U.S. patent application number 12/611645 was filed with the patent office on 2011-05-05 for low visibility landing system.
Invention is credited to Gary M. Freeman, Robert S. Takacs.
Application Number | 20110106345 12/611645 |
Document ID | / |
Family ID | 43926280 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110106345 |
Kind Code |
A1 |
Takacs; Robert S. ; et
al. |
May 5, 2011 |
LOW VISIBILITY LANDING SYSTEM
Abstract
Examples of the present invention may include a low visibility
landing system for guiding aircraft on landing approaches. The low
visibility landing system may aid a pilot during landing in low
visibility conditions such that an aircraft may descend to lower
altitudes without visual contact with the runway than is possible
with other landing systems. The system may use various navigational
systems to produce a hybrid signal that may be more stable than
individual signals of those navigational systems. The hybrid signal
is compared to a predetermined landing approach plan to determine
the deviation of the aircraft from the landing approach plan and to
provide guidance to the pilot to get the aircraft back onto the
landing approach plan. The system may also use multiple
navigational systems to perform checks on an operation of a primary
navigational system to ensure that the primary navigational system
is operating accurately.
Inventors: |
Takacs; Robert S.; (Richmond
Hill, GA) ; Freeman; Gary M.; (Savannah, GA) |
Family ID: |
43926280 |
Appl. No.: |
12/611645 |
Filed: |
November 3, 2009 |
Current U.S.
Class: |
701/17 ;
701/16 |
Current CPC
Class: |
G08G 5/025 20130101;
G05D 1/0676 20130101 |
Class at
Publication: |
701/17 ;
701/16 |
International
Class: |
G05D 1/00 20060101
G05D001/00; G06F 19/00 20060101 G06F019/00; G05D 1/10 20060101
G05D001/10 |
Claims
1. A landing system for an aircraft, comprising: a first
navigational device to generate a first navigational signal
representative of a deviation of an aircraft from a first
predetermined landing approach plan; a second navigational device
to generate a second navigational signal representative of a
deviation of the aircraft from a second predetermined landing
approach plan, the second predetermined landing approach plan being
different from the first predetermined landing approach plan; and a
flight computer to combine the first navigational signal and the
second navigational signal to produce a hybrid signal, the flight
computer providing guidance for the aircraft based on the hybrid
signal.
2. The landing system of claim 1, wherein providing guidance
comprises alerting a pilot to abort a landing approach if the
hybrid signal exceeds a first predetermined threshold.
3. The landing system of claim 1, wherein the first navigational
device comprises at least one of: an Instrument Landing System
(ILS) or a Wide Area Augmentation System (WAAS); and the second
navigational device comprises at least one of: an ILS or a WAAS,
the second navigational device being different from the first
navigational device.
4. The landing system of claim 1, wherein the flight computer
further determines a failure of the first navigational signal if
the deviation of the first navigational signal from the first
landing approach plan exceeds a second predetermined threshold; and
the flight computer further determines a failure of the second
navigational signal if the deviation of the second navigational
signal from the second landing approach plan exceeds a third
predetermined threshold; wherein the flight computer instructing
the pilot to abort a landing approach if the flight computer
determines at least one of: the failure of the first navigational
signal or the failure of the second navigational signal.
5. The landing system of claim 1, wherein the flight computer
determines a difference between the first navigational signal and
the second navigational signal, the flight computer instructing the
pilot to abort the landing if the difference exceeds a
predetermined threshold.
6. The landing system of claim 1, wherein the first navigational
device and the second navigational device are housed within a
single navigational instrument.
7. A landing system for an aircraft, comprising: a first
navigational device to generate a first navigational signal
representative of a deviation of an aircraft from a first approach;
a second navigational device to generate a second navigational
signal representative of a deviation of the aircraft from a second
approach; and a flight computer to provide guidance to a pilot in
directing the aircraft onto a predetermined landing approach plan,
the flight computer alerting a pilot to abort a landing approach if
a difference between the first navigational signal and the second
navigational signal exceeds a first predetermined threshold.
8. The landing system of claim 7, wherein the flight computer
alerts the pilot to abort the landing approach if at least one of:
the deviation represented by the first navigational signal exceeds
a second predetermined threshold; and the deviation represented by
the second navigational signal exceeds a third predetermined
threshold.
9. The landing system of claim 7, wherein the first navigational
device comprises at least one of: an Instrument Landing System
(ILS) or a Wide Area Augmentation System (WAAS); and the second
navigational device comprises at least one of: an ILS or a WAAS,
the second navigational device being different from the first
navigational device.
10. The landing system of claim 7, wherein the first navigational
device and the second navigational device are housed within a
single navigational instrument.
11. A method for landing an aircraft, comprising: generating a
first navigational signal from a first navigational device
representative of a deviation of an aircraft from a first
predetermined landing approach plan; generating a second
navigational signal from a second navigational device
representative of a deviation of the aircraft from a second
predetermined landing approach plan; combining the first
navigational signal and the second navigational signal to produce a
hybrid signal; and providing guidance for the aircraft based on the
hybrid signal.
12. The method of claim 11, further comprising: advising the pilot
to abort a landing approach if the deviation of the hybrid signal
exceeds a first predetermined threshold.
13. The method of claim 11, wherein the first navigational device
comprises at least one of: an Instrument Landing System (ILS) or a
Wide Area Augmentation System (WAAS); and the second navigational
device comprises at least one of: an ILS or a WAAS, the second
navigational device being different from the first navigational
device.
14. The method of claim 11, further comprising: rejecting the first
navigational signal if the deviation represented by the first
navigational signal exceeds a second predetermined threshold, and
rejecting the second navigational signal if the deviation
represented by the second navigational signal exceeds a third
predetermined threshold.
15. The method of claim 11, wherein the first navigational device
and the second navigational device are housed within a single
navigational instrument.
16. A method for landing an aircraft, comprising: generating a
first navigational signal from a first navigational device
representative of a deviation of an aircraft from a first
predetermined landing approach plan; generating a second
navigational signal from a second navigational device
representative of a deviation of the aircraft from a second
predetermined landing approach plan; guiding the aircraft along the
first predetermined landing approach plan based on the first
navigational signal; and alerting a pilot to abort a landing if the
difference between the first navigational signal and the second
navigational signal exceeds a first predetermined threshold.
17. The method of claim 16, further comprising: alerting the pilot
to abort the landing approach if at least one of: the first
navigational signal exceeds a second predetermined threshold; or
the second navigational signal exceeds a third predetermined
threshold.
18. The method of claim 16, wherein the first navigational device
comprises at least one of: an Instrument Landing System (ILS) or a
Wide Area Augmentation System (WAAS); and the second navigational
device comprises at least one of: an ILS or a WAAS, the second
navigational device being different from the first navigational
device.
19. The method of claim 16, wherein the first navigational device
and the second navigational device are housed in a single
navigational instrument.
Description
FIELD OF THE INVENTION
[0001] Embodiments of the present invention relate to aircraft
landing systems and, more particularly, to landing systems used in
low visibility conditions.
BACKGROUND OF THE INVENTION
[0002] Currently, commercial aircraft employ guidance systems that
warn pilots when the aircraft is deviating from a flight path.
Guidance systems must have certain levels of accuracy, integrity,
continuity, and availability during ordinary flight. Guidance
systems that are used for landing require additional levels of
accuracy, integrity, continuity, and availability. Landing systems
typically provide high precision data relating to position and
deviation of an aircraft from a landing approach path. This high
precision often requires special equipment, which can be beneficial
in situations where fog, clouds, and/or other conditions reduce
visibility.
[0003] Airport landing systems are categorized by the Federal
Aviation Administration (FAA) or other certification authority into
different categories (Category I, II, and III) depending upon
levels of accuracy, integrity, continuity, and availability
provided by the landing guidance system. Accuracy refers to a
volume that a position fix is contained within ninety-five percent
certainty. Integrity refers to the probability that the system will
unintentionally provide hazardous misleading information, such as
an undetected fault or lack of information. Integrity also refers
to a time required for a detected fault to be flagged by the
system. Continuity refers to the probability that the navigation
accuracy and integrity requirements will remain supported during
the approach.
[0004] Most airport landing systems fall in Category I (CAT I),
which enables the aircraft to initiate approach procedures from a
decision height (DH) of 200 feet. The decision height represents
the lowest altitude, above the touchdown zone, the aircraft can
descend to without the pilot making visual contact with the runway.
In a CAT I landing, if the pilot has not made visual contact with
the runway by the time the aircraft descends to 200 feet, then the
pilot must abort the landing and try again. Also, for a CAT I
landing, the plane has to be in a runway visual range (RVR) of at
least 1800 feet, which means that the pilot must also make visual
contact with the start of a center line of a runway with no less
than 1800 feet to the runway. In other words, if the aircraft
attempting a CAT I approach is located at least 200 feet above the
runway (DH) and at least 1800 feet from the start of the runway
(RVR) and the pilot is able to make visual contact with the runway
by that point, then the aircraft can continue with the CAT I
approach. Otherwise, the aircraft should abort the landing.
[0005] More restrictive than the CAT I landing is a Category II
(CAT II) landing, where airport landing systems allow the aircraft
to initiate approach procedures from a DH of at least 100 feet and
a RVR of at least 1200 feet. An aircraft that is capable of a CAT
II landing is able to descend below the CAT I landing requirements
before making a decision whether to land or abort the landing. In a
CAT II approach, the DH is located at least 100 feet above the
runway and the RVR is at least 1200 feet from the start of the
runway.
[0006] Airport landing systems categorized for CAT III, like the
system currently found at John F. Kennedy International Airport,
allow for landing procedures from a DH of at least 50 feet and a
RVR of at least 650 feet. In an aircraft capable of a CAT III
approach, the DH is located at least 50 feet above the runway and
the RVR is at least 650 feet from the start of the runway.
[0007] Aircraft configured for CAT III landings require special
automatic landing or guidance systems, such as a triple redundant
autopilot system, and must meet stringent levels of integrity and
reliability. Generally, only a few airports have the equipment
necessary for CAT III landings because implementation of such
equipment requires special surveying. In addition, limited aircraft
crews have the requisite training to perform the CAT III landings,
such as the requisite simulator training, for example. Due to these
limitations, CAT I landing systems and approaches tend to be the
predominant methods used in smaller or private airplanes.
[0008] One of the landing systems used throughout the world for
high precision landing guidance and deviation data is an instrument
landing system (ILS), which includes a transmitter located on the
ground to project two sets of radio beams into space along the
approach corridor. An aircraft equipped for an ILS landing includes
specialized antennas and receivers that interpret the radio beams
and provide the pilot with navigational guidance. One of the radio
beams provides lateral guidance, which allows the pilot to align
the aircraft with the runway. A subsystem associated with the
lateral guidance is called the localizer. The other radio beam
provides vertical guidance. The subsystem associated with the
vertical guidance is called a glideslope and it provides guidance
for a steady descent into the airfield. The combination of the
localizer and the glideslope effectively defines an approach path
for an aircraft to fly along during a landing. The approach path is
often referred to as an ILS approach. Depending on the
configuration and equipment used, ILS is capable of CAT I, II, and
III landings.
[0009] Another guidance system used for landings is a Wide Area
Augmentation System (WAAS). WAAS is a system using both a
ground-based component and a GPS satellite component in order to
determine both the lateral and vertical position of the aircraft
during a landing approach. The ground-based component may comprise
a number of dispersed ground monitoring stations, while the GPS
satellite component may comprise a constellation of between
twenty-four and thirty-two Medium Earth Orbit satellites. The
satellites transmit precise microwave signals that are received by
GPS receivers on an aircraft to determine current location, time,
and velocity of the aircraft.
[0010] The navigational data provided by a WAAS is used with a
Localizer Performance with Vertical Guidance (LPV). The LPV is a
high precision GPS (WAAS enabled) aviation instrument approach
procedures that assists in determining a lateral position and a
vertical position of the aircraft. Similar to an ILS approach, the
LPV defines the approach path (referred to as an LPV approach) for
the aircraft to fly during an approach to a given airport. The LPV
approaches (for airports that have defined LPV approaches) are
contained in a database that is used by the aircraft and the WAAS
to generate deviation and guidance data for an LPV approach. In
most cases, the FAA has defined the LPV approaches such that they
match existing ILS approaches. Currently, WAAS is only qualified
for a CAT I landing and is currently unable to execute by a CAT II
or III landing.
SUMMARY OF THE INVENTION
[0011] In one embodiment of the invention, a low visibility landing
system may integrate a first signal from a first landing system and
a second signal from a second landing system to generate a hybrid
signal that has a greater accuracy than the first signal or second
signal individually. For example, a hybrid signal may be generated
from an ILS signal and a WAAS signal. In some cases, the use of a
hybrid signal may allow an aircraft to lower the DH and the RVR,
which would provide pilots the ability to descend further before
having to abort a landing in poor visibility conditions. The hybrid
signal may provide deviation and guidance data to the aircraft so
that the pilot or autopilot will be able to properly position the
aircraft along an approach path during landing. As in a
conventional landing system employing only ILS or only WAAS, for
example, if the deviation of the aircraft from the landing approach
exceeds a certain threshold, then the pilot may be need to abort
the landing approach.
[0012] In another embodiment of the invention, a low visibility
landing system may generate a hybrid signal for deviation and
guidance data, as discussed above, and also monitor the difference
between the first signal from the first landing system and the
second signal from the second landing system to provide additional
levels of accuracy, integrity, continuity, and availability. For
example, if the difference between the first signal and the second
signal becomes too large, exceeding a threshold, then the system
may alert the pilot to a possible failure or automatically require
the pilot to abort the landing and try again. Additionally, the
system could be configured such that if the difference between the
first signal and the second signal exceeds a predetermined
threshold, then the landing system may instruct the pilot to abort
the landing approach.
[0013] In another embodiment of the invention, a low visibility
landing system may use a first signal from a first landing system
as a primary signal in a conventional manner. In addition, the
system would then monitor the difference between the first signal
from the first landing system and a second signal from a second
landing system to provide additional levels of accuracy, integrity,
continuity, and availability. In particular, the landing system may
be configured to determine the difference between the primary
signal and the second signal as a redundancy measure to check the
operation of the primary signal. If the second signal deviates from
the primary signal by the predetermined threshold, the landing
system may alert the pilot and/or require that the pilot abort the
landing and try again. The system could also be configured such
that if the difference between the primary signal and the secondary
signal exceeds a threshold, then the pilot would be alerted and may
need to abort the landing. Additionally, if the deviation of the
aircraft from the approach path (such as the deviation of the
aircraft from an ILS approach) generated by the second system
exceeds a threshold, then the pilot could be alerted.
[0014] In one embodiment of the invention, a landing system for an
aircraft comprises: a first navigational device to generate a first
navigational signal representative of a deviation of an aircraft
from a first predetermined landing approach plan; a second
navigational device to generate a second navigational signal
representative of a deviation of the aircraft from a second
predetermined landing approach plan, the second predetermined
landing approach plan being different from the first predetermined
landing approach plan; and a flight computer to combine the first
navigational signal and the second navigational signal to produce a
hybrid signal, the flight computer providing guidance for the
aircraft based on the hybrid signal
[0015] In another embodiment of the invention, a landing system for
an aircraft comprises: a first navigational device to generate a
first navigational signal representative of a deviation of an
aircraft from a first approach; a second navigational device to
generate a second navigational signal representative of a deviation
of the aircraft from a second approach; and a flight computer to
provide guidance to a pilot in directing the aircraft onto a
predetermined landing approach plan, the flight computer alerting a
pilot to abort a landing approach if a difference between the first
navigational signal and the second navigational signal exceeds a
first predetermined threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an example of a block diagram for a low visibility
landing system in accordance with an embodiment of the present
invention.
[0017] FIG. 2 illustrates a landing approach of an aircraft in
accordance with an embodiment of the present invention.
[0018] FIGS. 3 and 4 illustrate predetermined landing approaches
into Savannah/Hilton Head International Airport.
[0019] FIG. 5 illustrates how the data from a low visibility
landing system in accordance with an embodiment of the present
invention could be displayed on an aircraft display.
[0020] FIG. 6 is an example of a computer display for displaying
the output of the low visibility landing system in accordance with
an embodiment of the present invention.
[0021] FIG. 7 is an example of a computer display for a low
visibility landing system in accordance with an embodiment of the
present invention.
[0022] FIG. 8 is another example of a computer display for a low
visibility landing system in accordance with an embodiment of the
present invention.
[0023] FIG. 9 is another example of a computer display for a low
visibility landing system in accordance with an embodiment of the
present invention.
[0024] FIG. 10 is an example a flow diagram representing the
operation of a low visibility landing system in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] CAT I, CAT II, and CAT III landing approaches use high
precision landing systems that may employ different ground,
satellite, and aircraft based equipment to aid in landing the
aircraft. In at least one embodiment of the invention, a low
visibility landing system may be configured such that aircraft
landing approaches may proceed to lower altitudes for a decision
height (DH) and to a closer distance for before the runway visual
range (RVR). In some cases, embodiments of the present invention
may utilize equipment configured for CAT I landings and use the
equipment to execute a landing procedure with lower DH and RVR than
would be possible under conventional CAT I landing procedures.
[0026] In one embodiment of the invention, a low visibility landing
system may be configured to generate a hybrid signal from the
separate signals of two landing systems. For example, the landing
system may use the signals from an Instrument Landing System (ILS)
and a Wide Area Augmentation System (WAAS) to generate a hybrid
signal.
[0027] Because the landing approach plans for the ILS and the LPV
generally coincide and because the ILS and the WAAS both produce
signals indicative of the lateral and the vertical deviations of
the aircraft from the ILS approach and LPV approach, respectively,
then the ILS and WAAS signals may be combined to form a hybrid
signal representative of the lateral and vertical deviations of the
aircraft from the airport approach path. The landing approach for
either ILS, WAAS, or other systems may include data representative
of lateral and vertical velocities along the landing approach. It
would be understood in the art that the hybrid signal may also
represent lateral and vertical velocities of the aircraft. In
addition, in the event the landing approach plans for the ILS and
those for the LPV do not coincide, the difference between the ILS
and WAAS signals will exceed the predetermined threshold, alerting
the pilot that an error has been made.
[0028] According to one embodiment of the invention, the hybrid
signal may be generated using the ILS and WAAS signals. The hybrid
signal comprises the lateral and vertical components (H.sub.HYB and
V.sub.HYB) determined according to the following formulas:
H HYB = ( .sigma. ILS - H 2 .sigma. ILS - H 2 + .sigma. WAAS - H 2
) H WAAS + ( .sigma. WAAS - H 2 .sigma. ILS - H 2 + .sigma. WAAS -
H 2 ) H ILS ##EQU00001## V HYB = ( .sigma. ILS - V 2 .sigma. ILS -
V 2 + .sigma. WAAS - V 2 ) V WAAS + ( .sigma. WAAS - V 2 .sigma.
ILS - V 2 + .sigma. WAAS - V 2 ) V ILS ##EQU00001.2##
H.sub.WAAS and .sub.ILS represent the lateral or horizontal signals
as provided by the WAAS and ILS, while V.sub.WAAS and V.sub.as
represent the vertical signals as provided by the WAAS and ILS.
[0029] The standard deviations (.pi..sub.ILS and .pi..sub.WAAS) for
ILS and WAAS signals may be calculated by using published
accuracies for CAT I ILS and WAAS approaches and assuming the
errors conform to a Gaussian distribution. The standard deviations
of the lateral and vertical values of the ILS and WAAS systems
(.pi..sub.ILS-H, .pi..sub.ILS-V, .pi..sub.WAAS-H, and
.pi..sub.WAAS-V) may also similarly calculated. Using this
information, the accuracy of the horizontal and the vertical
components of the hybrid signal may be calculated as a function of
the standard deviations according to the following equations:
.sigma. HYB - H = ( 1 1 .sigma. ILS - H 2 + 1 .sigma. WAAS - H 2 )
1 2 ##EQU00002## .sigma. HYB - V = ( 1 1 .sigma. ILS - V 2 + 1
.sigma. WAAS - V 2 ) 1 2 ##EQU00002.2##
[0030] The standard deviations of the hybrid signal may be less
than either or both of the standard deviations of the ILS and the
WAAS, reflecting the additional stability generated by the hybrid
signal in comparison to the separate ILS or WAAS signals.
[0031] One of ordinary skill in the art would appreciate that there
are additional methods and formulas for calculating the horizontal
and the vertical components of the hybrid signal and their
corresponding measures of accuracy.
[0032] By combining the signals in the manner described above, the
hybrid signal representative of the lateral and vertical deviations
of the aircraft from the airport approach path may have a greater
accuracy and stability than either the WAAS signal or the ILS
signal individually. Because of the greater accuracy and stability
of the hybrid signal, the landing system may be able to descend
further during a landing approach without visual contact with the
runway, possibly allowing the aircraft to perform a CAT II or
similar landing using equipment (the WAAS or the ILS) that
typically would only be able to perform a CAT I landing.
[0033] The hybrid signal may then be used by the aircraft avionics
system and the pilots in a similar manner to how a conventional
system would use a signal from an ILS or a WAAS separately. As
would be understood by those of skill in the art, if the horizontal
or vertical deviation of the aircraft (according to the hybrid
signal) exceeds a predetermined threshold, then the landing system
may alert the pilot to abort the landing. The predetermined
thresholds may be derived from FAA publications for allowable
deviations along either the ILS or the WAAS landing approach plans,
for example. The predetermined thresholds may be a function of the
location of the aircraft along the approach path. For example, as
the aircraft gets closer to the runway, the predetermined threshold
may decrease, representing a lower tolerance of a deviation from
the predetermined landing approach plan. The predetermined
thresholds may be set less than the FAA publications for allowable
deviations.
[0034] The deviation represented by the hybrid signal may
anticipate and warn against, for example, short landings, long
landings, wide landings, and an excessive sink rate, and
appropriately cue the pilot to execute a missed approach, if
necessary. Short landings occur when the aircraft does not make it
to the runway, while long landings occur when the aircraft lands
too far down the runway, thus preventing the ability to slow the
aircraft appropriately before the runway ends. A wide landing
occurs when the aircraft misses the runway to the side. An
excessive sink rate occurs when the aircraft descends at too quick
of a rate, causing the aircraft to land with excessive force. As
one of ordinary skill in the art would appreciate, the deviation of
the aircraft (according to the hybrid signal) may also provide
guidance to the pilot or an autopilot regarding how to direct the
aircraft back into alignment with the a proper landing
approach.
[0035] In another embodiment of the invention, a landing system may
again be configured to integrate a signal from a WAAS with a signal
from an ILS to create a hybrid signal as discussed above. In
addition, the landing system may monitor or cross-monitor the
signals from the WAAS and the ILS by determining the difference
between the lateral signals and vertical signals for the WAAS and
the ILS. For example, the landing system may monitor the difference
between the lateral signals and the difference between the vertical
signals for the WAAS and ILS to determine if the differences exceed
any predetermined thresholds. It is contemplated that the
thresholds for the allowed difference between the horizontal or
lateral signals may be different than the allowed thresholds for
the difference between the vertical signals.
[0036] So long as the difference between the WAAS and ILS signals
does not exceed a threshold, the landing system may display the
deviation (according to the hybrid signal) of the aircraft from the
approach path to the pilot, and provide guidance (according to the
hybrid signal) to the pilot or autopilot to direct the aircraft
back into a proper alignment with the runway for landing. Should
the difference between the WAAS and ILS signals exceed a threshold,
the landing system may be configured to alert the pilot. If the
system determines that either the ILS or WAAS signal has failed,
then the system may determine whether the pilot can continue under
the remaining valid system. For example, if the system determines
that the ILS signal has failed, the aircraft may continue its
landing approach using the WAAS system alone. It is also
contemplated that if only the difference between the lateral
signals (or the difference between the vertical signals) exceeds
its predetermined threshold, then the landing system may alert the
pilot.
[0037] In another embodiment of the invention, a low visibility
landing system may be employed that uses one landing system as a
primary system, while monitoring the primary system with another
landing system to verify the integrity of the primary system. For
example, the landing system may comprise a WAAS for generating a
primary signal for deviation and guidance data. The landing system
may then use an ILS to monitor or cross-monitor the primary signal.
The primary signal and primary landing system could then be used in
a conventional system using a single landing system. Alternatively,
the ILS may be used as the primary signal and the WAAS may be used
to monitor the ILS.
[0038] To monitor the primary signal, the landing system may
utilize, for example, the ILS signal. As discussed above, the
system may monitor whether the difference between the ILS signal
and the WAAS signal (for both horizontal and vertical deviations)
exceeds any predetermined thresholds. Although the primary signal
used in this embodiment of the invention may involve an existing
landing system, such as WAAS, the monitoring or cross-monitoring
may provide additional redundancies to the primary signal such that
the aircraft may descend further during the landing approach
without visual contact with the runway. Such an arrangement may
allow the aircraft to perform a CAT II or similar landing using
equipment (the WAAS or the ILS) that typically would typically only
be able to perform a CAT I landing.
[0039] FIG. 1 illustrates a low visibility landing system 100 and
various aircraft avionics that could implement embodiments of the
present invention. As would be apparent to those of skill in the
art, other arrangements of components and combinations of different
components could be used to implement embodiments of the invention
without deviating from the scope and spirit of the present
invention.
[0040] As shown in FIG. 1, the landing system 100 may include a
flight computer 110, an Advanced Flight Control System (AFCS) 120,
a Flight Management System (FMS) 130, an Enhanced Ground Proximity
Warning System (EGPWS) 140, an Inertial Reference Unit (IRU) 150,
an Instrument Landing System (ILS) 160, a Wide Area Augmentation
System (WAAS) 170, and a display unit 190. The FMS 130 may be
configured to provide to the flight computer 110 data regarding a
landing approach plan, while the EGPWS 140 may provide the flight
computer 110 with a geometric altitude, where the geometric
altitude represents a three-dimensional model of terrain. Other
devices 180 may optionally (as denoted by the dashed line) provide
additional navigational signals to the flight computer 110, such as
proprietary navigation data and proprietary systems. In addition,
the devices 180 may include other non-proprietary landing systems,
such as, for example, an VHF omni-directional range (VOR)
equipment; a non-directional beacon (NDB) system; a radio
altimeter; and a microwave landing system (MLS). Display unit 190
may display information regarding any failures of the navigational
devices and/or the status of the aircraft.
[0041] Combiner/Comparator 115 located within flight computer 110
may receive signals from different systems, such as the IRU 150,
the ILS 160, and the WAAS 170, for example. The signals from the
IRU 150, the ILS 160 and the WAAS 170 may represent a signal fed
into the combiner/comparator 115. One of ordinary skill in the art
would appreciate that the ILS or WAAS signal may be the result of
multiple signals from multiple ILS or WAAS systems combined into a
single ILS or WAAS signal. In addition, it would be understood in
the art that it is possible that both an ILS signal and a WAAS
signal may be generated by a single navigational instrument capable
of housing both an ILS and a WAAS, such as, for example, a Garmin
430W manufactured in Wichita, Kans.
[0042] Referring to the those embodiments of the invention
discussed above that use a hybrid signal, the combiner/comparator
115 may be configured to produce a hybrid signal from two separate
landing systems, such as, for example, the ILS 160 and the WAAS
170. The combiner/comparator 115 may also cross-monitor the signals
from the WAAS 170 and the ILS 160 to determine if the difference
exceeds a certain threshold. If so, the combiner/comparator 115 and
the flight computer 110 may output a signal that will alert the
pilot to the difference between the signals.
[0043] Also, referring to at least one embodiment of the invention,
the combiner/comparator 115 may be used to determine the difference
between two signals from two separate landing systems, such as, for
example, the signal from the ILS 160 and the signal from the WAAS
170. The combiner/comparator 115 may use the signal generated by
the WAAS 170 as a primary signal and use the signal from ILS 160 to
monitor the integrity of the WAAS signal. If the difference between
the signal from the ILS 160 and the signal from the WAAS 170
exceeds a certain threshold, the combiner/comparator 115 outputs a
signal that will later be used to instruct the pilot to abort the
landing. As previously stated, the threshold may be derived from
FAA publications detailing allowable deviations from the ILS or
WAAS landing approach plans.
[0044] The flight computer 110 receives the hybrid signal (or the
primary signal as discussed above with reference to some
embodiments of the invention) from the combiner/comparator 115. In
some cases, the FMS 130 may be configured to provide LPV approaches
to the flight computer 110 and the WAAS system 170. The flight
computer 110 provides the deviation to a deviation display 191
within the display unit 190 to indicate to the pilot how far the
aircraft deviates from the landing approach plan. The flight
computer 110 and the AFCS 120 collaborate in order to provide
proper instructions to the pilot in order to direct the aircraft
back along the landing approach plan. One of ordinary skill in the
art would appreciate that the AFCS 120, the FMS 130, and the EGPWS
140 may be disposed within the flight computer 110 or within other
avionics shown in FIG. 1 or on in an aircraft.
[0045] In accordance with at least one embodiment of the invention,
if the flight computer 110 and/or the combiner/comparator 115
determine that the signals received from the various navigational
systems indicate potential failure of one or more systems, then the
system could be configured to automatically alert the pilot. For
example, the flight computer 110 could send a signal to an
annunciator 193 within the display unit 190 to notify a pilot of
such a failure. In at least one embodiment of the present
invention, a WAAS signal, and an ILS signal, the annunciator 193
within the display unit 190 may have three announcements on an
annunciator board installed in the view of the crew: a hybrid fail
announcement, an ILS fail announcement, and a WAAS fail
announcement. The hybrid fail announcement may be displayed to the
pilot if the hybrid signal indicates that deviation of the aircraft
in excess of a predetermined threshold. The ILS fail announcement
may be displayed to the pilot if the ILS signal indicates that the
aircraft has deviated from the landing approach plan by a
predetermined threshold, or if the flight computer 110 determines
that the ILS signal deviates from the WAAS signal by a
predetermined threshold. Similarly, the WAAS fail announcement may
be displayed to the pilot if the WAAS signal indicates that the
aircraft has deviated from the landing approach plan by a
predetermined threshold, or if the flight computer 110 determines
that the WAAS signal deviates from the ILS signal by a
predetermined threshold.
[0046] The display unit 190 may also receive information from
various systems to provide additional information to the pilot. For
example, the IRU 150 may optionally provide (as illustrated by a
dashed line) a measure of the rate of descent or ascent in terms of
feet per minute, with a flight plan module (FPM) 195 the display
unit 190 displaying that information to the pilot. Also, the EGPWS
140 may generate information for a runway placement display 197 to
the pilot regarding the position of the aircraft with respect to
the runway, such that the pilot may be able to make the appropriate
adjustments to ensure that the aircraft is in proper alignment with
the runway. In addition, the AFCS 120 may provide to the display
unit 190 information sufficient to serve as a flight display 199,
such as, for example, attitude of the aircraft, speed, altitude and
other flight characteristics known to those of skill in the
art.
[0047] The boxes shown in FIG. 1 are representative of software
and/or hardware modules capable of implementation in a variety of
configurations. For example, flight computer 110 and the
combiner/comparator 115 may comprise a software module or software
modules that run in a display unit 190. Alternatively, the flight
computer 110 and the combiner/comparator 115 may also comprise a
hardware module or hardware modules.
[0048] FIG. 2 illustrates an approach of an aircraft along glide
path 200 utilizing the system in accordance with at least one
embodiment of the invention. Segment 210 of the glide path 200
represents the part of the path where the aircraft would start
generating a hybrid signal.
[0049] At point 215 of the glide path, approximately 1000 feet
above the runway, the advanced flight control system (AFCS) 120 in
FIG. 1 may be configured to use the hybrid signal to provide the
pilot or the autopilot the necessary guidance to correct the
deviation of the aircraft and align the aircraft with the landing
approach plan.
[0050] At point 225 of the glide path, approximately 500 feet above
the runway, the flight computer 110 may begin receiving a signal
from a radio altimeter shown as the other proprietary navigational
signal 180 in FIG. 1, which provides another possible confirmation
of position of the aircraft relative to the runway. As understood
by those of skill in the art, the radio altimeter may utilize
X-band weather radar technology and the aircraft may begin to
receive the radio altimeter signal before the aircraft descends
below decision heights for Category I approaches.
[0051] During segment 230 of the glide path, the hybrid signal may
provide guidance for the approach. It is during this segment of the
glide path that a pilot may make visual contact with the runway for
a CAT I or II landing. At point 235 of the glide path,
approximately 100 feet above the runway, the EVS may provide a
confirmation signal regarding the alignment of the flight path with
the runway. In addition, use of the EVS may result in enhanced
runway light detection, enhanced situational awareness, and
visibility during the flare and rollout portions of the flight.
During segment 240 of the glide path, the pilot may use the
inertial readings from the inertial reference unit (IRU) 150 and
radio signals 180 from the radio altimeter to manually continue
with the landing approach. At point 245 of the glide path,
approximately 50 feet above the runway, the pilot may visually make
a decision with respect to landing or aborting the landing. During
segment 250 of the glide path, the pilot manually performs rollout
of the aircraft.
[0052] It is also contemplated that systems in accordance with
embodiments of the invention may also operate as a rollout
performance monitor. For example, a landing system in accordance
with embodiments of the invention may provide a distance of
remaining runway and distance to exit data to the pilot to aid in
preventing the aircraft from going past the runway or missing any
turns when the aircraft is taxing to a gate.
[0053] FIG. 3 illustrates an appropriate flight plan of a GPS-based
area navigation for a LPV-based landing into Savannah/Hilton Head
International Airport, while FIG. 4 illustrates an appropriate
flight plan of an ILS device for a landing into the same airport.
Without the information provided by at least one embodiment of the
invention, pilot may have to either memorize the flight plan or
have a flight plan handbook. The flight plan for the LPV approach
shows that the decision altitude is 340 feet above the runway. In
other words, a plane with a WAAS can descend to 340 feet before
making a decision to land or initiate a go-around based on whether
the pilot makes visual contact with the runway. The flight plan for
the ILS device shows that the decision altitude is 241 feet above
the runway. Similarly, this means that a plane with an ILS device
can descend to 241 feet before making a decision to land or
initiate a go around.
[0054] FIG. 5 illustrates an image 500 generated on the display
unit 190 to show the deviation (according to the hybrid signal in
some embodiments of the invention and according to the primary
signal in some embodiments of the invention) of the aircraft from
the appropriate flight landing onto runway 510 with an approach
lead line 515. A diamond-shaped indicator 520 may represent a
current aim direction of the aircraft, while a circular indicator
525 of the flight director may represent an appropriate landing
direction according to the predetermined flight plan. Ideally, when
landing a plane, the diamond-shaped indicator 520 should directly
line up with the circular indicator 525. Synthetic visual approach
slope indicator (VASI) 530 may simulate the lights on the side of
the runway to provide descent guidance information. The synthetic
VASI 530 allows simulation of the red-green-white light systems
that commercial pilots normally see on descent to indicate whether
the landing slope is too steep or too shallow.
[0055] Go-around indicators 540 show a direction that an aircraft
may take if the system initiates a go-around. When the system
initiates a go-around, the system may require that the pilot take
the path as shown by the go-around indicators 540. The go-around
indicators may be configured to give the pilot advance notice of
what to do in the future. The low visibility system may also
include a crab director, which allows for alignment with the runway
in order to straighten out the plane if the pilot cannot see the
runway. A first crab director indicator 550 and a second crab
director indicator 555 may assist in landing the plane in zero
visibility or when it is difficult to see the runway. First crab
director indicator 550 is shown to be out to the right; this will
indicate to the pilot to yaw right. A decrab director 560 may be
shown both below a skid indicator 570 and on a flight path marker
580.
[0056] With regards to at least one embodiment of the invention, it
is contemplated that one of ordinary skill in the art could employ
a landing system including an ILS and a WAAS system as discussed
above. The landing system would be an ILS Monitored LPV Approach
System (IMLAS), where the ILS is used to monitor the operation of
the WAAS. It would be apparent to one of ordinary skill in the art
that a WAAS could be used to monitor an ILS instead. Referring back
to FIG. 1, the WAAS 170 may generate a WAAS signal representative
of the deviation of the aircraft from an LPV approach. The WAAS
signal could be provided to flight computer 110 and
combiner/comparator 115 as a primary signal. An ILS signal from ILS
160 would then be used to monitor the operation of the WAAS in the
combiner/comparator 115.
[0057] Regardless of the embodiments used, if the deviation of
either the ILS or the WAAS signals from the landing approach plan
exceeds a threshold, the pilot may be alerted and the landing may
be aborted.
[0058] FIG. 6 illustrates a graph 600 showing how a WAAS signal may
appear to a pilot when the deviation of the aircraft from an LPV
approach is displayed. Along the numbered axis 610 is a plot of a
vertical position of the LPV approach relative to a vertical course
guidance needle 630, which represents a current vertical position
of the aircraft. To align the aircraft with the LPV approach, the
pilot would fly the aircraft down slightly until the numbered axis
would scroll up, aligning the number 0 with the guidance needle
630. Along the numbered axis 620 is a plot of a lateral position of
the LPV approach relative to a lateral course guidance needle 640,
which represents a current lateral position of the aircraft. As
would be understood by those of skill in the art, a situation where
both the vertical course guidance needle 630 and the lateral course
guidance needle 640 are at zero indicates that the aircraft is
flying along the landing approach plan.
[0059] As shown in FIG. 6, the vertical course guidance needle 630
indicates that the vertical deviation of the aircraft is
approximately equal to +0.4, while the lateral course guidance
needle 640 indicates that the lateral deviation of the aircraft is
approximately equal to 0. Because the vertical course guidance
needle 630 is at +0.4, the aircraft is currently higher than the
recommended altitude of the landing approach plan, so the pilot
will lower the altitude of the aircraft to align it with the
approach plan. Because the lateral course guidance needle 640 is at
0, the pilot will not have to make any lateral adjustments to the
aircraft because the aircraft is currently aligned to the
runway.
[0060] Similarly, FIG. 7 illustrates a graph 700 showing how an ILS
signal may appear to a pilot when the deviation of the aircraft
from an ILS approach is displayed. Along the numbered axis 710 is a
plot of the glideslope position of the ILS approach relative to a
glideslope course guidance needle 730, which represents a current
vertical position of the aircraft. To align the aircraft with the
ILS approach, the pilot would fly the aircraft down slightly until
the numbered axis would scroll up, aligning the number 0 with the
guidance needle 730. Along the numbered axis 720 is a plot of a
localizer position of the ILS approach relative to a localizer
course guidance needle 740, which represents a current lateral
position of the aircraft. As would be understood by those of skill
in the art, when both the vertical course guidance needle 630 and
the lateral course guidance needle 640 are at zero, the aircraft is
flying along the landing approach plan.
[0061] As shown in FIG. 7, the glideslope guidance needle 730
indicates that the deviation from the glideslope is approximately
equal to +0.2, while the localizer guidance needle 740 indicates
that the localizer deviation is approximately equal to -0.2.
Because the vertical course guidance needle 730 is at +0.2, the
aircraft is currently higher than the recommended altitude of the
landing approach plan, so the pilot will lower the altitude of the
aircraft to align the aircraft with the glideslope. Because the
localizer guidance needle 740 is at -0.2, the ILS signal indicates
that the aircraft is currently to the left of the approach path and
the pilot will turn the aircraft to the right to properly align the
aircraft with the runway.
[0062] As discussed above, differences between the WAAS signal and
the ILS signal may be used to monitor the integrity of a hybrid
signal or a primary signal, in accordance with embodiments of the
invention. FIG. 8 illustrates a graph showing the difference
between the lateral component of the WAAS signal (shown in FIG. 6)
and a localizer component of the ILS signal (shown in FIG. 7). In
FIG. 8, the Y-axis 810 represents the difference and the X-axis 820
represents time. FIG. 8 illustrates how a predetermined threshold
830 can be set, for example, at 1.0. The difference 840 between the
lateral component of the WAAS signal and the localizer component of
the ILS signal is plotted in FIG. 8. As illustrated in FIG. 8, the
difference 840 is less than the predetermined threshold 830. Should
the difference 840 exceed the predetermined threshold 830, an alert
may be sent to the pilot to abort the landing. The predetermined
threshold 830 may be adjusted as a function of the location of the
aircraft along the approach path. For example, the threshold 830
may be reduced as the aircraft descends along the approach path,
allowing less difference between the ILS and WAAS signals as the
aircraft descends and gets close to the runway.
[0063] Similarly, FIG. 9 illustrates a graph showing the difference
between the vertical component of the WAAS signal (shown in FIG. 6)
and a glideslope component of the ILS signal (shown in FIG. 7). The
Y-axis 910 represents the difference and the X-axis 920 represents
time. A predetermined threshold 930 is set and plotted as
horizontal line at a value of 1.0. The difference 940 between the
vertical component of the WAAS signal and the guideslope component
of the ILS signal is plotted in FIG. 9. As illustrated in FIG. 9,
the difference 940 is less than the predetermined threshold 930,
indicating that an alert will not be sent to the pilot. However,
should the difference 940 exceed the predetermined threshold 930
for longer than a predetermined time, an alert may be sent to the
pilot to abort the landing. The predetermined threshold 930 may be
adjusted as a function of the location of the aircraft along the
approach path. For example, the threshold 930 may be reduced as the
aircraft descends along the approach path, allowing less difference
between the ILS and WAAS signals as the aircraft descends and gets
close to the runway.
[0064] FIG. 10 illustrates a flow diagram showing how an IMLAS, as
discussed above, may monitor the WAAS and ILS signals and provide
alerts in accordance with one embodiment of the invention. For
example, an IMLAS may alert a pilot if the difference between the
WAAS and ILS signal (including the vertical or horizontal
components) exceeds a predetermined threshold. As shown in FIG. 10,
the IMLAS starts in an armed state 1010. The armed state 1010
represents a ready state of the IMLAS, where the WAAS signal is
monitored by the ILS signal. In the armed state 1010, the ILS 160
and the WAAS 170 (shown in FIG. 1) are generating ILS and WAAS
signals for the IMLAS. As an example, the armed state would
represent the typical state of the IMLAS when an aircraft is
descending for a landing, as shown in sections 210 and 220 of the
glidepath 200 illustrated in FIG. 2.
[0065] As an example of how the IMLAS operates during a landing
approach, the IMLAS may proceed from the armed state 1010 to a
proceed state 1020 as shown in step 1, which instructs the pilot to
continue with the landing approach if the following conditions are
met: (1) the aircraft is on the landing approach plan, for example,
glidepath 200 as shown in FIGS. 2; and (2) the comparator/combiner
115 and/or the flight computer 110 determine differences between
the lateral and vertical components of the ILS and WAAS signals are
less than a predetermined threshold. FIGS. 8 and 9 both illustrate
a situation where IMLAS would enter into a proceed state 1020
because the horizontal deviation plot 840 and the vertical
deviation plot 940 both are under the thresholds 830 and 930. In
addition, FIG. 6 shows that the aircraft is on the landing approach
plan because the primary signal (WAAS signal) indicates that the
aircraft does not substantially deviate from the landing approach
plan by having values close to zero.
[0066] Once in proceed state 1020, the IMLAS may annunciate to the
pilots that they may continue with the approach, such as proceeding
along sections 230 and 240 of glidepath 200 as shown in FIG. 2. The
IMLAS may revert from the proceed state 1020 to the armed state
1010 along step 2 if the pilot aborts the landing or resets the
IMLAS into the armed state 1010.
[0067] The IMLAS may proceed from the proceed state 1020 to a
miscompare state 1030 along step 3 if the comparator/combiner 115
and/or the flight computer 110 of FIG. 1 determines that the
differences between the horizontal and vertical components of the
ILS and/or WAAS signals exceed the predetermined threshold. In the
miscompare state 1030, the IMLAS may reject either the ILS signal
or the WAAS signal and may alert the pilots to abort the approach.
The IMLAS then transitions to the armed state 1010 along step 4 if
the aircraft is no longer on approach or the IMLAS has been
manually reset. This could happen when the pilots abort a landing
to reattempt a successful landing.
[0068] From the proceed state 1020, the IMLAS will transition to a
fault state 1040 along step 5 if either the ILS or WAAS signal
becomes invalid due to malfunction, error, or other systemic
failure of the ILS or the WAAS. The fault state 1040 may also occur
when the ILS or WAAS signal indicates deviation from the landing
approach plan by a predetermined threshold, resulting in a
rejection of the ILS signal or the WAAS signal. Once in the Fault
state 1040, the IMLAS transitions back to the armed state 1010
along step 6 if the aircraft is no longer on approach or the IMLAS
has been manually reset.
[0069] It should be understood that the navigational systems,
displays, control systems, control functions, and aircraft systems
contemplated under the present invention should not be construed as
limited to those examples shown in the Figures. Given the
description above, one of ordinary skill in the art would be able
to implement embodiments of the invention using other displays,
control systems, control functions, and aircraft systems. In
addition, the low visibility landing system may also provide
guidance to the pilot in take-off operations by providing alignment
to the centerline of the runway in very low visibility and also by
providing visualization of decision points based upon the amount of
runway remaining.
[0070] The foregoing descriptions of specific embodiments of the
present invention are presented for purposes of illustration and
description. They are not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Many modifications and
variations are possible in view of the above teachings. For
example, more than two navigational systems may be employed to
generate a hybrid signal. While the embodiments were chosen and
described in order to best explain the principles of the invention
and its practical applications, thereby enabling others skilled in
the art to best utilize the invention, various embodiments with
various modifications as are suited to the particular use are also
possible. The scope of the invention is to be defined only by the
claims appended hereto, and by their equivalents.
* * * * *