is enabled when an aircraft 58 is within predetermined lateral limits α of a runway 60, and within predetermined track limits β of a heading 62 of the runway 60, and between an upper margin 63 and a lower margin 65 of the flight angle γ, and between an inner gate 67 and an outer gate 69 from a beginning of a touchdown zone 64 of the runway 60, and when landing gear (not shown) is down.
In one present embodiment the lateral limits α suitably define margins beginning at the touchdown zone 64 and extending along the angle α from each side of centerline of the runway 60. In one present embodiment, given by way of nonlimiting example the angle α suitably may be around ten degrees or so. In another embodiment, the angle α suitably is around twenty degrees or so. However, it will be appreciated that the angle α may have any value as desired for a particular application.
In an exemplary embodiment, the angle α is provided to an inverting input of a summing junction 71 and provided to a non-inverting input of a summing junction 73. The heading 62 of the runway 60 is provided to a non-inverting input of the junction 71 and provided to a non-inverting input of the junction 73. This defines a range of values of ±α about the heading 62 of the runway 60 that are provided to a block 75. The heading 66 of the aircraft 58 is also provided to the block 75. The block 75 outputs a logic one when the heading 66 of the aircraft 58 initially becomes within the range of the heading 62 of the runway 60 ±α. Once initially activated, the block 75 applies a hysterisis and continues to output a logic one so long as the heading 66 of the aircraft 58 remains within a hysterisis limit. Given by way of nonlimiting example, the hysterisis limit for the block 75 suitably is around twenty-five degrees or so. However, it will be appreciated that the hysterisis limit for the block 75 may have any value as desired for a particular application.
In a present embodiment the track limits β suitably define an angle between the heading 62 of the runway 60 and a heading 66 of the aircraft 58. In one present embodiment, given by way of nonlimiting example the angle β suitably may be around twenty degrees or so. However, it will be appreciated that the angle β may have any value as desired for a particular application.
The heading 62 of the runway 60 is provided to an input of a summing junction 68 and the heading 66 of the aircraft 58 is provided to an inverting input of the junction 68. The junction 68 subtracts the heading 66 from the heading 62 and provides this difference to a block 70. The block 70 outputs a logic one when the difference initially becomes less than a threshold, such as the angle β. Once initially activated, the block 70 applies a hysterisis and continues to output a logic one so long as the difference from the junction 68 remains less than a hysterisis limit. Given by way of nonlimiting example, the hysterisis limit for the block 70 suitably is around twenty-five degrees or so. However, it will be appreciated that the hysterisis limit for the block 70 may have any value as desired for a particular application.
The outer gate 69 defines an outer limit from the touchdown zone 64 beyond which alerts are not generated. Similarly, the inner gate 67 defines an inner limit inside of which alerts are not generated. In one present embodiment, given by way of nonlimiting example the outer gate suitably is around four miles or so, but may have a value of around five miles, three miles, three-and-a-half miles, or any value as desired for a particular application. Given by way of nonlimiting example the inner gate 67 suitable is around one- half mile or so. However, it will be appreciated that the inner and outer gates 67 and 69 may have any values as desired for a particular application.
The distance to the touchdown zone Dχoz is provided to a block 72. The block 72 outputs a logic one when the distance to the touchdown zone DXDZ initially becomes less than a threshold distance, such as the outer gate 69. Once initially activated, the block 72 applies a hysterisis and continues to output a logic one so long as the distance to the touchdown zone Dχoz remains less than a hysterisis limit that is further out than the outer gate 69. It will be appreciated that the hysterisis limit for the block 70 may have any value as desired for a particular application. In addition, the block 72 outputs a logic one when the distance to the touchdown zone D oz is greater than the inner gate 67. When the distance to the touchdown zone DXDZ is less than the inner gate 67, the block 72 outputs a logic zero.
In one present embodiment the upper margin 63 and lower margin 65 envelop the flight angle γ. As is known, a typical value for the flight angle γ during a landing approach is around three degrees or so. Accordingly and given by way of nonlimiting example, in a present embodiment the upper margin 63 may be around twelve degrees or so and the lower margin 65 may be around two degrees or so. However, it will be appreciated that the upper and lower margins 63 and 65 may have any values as desired for a particular application.
In one exemplary embodiment the height above touchdown IIAX is provided to a block 74. The block 74 is a logic element which enables the processor 12 when the aircraft 58 is within the desired upper and lower margins 63 and 65, respectively. The block 74 includes an upper limit and a lower limit each with hysterisis that are variable as a function of distance to runway. Given by way of nonlimiting example, the upper limit may be around 1000 feet or so and the lower limit may be around 100 feet or so, and the hysterisis for the upper and lower limits may be around ten percent or so. However, it will be appreciated that the upper and lower limits and their hysterisis may have any value as desired for a particular application.

Outputs from the blocks 75, 70, 72, and 74 are provided to inputs of a logical AND gate 76. In addition, a discrete 78 that is indicative of gear down status is provided to an input of the AND gate 76. The discrete 78 is a logical one when the landing gear (not shown) is indicated down. When all of the outputs from the blocks 70, 72, 74, or TBD, or the discrete

78 is a logical one, the AND gate 76 outputs a logical one. When the AND gate 76 outputs a logical one, the processor 12 (FIGURE 1) is enabled to predict specific energy as discussed above.
Referring now to FIGURE 4, comparison logic 80 compares the predicted excess specific potential energy Aep with a predetermined specific potential energy alert threshold

82, the predicted excess specific kinetic energy Aeκ with a predetermined specific kinetic

energy alert threshold 84, and the predicted excess specific total energy Δex oz with a predetermined specific total energy alert threshold 86. As will be discussed below, when any of the specific energies is at least the value of its corresponding alert threshold, an appropriate alert is generated.
The alert thresholds 82, 84, and 86 each are provided with distance to nearest runway end. Each of the thresholds 82, 84, and 86 is substantially linearly proportional to the distance to nearest runway end. This is because, in general terms, an aircraft may be expected to be at a faster groundspeed and a higher height above touchdown zone when the aircraft is at a farther distance from the touchdown zone. Again generally, as the aircraft makes a landing approach, the aircraft is expected to have slower groundspeed and lower height above touchdown zone. As a result, the alert thresholds 82, 84, and 86 generally are lower at close distances to nearest runway end and become higher in a substantially linear manner as distance to nearest runway end increases. It will be appreciated that some maneuvering (and hence some change in predicted specific energy) is to be expected beyond approximately 2 miles from the touchdown zone. Accordingly, in an exemplary embodiment the alert thresholds 82, 84, and 86 suitably are expanded at a greater rate with increasing distance beyond that point.
When the predicted excess specific potential energy Aeκ is at least the value of the

specific potential energy alert threshold 82 at the airplane's current distance to the nearest runway end, the alert message generator 22 (FIGURE 1) generates an appropriate alert message 88 that is indicative of the airplane having an excessive height above the touchdown zone at the airplane's current distance from the nearest runway end. Given by way of nonlimiting example, the message 88 may indicate "too high" or "high approach" or "steep approach" or the like. However, it will be appreciated that any appropriate wording may be included as desired in the alert message 88. The alert message 88 may be displayed as a visual alert on the display device 11 (FIGURE 1) and/or the aural alerting device 13

(FIGURE 1) as desired.
When the predicted excess specific kinetic energy Aeκ is at least the value of the

specific kinetic energy alert threshold 84 at the airplane's current distance to the nearest runway end, the alert message generator 22 (FIGURE 1) generates an appropriate alert message 90 that is indicative of the airplane having an excessive groundspeed at the airplane's current distance from the nearest runway end. Given by way of nonlimiting example, the message 90 may indicate "too fast" or "high groundspeed" or the like. However, it will be appreciated that any appropriate wording may be included as desired in the alert message 90. The alert message 90 may be displayed as a visual alert on the display device 11 (FIGURE 1) and/or the aural alerting device 13 (FIGURE 1) as desired.
When the predicted excess specific total energy Δeχ;χoz is at least the value of the specific total energy alert threshold 86 at the airplane's current distance to the nearest runway end, the alert message generator 22 (FIGURE 1) generates an appropriate alert message 92 that is indicative of the airplane having an excessive height above the touchdown zone and an excessive groundspeed at the airplane's current distance from the nearest runway end. Given by way of nonlimiting example, the message 92 may indicate "high and fast" or "approaching high and fast" or the like. However, it will be appreciated that any appropriate wording may be included as desired in the alert message 92. The alert message 92 may be displayed as a visual alert on the display device 11 (FIGURE 1) and/or the aural alerting device 13 (FIGURE 1) as desired.
Referring now to FIGURES 5-7, the alert thresholds 82, 84, and 86 provide design safety margins to empirically-determined flight data for corresponding specific energies. Actual specific potential energy 94, actual specific kinetic energy 96, and actual specific energy 98 were empirically determined on a Beach King Air aircraft. Advantageously, the alert thresholds 82, 84, and 86 are all defined at values sufficiently in excess of their respective actual specific energies 94, 96, and 98 such that the alert thresholds 82, 84, and 86 all allow margins from stable approach criteria. As a result, increased visual and aural clutter in the flight deck is avoided.
While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.