Patent Description:
The present disclosure relates to drain systems and methods for improved waste level and overflow detection and, more particularly, improved wastewater overflow detection systems and methods for use in aircraft lavatories.

Accurately detecting the quantity of a liquid waste within a waste tank is a challenge within the industry. Challenges arise primarily due to the variances of different types of media present in a waste tank including but not limited to dense or fluffy waste paper, air bubbles, human waste of different densities, soap foams, coffee grounds, leftover food, etc. An inaccurate measurement of a waste tank level may lead to false positive indications as well as an unsanitary or dangerous leakage situation. A standard aircraft waste tank may be limited to two invasive sensors. This limitation may ensure safety against additional opportunity for a fluid leak. <CIT> relates to continuous level sensing of a tank, wherein a system employs a continuous level sensing strain gauge measuring a weight of an aircraft waste tank, a lower and upper point level sensors to signal the system as the liquid level reaches each sensor, and a flush counter to correlate with the CLS and the PLS to determine an average flush volume (AFV). Once the AFV is known and updated, the system determines a weighted waste tank level based on a weighted addition of the flush count and the quantity as measured by the CLS. As the aircraft tank reaches a predetermined value, the system alerts a crewmember to the status.

<CIT> relates to a method for determining a filling level of a waste water tank.

A waste level monitoring system for an aircraft waste tank is disclosed herein, comprising a point level sensor disposed on the aircraft waste tank, a load cell disposed on the aircraft waste tank, a flush counter configured to count a number of toilet flushes since a previous service to the aircraft waste tank, and a controller electronically coupled to the point level sensor, the load cell, and the flush counter. The controller is configured to receive, via the point level sensor, a first signal indicating a level of waste within the aircraft waste tank, receive, via the load cell, a second signal indicating a weight of the aircraft waste tank, receive, via the flush counter, a third signal indicating the number of toilet flushes since the previous service to the aircraft waste tank, and determine whether the point level sensor is faulted. In response to the point level sensor being faulted, the controller is configured to determine whether (a) the weight of the aircraft waste tank is between a minimum weight threshold and a maximum weight threshold and (b) the number of toilet flushes is greater than a minimum flush threshold. In response to both (a) and (b) being true, the controller is configured to send a waste system status signal to a display device onboard an aircraft indicating that the aircraft waste tank is full.

In various embodiments, in response to the point level sensor not being faulted, the controller is configured to determine whether (a) the weight of the aircraft waste tank is between the minimum weight threshold and the maximum weight threshold, (b) the number of toilet flushes is greater than the minimum flush threshold, and (c) the first signal indicates that the aircraft waste tank is full. In response to (a), (b), and (c) being true, the controller is configured to send the waste system status signal to the display device onboard the aircraft indicating that the aircraft waste tank is full.

In various embodiments, in response to at least one of (a) or (b) being false, the controller is configured to proceed with a flush cycle and increment the number of toilet flushes.

In various embodiments, in response to at least one of (a), (b), or (c) being false, the controller is configured to proceed with a flush cycle and increment the number of toilet flushes.

In various embodiments, the waste level monitoring system further comprises the display device.

In various embodiments, the point level sensor is an ultrasonic point level sensor.

A method for monitoring a level of waste within a waste tank is disclosed. The method comprises receiving, by a controller, a first signal from a point level sensor indicating the level of waste within the waste tank, receiving, by the controller, a second signal from a load cell indicating a weight of the aircraft waste tank, receiving, by the controller, a third signal from a flush counter indicating a number of toilet flushes since a previous service to the aircraft waste tank, and determining, by the controller, whether the point level sensor is faulted. In response to determining that the point level sensor is faulted, the controller is configured to determine whether (a) the weight of the aircraft waste tank is between a minimum weight threshold and a maximum weight threshold and (b) the number of toilet flushes is greater than a minimum flush threshold. In response to both (a) and (b) being true, the controller is configured to send a waste system status signal to a display device onboard an aircraft indicating that the aircraft waste tank is full.

In various embodiments, the method further comprises, in response to the point level sensor not being faulted, determining, by the controller, whether (a) the weight of the aircraft waste tank is between the minimum weight threshold and the maximum weight threshold, (b) the number of toilet flushes is greater than the minimum flush threshold, and (c) the first signal indicates that the aircraft waste tank is full. The method further comprises, in response to (a), (b), and (c) being true, sending, by the controller, the waste system status signal to the display device onboard the aircraft indicating that the aircraft waste tank is full.

In response to at least one of (a) or (b) being false, the controller is configured to proceed with a flush cycle and increment the number of toilet flushes.

In response to at least one of (a), (b), or (c) being false, the controller is configured to proceed with a flush cycle and increment the number of toilet flushes.

In various embodiments, the method further comprises computing, by the controller, a number of successful flush cycles needed to reach the maximum capacity of the waste tank.

In various embodiments, the method further comprises determining, by the controller, whether the waste tank has undergone maintenance, and in response to the waste tank having undergone maintenance, resetting, by the controller, the number of toilet flushes since the previous service to the aircraft waste tank to zero.

In various embodiments, the method further comprises computing, by the controller, at least one of the minimum weight threshold, the maximum weight threshold, and the minimum flush threshold.

In various embodiments, the method further comprises determining whether the point level sensor is faulted includes validation of a discrete input received from the point level sensor which indicates the state of the point level sensor.

An aircraft is disclosed, comprising a toilet disposed in a lavatory, a waste tank, a fluid conduit extending from the toilet to the waste tank, a point level sensor disposed in the waste tank, the point level sensor configured to measure a wastewater level within the waste tank, a load cell coupled to the aircraft waste tank, a flush counter configured to count a number of toilet flushes since a previous service to the waste tank, and a controller electronically coupled to the point level sensor, the load cell, and the flush counter. The controller is configured to receive, via the point level sensor, a first signal indicating a level of waste within the waste tank, receive, via the load cell, a second signal indicating a weight of the aircraft waste tank, receive, via the flush counter, a third signal indicating the number of toilet flushes since the previous service to the aircraft waste tank, and determine whether the point level sensor is faulted. In response to the point level sensor being faulted, the controller is configured to determine whether (a) the weight of the aircraft waste tank is between a minimum weight threshold and a maximum weight threshold, and (b) the number of toilet flushes is greater than a minimum flush threshold. In response to both (a) and (b) being true, the controller is configured to send a waste system status signal to a display device onboard an aircraft indicating that the aircraft waste tank is full.

These features and elements as well as the operation of the disclosed embodiments will become more apparent considering the following description and accompanying drawings.

The detailed description of exemplary embodiments herein refers to the accompanying drawings, which show exemplary embodiments by way of illustration and their best mode. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that logical, chemical, and mechanical changes may be made without departing from the scope of the disclosure. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option.

Point Level Sensors (PLS) are mounted on vacuum waste collection tanks to detect the level of waste (sewage) inside the tank and communicate the same to the cabin crew to decide further usability of the lavatory. Ultrasonic technology detects a wet/dry condition when media is in close proximity to the bottom of the sensor face (e.g., within <NUM> inch from the bottom of sensor face). It is typically desirable that the criteria for generating a DRY or WET signal be met for a predetermined continuous duration, such as <NUM>-<NUM> seconds continuously.

Ultrasonic PLSs tend to generate erroneous FULL/WET status even when waste tank is not full due to the accumulated solid debris in between the prongs of the sensor. For example, when an aircraft climbs, there is a possibility of debris being stuck between two prongs of the ultrasonic PLS which accounts for erroneous readings for the waste tank. Due to the erroneous FULL/WET status from the PLS, crew members may be alerted for a full waste tank. This tends to unnecessarily prohibit further use of the lavatory since the sensor is generating erroneous output.

Disclosed herein are triple authentication systems and algorithms to determine usability of a lavatory. In contrast to legacy systems, which typically only considering PLS status to determine usability of lavatories, systems, apparatus, and methods of the present disclosure, considers real time weight of the waste tank, a counter value maintained by a controller and associated hardware, as well as with the PLS status for more accurate and reliable operation.

A triple authentication waste level monitoring system of the present disclosure may prevent unnecessary restrictions on lavatory usage when the vacuum waste collection tank is not full. A triple authentication waste level monitoring system of the present disclosure may prevent unnecessary flooding of a lavatory floor when a vacuum waste collection tank is full. A triple authentication waste level monitoring system of the present disclosure may reduce the non-operability of lavatories by <NUM>-<NUM>% when they are not full. A triple authentication waste level monitoring system of the present disclosure may ensure that flooding of a lavatory does not occur during a flight operation, which may result in less downtime on the usage of an aircraft lavatory and more reliable information to the crew allowing the crew to focus on other priority activities.

Referring now to <FIG>, a perspective view of a lavatory <NUM> of an aircraft is illustrated in accordance with various embodiments. The lavatory <NUM> comprises a toilet <NUM>, a water basin <NUM> (e.g., a sink), and a faucet <NUM>. In various embodiments, the lavatory <NUM> further comprises a plumbing system <NUM>. The plumbing system <NUM> is in fluid communication with the toilet <NUM>, the water basin <NUM>, and the faucet <NUM>. In this regard, in response to flushing the toilet <NUM>, wastewater may be transferred throughout the plumbing system <NUM> as described further herein. Similarly, in response to running water via the faucet <NUM>, wastewater may be transferred throughout the plumbing system <NUM> as described further herein.

Referring now to <FIG>, a diagram of an overview of a continuous level sensing waste tank of the plumbing system <NUM> in accordance with various embodiments of the present disclosure is shown. An aircraft waste tank <NUM> (also referred to herein as a vacuum waste collection tank) may include a plurality of components. To couple with the host aircraft, a side attachment point <NUM> may operate as an attachment point. Side attachment point <NUM> may operate only as an attachment point, in accordance with various embodiments. A load cell <NUM> may be provided beneath the aircraft waste tank <NUM> for monitoring the real time weight of the waste tank <NUM>. In various embodiments, load cell <NUM> functions both as a coupling with the host aircraft as well as a force sensor or strain gauge to measure a weight of the aircraft waste tank <NUM>. An inlet <NUM>, a rinse port <NUM>, and tank drain <NUM> with associated drain valve <NUM> may function as fluid ports for the aircraft waste tank <NUM>.

A lower point level sensor (PLS) <NUM> and an upper PLS <NUM> may be sited at various measuring points and configured to send a binary signal as the internal fluid physically reaches the individual PLS. In this manner the lower PLS <NUM> and the upper PLS <NUM> may output a signal indicative of a level of waste (e.g., sewage) within waste tank <NUM>. The lower PLS <NUM> and/or the upper PLS <NUM> may be an ultrasonic PLS sensor configured to emit a high frequency pulse, generally in the <NUM> to <NUM> range in various embodiments, <NUM> to <NUM> range in various embodiments, and <NUM> to <NUM> range in various embodiments, and further configured to detect echo pulses in return. In various embodiments, the lower PLS <NUM> may be sited at <NUM>% of full and the upper PLS <NUM> may be sited at <NUM>% full. Selection of <NUM>% and <NUM>% of full may be adjusted to any suitable value. In various embodiments, the upper PLS <NUM> is situated above <NUM>% and the lower PLS <NUM> is situated at or below <NUM>%.

In various embodiments of the present disclosure, the aircraft waste tank <NUM> may function onboard and aircraft. However, contemplated herein, the inventive concepts described herein may apply to a waste tank on any moving vehicle which may include a waste tank and a flush apparatus.

Also, a plurality of sizes of aircraft waste tank <NUM> and PLS locations may function within the scope of the inventive concepts disclosed herein. The inventive concepts herein may directly apply to aircraft waste tanks of various sizes mounted on aircraft of various sizes.

Referring now to <FIG>, a diagram of plumbing system <NUM> comprising a triple authentication waste level monitoring system <NUM> for continuous waste level sensing of vacuum waste collection tank <NUM> in accordance with various embodiments of the present disclosure is shown. The system <NUM> includes the load cell <NUM> mechanically coupled with the host aircraft attachment as well as with the aircraft waste tank <NUM>. Load cell <NUM> may be installed beneath the waste tank <NUM> and calibrated to measure the actual weight of the waste tank <NUM>. In various embodiments, the load cell <NUM> may be embodied as a strain gauge and configured to measure the weight of the aircraft waste tank <NUM>. The load cell <NUM> may operatively couple with the ISC <NUM>. The load cell <NUM> may send a signal to ISC <NUM> indicative of the weight of waste tank <NUM>. In this regard, load cell <NUM> may be in electronic communication with ISC <NUM>.

To control function of the system <NUM>, an integrated system controller (ISC) <NUM> having a processor operatively coupled with the ISC <NUM> may be employed. In various embodiments, ISC <NUM> may comprise a processor. In various embodiments, ISC <NUM> may be implemented in a single processor. In various embodiments, ISC <NUM> may be implemented as and may include one or more processors and/or one or more tangible, non-transitory memories (e.g., memory <NUM>) and be capable of implementing logic. Each processor can be a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programable gate array (FPGA) or other programable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. ISC <NUM> may comprise a processor configured to implement various logical operations in response to execution of instructions (e.g., see flow chart in <FIG>), for example, instructions stored on a non-transitory, tangible, computer-readable medium (e.g., memory <NUM>) configured to communicate with ISC <NUM>.

System program instructions and/or controller instructions may be loaded onto a non-transitory, tangible computer-readable medium having instructions stored thereon that, in response to execution by a controller, cause the controller to perform various operations.

In various embodiments, the ISC <NUM> may output a vacuum waste system (VWS) status <NUM> including current waste levels in the vacuum waste tank <NUM> to the host aircraft. The VWS status <NUM> may alert crew (e.g., via a display device <NUM> onboard the host aircraft) when waste tank <NUM> is full.

A communication network such as an ARINC <NUM> standard <NUM> may allow the ISC <NUM> to communicate in a standardized manner with the host aircraft. The ISC <NUM> may use the flush counter <NUM> input, the load cell <NUM> input, and the PLS <NUM> input to determine a waste tank level percentage and output this percentage to the host aircraft via VWS status <NUM>.

System <NUM> may include a vacuum generator/pump <NUM> which may be in communication with ISC <NUM> via a controller area network (CAN) bus <NUM>. Vacuum generator/pump <NUM> may be configured to apply vacuum to waste tank <NUM>. By reducing pressure within waste tank <NUM>, the pressure differential tends to assist waste in reaching waste tank <NUM> through the associated plumbing. The vacuum pressure in the waste tank <NUM> may be directly sensed and maintained at a predetermined amount. An altimeter or barometric pressure type instrument could also be used for operating the vacuum generator/pump <NUM>. In various embodiments, a frequency of the CAN bus input from the load cell <NUM> may be between <NUM> to <NUM> in various embodiments, between <NUM> to <NUM> in various embodiments, and between <NUM> to <NUM> in various embodiments.

To count each flush, the system <NUM> may employ a flush counter <NUM> mechanically coupled with an aircraft lavatory flush valve and operatively coupled with the ISC <NUM>. Each flush from each onboard lavatory may increase the flush counter by one. In this regard, flush counter <NUM> keeps track of number of successful flushes since last maintenance/service of the waste tank <NUM>. Flush counter <NUM> data may be stored in nonvolatile memory <NUM> of ISC <NUM>. In this regard, flush counter <NUM> is in electronic communication with ISC <NUM>. Flush counter <NUM> data is reset to zero when waste tank <NUM> undergoes maintenance/service (i.e., when waste tank <NUM> is emptied).

With momentary combined reference to <FIG> and <FIG>, the plumbing system <NUM> may comprise a rinse valve associated with each toilet <NUM>. The rinse valve may be configured to open in response to external activation (e.g., via flushing of a handle, via a sensor detecting a person is no longer in front of the sensor, or the like). In response to opening the rinse valve, wastewater may flow from the toilet (e.g., toilet <NUM>) to waste tank <NUM> (e.g., via inlet <NUM>). In various embodiments, during the flushing process, potable water may be dispensed through a potable water port disposed in each toilet bowl (e.g., toilet <NUM>). In this regard, any solid waste may be transported from the toilet <NUM> to the waste tank <NUM> as wastewater, in accordance with various embodiments.

Referring now to <FIG>, a flow chart for control of system <NUM> is shown, in accordance with various embodiments. With combined reference to <FIG> and <FIG>, ISC <NUM> employs a three step authentication model to determine usability of a lavatory utilizing flush counter <NUM> output, load cell <NUM> output, and PLS <NUM>, <NUM> outputs. Upon start up (step <NUM>), ISC <NUM> computes the number of successful flush cycles (N1) needed to reach the maximum capacity of the waste tank <NUM> (step <NUM>). This number may be based on the total volume of the waste tank <NUM> and the maximum volume of the waste that can be pushed to the tank during a successful flush cycle. The number of successful flush cycles needed may be equal to the maximum volume of the waste tank <NUM> divided by the maximum volume of waste that goes into the waste tank during a successful flush cycle. ISC <NUM> may further define and store a maximum weight of the waste tank <NUM> (N2) when the waste tank <NUM> is full. Moreover, ISC <NUM> may monitor the weight of the waste tank <NUM> (N3).

At step <NUM>, the ISC <NUM> may determine whether the waste tank <NUM> has undergone maintenance/service since the last flush cycle. When the aircraft operating mode is set to maintenance mode while the aircraft is on the ground and the service panel door of the waste tank is open and weight of the waste tank is equivalent to zero waste weight (empty waste tank), the ISC <NUM> may determine that the waste tank has undergone maintenance / service since the last flush cycle. If the waste tank <NUM> has undergone maintenance/service, the flush counter is reset to zero (step <NUM>). If the waste tank <NUM> has not undergone maintenance/service, the flush counter retains its previous value (step <NUM>).

At step <NUM>, ISC <NUM> may compute a minimum number of flushes to fill the waste tank <NUM> (N1min) (also referred to herein as a minimum flush threshold) by multiplying the number of successful flush cycles (N1) needed to reach the maximum capacity of the waste tank <NUM> with a tolerance or factor (e.g., of <NUM>%) and subtracting that product from the number of successful flush cycles (N1) needed to reach the maximum capacity of the waste tank <NUM>, as provided in equation <NUM> below: <MAT>.

ISC <NUM> may further compute a maximum number of flushes to fill the waste tank <NUM> (N1max) (also referred to herein as a maximum flush threshold) by multiplying the number of successful flush cycles (N1) needed to reach the maximum capacity of the waste tank <NUM> with a tolerance or factor (e.g., of <NUM>%) and adding that product to the number of successful flush cycles (N1) needed to reach the maximum capacity of the waste tank <NUM>, as provided in equation <NUM> below: <MAT>.

In this manner, since N1 indicates an average number of flushes to fill the tank, the ISC <NUM> shall apply a predetermined tolerance, such as <NUM>%, to indicate a range of possible flushes at which the waste tank <NUM> may be filled.

At step <NUM>, ISC <NUM> may further compute a minimum weight at which waste tank <NUM> may be full (N2min) (also referred to herein as a minimum weight threshold) by multiplying the average weight of a full waste tank <NUM> (N2) with a tolerance or factor (e.g., of <NUM>%) and subtracting that product from the average weight of a full waste tank <NUM> (N2), as provided in equation <NUM> below: <MAT>.

ISC <NUM> may further compute a maximum weight at which waste tank <NUM> may be full (N2max) (also referred to herein as a maximum weight threshold) by multiplying the average weight of a full waste tank <NUM> (N2) with a tolerance or factor (e.g., of <NUM>%) and adding that product to the average weight of a full waste tank <NUM> (N2), as provided in equation <NUM> below: <MAT>.

In this manner, since N2 indicates an average weight of the waste tank <NUM> at which the waste tank is at capacity or filled, the ISC <NUM> shall apply a predetermined tolerance, such as <NUM>%, to indicate a range of possible weights at which the waste tank <NUM> may be at capacity.

At step <NUM>, ISC may determine if the tank full sensor is faulted. In this regard, ISC <NUM> may monitor the health status of the PLS which indicates the waste tank <NUM> is <NUM>% full (e.g., upper PLS <NUM>). ISC <NUM> may determine that upper PLS <NUM> is faulty by validating the discrete input from the PLS which indicates the state (Healthy/Faulty) of the PLS.

If the health status of the upper PLS <NUM> is faulted, ISC <NUM> moves to step <NUM> to determine if both N3 is between N2min and N2max and the flush counter <NUM> is greater than N1min. In response to one or both of these determinations being false, ISC <NUM> may proceed with the flush cycle (i.e., accept further waste into the waste tank <NUM>) and increment the counter (step <NUM>). Stated differently, in response to one or both of these determinations being false, ISC <NUM> may determine that the waste tank <NUM> is not full and continue normal operation of waste tank <NUM> until it is determined that the waste tank <NUM> is full. In contrast, in response to both of these determinations being true, ISC <NUM> may abort the flush cycle (step <NUM>) and send an indication signal to a display device <NUM> onboard the host aircraft indicating that the waste tank <NUM> is full. Stated differently, in response to detecting that the upper PLS <NUM> is faulty, ISC <NUM> may detect that the waste tank <NUM> is full only if both the weight of the waste tank <NUM> (N3) as monitored by load cell <NUM> is between the minimum weight at which waste tank <NUM> may be full (N2min) and the maximum weight at which waste tank <NUM> may be full (N2max) and the flush counter <NUM> is greater than computed minimum number of flushes required to fill the waste tank <NUM> (N1min). In this manner, ISC <NUM> may evaluate if the waste tank <NUM> is full by comparing the flush counter <NUM> value against N1min and N1max as well as by comparing the N3 value against N2min and N2max. The flush cycle will be aborted only when N3 is in Range of N2min to N2max and the flush counter <NUM> is greater than N1min.

If the health status of the upper PLS <NUM> is not faulted (i.e., step <NUM>, NO), ISC <NUM> moves to step <NUM> to determine if the upper PLS <NUM> is wet (i.e., upper PLS <NUM> indicates that the waste has reached upper PLS <NUM> for a predetermined duration thereby indicating the waste tank <NUM> is full). Stated differently, at step <NUM> ISC <NUM> determines if the upper PLS <NUM> is indicating a tank full status. The flush cycle will be aborted only when all three sensors (i.e., upper PLS <NUM>, load cell <NUM>, and flush counter <NUM>) indicate a full waste tank <NUM>. Stated differently, ISC <NUM> determines if upper PLS <NUM> is indicating a tank full status, N3 is between N2min and N2max, and the flush counter <NUM> is greater than N1min. In response to one or more of these determinations being false, ISC <NUM> may determine that the waste tank <NUM> is not full (step <NUM>) and continue normal operation of waste tank <NUM> until it is determined that the waste tank <NUM> is full. In contrast, in response to all three of these determinations being true, ISC <NUM> may abort the flush cycle (step <NUM>) and send an indication signal to the host aircraft indicating that the waste tank <NUM> is full. Stated differently, in response to detecting that the upper PLS <NUM> is not faulty, ISC <NUM> may detect that the waste tank <NUM> is full only if the upper PLS <NUM> indicates a wet condition (i.e., is indicating a tank full status), the weight of the waste tank <NUM> (N3) as monitored by load cell <NUM> is between the minimum weight at which waste tank <NUM> may be full (N2min) and the maximum weight at which waste tank <NUM> may be full (N2max), and the flush counter <NUM> is greater than computed minimum number of flushes required to fill the waste tank <NUM> (N1min).

Systems, methods, and apparatus are provided herein. In the detailed description herein, references to "one embodiment", "an embodiment", "an example embodiment", etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic.

Claim 1:
A waste level monitoring system for an aircraft waste tank, comprising:
a point level sensor (<NUM>) disposed on the aircraft waste tank;
a load cell (<NUM>) disposed on the aircraft waste tank;
a flush counter (<NUM>) configured to count a number of toilet flushes since a previous service to the aircraft waste tank; and
a controller (<NUM>) electronically coupled to the point level sensor, the load cell, and the flush counter, the controller configured to:
receive, via the point level sensor (<NUM>), a first signal indicating a level of waste within the aircraft waste tank;
receive, via the load cell (<NUM>), a second signal indicating a weight of the aircraft waste tank;
receive, via the flush counter (<NUM>), a third signal indicating the number of toilet flushes since the previous service to the aircraft waste tank;
characterized in that the controller is configured to:
determine whether the point level sensor (<NUM>) is faulted;
in response to the point level sensor (<NUM>) being faulted, determine whether:
(a) the weight of the aircraft waste tank is between a minimum weight threshold and a maximum weight threshold; and
(b) the number of toilet flushes is greater than a minimum flush threshold; and
in response to both (a) and (b) being true, send a waste system status signal to a display device (<NUM>) onboard an aircraft indicating that the aircraft waste tank is full.