Patent Description:
<CIT> describes a system to automatically initiate a rejected takeoff operation (RTO), based on predetermined airplane alert signals, in which the system uses a plurality of sensors for monitoring operating parameters of an aircraft and a control unit receives data from the sensors.

<CIT> discloses a system for predicting where an aircraft will be during takeoff when reaching V1, and if an incorrect weight has been used to compute V speeds (and consequently other parameters for the takeoff operation) and if V1 cannot be reached given the length of the runway, the system outputs an alert to the flight crew.

<CIT> is a document pursuant to Art. <NUM>(<NUM>) EPC. <CIT> discloses a safe takeoff monitoring system which checks the actual physical parameters of an airplane during takeoff, determines the actual takeoff weight, and warns the pilot to interrupt the takeoff if any dangerous situation is developing, before a high energy abort is necessary.

Commercial airlines perform tens of millions of takeoffs annually. Only a very small percentage of attempted takeoffs result in rejected takeoffs (RTO's). Pilots decide to execute RTO's due to a variety of factors including engine failure, wheel/tire failure, incorrect pre-flight configuration, indicator/warning lights, lack of crew coordination, and bird strikes. An RTO at a low speed rarely results in any adverse consequences. High-speed RTO's, on the other hand, can potentially cause the airplane to overrun the end of the runway, with catastrophic consequences. See Federal Aviation Administration, "Pilot Guide to Takeoff Safety", retrieved from https://www. gov/other_visit/aviation_industry/airline_operators/training/media /takeoff_safety.

A recurring issue in aviation is errors in aircraft dispatch and/or the incorrect pilot inputs of takeoff parameters. Before takeoff, the flight control computer is typically initialized with certain parameters pertinent to the takeoff. These inputs include weight, configuration (flap position), thrust and takeoff speeds (V<NUM>, VR and V<NUM>). Since thrust and V speeds are critical to proper takeoff, errors in inputting these parameters can lead to serious aircraft accidents. The table below presented some accidents related to wrong takeoff data:.

Such types of accidents are often consequences of a lower aircraft capability to accelerate and/or climb. A particularly terrible example where an accident was related to wrong takeoff configuration (and overweight) is the case of Union des Transports Africains de Guinee (UTA) Flight <NUM> which departed Conakry, Guinea for a scheduled flight to Beirut, Lebanon on Christmas Day, December <NUM>, <NUM>. The Boeing <NUM> departed at <NUM>:<NUM> carrying <NUM> passengers and a crew of <NUM>. It arrived at Cotonou at <NUM>:<NUM> where nine passengers disembarked. A total of <NUM> people had checked in at the Cotonou airport check-in-desk. Ten others boarded from a flight that had arrived from another airport. Passenger boarding and baggage loading took place in a climate of great confusion. The plane was full and it is thought that there were more passengers aboard the plane than had officially checked in.

The flight crew began pre-flight checklist at <NUM>:<NUM> and were cleared to roll at <NUM>:<NUM>. Passengers were still standing in the aisles at that time. At <NUM>:<NUM>:<NUM>, the thrust lever was advanced, <NUM> seconds later the brakes were released and the Boeing <NUM> began accelerating down the runway. <NUM> seconds after the brakes were released, the captained announced V1 and VR speeds. At that moment the aircraft was <NUM> meters down the runway at a speed of <NUM>/s (<NUM> knots).

The co-pilot pulled back on the control column to rotate the plane at VR. This action initially had no effect on the airplane's angle of attack. The Captain called "Rotate, rotate", and the co-pilot pulled back harder. The angle of attack only increased slowly. The pilot did not command an RTO. Seven seconds later, at a speed of <NUM>/s (<NUM> knots) and <NUM><NUM> meters down the runway, the nose just slowly rose. The <NUM> barely climbed away from the ground, causing its main undercarriage to strike localizer antennas at the end of the runway and strike a <NUM>- meter-high small building housing radio equipment. The plane continued beyond the end of the runway, smashing through a concrete airport boundary fence and slamming into the beach. The fuselage broke into several pieces. At least <NUM> people died in the crash.

The official explanation of the crash was that the aircraft's weight exceeded its maximum weight capacity. The accident resulted from difficulty that the flight crew encountered in performing rotation with an overloaded airplane whose forward center of gravity was unknown to them.

To avoid such disasters, the preflight operational engineer typically carefully calculates the takeoff weight (TOW) of the aircraft based on a weight & balance spreadsheet. The spreadsheet and/or calculation presents some statistical simplifications which decrease the level of accuracy. An example is the passenger estimated weight that can significantly differ from the real one. The same can be related to the baggage and other cargo.

The takeoff "Vspeeds" (V<NUM>, VR, V<NUM>) evaluation is based on the takeoff weight. Therefore, if the weight is wrong, so are the takeoff speeds. It is also possible to incorrectly calculate the V-speeds even if the weight determination is right. Even if the operational engineer's calculations are all correct, the pilot and/or dispatch inputs into the flight computer can be wrong.

Today, the only way to confirm if the data is right is to recalculate and/or re-check the input data. This is of course not a failure-proof processes.

Some in the past have proposed ways to monitor if the data are correct and, in case of a detected error, alert the pilot to make some action. But since the pilot workload is higher at takeoff, such proposals must somehow assure that there is enough runway remaining to stop the aircraft without a runway excursion (overrun) in case the pilot decides to abort the takeoff.

Although such prior techniques propose a way to check if there are some errors on dispatch, they all introduce a higher pilot workload, since the pilot must understand the situation and must decide to make the first action to abort the takeoff. The invention provides a system according to claim <NUM> and a method according to claim <NUM>, with embodiments defined in the dependent claims.

The invention provides a system for an aircraft and a method of automatically rejecting take off as laid out in independent claims <NUM> and <NUM>.

The following detailed description of examples of this invention is to be read in conjunction with the drawings, of which:.

<FIG> shows forces including drag <NUM> and wheel friction <NUM> that an aircraft typically experiences during the takeoff phase of flight. The Figure shows an aircraft moving down a runway at a longitudinal acceleration that is determined in accordance with F=ma, where F are the forces being exerted on the aircraft, m is the mass of the aircraft, and a is the acceleration.

The mass a is determined based on the total weight of the aircraft, including the aircraft itself, fuel, passengers, baggage and cargo.

The force F on the aircraft has several components. One component is the amount of thrust produced by the engines. Another component is the friction and drag exerted on the aircraft. Drag is defined as the resistance that opposes the direction <NUM> that an aircraft is moving.

Graphic <NUM>' is a free-body-diagram used to show that the force related to forward acceleration (Fa) is greater than all other forces involved in the aircraft's takeoff phase. Such other forces include the force of gravity (Fg) that is pulling the aircraft towards the ground, the force of friction (Fµ) (opposite to the direction of aircraft movement) and the normal force (Fn), which are responsible for the drag that the aircraft incurs during takeoff.

There are many factors that affect the magnitude of the drag force <NUM> including the aerodynamic shape of the aircraft (including its current configuration, such as the position of the flaps), the viscosity of the air (which depends on air temperature and altitude), and the velocity of the aircraft. All of the individual components of drag are combined into a single aircraft drag magnitude.

Rolling friction <NUM> is the resistive force that slows down the motion of a rolling wheel. It is also called rolling resistance.

Once a wheel is rolling, the resistance to the motion is typically a combination of several friction forces at the point of contact between the wheel and the ground or other surface. This assumes the brakes are off - since the brakes are designed to increase rolling friction. The amount of rolling friction depends on several factors including the weight of the aircraft (since the weight exerts a downward force on the wheels that increase the friction coefficient), the inflation and type of tires, and the composition of the runway surface.

One of the insights provided by the present non-limiting technology: the longitudinal acceleration can be directly measured using an inertial sensor, and used as a check against the weight and associated parameters calculated by the flight engineer/dispatch.

<FIG> illustrates schematic logic following the flight computer <NUM> to decide whether to reject takeoff. The flight computer/fly-by-wire (FBW) controller <NUM> is in this case comprised of at least one processor <NUM>, a memory <NUM>, and a safe takeoff program <NUM>'. It is configured to automatically and autonomously reject takeoff under certain criteria. The flight computer <NUM> determines takeoff rejection by processing various takeoff parameters including:.

Flight computer <NUM> conditionally outputs:.

In appropriate cases, the flight computer <NUM>'s output signals command the aircraft automatically execute an RTO by reducing or reversing thrust, applying brakes, increasing drag by controlling flaps down, and decelerate safely to a stop.

In determining whether to execute an RTO, the flight computer <NUM> is able to determine whether the operational procedures of the aircraft during takeoff are either safe or unsafe. The operational procedures during takeoff are defined by the input takeoff parameters. A safe takeoff involves agreement between (a) estimated longitudinal acceleration calculated based on presumed weight of the aircraft, and (b) current actual acceleration as measured by an inertial sensor. An unsafe set of parameters, which leads to a rejection of takeoff, is detected based on an incongruence in the comparison of the estimated longitudinal acceleration and the current measured acceleration.

However, not all such incongruences are the basis for an automatic RTO. In particular, the flight computer <NUM> also determines whether an RTO can be safely executed. It is well known that RTO's at high speeds approaching or exceeding V1 can be dangerous. Therefore, the flight computer <NUM> will only perform an automatic RTO if the measured speed of the aircraft is within a safe range.

If an incongruence is detected, the flight computer <NUM> executes the rejection of takeoff by displaying on the cockpit that the system has decided to reject takeoff, while reducing the thrust of the aircraft, activating the wheel brakes, and controlling the aerodynamic surfaces (e.g., raising spoilers, lowering flaps, etc.) in order to increase drag to try and bring the aircraft to a safe stop.

<FIG> depicts a non-limiting example data evaluation and system decision process. In response to estimated weight <NUM>' provided by the flight engineer/dispatch system, weather parameters <NUM>' (e. , temperature, wind, etc.) and airport data <NUM>' (runway information), a computer (either the flight computer <NUM> on board the aircraft, a ground computer at dispatch, or some other computer) is configured to calculate the thrust <NUM>' and V-speeds <NUM> that should be applied during a takeoff procedure. V-speeds or Velocity-speeds are well-known conventional velocity terms used to define critical airspeeds for the operational procedures of aircraft.

V<NUM> is the socalled "decision point" - namely the maximum speed during takeoff at which a pilot can safely execute an RTO without overrunning the runway. V<NUM> is defined as the takeoff safety speed. And VR is the rotation speed, the speed at which the pilot may rotate the aircraft so its nosewheel leaves the ground and it begins to climb into the air.

Based on these same parameters inputted into the dispatch computer <NUM>, (weight <NUM>', takeoff configuration <NUM>', V-speeds <NUM>, and thrust <NUM>') it is also possible to estimate the aircraft's drag <NUM> and wheel friction forces <NUM>. By estimating thrust <NUM>', drag <NUM>', and wheel friction forces <NUM>' it is possible to estimate a longitudinal acceleration value <NUM>-A of the aircraft based on the dispatch information. This estimated acceleration value is checked to measured acceleration <NUM>-B that is obtained from the inertial sensor(s) <NUM>' of the aircraft as the aircraft accelerates down the runway.

In simple terms, if the measured acceleration differs significantly from the estimated acceleration, then the actual weight of the aircraft is likely not the same as the estimated weight used to calculate the estimates acceleration. F=ma can be rewritten as a = F/m. So for the equation: <MAT> if the estimated mass (m) is very wrong, then the measured acceleration will not match the estimated acceleration calculated based on the estimated mass.

In the example shown, the expected longitudinal acceleration value <NUM>-A and the measured acceleration value <NUM>-B are compared in the flight computer <NUM>' of the aircraft as the aircraft begins moving down the runway. This is in the nature of a physics experiment with practical consequences: if the flight computer <NUM> determines that the two acceleration values are consistent, then normal takeoff procedure <NUM> is followed and no intervention is required. However, if the flight computer <NUM>' determines that the two acceleration values are not consistent, then there is a problem. Specifically, the estimated weight of the aircraft has been experimentally determined to be incorrect. The pilot is notified of this discrepancy; and the flight computer <NUM> autonomously performs an RTO if it is safe to do so.

To determine safety of an RTO, the safe takeoff program <NUM>'-B is configured to determine whether the aircraft's speed <NUM>' is inside a safe "speed window". Therefore, takeoff rejection <NUM> is conditioned on whether the measured speed of the aircraft is below a safe stopping speed. If the aircraft is within the safe speed window, then the flight computer <NUM>' automatically aborts the takeoff <NUM>. On the other hand, if the aircraft speed is outside the defined margin of a safe stopping speeds, then the safe takeoff program <NUM>'-B is configured to repeat <NUM> the comparison of the acceleration values while potentially also warning the pilot that something may be wrong.

In one example non-limiting embodiment, the entire process is transparent to the pilot. The pilot does not need to perform any procedure. This will reduce the pilot's workload in a very demanding flight phase, as well as to produce a more consistent operation.

The new non-limiting technology herein thus proposes a system that automatically rejects or aborts takeoff if erroneous takeoff parameters or data are detected. In order to prevent a runway excursion or overrun, the rejected takeoff shall occur only in a well-defined "speed window" between a Lower limit speed and an upper limit speed, where:.

<FIG> depicts a graph wherein the concept of a "speed window" is defined. The speed window <NUM> is a margin, bounded by an upper threshold <NUM> and a lower threshold <NUM>. The lower threshold <NUM>, referred to as the Lower Limit Speed ("LLS"), is the specific value where any airspeed below this limit is unmeasurable by the anemometric system due to the fact that the aircraft is not moving fast enough. In the same manner, the upper threshold <NUM>, referred to as the Upper Limit Speed ("ULS"), is the limit that guarantees a safe rejection of takeoff without the risk of a runway excursion. Although the graph compares the ratio of calculated and actual weight, acceleration should be the parameter compared, but weight and acceleration are correlated and the final effect is similar.

<FIG> considers a non-limiting embodiment of a "speed window", that has a:.

In the non-limiting example, with the speed window considered, it is not necessary to estimate the remaining distance on the runway, since with low energy the aircraft will be capable to abort the takeoff in any runway that it can be dispatched to.

It should be noted that the safety aspect of the safe speed window results from the upper speed limit. In the example embodiment, the lower speed limit is used merely to ensure that the measured aircraft speed is accurate. As is well known, typical anemometric speed sensors do not begin providing valid speed data until the aircraft is moving at above a minimum speed. However, there are other known ways to measure aircraft speed such as GPS, and the particular nature of the low speed threshold (or if any is applied) may depend on the type of speed sensor(s) being used.

However, it can be seen from <FIG> and <FIG> that for a wide range of estimated to actual weight values, the resulting speed data statistically converge at above a low speed threshold. This is because for a given thrust, the rate of change of velocity depends on weight. This means that above a low speed threshold, the same procedure can be applied to a wide variety of weight discrepancies to result in a valid test.

<FIG> illustrates example non-limiting signal flow of the aircraft's auto rejection system. The system is configured to receive dispatch data (e.g., estimated weight <NUM>', weather parameters <NUM>', runway info <NUM>', takeoff configuration <NUM>', etc.) from the ground computer. Among the parameters calculated by the dispatch computer <NUM>' using the dispatch data are V-speeds (e.g., V<NUM>, VR, V<NUM>), and thrust lever <NUM> selection. As explained before, with these parameters inputted into the dispatch computer <NUM> it is also possible to estimate the aircraft's drag <NUM>' and wheel friction forces <NUM>'. With drag <NUM>' and wheel friction forces <NUM>' calculated, it is possible to estimate a longitudinal acceleration value <NUM>-A. This estimated acceleration value is compared <NUM>'-A to measured acceleration <NUM>' that is obtained from the inertial sensor(s) <NUM>'.

If the measured and estimated acceleration values match within a certain tolerance, then normal takeoff procedure <NUM>' is followed from the safe takeoff program <NUM>'-A. However, if the flight computer <NUM>' determines that the acceleration values are very different, then the safe takeoff program <NUM>'-B is configured to determine whether the aircraft's speed <NUM>' is inside a safe "speed window". If the aircraft is within the speed window, then the flight computer <NUM>' automatically aborts the takeoff <NUM>' and autonomously performs an RTO. On the other hand, if the measured speed of the aircraft is outside of the safe speed window, then the safe takeoff program <NUM>'-B is configured to take no action and repeat <NUM>' the comparison of the acceleration values.

<FIG> shows a non-limiting means that can be used by the aircraft to calculate the estimated longitudinal acceleration. Some inputs used to calculate the estimated longitudinal <NUM> acceleration come from different sensors or state information that indicate aircraft takeoff configuration <NUM>' (e.g., flap/slat configuration). Other input parameters (the ones to be tested) are obtained from dispatch, such parameters including estimated weight <NUM>'. Dispatch also supplies additional information such as weather <NUM>' (including air density), runway info <NUM>', etc.). Criteria such as V-speeds <NUM>' and thrust settings <NUM>' are calculated using such inputs (e.g., estimated weight <NUM>' weather <NUM>', runway information <NUM>', etc., as explained above). All inputs are processed by a processing unit (e.g., microprocessor) <NUM> in the aircraft's flight computer <NUM>' and/or by the ground computer or some other computer. The processing unit is able to calculate the aircraft's drag and wheel friction forces, making it possible to estimate the longitudinal acceleration of the aircraft <NUM>-A.

<FIG> illustrates an example non-limiting means of determining takeoff rejection by comparing the estimated longitudinal acceleration with the measured acceleration, and determining whether the aircraft is moving at a safe stopping speed. Such logic can be implemented in a variety of ways such as by a software controlled process, a gate/logic array, or any other suitable implementation. The estimated longitudinal acceleration signal <NUM> and the measured acceleration signal <NUM> are received by a subprocessing unit <NUM> in the flight computer <NUM>'. The flight computer is configured to receive both acceleration values and compare them using a comparator <NUM>. Comparator <NUM> determines whether to output a safe takeoff signal <NUM>' (meaning that both accelerations are substantially equal) or send a signal <NUM> to a structural and/or software based logic to check whether it is safe to reject takeoff.

Concurrently, the anemometric system <NUM> measures wind speed to determine whether the aircrafts' speed is within a range defined by a safe speed window. The anemometric system <NUM> measures the speed of the wind relative to the aircraft and thus the speed of the aircraft (once wind speed and direction is taken into account). The anemometric system <NUM> outputs a measurement value to comparator <NUM>, which determines whether the measured wind speed value is between the lower limit and the upper limit defined by the speed window. If the measured value is within the range defined between the limits, then a signal <NUM> is sent to the structural and/or software based logic AND gate.

The structural and/or software based logic AND gate is configured to follow the Boolean logic of an AND gate, meaning that both conditions must be true in order for the gate to generate a true output. Positive or negative logic (e.g., NAND) can be used in a well-known manner. For the system to execute the automatic takeoff rejection, both discrepancy in acceleration values and airspeed within designated speed window, must be true.

<FIG> illustrates a non-limiting example of how an aircraft's inertial sensors <NUM>' can be used to measure longitudinal acceleration. Generally speaking, inertial sensors are devices designed to measure inertial values such as acceleration and rotation. Examples of inertial sensors include gyrosensors <NUM> and accelerometers <NUM>.

There are many types of accelerometers <NUM>, such as mechanical accelerometers that consists of devices that measures the displacement of an inertial mass suspended by a spring. Another type of accelerometer is the surface acoustic wave (SAW) accelerometer which consists of a cantilever beam which resonates at a particular frequency, when acceleration is applied the beam bends changing the frequency, the change in frequency can be used to determine the acceleration. Yet another type of accelerometer is the MEMS accelerometers that uses capacitance to measure displacement of a minute mass floating on springs.

There are many different varieties of gyrosensors, such as mechanical, optical, and MEMS. Mechanical gyroscopes often used in the aircraft industry to determine aircraft attitude during flight consist of a spinning wheel mounted on two gimbals which allow the wheel to rotate in all three axes. Optical gyroscopes (e.g., fiber optic gyroscopes "FOG") use the interference of light to measure angular velocity. A MEMS gyrosensor usually contains a vibratory elements to measure the Coriolis effect. For example, a single mass which is driven to vibrate along a drive axis. When the gyroscope is rotation a secondary vibration is induced along the perpendicular axis due to the Coriolis force. The angular velocity or rate output by such a system indicates the rate of change of attitude. This can be differentiated to determine acceleration.

Such devices can have any number of axes, including triaxial meaning that they measure all three degrees of freedom. Once such inertial values are sensed, they can be processed using conventional matrix multiplication to determine the component of acceleration in any desired particular direction.

Claim 1:
A system for an aircraft, the system comprising:
at least one inertial sensor (<NUM>') producing a first signal;
at least one wind speed sensor (<NUM>) producing a second signal; and
at least one flight computer (<NUM>), operatively coupled to the at least one inertial sensor (<NUM>') and the at least one wind speed sensor (<NUM>), the at least one flight computer (<NUM>) configured to:
measure an acceleration (<NUM>-B) in response to the first signal;
calculate an expected estimated acceleration value (<NUM>-A) in response to an estimated aircraft weight (<NUM>'), runway information (<NUM>'), weather parameters (<NUM>'), and takeoff configuration (<NUM>');
compare the measured acceleration (<NUM>-B) with the expected estimated acceleration value (<NUM>-A);
determine whether the measured acceleration differs significantly from the expected estimated acceleration value;
in response to the second signal, determine whether the aircraft is operating below an upper limit speed guaranteeing that the aircraft can safely perform a low kinetic energy rejected takeoff without the risk of a runway excursion or overrun;
if the measured acceleration is determined to differ significantly from the expected estimated acceleration value and the aircraft is determined to be operating below the upper limit speed, automatically issue control signals to automatically abort takeoff conditioned on both the comparison and the speed determination, the control signals controlling the aircraft to automatically execute a rejected takeoff by reducing or reversing thrust, applying brakes and increasing drag by controlling aerodynamic control surfaces to bring the aircraft to a safe stop.