Least time alternate destination planner

An alternate destination planner for searching a navigation database in an aircraft and identifying a plurality of alternate destinations at which the aircraft can land in the event of an emergency. For each identified alternate destination, the alternate destination planner calculates an estimated time of arrival (ETA) and an amount of fuel remaining upon arrival at the destination. The calculation of the ETA and the remaining fuel is based on user-modifiable parameters of aircraft speed, aircraft altitude, wind direction and speed, outside air temperature, and the type of routing the aircraft will follow from a diversion point to the alternate destination. The plurality of alternate destinations are displayed to a pilot of the aircraft according to the ETA to each alternate destination, with the closest alternate destination by time listed first. The plurality of alternate destinations are also displayed to the pilot on a map of the surrounding region that is provided to the pilot on a navigation display. A pilot may select and divert to one of the plurality of alternate destinations using a minimal number of keystrokes on a control display unit.

FIELD OF THE INVENTION 
The present invention relates to flight management systems for aircraft 
and, more particularly, to flight management systems that provide 
emergency landing information to a pilot. 
BACKGROUND OF THE INVENTION 
It has become increasingly common for large commercial aircraft to 
incorporate an alternate destination planner in their flight management 
systems to provide the pilot of the aircraft with information about 
alternate landing destinations. Alternate destination planners currently 
incorporated in aircraft generally contain a database of airports from 
which a list of alternate destinations at which the aircraft can land may 
be selected and displayed. In addition to listing the alternate landing 
locations, alternate destination planners typically provide arrival data 
such as the distance to each alternate destination, the estimated time 
until arrival at each alternate destination, and the estimated amount of 
fuel remaining upon landing at each alternate destination. The alternate 
landing destination information is usually only used in emergency 
situations that would prevent the aircraft from landing at the intended 
destination such as inclement weather of the intended destination or an 
onboard emergency. 
During an emergency situation, the pilot of the aircraft is apprised by the 
alternate destination planner of a number of alternate destinations to 
which the aircraft can be diverted. The decision of which destination to 
select is ultimately made by the pilot, who may base his or her decision 
upon a number of factors, including the flight time to the alternate 
destination, the emergency facilities contained at the alternate 
destination, and the length of the runway at the alternate destination. 
Providing the pilot of the aircraft an onboard list of alternate 
destinations is more efficient than having the pilot contact air traffic 
control to determine the nearest alternate destination. Instead of relying 
upon an air traffic controller to make critical decisions about how to 
route the aircraft, the alternate destination planner provides the pilot 
with sufficient onboard information to make an autonomous decision during 
flight before communicating the decision to air traffic control. 
While it has been recognized that having an alternate destination planner 
on an aircraft greatly facilitates the handling of emergency situations, 
the current generation of alternate destination planners still require 
significant pilot effort in order to change the course of the aircraft and 
divert to an alternate destination. One alternate destination planner 
currently in use is disclosed in U.S. Pat. No. 5,398,186, entitled 
"Alternate Destination Predictor for Aircraft" and commonly assigned to 
The Boeing Company (herein expressly incorporated by reference). The '186 
patent discloses a modification to the flight management computer (FMC) 
that provides a pilot of an aircraft with a list of alternate landing 
destinations at which the aircraft can be landed in the event of an 
emergency. For each alternate landing destination displayed, the FMC 
system modification displays to the pilot the distance between the 
aircraft's present position and the alternate destination, an estimated 
time of arrival (ETA) at the alternate destination, and an estimate of the 
fuel remaining onboard the aircraft if the aircraft were to land at the 
alternate destination. The ETA and remaining fuel are calculated by 
estimating the flight path that the aircraft would have to take from the 
current position to the alternate airport. To minimize the computational 
time necessary to generate the trip information to each alternate 
destination, a rough estimation technique is used to calculate both the 
ETA and fuel remaining. As a result, the displayed trip information has 
generally less accuracy than would be normally be displayed by the flight 
management computer when estimating and displaying the time to and fuel 
remaining at the intended destination of the aircraft. 
To select and implement a diversion to an alternate destination using the 
system disclosed in the '186 patent requires a significant amount of 
effort by the pilot. The flight management computer generates a series of 
screens on a control and display unit (CDU) which allow the pilot to 
compare the ETA and remaining fuel for a number of different alternate 
destinations. If a pilot were actually to divert to one of the alternate 
destinations, however, the routing information to that destination has to 
be programmed into the flight management computer by the pilot. Those 
skilled in the art will recognize that the programming procedure takes a 
significant amount of time and effort by the pilot when the pilot's 
attention may be more effectively used elsewhere. For example, in the 
preferred embodiment of the flight management computer disclosed in the 
'186 patent, the following steps must be followed to divert an aircraft to 
an alternate destination. First, the pilot must select a RTE LEGS page, 
and enter any alternate waypoints into the active flight plan currently 
stored in the computer. Second, the pilot must select a RTE page and enter 
the alternate destination into the active flight plan. Once the waypoints 
and destination have been stored in the flight management computer, any 
changes to the vertical profile of the airplane must be made by the pilot 
by accessing the CLB (climb), CRZ (cruise), or DES (descent) page. 
Finally, if the emergency is a result of a failed engine, the pilot must 
select a VNAV page and select engine-out performance for the aircraft. 
Once all changes have been made, the modified flight plan must then be 
executed. In the event of a diversion to an alternate destination, it will 
therefore be appreciated that during the critical initial stages of the 
emergency when the pilot is deciding the diversion destination and 
implementing the diversion, the pilot will have to concentrate on 
accurately inputting the diversion information into the flight management 
computer. This takes a significant amount of time, and distracts the pilot 
during a period when the pilot can be concentrating on responding to other 
aspects of the emergency. It will therefore be appreciated that there is a 
need for an alternate 20 destination planner that quickly allows a pilot 
to select an alternate destination and implement the aircraft's diversion 
to that alternate destination. 
Another limitation in the alternate destination planner disclosed in the 
'186 patent is that the estimate of the ETA and remaining fuel provided by 
the flight management computer has limited accuracy due to the estimation 
procedure used to calculate the arrival data. In particular, in order to 
calculate the arrival data to each alternate destination in a minimum 
amount of time, the alternate destination planner of the '186 patent 
assumes a direct flight path to the alternate destination, a constant 
speed equal to the airplane's current speed, and certain environmental 
conditions such as the external temperature. Although normally the 
requisite amount of accuracy is provided to the pilot by an alternate 
destination planner using these assumptions, in extreme cases a more 
accurate estimate of the trip information may prove to be invaluable to a 
pilot. For example, when an engine fails in an extended-range twin-engine 
operation (ETOPS) environment, the pilot is expected to land at the 
nearest suitable airport. When making the decision on which suitable 
airport to divert to, the pilot's decision is ideally based on the most 
accurate information available. It will be appreciated that there 
therefore exists a need for an alternate destination planner for aircraft 
that provides a more reliable estimate of the ETA and remaining fuel when 
arriving at the alternate destination. 
A further limitation of the alternate destination planner disclosed in the 
'186 patent is that it provides limited routing options between the 
current position and the selected alternate destination. In particular, 
the alternate destination planner assumes that a direct or missed approach 
course will be taken from the aircraft's current position to the alternate 
destination. Although a direct course is the most common routing that 
would occur when flying to an alternate destination, there are a number of 
additional routing options that are possible and desirable for a pilot to 
follow. It will therefore be appreciated that an alternate destination 
planner that allowed a pilot to select a number of different routing paths 
between the aircraft's current position and the alternate destination 
would allow the pilot greater flexibility in planning and when it became 
necessary to divert to the alternate destination. 
The present invention is directed to an improved alternate destination 
planner within a flight management computer that reduces the time and 
effort required by a pilot to divert an aircraft to an alternate 
destination. 
SUMMARY OF THE INVENTION 
The present invention is a modification to an aircraft's flight management 
computer (FMC) system to incorporate an improved alternate destination 
planner in the FMC. The alternate destination planner disclosed herein 
provides a pilot with a list of alternate landing destinations based on a 
navigational database of available landing sites stored in the memory of 
the FMC, or based on a list of alternate destinations transmitted to the 
aircraft from a ground station. For each alternate destination, the 
alternate destination planner advises the pilot of an expected time of 
arrival (ETA) and an amount of fuel remaining upon arrival at the 
alternate destination. The displayed arrival data allows the pilot to make 
an informed decision about which alternate landing destination to choose 
in the event of an emergency requiring diversion from the intended 
destination. 
In accordance with one aspect of the invention, the alternate destination 
planner automatically lists the alternate destinations according to the 
ETA at each of the destinations. In ordering the alternate destinations, 
the planner disclosed herein takes into account the user-modifiable 
parameters of aircraft altitude, aircraft speed, wind direction and speed, 
outside air temperature, and selected routing option. When a parameter is 
modified by the pilot, the estimates of the ETA and remaining fuel are 
automatically recalculated and redisplayed based on the specific parameter 
defined by the pilot. The alternate destination planner disclosed herein 
therefore provides the pilot with a highly accurate estimate of the 
arrival data corresponding to each alternate destination, from which the 
pilot can select the most appropriate flight path diversion during an 
emergency. 
In accordance with another aspect of the invention, several different 
routing options are provided from the aircraft's current position to the 
alternate destinations. As provided in prior systems, the pilot may opt to 
fly directly from the current position to the alternate destination. The 
pilot is also provided, however, with the option of flying either an 
offset route or an overhead route from the present position. An offset 
route is a route that parallels the direct route to the alternate 
destination, but is offset to the left or right of the direct route by a 
desired number of nautical miles. An overhead route allows a pilot to 
continue along the original flight plan to a specified waypoint, and then 
to fly directly from the point overhead the waypoint to the selected 
alternate destination. The three routing options allow a pilot greater 
flexibility when diverting to the alternate destination. 
In accordance with a further aspect of the invention, the selection and 
diversion of an aircraft to an alternate destination is automatically 
performed using a minimal amount of pilot input. In an emergency 
situation, the pilot merely has to press two keys to automatically select 
an alternate destination and reprogram the flight management computer with 
the flight plan to the selected destination. The pilot may also indicate 
during such a diversion when one of the aircraft's engines has failed. 
After receiving notification of the engine failure, the alternate 
destination planner automatically recomputes the ETA and remaining fuel 
for the alternate destination based on the limited performance of the 
aircraft. 
In yet another aspect of the invention, data may be transmitted from a 
ground station to the alternate destination planner in order to provide 
accurate conditions for estimation of the ETA and remaining fuel for each 
alternate destination. An airline may also transmit data to the aircraft 
which provide a list of alternate destinations as well as a desired 
routing to those destinations. The capability of the alternate destination 
planner to receive and incorporate updated data into its calculations 
ensures that accurate diversion information can be continuously provided 
to the pilot. 
In a still further aspect of the invention, the FMC generates a visual 
indication of the location of the alternate airports on a navigation 
display. The visual indication of the location of the alternate 
destinations with respect to the current aircraft position and the active 
flight plan route allows the pilot to quickly judge the distance and 
orientation to a number of different alternate airports. The display 
allows the pilot to more rapidly select the airport to divert to, 
minimizing the amount of time that the diversion takes when an emergency 
occurs. 
It will be appreciated that the above features of the alternate destination 
planner allow a pilot to quickly and efficiently divert an aircraft to an 
alternate destination during an emergency situation. The improved visual 
identification of the location of the alternate destinations, as well as 
the more accurate estimation of the ETA and remaining fuel for each 
alternate destination improves the decision-making of the pilot. The 
capability or preprogramming the alternate destination planner with 
specific diversion parameters also allows the pilot and the airline a 
flexible means to tailor their diversion response to specific emergency 
situations. The alternate destination planner disclosed herein therefore 
allows a pilot to respond to emergency situations in an efficient and 
expeditious manner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a pictorial diagram of the face of a control and display unit 
(CDU) 30 that is typically used in commercial aircraft as an interface to 
a flight management computer system. One of the functions of an aircraft's 
flight management computer system is to perform navigation functions. The 
flight management computer typically stores a predetermined flight plan in 
memory, and tracks the current location of the aircraft along the flight 
plan from the originating airport to the destination airport. To 
accurately monitor the aircraft's location, the flight management computer 
receives data from a variety of aircraft subsystems and sensors that are 
well known in the aircraft art. Flight management computers and CDUs are 
well known in the aircraft art, so the following disclosure will not 
discuss the specific implementation of the flight management computer and 
CDU except as required to disclose the present invention. Further details 
of the cooperation of the flight management computer and the CDU may be 
found in U.S. Pat. No. 5,398,186, entitled "Alternate Destination 
Predictor for Aircraft" (expressly incorporated herein by reference). 
The CDU acts as an interface to the flight management computer, and 
includes a display 32 and a keyboard 34 to allow the aircraft pilot to 
selectively view and manipulate navigation and other data. As shown in 
FIG. 1, the display 32 of the CDU 30 includes a central display area 36 in 
which data is displayed to the pilot. Above the central display area 36 is 
an area 36a in which a data status block is displayed, an area 36b in 
which a title of the screen is displayed, and an area 36c on which a page 
number of the screen is displayed. In order to identify and manipulate 
data on the screen, two sets of keys are disposed on either side of the 
central area of the display. A first set of keys, identified as 1L through 
6L, is disposed on the left side of the display area 36, and a second set 
of keys, identified as 1R through 6R, is disposed on the right side. Each 
key corresponds to a display line which makes up the central display area 
36 of the CDU. Pressing one of the keys on the left side or the right side 
of the display area typically implements a function that is displayed in 
the central area 36 immediately adjacent to the key that is depressed. A 
pilot may also enter data into the CDU using a set of alphanumeric keys 
34. Data entered by the pilot is first displayed in a scratch pad area 38 
located beneath the central display area 36. After entry into the scratch 
pad area, the pilot may move the data to a particular line of the central 
display area 36 by depressing one of the left keys, 1L through 6L, or 
right keys, IR through 6R The data contained in the scratch pad area is 
then typically moved to a position adjacent to the key that was depressed. 
A plurality of function keys are also provided to directly implement 
predefined functions. A pair of keys 40 denoted next page and previous 
page allow the pilot to view the next screen of data or to review a 
previous screen of data displayed on the CDU 30. Two function keys are 
provided to access details of active or alternate route information. An 
RTE key 42 allows a pilot to view details about the active flight plan, 
and an LEGS key 44 allows the user to select and view data about a 
particular leg in the predefined or alternate flight plan. As will be 
described in further detail below, two function keys are of particular 
interest to the present invention. An ALTN key 46 is used to access an 
alternate destination summary page. A pilot pressing the ALTN key directly 
jumps to a family of ALTN data pages, the first page containing a list of 
alternate destinations surrounding the current position of the aircraft. 
An EXEC key 48 is also provided to confirm execution of certain user 
selected functions. In particular, when performing a diversion to an 
alternate destination, the EXEC key is used by the pilot to implement a 
change in course from the active flight plan. 
I. Alternate Destination Planner Displays 
The flight management computer is connected to the CDU to aid a pilot in 
navigating to an intended destination airport. If the aircraft is unable 
to land at the intended destination, for example because of inclement 
weather, engine failure, or a medical emergency onboard the aircraft, a 
pilot must select and divert to an alternate destination. The alternate 
destination may be a commercial airport, a military airport, or any other 
facility having sufficient area for the aircraft to land. To facilitate 
the pilot's selection and diversion to the alternate airport, according to 
the present invention the flight management computer is programmed with an 
alternate destination planner. More specifically, as will be better 
understood from the following description, the flight management computer 
system is modified to compute and display for a plurality of alternate 
destinations the estimated time of arrival (ETA) and remaining fuel if the 
aircraft were to fly from the current position to each of the 
destinations. Using the estimated flight data, the pilot may determine the 
appropriate alternate destination to which the aircraft should be 
diverted. The alternate destination planner disclosed herein facilitates 
the diversion by minimizing the amount of data manipulation required by 
the pilot, and by providing more accurate information on which the pilot 
may base their decision. 
When a pilot is initially presented with an emergency situation, or when 
the pilot desires to preevaluate alternate destinations to which the 
aircraft might divert, the pilot presses ALTN key 46 on the CDU function 
key pad. Upon depressing the ALTN key, a data screen providing a summary 
of alternate destinations is automatically displayed on central area 36 of 
display 32. A series of screens representative of the data screens that 
may be accessed by the pilot on the CDU is depicted in FIGS. 2A and 2B. 
Upon pressing the ALTN key, a first screen 50 is displayed to the pilot. 
First screen 50 provides a summary of the nearest alternate destinations 
within range of the aircraft based on the current aircraft position and 
remaining fuel. The first four lines of display area 36 provide the 
closest four alternate destinations, automatically listed according to the 
time that it would take to fly to each particular alternate destination. 
The first entry on the list is therefore always the closest in time 
alternate destination. As shown on representative first screen 50, the 
closest in time alternate destinations are identified by their 
International Civil Aviation Organization (ICAO) identifiers, and include 
airports at KRNO (Reno, Nev.), KTLV (Las Vegas, Nev.), KSMF (Sacramento, 
Calif.), KLAX (Los Angeles, Calif.). 
In addition to automatically identifying the nearest alternate destinations 
by time, the alternate destination planner also calculates and displays an 
estimated time of arrival ETA) at the alternate airport, and an amount of 
remaining fuel if the aircraft were to fly from the current position to 
the alternate airport via a selected routing option. The ETA and remaining 
fuel calculated by the alternate destination planner will hereinafter be 
referred to collectively as the arrival data. As shown on first screen 50, 
each line on the screen containing an alternate destination includes the 
alphanumeric identifier for the destination, the ETA, and the fuel 
remaining. The method of determining the four closest alternate 
destinations will be discussed in further detail below with respect to 
FIG. 3, and the method of calculating the arrival data will be discussed 
below with respect to FIGS. 4A-4G. 
In addition to the automatic inclusion of alternate destinations in the 
summary list of alternate destinations, the pilot may also manually 
include or inhibit an alternate destination in the summary list. To 
manually include an alternate destination, the pilot keys the ICAO 
identifier in the scratch pad, and depresses one of the keys 1L through 4L 
to transfer the manually entered destination into the destination list. 
Once entered, the alternate destination planner will automatically 
calculate and display the arrival data for the manually entered 
destination. The alternate destination planner will also sort the summary 
list of alternate destinations so that the manually entered destination 
will appear in proper order of ETA. Once a destination is manually 
entered, it will remain in the summary list until deletion by the pilot. 
The other alternate destinations will change, however, as other alternate 
destinations are brought within closer ETA proximity to the position of 
the aircraft. 
To manually inhibit the listing of an alternate destination in the summary 
list of alternate destinations, a pilot enters the ICAO identifier of the 
alternate destination and depresses key 5R, labeled ALTN INHIB, to 
transfer the manually entered destination into the inhibit list. As shown 
in first screen 50, adjacent key 5R are two fields that make up the 
inhibit list. Each field can contain an ICAO identifier. When an alternate 
destination is transferred to one of the fields, the alternate destination 
is inhibited from automatically appearing in the summary list of alternate 
destinations. 
From first screen 50, the pilot may obtain more information about a 
particular alternate destination by depressing a corresponding key 1R 
through 4R. If, for example, the pilot were to press the 1R key to obtain 
more information about the alternate destination KRNO, a second screen 52 
would be displayed on the CDU. The second screen 52 provides detailed 
information about the routing options for diverting from the active flight 
plan to the alternate destination. The second screen also provides a list 
of operating conditions used to calculate the arrival data for that 
particular alternate destination. 
As shown on second screen 52, a list of three routing options 54 is 
provided to allow the pilot to specify the type of routing that will occur 
when the aircraft diverts from the active flight plan to a selected 
alternate destination. The first routing option, corresponding to key IL, 
is direct routing. When direct routing is selected, the aircraft is 
directly routed from the location of the aircraft when the diversion 
occurs to the selected alternate destination. The direct routing option is 
the default routing option automatically selected by the alternate 
destination planner, the selection of which is indicated by the characters 
&lt;SEL&gt; following the option on second screen 52. The second routing option 
is offset routing, corresponding to the 2L key. When offset routing is 
selected, at the diversion point the aircraft will fly a path parallel to 
the active flight plan, but offset to the left or to the right of the 
active flight plan by a specified number of nautical miles. The amount of 
offset selected by the pilot is indicated by an alphanumeric identifier 
"L" or "R," indicating "left" or "right," and a number representing the 
nautical miles of the offset. As shown on screen 52, the offset is 
currently set to L10, indicating a left offset of 10 nautical miles. In a 
preferred embodiment of the invention, the offset may extend up to 99 
nautical miles. At a point in the offset continuation of the aircraft 
along the original flight plan, it is presumed that the aircraft will 
leave the offset path and fly a direct path to the alternate destination. 
The offset maneuver is therefore used to temporarily remove an aircraft 
from a heavy air traffic route before the direct diversion to the 
alternate destination occurs. The third routing option is overhead 
routing, corresponding to the 3L key. When overhead routing is selected, 
the aircraft will continue along the active flight plan to a selected 
waypoint. Upon reaching the selected waypoint, the aircraft then diverts 
from the active flight plan and flies directly to the alternate 
destination. The waypoint at which the aircraft diverts from the active 
flight plan is indicated by the ICAO identifier for the waypoint. As shown 
on second screen 52, the selected waypoint is KSEA, corresponding to the 
airport at Seattle, Wash. In a preferred embodiment of the invention, the 
default waypoint at which the aircraft leaves the active flight plan is 
the next waypoint along the active flight plan from the aircraft's current 
position. Alternatively, the pilot may specify the waypoint by entering in 
the alphanumeric code for the waypoint. 
The pilot may select which of the three routing options 54 to use in the 
event of a diversion by pressing the appropriate key, 1L-3L, adjacent the 
routing option. As discussed above, when selecting offset or overhead 
routing, the pilot may also vary the desired offset or waypoint in the 
routing option. For example, as shown by the series of keystrokes in FIG. 
2A, if the pilot desired to change the offset from left 10 nautical miles 
to right 20 nautical miles, the pilot would use the alphanumeric keypad to 
enter R-2-0- followed by pressing the 2L key twice. These keystrokes will 
initially display R20 in scratch pad area 38 of the CDU. Pressing the 2L 
key the first time moves the scratch pad data to a position adjacent the 
2L key, changing the offset from L10 to R20. Pressing the 2L key the 
second time selects offset routing as the routing choice. As shown in 
screen 58 in FIG. 2B, the routing option has therefore been changed from 
direct routing to offset routing. Those skilled in the art will recognize 
that the alternate waypoint may similarly be changed by the entry of an 
appropriate alphanumeric keystroke sequence. 
In a preferred embodiment of the invention, the selection of a routing 
option is a global selection that applies to all four of the alternate 
destinations displayed on first screen 50. That is, once a pilot has 
selected a routing option, a diversion to any of the four alternate 
destinations will take place along the selected routing option. If 
overhead routing is globally selected, however, each alternate destination 
may have a different waypoint specified at which the diversion from the 
active flight plan occurs. 
In addition to providing a list of routing options, second screen 52 also 
displays a list of operating conditions 56 that are used by the alternate 
destination planner to calculate the ETA and fuel remaining at each of the 
alternate destinations. The first operating condition, corresponding to 
the 1R key, is the altitude of the aircraft to be used during diversion. 
The altitude of the aircraft may be entered by the pilot in either of two 
formats that are automatically recognized by the alternate destination 
planner. In an altitude format, the pilot enters the altitude of the 
aircraft in feet. For example, the pilot may enter "12000" to indicate 
that during diversion the aircraft should operate at 12,000 feet. In a 
second flight level format, the pilot may enter a flight level code 
indicative of the altitude. For example, the pilot may enter "FL250" to 
indicate that the aircraft should operate at 25,000 feet. To enter the 
appropriate altitude, the pilot keys the formatted altitude using the 
alphanumeric key pad of the CDU and then presses the 1R key to move the 
altitude level to a position on the screen. After entry of the altitude on 
one screen, the altitude of the aircraft is globally applied to all 
alternate destinations. That is, the calculation of the arrival data for 
all four alternate destinations on first screen 50 is based on the same 
altitude. 
The second operating condition is the speed of the aircraft at which 
diversion is to occur. The speed of the aircraft may be entered by the 
pilot in one of several formats. In a first format, the pilot may enter a 
three-digit airspeed indicative of the aircraft's speed in knots. For 
example, the pilot may enter "300" to indicate a speed of 300 knots. The 
three-digit airspeed is typically only used to represent a low altitude 
diversion. In a second format, the pilot may enter a three-digit mach 
number, indicative of the aircraft's speed as a fraction of the speed of 
sound. In a preferred embodiment of the invention for subsonic aircraft, 
the mach number is always a fraction less than one. As shown in second 
screen 52, for example, the entered speed is mach 0.810. The mach number 
is typically entered by the pilot for a high altitude diversion. In a 
third format, the pilot may enter an alphanumeric speed code indicative of 
a certain type of performance. For example, in a preferred embodiment of 
the invention, the pilot may enter the code "LRC" to represent a long 
range cruise mode. In long range cruise mode, the alternate destination 
planner calculates the most fuel efficient speed for the aircraft to fly 
at given the current weight of the aircraft. It will be appreciated that 
several other alphanumeric speed codes may be provided, including codes 
for engine out operation, economy operation, and an airline defined 
default cruise mode. After entry of the speed on one screen, the speed of 
the aircraft is globally applied to all alternate destinations. That is, 
the calculation of the arrival data for all four alternate destinations on 
first screen 50 is based on the same speed. 
In contrast to the speed and altitude which are globally defined for the 
alternate destinations, the remaining operating conditions are locally 
defined for each alternate destination. The third operating condition 
corresponds to the wind at the particular alternate destination. In a 
preferred embodiment, the pilot enters the value of the wind at the 
alternate destination by entering a three-digit value indicative of the 
direction of the wind in degrees, followed by a slash, followed by an up 
to three-digit value for the wind velocity measured in knots. For example, 
the pilot may enter a wind value of 093/15 to indicate a wind bearing 
93.degree. at a velocity of 15 knots. A different wind value may be 
entered by the pilot for each of the alternate destinations displayed on 
first screen 50. 
The fourth operating condition is the outside air temperature associated 
with a particular altitude at an alternate destination. The format for the 
outside air temperature is the altitude, followed by a slash, followed by 
a temperature at the destination in plus or minus degrees Celsius. The 
altitude may be entered in either the altitude format or the flight level 
format discussed above with respect to the altitude condition. For 
example, a pilot may enter FL250/-25 to indicate a temperature of 
-25.degree. C. at an altitude of 25,000 feet. As shown on second screen 
52, when no values have been entered by the pilot for the wind or the 
outside air temperature, hyphens are inserted at the appropriate location 
to indicate the number of characters and appropriate format for each 
condition. A different outside air temperature value may be entered by the 
pilot for each of the alternate destinations displayed on first screen 50. 
To enter or change any of the operating conditions, the pilot uses the 
alphanumeric keypad on the CDU to enter the updated condition using the 
appropriate format. The pilot then presses the appropriate key, 1R-4R, to 
move the value from the scratch pad to a position adjacent the selected 
key. For example, as shown by the keystrokes in FIG. 2B, a pilot may enter 
a wind bearing 93.degree. at a velocity of 15 knots using the keystrokes 
0-9-3-/-1-5. By pressing the 3L key, the wind data is then transferred 
from the scratch pad to a position adjacent the 3L key on fourth screen 
60. 
In addition to values entered by the pilot, typical operating conditions 
may be included in an airline modifiable information (AMI) file that is 
stored in the FMC and accessible to the alternate destination planner. The 
AMI file maintains a number of preselected values that the airline company 
has decided are suitable for describing the flight of the aircraft in the 
absence of a pilot preference. In particular, an airline defined aircraft 
speed and aircraft altitude are typically defined in the AMI file. When an 
individual alternate destination page is therefore initially accessed, the 
values stored in the AMI file will be displayed as the operating 
conditions until modified by the pilot. 
Below the listing of the operating conditions, the arrival data is also 
repeated for the particular alternate destination represented on the 
screen. As shown on second screen 52, adjacent to key 5R is arrival data 
showing the estimated time of arrival at KRNO and the amount of fuel 
remaining upon landing. The arrival data displayed on the particular 
alternate destination screen corresponds to the data that is displayed on 
first screen 50. The arrival data is calculated by the alternate 
destination planner, and is not modifiable by the pilot. 
II. Determining Least Time Alternate Destinations and Calculating Arrival 
Data 
Having described the data provided by the alternate destination planner to 
the pilot, the methods of determining the closest alternate destinations 
by time, the estimated time of arrival, and the remaining fuel will now be 
discussed. FIG. 3 is a flowchart of a main program 70 incorporated within 
the alternate destination planner that is used to identify according to 
flight time the four closest airports to the aircraft's current position. 
In addition to identifying the closest airport by time, the program 
calculates the ETA and remaining fuel to each alternate destination and 
displays the alternate destinations, ETAs and remaining fuel on the CDU. 
Initially, the program enters a loop to search a navigation database 
contained within the flight management computer and identify suitable 
alternate destinations in the database. Those skilled in the art will 
recognize that modern flight management computers typically incorporate a 
database containing a list of all airports and other landing destinations 
around the world. Although the format may vary, the database typically 
contains a four-digit destination identifier, a set of coordinates 
representing the precise latitude and longitude of the destination, and a 
data field indicating the runway length at the particular destination. 
Additional data fields containing further information about the facilities 
at each of the destinations may be included in the navigation database, 
depending upon the size and complexity of the database incorporated in the 
flight management computer. 
To search the navigation database, the main program initially loads a 
destination from the database at a block 72 and, at a decision block 74, 
examines the destination to determine if the runway is of sufficient 
length to land the aircraft containing the alternate destination planner. 
A minimum runway length for the particular aircraft is defined by the 
airline and included in the AMI file stored in the FMC. If the runway at 
the destination is not of sufficient length, the program returns to block 
72 where a new destination is loaded and examined by the program. If the 
runway is of sufficient length, however, the main program proceeds to a 
block 76 where the destination is added to a destination list. At a 
decision block 78, the main program determines if there are any more 
entries in the navigation database. If the database contains additional 
entries, the main program returns to a block 72 to examine the next entry 
in the database. If the entire database has been searched, however, the 
main program proceeds to a block 80. 
At block 80, the main program examines the suitable destinations selected 
from the navigation database to determine the eight closest destinations 
to the airplane's current position. A straight line distance between the 
airplane's current position and the latitude and longitude of the 
destination is calculated, and the resulting distances compared to select 
the eight closest destinations by distance. The calculation of the 
distance between two points identified by latitude and longitude 
coordinates is well known in the navigation art. It will be appreciated 
that an additional step may be incorporated in block 80, wherein a direct 
comparison is made with the latitude and longitude of the current aircraft 
position to quickly eliminate distant destinations without calculating a 
straight line distance. 
At a block 82, the main program calculates an ETA to the eight closest 
destinations. A flow chart of an ETA subroutine 100 for calculating the 
ETA to a given alternate destination is shown in FIG. 4A To estimate the 
ETA, the ETA subroutine divides the diversion path into two or three 
flight segments, depending upon the routing option that is selected. A 
diagram of two flight profiles showing the flight segments used by the 
alternate destination planner to calculate the ETA during diversion from 
an original flight plan to an alternate destination are shown in FIGS. 5A 
and 5B. 
The flight profile shown in FIG. 5A represents the flight profile used by 
the alternate destination planner when the direct or offset routing 
options have been selected by the pilot. In the representative flight 
profile, the aircraft initially enters a cruise segment where it maintains 
a desired altitude and a desired speed. The cruise segment extends until 
the aircraft hits a top of descent point, after which the aircraft begins 
to descend to the alternate destination. The aircraft is presumed to 
descend along the following predefined descent path: 
(a) From the top of descent point, the aircraft follows a linear path 
having a 3.degree. glide slope until a point 1000 feet above the Federal 
Aviation Administration (FAA) defined speed transition altitude at the 
speed used during the cruise segment; 
(b) From the end of segment (a), the aircraft follows a linear path having 
a 1.5.degree. glide slope until the speed transition altitude at a scaled 
value of the speed used during the cruise segment; 
(c) From the end of segment (b), the aircraft follows a linear path having 
a 3.degree. glide slope to a point 1000 feet above the altitude of the 
airport at a speed 10 knots below the transition speed; and 
(d) From the end of segment (c), the aircraft follows a linear path having 
a 1.5.degree. glide slope until touchdown at a speed of 170 knots. 
The location of the descent point is therefore determined by calculating 
back from the location of the alternate destination until the cruise 
altitude of the aircraft is reached. Those skilled in the art will 
recognize that knowing the speed and path of the aircraft during the 
descent, the location of the alternate destination, and the initial 
cruising altitude of the aircraft allows the alternate destination planner 
to determine the point in the cruise segment at which the aircraft should 
begin to descend. 
FIG. 5B shows a flight profile used by the alternate destination planner 
when overhead routing has been selected by the pilot. In FIG. 5B, the 
aircraft continues along the original flight plan until the desired 
diversion point is reached overhead a waypoint. The first segment of the 
flight is therefore identified as the original route segment. Following 
the original route segment of the flight, the aircraft assumes a flight 
profile identical to the profile used in direct or offset routing. That 
is, upon reaching the diversion point, the aircraft enters a cruise 
segment at a desired speed and a desired altitude. Upon entering the 
cruise segment, the aircraft will typically ascend or descend to a more 
efficient altitude from the altitude of the original flight segment. 
Following the cruise segment, the aircraft reaches a top of descent point 
where it begins to descend along a predefined descent path to the 
alternate destination. The length of the descent segment and the top of 
descent point is calculated in a similar manner to the direct and offset 
methods described above. 
Returning to FIG. 4A, the ETA subroutine determines whether the overhead 
routing option has been selected by the pilot at a decision block 102. If 
overhead routing has been selected, at a block 104, the program calculates 
an estimated time enroute (ETE) along the original flight segment of the 
flight profile, corresponding to the continuation of the aircraft along 
the original flight plan. Those skilled in the art will recognize that the 
original flight plan contains sufficient information for the ETA 
subroutine to calculate the amount of time it will take for the aircraft 
to reach the waypoint at which a diversion is to occur. The ETA subroutine 
then stores the ETE for the original route segment. 
If the pilot selected direct or offset routing, the ETA subroutine 
continues to a block 106 after decision block 102. Block 106 begins a 
portion of the ETA subroutine where the subroutine calculates the ETE for 
the cruise segment. The ETA subroutine initially calls three nested 
subroutines to calculate the speed of the aircraft to be used during the 
cruise segment, the altitude of the aircraft to be used during the cruise 
segment, and the average wind to be encountered over the cruise segment. 
At block 106 the ETA subroutine calls a subroutine to determine the speed 
of the aircraft to be used during the cruise segment, represented by a 
variable Spd(a). A speed subroutine 150 for determining the speed of the 
aircraft is shown in FIG. 4B. 
When the speed subroutine is called, at a decision block 152 the routine 
determines whether there has been a manual speed entry by the pilot. If 
the pilot has manually entered a speed, the subroutine proceeds to a 
decision block 154. At decision block 154, the speed subroutine determines 
if the manual entry is in airspeed or mach format. As discussed above, the 
current speed may be entered by a pilot in knots or as a fraction of the 
speed of sound. If the manual entry is in airspeed or mach format, the 
subroutine proceeds to a block 156 where the variable Spd(a) is set equal 
to the manually entered value. 
If at decision block 154 the speed subroutine determines that the manual 
entry is not in the airspeed or mach format, the program proceeds to a 
series of blocks 158 through 172 which determine the speed based on a 
number of preprogrammed alphanumeric codes representing a desired air 
speed. For example, at a decision block 158 the subroutine determines if 
the manual entry is equal to the characters "EO." If the manual entry is 
EO, the subroutine proceeds to a block 160 where it sets the variable 
Spd(a) equal to a computed engine out speed. Those skilled in the art will 
recognize that the computed engine out speed is less than the normal 
flight speed of the aircraft, and is determined by evaluating a number of 
different factors that are beyond the scope of the present disclosure. 
Similarly, blocks 162 and 164 represent a branch setting the variable 
Spd(a) equal to a computed long-range cruising speed if a pilot has 
manually entered the code "LRC." The long-range cruising speed is the 
minimum fuel-burn speed for the aircraft over a long-range flight, and is 
computed using an algorithm that is beyond the scope of this disclosure. 
Blocks 166 and 168 determine whether the pilot has entered the code for an 
engine out long-range cruising speed, and blocks 170 and 172 determine 
whether the pilot has entered the code for a company defined speed stored 
in the memory of the flight management computer. It will be appreciated 
that the number and alphanumeric codes represented in blocks 158 and 172 
may be expanded or reduced to include additional or fewer codes indicative 
of a desired speed. 
Returning to decision block 152, if the pilot has not entered a manual 
speed entry, the speed subroutine proceeds to a decision block 174 where 
the altitude of the aircraft is determined. It will be appreciated that in 
the United States, the FAA has mandated that under a certain altitude 
commercial aircraft must operate below a maximum speed. If the altitude of 
the aircraft indicates it is below the mandated speed transition level, at 
a block 176 the variable Spd(a) is set equal to the maximum speed below 
the transition altitude minus 10 knots. It will be appreciated that in 
other countries having different maximum speeds below a certain altitude, 
the variable Spd(a) will be set accordingly. It the aircraft is currently 
operating above the speed transition altitude, the speed subroutine 
proceeds to a decision block 178 where the subroutine determines whether 
there is a speed value stored in the AMI file. If there is a stored speed 
value in the AMI file, the subroutine proceeds to a block 180 where the 
variable Spd(a) is set equal to the stored AMI value. 
If there is no speed value stored in the AMI file, the subroutine proceeds 
to a block 182 where the variable Spd(a) is set equal to a computed 
economy speed. The economy speed is determined based on a variety of 
environmental and aircraft conditions to be equal to the speed providing 
optimal fuel economy at a reasonable aircraft speed. The speed subroutine 
150 therefore returns a value to the ETA subroutine for the variable 
Spd(a). It will be appreciated that the speed subroutine can be modified 
to include the measurement of the actual speed of the aircraft when the 
diversion is to occur. In a preferred embodiment of the invention, 
however, the speed must be either stored in the flight management 
computer, or entered by the pilot. 
With reference to FIG. 4A, after estimating the speed during the cruise 
segment, the ETA subroutine proceeds to a block 108 where the altitude of 
the aircraft during the cruise segment is estimated. FIGS. 4C through 4E 
are flowcharts of an altitude subroutine 200 that estimates an altitude 
value Alt(a) at which the aircraft should operate during the cruise 
segment of the diversion. It will be appreciated that in the alternate 
destination planner described herein it is presumed that the aircraft will 
fly at a constant altitude from the point at which a diversion is made 
until the point at which the aircraft begins to descend to the alternate 
airport. 
At a decision block 202 the altitude subroutine initially determines 
whether the aircraft is currently climbing. If the aircraft is climbing, 
the altitude subroutine proceeds to a decision block 204 where it is 
determined whether a manual altitude has been entered by the pilot. If the 
pilot has entered a manual altitude, at a block 206 the altitude 
subroutine sets the variable Alt(a) equal to the manual altitude entered 
by the pilot. As discussed above, the altitude entered by the pilot will 
be displayed using an altitude format or a flight level format. At block 
206, the altitude subroutine therefore sets the variable Alt(a) equal to 
the desired altitude whether expressed in altitude format or flight level 
format. 
If the airplane is in climb and the pilot has not entered a manual 
altitude, the subroutine proceeds to a decision block 208, where it is 
determined if the airplane is operating above an optimum altitude. It will 
be appreciated that the optimum altitude for an aircraft to operate varies 
with a number of conditions, but is based primarily on the gross weight of 
the aircraft including fuel. Generally, it is more efficient for a lighter 
aircraft to operate at a higher altitude than a heavier aircraft. If the 
airplane is above the optimum altitude, the subroutine proceeds to a block 
210 where it sets the variable Alt(a) equal to the cruise altitude. The 
cruise altitude is the altitude cleared by air traffic control for 
operation of the aircraft, and is typically set by the pilot upon takeoff. 
If the airplane is currently operating below the optimum altitude, the 
altitude subroutine proceeds to a decision block 212 where the subroutine 
compares the cruise altitude with the optimum altitude. If the cruise 
altitude is less than the optimum altitude, at a block 214 the variable 
Alt(a) is set equal to the cruise altitude. If the cruise altitude is 
greater than the optimum altitude, however, at a block 216 the variable 
Alt(a) is set equal to the optimum altitude. 
Returning to decision block 202, if the aircraft is not currently climbing, 
the altitude subroutine 200 proceeds to a decision block 218 where it 
determines whether the airplane is in a level flight. If the aircraft is 
not in level flight, the altitude subroutine proceeds to a decision block 
220 shown in FIG. 4D. Upon reaching decision block 220, it is presumed 
that the aircraft is in descent. At decision block 220, the altitude 
subroutine initially determines whether the aircraft will be routed via 
direct or offset routing. If the routing is not direct or offset (i.e., 
the routing is overhead), the altitude subroutine proceeds to a block 222 
where the variable Alt(a) is set equal to the optimum altitude. In the 
event of a diversion, the aircraft will therefore descend or climb to the 
optimum altitude from the altitude at which the aircraft arrives at the 
waypoint for diversion. 
If the routing will be via direct or offset routing, the altitude 
subroutine proceeds to a decision block 224. At decision block 224 the 
subroutine compares the current altitude with the optimum altitude to 
determine if the current altitude is greater than the optimum altitude. If 
the current altitude exceeds the optimum altitude, at a block 226 the 
variable Alt(a) is set equal to the current altitude. If the current 
altitude is, however, less than the optimum altitude, at a block 228 the 
subroutine sets the variable Alt(a) equal to the optimum altitude. During 
a diversion, the aircraft will therefore continue to operate at its 
current altitude unless the current altitude is less than the optimum 
altitude, in which case the aircraft is to climb to operate at the optimum 
altitude. 
Returning to FIG. 4C, if the airplane is in level flight the altitude 
subroutine proceeds to a decision block 230 where it determines whether 
engine out performance has been selected by the pilot. If engine out 
performance has not been selected, the subroutine branches to a decision 
block 232 as shown in FIG. 4E. The branch starting with decision block 232 
is therefore representative of the typical operating condition of an 
aircraft. That is, the airplane is in level flight and both engines are 
currently operating. At decision block 232, the altitude subroutine 
examines the routing option that the aircraft will take in the event of a 
diversion. If the routing is direct or offset, the altitude subroutine 
proceeds to a block 234 where the variable Alt(a) is set equal to the 
cruise altitude. If the routing is overhead, however, the subroutine 
proceeds to a decision block 236. 
At decision block 236, the subroutine determines if the overhead waypoint 
where diversion from the active flight plan occurs is within the cruise 
segment of the flight profile. It will be appreciated that the overhead 
waypoint may come before or after the top of descent point on the flight 
profile, depending on the proximity of the waypoint to the alternate 
destination. If the overhead waypoint is after the top of descent point 
and not in the cruise segment, at a block 238 the variable Alt(a) is set 
equal to the cruise altitude. If the overhead waypoint is prior to the top 
of descent point and in the cruise segment, the altitude subroutine 
proceeds to a decision block 240. At block 240, the altitude subroutine 
forecasts whether there will be a step climb, or increase in altitude, 
during the original route segment. Those skilled in the art will recognize 
that at periodic intervals as an aircraft travels along a flight plan, the 
aircraft may increase its altitude to operate at a more efficient 
altitude. Operating at a higher altitude increases the efficiency as the 
weight of the aircraft decreases due to fuel consumption. If there is no 
step climb forecast during the original route segment, at a block 242 the 
altitude subroutine sets the variable Alt(a) equal to the cruise altitude. 
If there is a step climb forecast during the original route segment, 
however, at a block 244 the subroutine sets the variable Alt(a) equal to 
the altitude that the aircraft is expected to step to. The method of 
forecasting and calculating the magnitude of the step climb is well known 
in the art, and is not discussed in further detail herein. 
With reference to FIG. 4C, if engine out performance is indicated at 
decision block 230 the altitude subroutine continues to a decision block 
246. At decision block 246, the altitude subroutine compares the cruise 
altitude with an engine out maximum altitude. The engine out maximum 
altitude is the maximum altitude that the aircraft can operate at with one 
engine turned off. If the aircraft has been confirmed for a cruise 
altitude that is less than the engine out maximum altitude, at a block 250 
the variable Alt(a) is set equal to the cruise altitude. If, however, the 
cruise altitude is greater than the engine out maximum altitude, at a 
block 248 the subroutine sets the variable Alt(a) equal to the engine out 
maximum altitude. An aircraft operating with engine out performance will 
therefore maintain its cruise altitude unless the cruise altitude is in 
excess of the engine out maximum altitude. If the cruise altitude is above 
the engine out maximum altitude, the aircraft will descend to that maximum 
altitude. 
Returning to FIG. 4A, after determining the altitude to be used during the 
calculation of the ETE during the cruise segment, the ETA subroutine then 
proceeds to a block 110 where the wind during the cruise segment is 
estimated. FIG. 4F is a flow chart of a wind subroutine 250 that 
calculates an average wind to be encountered by the aircraft during the 
cruise segment of the diversion. 
With reference to FIG. 4F, at a decision block 252 the wind subroutine 
initially determines whether the pilot has manually entered a value of the 
wind at the alternate destination. As discussed above, one of the 
operating conditions that the pilot may specify for each alternate 
destination is the wind direction and velocity. If the pilot has entered a 
value for the wind, at a block 254 the value of the wind at the alternate 
airport is set equal to the entered value. If the pilot has not entered a 
value for the wind, at a block 256 the wind value at the alternate 
destination is set equal to zero. At a block 258, the wind subroutine then 
uses the wind value at the alternate destination and a known wind at the 
diversion point to determine the average wind over the diversion route. If 
overhead routing is used, the wind at the diversion point is the wind at 
the waypoint where diversion to the alternate destination occurs. For 
direct or offset routing, the wind at the diversion point is presumed to 
be the current wind. For estimation purposes, the wind is also assumed to 
linearly change in direction and velocity from the wind measured at the 
diversion point to the wind measured at the alternate destination. The 
average wind is therefore the value of the wind at a point halfway along a 
linear interpolation between the wind at the diversion point and the wind 
at the alternate destination. After the wind subroutine calculates the 
average wind, the wind value is stored in a variable Wind(a). 
With reference to FIG. 4A, after estimating the speed, altitude, and wind 
during the cruise segment of the diversion, the ETA subroutine proceeds to 
a block 112 where the length in nautical miles of each segment in the 
diversion plan to the alternate destination are calculated and stored. The 
length of the original route segment is determined from the original 
flight plan data. As was discussed above with respect to FIG. 5, the 
length of the cruise segment is dependent upon the location of the top of 
descent point. At block 112, the ETA subroutine therefore initially 
calculates the distance between the diversion point and the alternate 
destination. In a preferred embodiment, the subroutine then interpolates 
from an altitude of 1000 feet above the airport back to the estimated 
altitude of the aircraft during the cruise segment using the predefined 
descent path. The altitude where the descent path intersects the cruise 
segment is determined, thereby fixing both the length of the cruise 
segment and the length of the descent segment. The length of the cruise 
segment, descent segment, and, if applicable, original route segment are 
then stored by the ETA subroutine. 
The ETA subroutine continues to a block 114 where the subroutine calculates 
the ETE during the cruise segment of the diversion, based on the stored 
values of Spd(a), Alt(a), and Wind(a). A flow chart of an ETE subroutine 
280 for calculating the estimated time enroute for the cruise segment is 
shown in FIG. 4G. 
At a decision block 282, the ETE subroutine initially determines whether 
the pilot has made a manual temperature entry in the alternate destination 
planner. As was discussed above, the pilot may enter the temperature at a 
certain altitude for each of the alternate destinations. If the pilot has 
entered a temperature, the ETE subroutine proceeds to a block 284 where 
the true air speed of the aircraft is computed based on the altitude 
Alt(a), speed Spd(a), and manually entered outside air temperature. The 
relationship of these factors to the true air speed of the aircraft is 
well known in the art, and is not discussed in additional detail herein. 
If the pilot did not enter a temperature for the alternate destination, at 
a block 286 the ETE subroutine computes the true air speed based on the 
altitude Alt(a), speed Spd(a), and a standard atmospheric model. After 
computing the true airspeed of the aircraft, the airspeed is stored at a 
block 288. 
At a block 290, the ETE subroutine computes the actual ground speed of the 
aircraft based on the stored value of the true airspeed of the aircraft 
and the average wind Wind(a). At a block 292, the ETE subroutine then 
computes and stores the ETE of the aircraft along the cruise segment based 
on the length of the segment and the ground speed. 
With reference to FIG. 4A, after calculating the ETE of the cruise segment 
at a block 114, the ETA subroutine calculates the ETE for the descent 
segment at a block 116. As discussed above, the estimation technique 
disclosed herein uses an predefined descent path having a linear slope and 
predefined speeds. Those skilled in the art will recognize that it is a 
straightforward matter to calculate the ETE of the descent path knowing 
the initial altitude of the aircraft, the speed of the aircraft, and the 
length of the descent segment. In a preferred embodiment of the alternate 
destination planner, the wind is assumed to be zero and the temperature 
nominal during the descent segment. After calculating the ETE for the 
descent segment, the ETE value is stored by the ETA subroutine. 
At a block 118, the ETA subroutine adds the ETEs for each of the segments 
of the diversion flight plan to arrive at a total time enroute. If 
overhead routing is selected, the ETEs for the original route segment, 
cruise segment, and descent segment are added. If direct or offset routing 
is selected, the ETEs for the cruise segment and descent segment are 
added. At a block 120, the total time enroute is added to the current time 
maintained in the flight management computer to determine an ETA at the 
alternate destination. The ETA for the alternate destination is stored and 
the ETA subroutine returns to the main program. 
Returning to the flow chart of the main program in FIG. 3 at block 82 ETA 
subroutine 100 is called eight times to calculate an ETA for each of the 
eight closest destinations. At a block 84, the main program calculates the 
remaining fuel at each of the eight closest alternate destinations. It 
will be appreciated that there are several techniques known in the art for 
calculating an aircraft's fuel consumption given the aircraft's operating 
altitude and speed, as well as the outside air temperature and wind. Since 
the length of each segment of the diversion path is known, the amount of 
fuel remaining at the end of each segment may be readily determined. At a 
block 86, the main program compares the ETA to the eight closest 
destinations and selects four destinations that have the lowest ETA. The 
alternate destination planner therefore identifies those alternate 
destinations that are the closest based on time, rather than distance. 
At a block 88, the main program displays the list of the four closest 
destinations with the ETA and remaining fuel on the CDU. As shown in 
representative first screen 50 in FIG. 2A, the alternate destinations are 
ordered according to the ETA, with the closest alternate destination 
listed first. In a preferred embodiment of the alternate destination 
planner, absent any information input by the pilot or flight plan changes 
the list of alternate destinations and arrival data are updated every five 
minutes. The period between updates may be extended or reduced, however, 
depending upon the performance of the aircraft and the importance of 
maintaining timely information on the display. If the pilot changes the 
operating conditions or routing options, the displayed data is immediately 
recalculated. It will be appreciated that the method disclosed herein for 
estimating the arrival data for each alternate destination provides 
greater accuracy because it takes into account the aircraft altitude, the 
aircraft speed, the outside air temperature, the wind, and the selected 
routing to the alternate destination. Moreover, each of the factors may be 
modified by the pilot to more accurately reflect the current conditions. 
The pilot may therefore rely on the arrival data with a higher degree of 
confidence than prior alternate destination planners. 
III. Alternate Destination Planner Operation 
Once the CDU displays a list of alternate destinations, ETA, and remaining 
fuel, the pilot may select the alternate destination to which the aircraft 
is to divert. As shown in FIG. 2A, to increase the response time of the 
pilot the closest alternate destination by time is automatically 
preselected for diversion. The preselection is indicated on first screen 
50 by a "&lt;A&gt;" following the four character identifier of the first 
alternate destination Alternatively, if the pilot elects to divert to one 
of the other alternate destinations listed, the pilot may select the 
alternate destination by pressing the appropriate key, 1L to 4L, next to 
the alternate destination. With reference to FIGS. 6A and 6B, a series of 
representative data screens that may be accessed by the pilot on the CDU 
are provided. The manual selection of the third alternate selection on 
representative screen 300 FIG. 6A was performed by pressing key 3L. A 
manual selection of a different alternate destination is indicated by a 
"&lt;SEL &gt;" following the identifier of the destination. 
At any point in the process of selecting an alternate destination, editing 
the routing options, or editing the operating conditions, the pilot may 
immediately divert to the automatically- or manually-selected alternate 
destination by pressing key 6R. As shown on screen 300, key 6R is labeled 
with the text "DIVERT NOW" under the identifier of the airport that is 
currently selected for diversion. Pushing the divert now key 6R causes the 
text next to key 6R to change to "SELECTED" as shown in a representative 
screen 302. Additionally, the word "MOD" appears in the screen title to 
indicate that a flight plan modification has been selected. Pressing the 
divert now key causes a route modification to be loaded into the flight 
management computer. To implement the change in flight plan to the 
alternate destination, the pilot must press the EXEC function key 48. 
Pressing the EXEC key loads the alternate destination into the flight 
management computer, and starts the aircraft on the desired diversion if 
lateral navigation (LNAV) and autopilot are engaged. It will be 
appreciated that the minimal amount of time and keyed entry required by 
the pilot to implement a diversion improves the response time of the pilot 
in an emergency requiring a diversion. 
If a pilot would like to cancel the diversion prior to pressing the EXEC 
key, the pilot may do so by selecting the alternate destination page 
showing the routing and operating conditions. As shown by a representative 
screen 304 in FIG. 6B, after pressing the divert now key, an "ERASE" 
option is added on the individual alternate destination page next to key 
6L. Pressing the erase key clears the flight plan modification and 
associated information and returns the page to the previous unmodified 
state. The pilot may also modify the diversion to incorporate engine out 
performance. Provided to the pilot on screen 304 is an "ENG OUT" option 
adjacent key 5L. Pressing the engine out key causes the alternate 
destination planner to recalculate the arrival data for all of the 
alternate destinations based on the reduced performance available when the 
aircraft is only operating on a single engine. In particular, a new cruise 
altitude is determined if the current cruise altitude is above the engine 
out ceiling, and a new engine out speed is loaded for the reduced maximum 
speed of the aircraft. It will be appreciated that the preferred 
embodiment of the invention was adapted for use in the two-engine Boeing 
777. An alternate destination planner incorporated in other aircraft 
having more than two engines would require a modification to the manner in 
which the engine out performance was selected. 
A representative screen 306 is provided in FIG. 6B to further show the 
effect of implementing a diversion by pressing the EXEC key. Screen 306 
was accessed on the CDU by depressing the LEGS key 44. Those skilled in 
the art will recognize that when the modification to the flight plan is 
executed, the active flight plan is discarded and the alternate 
destination is loaded as the current destination. As shown on screen 306, 
the alternate destination is automatically loaded as the first leg in the 
new flight plan. Additional data regarding the newly loaded flight plan 
may be accessed using techniques known to those skilled in using a CDU and 
flight management computer. 
The alternate destination planner of the present invention also includes 
the capability of loading alternate destination data that is transmitted 
via air-ground data link from a ground station to the aircraft during 
flight. FIGS. 7A, 7B, and 7C show a series of representative data screens 
that may be accessed by the pilot on the CDU in order to request and 
receive ground station data. To request data about routing options and 
operating conditions for the four alternate destinations displayed on the 
alternate destination summary page (see screen 300 of FIG. 6A), a pilot 
presses key 5L, labeled as "ALTN REQUEST." Pressing the 5L key transmits a 
request from the aircraft to the ground station for updated information 
about each of the four alternate destinations displayed on the summary 
page. As shown in representative first screen 320 in FIG. 7A, after 
depressing the key the text adjacent the key changes to "REQUESTING," 
indicating that the downlink request has been transmitted. As shown in a 
second screen 322, the text changes to "REQUEST SENT" upon receipt from 
the ground station of an acknowledgment of the request. The coding and 
transmission of information between an aircraft and a ground station is 
well known in the art. 
In a preferred embodiment of the alternate destination planner, the ground 
station may transmit to the aircraft a new list of up to four alternates 
along with a priority of the alternates. For each alternate, the ground 
station may transmit a value of the wind, outside air temperature, and 
overhead diversion waypoint. Additionally, a single diversion speed, 
altitude, and offset distance for all alternates may be uplinked from the 
ground station. Upon receipt of the requested information from the ground 
station, the alternate destination summary page is updated as shown in a 
representative third screen 324 in FIG. 7B. The numbers above each of the 
alternate destination identifiers indicate the priority of the alternate 
destinations as selected by the transmitting ground station. The pilot has 
the option of receiving the entirety of the uplinked data by pressing key 
6R, or rejecting the entirety of the uplinked data by pressing key 6L. As 
shown in representative fourth screen 326, the pilot may view the 
individual alternate destination data before deciding whether to accept or 
reject the uplinked data. It will be appreciated that until the pilot 
accepts or rejects the uplinked data, the pilot may not divert the 
aircraft to an alternate destination. During the uplink accept/reject 
period, the DIVERT NOW alternative is removed from both the summary 
alternate destination page and the individual alternate destination page. 
In a preferred embodiment of the alternate destination planner, the pilot 
also has the capability to request and receive via data link an alternate 
destination list that is used in place of the navigation database 
contained in the flight management computer. To load an alternate 
destination list, from the alternate destination summary page the pilot 
initially presses either the previous page or next page function keys 40 
to arrive at an alternate list page as shown in a representative fifth 
screen 328 in FIG. 7C. To request an alternate destination list, a pilot 
presses key 5L, labeled as "ALTN LIST REQUEST." When the list is received 
from the ground station, the alternate list is displayed on the screen as 
shown in a representative sixth screen 330. In a preferred embodiment of 
the invention, an airline may uplink a list of up to twenty alternate 
airports from the ground station. 
The received alternate destination list is automatically used by the 
alternate destination planner in place of the navigation database. That 
is, the alternate destination planner selects the four closest alternate 
destinations for display on the alternate destination summary page 
exclusively from the uplinked list. If the pilot desires to return to 
selecting the alternate destinations from the navigation database, the 
pilot may purge the uplinked list by pressing key 5R, labeled "ALTN LIST 
PURGE." 
In accordance with another aspect of the alternate destination planner 
disclosed herein, in addition to providing a text listing of the alternate 
destinations available for diversion, the alternate destination planner 
also provides a graphical display of the location of the alternate 
destinations with respect to the current flight plan. FIG. 8 is a 
pictorial diagram of a representative screen of a navigation display 350 
that is coupled to the alternate destination planner through the flight 
management computer. As those skilled in the art will appreciate, the 
depicted screen of the navigation display includes an aircraft icon 358 
indicating the position and orientation of the aircraft containing the 
display and a rotating compass scale 352 from which the current heading of 
the aircraft can be ascertained. A distance scale 353 is also provided to 
allow a pilot to judge the distances to locations represented on the 
navigation screen. It will be appreciated that other screens may be 
generated on the typical navigation display other than the one shown in 
FIG. 8. 
Superimposed over the compass scale, distance scale, and aircraft icon is a 
line 354 indicative of a flight plan of the aircraft. Line 354 is of a 
distinguishing color, and indicates a portion of the flight plan of the 
aircraft through a series of waypoint icons 356. The representative flight 
plan shown in FIG. 8 passes through a waypoint in SEA (Seattle, Wash.) 
before proceeding through a waypoint in ELN (Ellensburg, Wash.). It will 
be appreciated that due to the scale of the display, only a portion of the 
active flight plan is displayed. By adjusting the scale of the navigation 
display, however, a pilot may expand or contract the amount of the flight 
plan that is represented on the screen. 
In cooperation with the flight management computer, the alternate 
destination planner disclosed herein provides a visual display of the 
alternate destinations that are within the range of the area represented 
on the navigation display. In particular, for each alternate destination, 
the alternate destination planner generates a destination icon 360 on the 
navigation display. The destination icon 360 consists of an "A" in a 
circle and an adjacent listing of the ICAO destination identifier. It will 
be appreciated that depending upon the scale of the navigation display and 
the number of alternate destinations in the area surrounding the aircraft, 
a greater or lesser number of alternate destinations may be displayed on 
the screen. Moreover, in a preferred embodiment of the alternate 
destination planner, a pilot may toggle a switch to display either the 
closest alternate destination or all four of the alternate destinations 
contained in the alternate destination summary list. 
The position of each destination icon 360 on the display is accurately 
represented with respect to the location of the aircraft icon, allowing a 
pilot to estimate the heading and distance to the alternate destination. 
For example, on the representative screen shown in FIG. 8 it is readily 
apparent to a pilot that the alternate destination KPDX is the closest 
alternate destination, and that KPDX lies to the right of the current 
flight plan at a heading of approximately 170 degrees and a distance of 
approximately 100 nautical miles. Although an exact comparison of the 
relative distances and headings to each of the alternate destinations 
cannot be made by the pilot from the display, the navigation display does 
provide sufficient information to a pilot to make an initial estimation of 
the flight maneuver required to divert to each destination. 
While the preferred embodiment of the invention has been illustrated and 
described, it will be appreciated that various changes can be made therein 
without departing from the spirit and scope of the invention.