Method and device for resetting a target altitude for an emergency decent of an aircraft

CA 02746580 2011-07-12 1 Method and device for resetting a target altitude for an emergency descent of an aircraft.

The present invention relates to a method and a device for resetting a target altitude intended for an emergency descent of an aircraft, in particular of a transport aircraft.

It is known that civilian transport aircraft must be pressurized, because in cruising flight, an aircraft operates at an altitude which is often above 30,000 feet (approximately 9,000 meters), for which the outside air is too poor in oxygen (and also too cold and too dry) to be compatible with life.

Also, pressurization systems are fitted to the planes in order to keep a breathable atmosphere on board.

In particular, international aviation regulations require that any public transport aircraft that flies at an altitude above 20,000 feet (approximately 6,000 meters) be pressurized and that it establish in the cabin an equivalent altitude which does not exceed 8,000 feet (approximately 2400 meters) in normal flight.

However, it may happen, following a breakdown or an incident, that the pressurization of the airplane can no longer be maintained at an acceptable level.

A regulatory procedure then requires the pilot to descend the aircraft, as quickly as possible, to a breathable altitude of 10,000 feet (approximately 3,000 meters) or to the current safety altitude if it is not possible to descend to. 'at 10,000 feet due to the terrain.

This procedure is called emergency descent.

In this case, the crew is responsible for the various tasks related to the initiation of the descent, as well as the adjustment of the descent parameters (speed, target altitude, lateral trajectory, ...), and this up to 'when the aircraft leveled off at low altitude.

It may however happen, although very rarely, that the crew is no longer able to apply the procedure described above, for example in the event of a pressurization failure which caused the crew to lose consciousness.

CA 02746580 2011-07-12 2 In this case, the aircraft is left to its own devices, although it is absolutely necessary to perform an emergency descent.

If, in such a situation, the autopilot is engaged, the flight is continued automatically until the total exhaustion of fuel reserves.

To avoid such a situation, an automatic piloting system is known which, when engaged, makes it possible to perform the emergency descent automatically, that is to say without requiring the assistance of a pilot.

In addition, the engagement of such an automatic emergency descent can be carried out, either manually by the pilot, or also automatically.

In particular, document FR 2 928 465 discloses a specific method for automatically controlling an emergency descent of an aircraft.

According to this method, when an automatic emergency lowering function is engaged, the following successive operations are carried out:

a) a set of vertical setpoints is automatically determined comprising:

- a target altitude which represents an altitude to be reached by the aircraft at the end of the emergency descent; and a target speed which represents a speed that the aircraft must respect during the emergency descent;

b) a set of lateral instructions is automatically determined, which represents a lateral maneuver to be carried out during the emergency descent;

and c) the aircraft is automatically guided so that it simultaneously complies with said set of vertical instructions and said set of lateral instructions until it reaches said target altitude which it then maintains, said automatic guidance being able to be interrupted by an action of 'a pilot of the aircraft.

In addition, this known method provides special means for automatically engaging the emergency descent function, taking into account the variation in altitude of the cabin, that is to say of the variation of the pressure inside the cabin.

Regarding the determination of a target altitude in the context of an automated emergency descent, we know:

- by document US ¨4 314 341, an automated emergency descent to a safety altitude, the value of which is fixed at 12,000 feet (approximately 3,600 m).

This value corresponds to a breathable and satisfactory altitude from a physiological point of view, but it presents the risk of being lower in the highest areas (Alps, Himalayas, Andes, Rockies ...).

It is therefore not sufficient to guarantee a safe end of the maneuver in the event of an unconscious crew (possible collision with the ground);

- by the document US ¨ 6 507 776 B1, a coupling between an automatic pilot and a GPS system which has a database in which are stored the altitude values ​​for all the reliefs, the altitude of which is higher or equal to a fixed maximum value.

This GPS system is equipped with a device for identifying the relief along the current trajectory.

This device makes it possible to provide the autopilot with the lowest possible safety target altitude, accessible by adjusting the heading of the aircraft if necessary, to circumvent the terrain.

This device has the drawback of potentially directing the aircraft outside the area covered by the air corridor initially taken.

The associated risk is to increase the workload of the crew when they regain consciousness, because the aircraft could then be far from the flight plan initially followed and, moreover, no longer have sufficient fuel to reach the nearest diversion airport.

In addition, this device includes a margin of only 1000 feet vis-à-vis the terrain, which is not sufficient to cover all possible fluctuations in barometric pressure along the emergency descent; and - by document US - 2007/0043482, another device integrated into the autopilot capable of automatically performing an emergency descent CA 02746580 2011-07-12 4 = to a safety altitude whose calculation is based on altitudes MSA (Minimum Safe Altitude) type safety standards.

More precisely, a database containing the MSA altitudes is used to determine the associated safety altitude, either with the current flight plan or, if it exists, with the diversion trajectory provided by the company.

When the airplane is outside the flight plan or outside any diversion path, the safety altitude is calculated from the terrain database by taking as a value the maximum altitude on a trajectory maintaining the current heading, to which is added a safety margin of 1000 feet or 2000 feet (in the case of a mountainous region).

However, this safety margin with respect to the terrain can be led to decrease sharply if no readjustment of the target altitude is carried out to take account of the barometric pressure reference.

It is known that the local atmospheric pressure is subject to non-negligible variations over a distance such as the distance covered during an emergency descent, for example around 40 NM.

In addition, the values ​​of the safety altitudes (MSA or MORA) taken from known databases and accessible by the flight management system FMS (Flight Management System) are barometric altitude values, referenced in relation to the sea ​​level (MSL for Mean Sea Level in English).

In addition, in cruising flight, the barometric reference of aircraft onboard instruments is generally a standard reference (STD), which corresponds to a nominal pressure of 1013.25 hPa.

This reference is used by all the aircraft in the cruising phase as well as by air traffic control, and makes it possible to have consistency between the altitude information exchanged.

Flight levels are taken into account.

When an aircraft flies at flight level FL350 for example, it means that it is flying at an altitude of 35,000 feet, referenced to 1013.25 hPa / 15 C (standard ISA model).

As the local atmospheric pressure is constantly changing as the aircraft passes through different CA 02746580 2016-07-05 air masses, the aircraft actually changes elevation above sea level while following the same flight level.

Since the reference is the same for all air traffic, this does not pose a problem for air traffic control to know precisely the relative altitudes of each of the airplanes and to ensure a satisfactory level of safety.

By taking into account all of these constraints, it is understood that if the barometric reference of the airplane is the standard reference and knowing the safety altitude referenced MSL, it is necessary to know the local pressure QNH of the point overflown, c 'that is to say the pressure brought back to sea level, to precisely reset the target altitude on the local reference while maintaining the barometric adjustment of the onboard instruments (STD).

This last point is important, because it is desirable not to modify the barometric settings of the cockpit for two main reasons:

- maintain consistency with the barometric reference usually used in cruising by all traffic and by air traffic control; and - allow the pilot to quickly find his bearings, in the event that he has lost and then regained consciousness following a depressurization causing the automatic emergency descent.

It is known that the QNH pressure is supplied by ground stations which are located near airports, but there is no simple way to obtain the local QNH pressure automatically.

Also, in the absence of readjustment of the target altitude to take account of the pressure reference differences, there is a risk of considerably reducing the safety margins with respect to the terrain.

The object of the present invention is to remedy the aforementioned drawbacks.

It relates to a method for resetting a target altitude intended for an emergency descent of an aircraft, said target altitude representing the altitude to be reached by the aircraft at the end of the emergency descent.

,, 5a The present invention relates to a method for resetting a target altitude for an emergency descent of an aircraft with a resetting device on board the aircraft, the target altitude representing the altitude to be reached by the aircraft. aircraft at the end of the emergency descent, the method by which:

a) determining, with a device for determining a safety target altitude included in the resetting device, a safety target altitude as a function of the emergency descent, by performing, automatically and repetitively, from 'an activation of the emergency descent, and over a horizontal reference distance in front of the aircraft relative to an initial position of said aircraft when the emergency descent is activated, the following operations:

a remaining horizontal distance is calculated, which represents a horizontal distance which remains to be covered by the aircraft from its current position to a position situated at said reference horizontal distance in front of said initial position;

- A safety altitude representative of said remaining horizontal distance is determined;

- This safety altitude is compared to a threshold altitude; and the highest value between said safety altitude and said threshold altitude is selected as the safety target altitude, the safety target altitude being measured in units of measurement chosen from among feet and meters;

b) calculating, with a device for calculating a correction value included in the resetting device, a correction value taking account of variations in barometric pressure appearing during the emergency lowering, the correction value being measured in the same units of measurement as the safety target altitude and the correction value corresponding to a potential error between an actual current altitude of the aircraft and a measured barometric altitude which is based on a pressure of standard reference affected by a local QNH pressure of the current position; and CA 2746580 2017-10-31 5b c) the sum of said safety target altitude and of said correction value is calculated with a device for calculating the resetting of a target altitude included in the resetting device. reset target altitude which replaces the target altitude to be reached at the end of the emergency descent, the readjusted target altitude being corrected for a potential risk of collision caused by the potential error between the actual current altitude and the calculated barometric altitude; and d) transmitting the readjusted target altitude to an automatic control system of the aircraft to automatically conduct the emergency descent using the reset target altitude.

Preferred modes of the process are described below.

To this end, according to the invention, said method is remarkable in that:

/ CA 2746580 2017-10-31 CA 02746580 2011-07-12 6 a) a safety target altitude is determined based on the emergency descent;

b) a correction value is determined taking account of variations in barometric pressure appearing during the emergency descent; and c) the sum of said safety target altitude and of said correction value is calculated to obtain a readjusted target altitude which is capable of replacing a target altitude to be reached at the end of the emergency descent. 'invention, a reset target altitude is determined which takes account of variations in barometric pressure appearing during the emergency descent and which is capable of replacing a target altitude to be reached at the end of the emergency descent.

The method according to the invention thus makes it possible to avoid a potentially significant reduction in the safety margin taken into account in the databases commonly used.

In a first embodiment, in step b), to determine the correction value:

- the lowest atmospheric pressure and the highest atmospheric pressure encountered on this day are taken into account;

- Determining first and second differences between a barometric reference and, respectively, said lowest atmospheric pressure and said highest atmospheric pressure; and - the greatest difference in absolute value, between these first and second differences, is transposed into a height value which represents said correction value. Furthermore, in a second embodiment, in step b), to determine the correction value, the following operations are carried out automatically and repeatedly:

the current barometric altitude of the aircraft is determined;

the current height of the aircraft with respect to sea level is determined, using means other than barometric measurement means; and CA 02746580 2011-07-12 7 - said current height is subtracted from said current barometric altitude so as to obtain said correction value.

Moreover, in a first variant implementation, in step c), the target altitude is replaced by the reset target altitude, repetitively on each determination of a new reset target altitude, and this preferably. until the target altitude is captured.

In addition, in a second variant implementation, in step c), the target altitude is replaced by the reset target altitude, only if the reset target altitude is greater than said target altitude.

This second variant implementation makes it possible to prevent the aircraft from descending below a safety target altitude.

In addition, in a third variant implementation, said readjusted target altitude and the target altitude being calculated repetitively by calculation steps, in step c):

the difference between the target altitude for a pitch N-1, N being an integer, and the target altitude readjusted for a pitch N is calculated;

the absolute value of this difference is compared with a threshold value;

and the target altitude for a pitch N is replaced by the target altitude readjusted for this pitch N, only if the absolute value of said difference is greater than or equal to said threshold value.

This third variant implementation makes it possible to avoid refreshing the target altitude too often in the event that the difference in altitude between two updates is not significant, which could appear inappropriate and even disturbing for the user. crew in the event that he remained conscious.

In a preferred embodiment, in step a), to determine a safety target altitude as a function of the emergency descent, it is carried out, automatically and repetitively, from the activation of the descent of emergency, and over a horizontal reference distance in front of the aircraft relative to an initial position of said aircraft when emergency descent is activated, the following operations:

8 - a remaining horizontal distance is determined, which represents a horizontal distance which remains to be covered by the aircraft from its current position to a position situated at said reference horizontal distance in front of said initial position;

- A safety altitude representative of said remaining horizontal distance is determined;

- This safety altitude is compared to a threshold altitude; and the highest value between said safety altitude and said threshold altitude is selected as the safety target altitude.

The method according to the invention, as mentioned above, for resetting an optimum target altitude for an emergency descent of an aircraft, is suitable for any type of emergency descent method, partially or totally automated.

However in a preferred application, this method is used to reset a target altitude in a method of automatic control of an emergency descent of an aircraft, method according to which the following successive operations are carried out:

a) a set of vertical instructions is automatically determined comprising the readjusted target altitude which represents the altitude to be reached by the aircraft at the end of the emergency descent and a target speed which represents a speed which the aircraft must comply with during the emergency descent;

b) a set of lateral instructions is automatically determined, which represents a lateral maneuver to be carried out during the emergency descent; and c) the aircraft is automatically guided (AC) so that it simultaneously complies with said set of vertical instructions and said set of lateral instructions until said target altitude is reached, according to which, in step a), we reset said target altitude according to the method described below.

The present invention relates to a device for resetting a target altitude intended for an emergency descent of an aircraft, this target altitude representing CA 2746580 2017-10-31 9 an altitude to be reached by the aircraft at the end of the flight. emergency descent, said device comprising:

- a device for determining a safety target altitude which automatically and repetitively determines a safety target altitude as a function of the emergency descent, from the activation of the emergency descent, and over a distance horizontal reference at the front of the aircraft relative to an initial position of said aircraft on activation of the emergency descent, said device for determining the safety target altitude comprising:

= a first element for determining a remaining horizontal distance, which represents a horizontal distance which remains to be traveled by the aircraft from its current position to a position situated at said reference horizontal distance in front of said initial position ;

= a second element for determining a safety altitude representative of said remaining horizontal distance;

= a third element for comparing this safety altitude with a threshold altitude; and = a fourth element for selecting as the safety target altitude a higher value between said safety altitude and said threshold altitude;

- a device for calculating a correction value which calculates a correction value taking into account variations in barometric pressure appearing during the emergency descent, the correction value being measured in the same units of measurement as the safety target altitude and the correction value corresponding to a potential error between an actual current altitude of the aircraft and a measured barometric altitude which is based on a pressure of standard reference affected by a local QNH pressure of the current position;

and a device for calculating a readjusted target altitude which calculates a sum of said safety target altitude and of said correction value to obtain a readjusted target altitude CA 2746580 2017-10-31 9a which replaces a target altitude to be reached at the end of the emergency descent, the readjusted target altitude being corrected for a potential risk of collision caused by the potential error between the actual current altitude and the calculated barometric altitude, according to which the resetting device transmits the readjusted target altitude to an automatic control system of the aircraft to automatically conduct the emergency descent using the reset target altitude.

Preferred embodiments of the device are described below.

The present invention also relates to an automatic control system for an emergency descent of an aircraft, comprising:

a device for determining vertical setpoints for automatically determining a set of vertical setpoints comprising the reset target altitude which represents the altitude to be reached by the aircraft at the end of the emergency descent and determined by the resetting device, said resetting device being included in the device for determining vertical setpoints; and the set of vertical instructions comprising a target speed which represents a speed that the aircraft must respect during the emergency descent;

a device for determining lateral instructions to automatically determine a set of lateral instructions, which represents a lateral maneuver to be carried out during the emergency descent; and a guidance system for automatically guiding the aircraft so that it simultaneously complies with said set of vertical instructions and said set of lateral instructions until said target altitude is reached.

This device therefore enables the target altitude to be readjusted during an automatic emergency descent, in particular, by overcoming the local pressure QNH.

The present invention further relates to an automatic control system for an emergency descent of an aircraft, of the type comprising:

- first means for automatically determining a set of vertical setpoints comprising:

- a target altitude which represents an altitude to be reached by the aircraft at the end of CA 2746580 2017-10-31 9b of the emergency descent; and a target speed which represents a speed that the aircraft must respect during the emergency descent;

- second means for automatically determining a set of lateral instructions, which represents a lateral maneuver to be carried out during the emergency descent; and third means for automatically guiding the aircraft so that it simultaneously complies with said set of vertical instructions and said set of lateral instructions until said target altitude is reached, in which said first means comprise the aforementioned device for resetting said altitude target.

CA 2746580 2017-10-31 CA 02746580 2011-07-12 The present invention also relates to an aircraft, in particular a transport aircraft, which is provided with a device and / or a system, such as those mentioned above.

The figures of the accompanying drawing will make it clear how the invention can be implemented.

In these figures, identical references designate similar elements.

FIG. 1 is the block diagram of a device according to the invention.

FIG. 2 is a graph for explaining the registration performed in accordance with the present invention.

FIG. 3 is the block diagram of an automatic control system for an emergency descent of an aircraft, comprising a device in accordance with the invention.

The device 1 in accordance with the invention and shown schematically in FIG. 1 is intended to reset, automatically, a target altitude for an emergency descent of an aircraft AC, in particular of a transport aircraft, said target altitude representing the altitude to be reached by the aircraft AC at the end of the emergency descent.

Said device 1 comprises:

- Means 2 for determining a safety target altitude ZS as a function of the emergency descent;

- Means 3 which are formed so as to determine a correction value ZC taking into account variations in barometric pressure appearing during the emergency descent; and - means 4 which are connected via links 5 and 6 respectively to said means 2 and 3 and which are formed so as to calculate the sum of said safety target altitude ZS and of said correction value ZC to obtain a reset target altitude ZR which is likely to replace a target altitude to be reached at the end of the emergency descent.

CA 02746580 2011-07-12 11 Thus, the device 1 according to the invention determines a readjusted target altitude ZR which takes account of variations in barometric pressure appearing during the emergency descent and which is capable of replacing a target altitude in front of be reached at the end of the emergency descent.

Said device 1 further comprises means 7 which are connected by means of a link 8 to said means 4 and which are formed so as to replace the target altitude by the readjusted target altitude ZR, generally as a function of special conditions specified below, this readjusted target altitude ZR being able to be transmitted via a link 9.

Said device 1 thus makes it possible to avoid a potentially significant reduction in the safety margin taken into account in commonly used databases.

In a first embodiment, said means 3 comprise the following elements (not shown), to determine the correction value ZC:

- an element which takes into account the lowest atmospheric pressure Rmin and the highest atmospheric pressure Rmax, recorded on the day when the adjustment is carried out;

- an element which determines first and second differences between a barometric reference R and, respectively, said lowest atmospheric pressure Rmin and said highest atmospheric pressure Rmax; and - an element which transposes the highest difference in absolute value, between these first and second differences, into a height value which represents said correction value.

Therefore, in this first embodiment, the correction value ZC satisfies the following relationship:

ZC = max (IR-Rmini; IR-Rmaxl) .28 in which:

- R, Rmin and Rmax are expressed in hPa;

- ZC is expressed in feet; and CA 02746580 2011-07-12 12 - 28 is a value making it possible to carry out the transposition, as specified below.

Furthermore, in a second embodiment, said means 3 comprise the following elements (not shown) for determining the correction value:

an element which determines the current barometric altitude Zbaro of the aircraft AC, for example an anemometric and inertial data reference system of ADIRS (Air Data lnertial Reference System) type;

an element which determines the current height Zgeo of the aircraft AC with respect to sea level MSL, using means other than barometric measurement means, in particular using a global positioning system of GNSS type (Global Navigation Satellite System), for example of GPS type; and an element which subtracts said current height Zgeo from said current barometric altitude Zbaro so as to obtain said correction value ZC.

Therefore, in this second embodiment, the correction value ZC satisfies the following relationship:

ZC = Zbaro - Zgeo Furthermore, in a first variant embodiment, said means 7 replace the target altitude AL by the reset target altitude ZR, repetitively each time a new reset target altitude ZR is determined, and this from preferably until the target altitude is captured.

Furthermore, in a second variant embodiment, said means 7 replace the target altitude AL by the readjusted target altitude ZR, only if the readjusted target altitude ZR is greater than said target altitude AL.

This second variant embodiment makes it possible to prevent the aircraft AC from descending below a safety target altitude.

In addition, in a third variant embodiment, said means 7 comprise the following elements (not shown):

CA 02746580 2011-07-12 13 - an element which calculates the difference between the target altitude AL for a pitch N let the reset target altitude ZR for a pitch N, N being an integer, said reset target altitude ZR and the target altitude AL being calculated repetitively by calculation steps;

- an element which compares the absolute value of this difference with a predetermined threshold value; and an element which replaces the target altitude for a pitch N by the target altitude readjusted for this same pitch N, only if said absolute value of the difference is greater than or equal to said threshold value.

This third variant implementation makes it possible to avoid refreshing the target altitude too often in the case where the difference in altitude between two updates is not significant, which can be inconvenient and even disturbing for the user. crew, in the event that it remains conscious.

In a preferred embodiment, said means 2 for determining a safety target altitude ZS as a function of the emergency descent, comprise elements (not shown) for, automatically and repetitively, from the activation of the emergency descent, and over a horizontal reference distance in front of the aircraft AC relative to an initial position of said aircraft AC when emergency descent is activated, perform the following operations:

determining a remaining horizontal distance, which represents a horizontal distance which remains to be covered by the aircraft from its current position to a position situated at said reference horizontal distance in front of said initial position;

- determining a safety altitude representative of said remaining horizontal distance;

- compare this safety altitude with a threshold altitude; and - selecting as the safety target altitude ZS the highest value between said safety altitude and said threshold altitude, In addition, from the activation of the emergency descent:

CA 02746580 2011-07-12 14 - an initial target altitude representative of said initial position of the aircraft is automatically determined on said activation of the emergency descent; and - the following operations are also carried out automatically and repetitively over said horizontal reference distance:

the safety target altitude ZS (which has been determined in the aforementioned manner), known as the current target altitude, is compared with said initial target altitude; and - if said current target altitude is lower than said initial target altitude, the target altitude used during the emergency descent is updated, taking into account said current target altitude.

It is thus possible to determine an optimized safety target altitude ZS over said remaining horizontal distance located in front of the aircraft AC, which maximizes the possibility of returning to a nominal state in the case of a crew or passengers unconscious or victims of hypoxic symptoms, without reducing the safety margins with respect to the relief along the path followed.

Preferably, said reference horizontal distance corresponding to a maximum horizontal distance that the aircraft AC is likely to cover during an emergency descent from the highest cruising flight level for the aircraft, at which one can add a margin.

The example of FIG. 2 makes it possible to clearly demonstrate the characteristics of the present invention.

Before the emergency descent, the aircraft AC is cruising at a flight level FL350 (i.e. at 35,000 feet) with a standard barometric reference REFbaro, i.e. 1013.25 hPa / 15 C (standard ISA temperature ), when an incident occurs illustrated by a symbol 10.

The terrain database, with which the aircraft AC is equipped, indicates a maximum safety altitude Z1 (MORA type) of 12,000 feet on the trajectory of the aircraft AC.

If the emergency descent control system is content to take as target altitude this altitude value Z1 during the entire descent, therefore corresponding to flight level FL120 (relative to REFbaro), the local pressure (977 hPa in example) CA 02746580 2011-07-12 introduces a Zbiais bias (about 1000 feet, as specified below) with respect to the ALS altitude (above relief 11) that we wanted to reach. The aircraft AC will then be at an altitude Z2 of 11,000 feet above sea level MSL, and not at an altitude Z1 of 12,000 feet 5 (above sea level MSL).

Regarding the Zbiais bias, if we consider, as a first approximation, that an atmospheric pressure differential of one hectopascal corresponds to an altitude differential of about 28 feet, we obtain:

Zbiais = AP.28 10 with AP = 1013.25 ¨ 977 = 36.25 hPa, hence:

Zbiais = 1008 feet.

This example shows that, without resetting the target altitude to take account of the pressure reference differences, there is a risk of considerably reducing the safety margins with respect to the terrain.

The device 1 also comprises an indication means 13 which is, for example, connected to the means 7 via a link 14.

This indication means 13 makes it possible, in particular, to present to the pilots of the aircraft AC the reset target altitude, calculated by the device 1, and to verify its relevance with respect to the safety altitude values ​​indicated on the navigation charts, or on the navigation screens of the aircraft AC.

The device 1 according to the invention, as mentioned above, for resetting a target altitude for an emergency descent of an AC aircraft, is suitable for any emergency descent system, partially or totally automated.

However, in a preferred application, this device 1 is used to reset the target altitude in a system 15 for automatically controlling an emergency descent of an aircraft AC.

Preferably, this system 15 for automatic control of an emergency descent is of the type comprising, as shown in FIG. 3:

CA 02746580 2011-07-12 16 - engagement means 17 which are capable of initiating an automatic emergency lowering function;

- control means 18 which are connected by means of a link 19 to said engagement means 17 and which are formed so as to implement an automatic emergency descent function, when it is engaged by said means 17, by automatically performing longitudinal guidance, lateral guidance and control of the speed of the aircraft AC; and - disengagement means 20 which are connected via a link 21 to said control means 18 and which make it possible to control a disengagement of an automatic emergency lowering function during execution.

This automatic emergency descent function thus makes it possible to bring the aircraft AC back to a breathable altitude (target altitude) and in a stabilized situation, in particular in order to revive (if necessary) the crew and passengers and to continue the flight. flight.

Said control means 18 comprise:

- Means 22 for determining, automatically, a set of vertical setpoints, comprising in particular:

= the target altitude which represents the altitude to be reached by the aircraft AC at the end of the emergency descent; and = a target speed which represents the speed that the aircraft AC must respect during the emergency descent;

- Means 23 for determining, automatically, a set of lateral instructions.

This assembly represents a lateral maneuver to be carried out during the emergency descent; and - usual means 24 for automatically guiding the aircraft, when an automatic emergency descent function is engaged, so that it simultaneously complies with said set of vertical instructions and said set of lateral instructions, and this until said target altitude is reached, target altitude that it maintains as soon as it has reached it.

CA 02746580 2011-07-12 17 This system 15 for automatically controlling an emergency descent can, in particular, be similar to the system described in document FR-2 928 465 from the Applicant.

In this case, said means 22 comprise said device 1 for resetting the target altitude.

This system 15 can have, moreover, in particular the following characteristics:

- two types of arming can be considered: voluntary arming and automatic arming.

When the crew decides to make an emergency descent following depressurization, a fire alarm or any other reason, they can arm the function by activating a dedicated push button.

A logic makes it possible to validate this arming condition as a function in particular of the current altitude of the aircraft AC. Automatic arming is linked to a depressurization event.

It occurs when certain criteria involving the air pressure or the variation in air pressure inside the cabin are verified.

The arming of the function always precedes the engagement of this one;

- the crew retains the possibility of manually disarming the function at any time, regardless of the type of arming (voluntary or automatic);

- two types of engagement are possible depending on the previous type of arming.

Following voluntary arming, engagement does not take place until the speedbrakes are fully deployed by the crew.

On the other hand, if the arming was automatic, the engagement also occurs automatically at the end of a countdown initiated at the arming, if the crew has not reacted before the end of it. this.

However, if by procedure the crew fully deploys the airbrakes CA 02746580 2011-07-12 18 before the end of the countdown, the engagement of the function is anticipated compared to the automatic engagement;

- when the automatic emergency descent function is engaged, the guidance and control of the speed of the aircraft are carried out in the vertical and lateral planes as follows:

= in the vertical plane, the speed adopted to operate the automatic emergency lowering is chosen by default by the automatic system, so as to minimize the lowering time. The crew can freely adjust this speed during the descent maneuver, in order to take into account any structural damage, without disengaging the function;

= the lateral maneuver, carried out simultaneously with the longitudinal maneuver, is intended to move the aircraft AC away from the current route in order to avoid encountering other aircraft operating on the same route, but at lower altitudes;

- the exit of the automatic emergency descent coincides with the capture, then the maintenance of the target altitude during the maneuver; and - during the automated emergency descent maneuver, the crew can take control of the automated system at any time by usual means: manual action on the control stick, engagement of a new mode of guidance of the AC aircraft, disconnection button, speed or heading adjustment, ...