US RE41381 E1
A system useable in a jet aircraft having installed therein a pressurized oxygen supply which feeds oxygen into the interior of the plane when it flies at high cabin altitudes, the system indicating the changing status of the supply as oxygen is drained therefrom. The system includes a pressure transducer coupled to the supply and means associated with the transducer to determine the lapse rate at which the pressure of the supply is reduced as oxygen is drained therefrom to yield a first signal representing this pressure lapse rate, and to concurrently determine the lapse rate at which the number of liters of oxygen in the supply is reduced as oxygen is drained therefrom to yield a second signal representing the liter lapse rate. These signals are applied to a microprocessor in whose data base is entered the total oxygen inventory of the supply and the oxygen demand of the plane in which the supply is installed. When oxygen is being drained from the supply, the microprocessor calculates and reads out the prevailing supply pressure, the number of liters remaining in the supply, and the time in hours and minutes remaining before the supply is exhausted based on the current rate of oxygen consumption.
The invention provides both a method for calculating the oxygen required, as well as a real time monitoring and calculating system for emergency conditions. The invention is applicable to any pressurized gas system, such as for divers, compressed gas cooking or vehicles, therapeutic oxygen, and the like.
1. A system for determining a safe flight level in an aircraft having a pressurized oxygen supply, comprising:
a pressure transducing system sending a data signal indicative of the pressure in the oxygen supply;
means for providing a data signal indicative of the amount of fuel in the aircraft;
computecomputer data storage for maintaining aircraft engine performance data and equal time point (ETP) data between two predetermined diversion airports;
a computer processor receiving said pressure and fuel data and calculating (i) fuel usage versus time as a function of the engine performance data, (ii) oxygen usage versus time as a function of altitude, and (iii) ETP versus time as a function of altitude; and
a screen for graphically displaying at least one of (i), (ii), and (iii) superimposed, and optionally superimposing at least two of (i), (ii), and (iii) when said at least two are graphically displayed .
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11. A method for determining a safe flight level in an aircraft having a pressurized oxygen supply, comprising:
providing a computer processor with display and interface;
transducing the pressure in the pressurized oxygen supply and providing a signal to the computer indicative of the pressure;
providing as input to the computer at least one of (a) a transduced signal indicative of the amount of fuel in the aircraft and (b) a manually input value indicative of the amount of fuel in the aircraft and optionally a reserve fuel quantity;
storing as data aircraft engine performance data and equal time point (ETP) data between two predetermined diversion airports;
transducing the altitude of the aircraft and providing a signal to the computer indicative of the altitude;
calculating in said computer processor (i) fuel usage versus time as a function of the engine performance data, (ii) oxygen usage versus time as a function of altitude, and (iii) ETP versus time as a function of altitude; and
displaying on said computer display (i), (ii), and/orand (iii), optionally superimposed, and superimposing at least two of (i), (ii), and (iii) when said at least two are graphically displayed.
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This application is a continuation in part of Ser. No. 09/080,187, filed May 18, 1998 abandoned.
1. Field of Invention
This invention relates generally to a system associated with a gas supply which is adapted to monitor the supply and to indicate its status as gas is drained therefrom, and more particularly, to a system of this type which is installed in a jet aircraft provided with an oxygen supply that is drained only when the plane flies at high cabin altitudes, the system in a dynamic displaying the time in hours and minutes that remain before the oxygen is exhausted based on the current rate of oxygen consumption, while in a static mode the system refers to a database to predict duration based on existing conditions.
2. Status of Prior Art
In propeller-driven aircraft, the propulsion medium is ambient air that is accelerated to the rear of the plane by the action of the rotating propeller. Hence, propeller-driven planes (other than turboprops) do not function efficiently at high altitudes where the propulsion medium is relatively tin.. But a jet aircraft depends on jet propulsion created by a force developed in reaction to the ejection of a high-velocity jet of gas. In the combustion chamber of a jet propulsion engine, combustion of the fuel mixture generates expanding gases which are discharged through an orifice to form the jet. Hence in a jet plane with a bypass engine, where ambient air is not the propulsion medium, the ambient air impedes the forward motion of the plane unless it is bypassed around the combustion zone (that is, the air is funnelled through the engine so that the total mass flow rate through the engine is increased, and hence more thrust is developed).
When a jet plane flies at high altitudes, 35,000 ft (FL 350) for commercial jets and 41,000 ft. (FL 410), the FAA regulations set forth that at least one pilot must have a mask on and be breathing oxygen. Further, the FAA regulations prescribe quantity of oxygen required for the passengers in the cabin and for the flight crew in the flight deck or cockpit. It is for this reason that all commercial jet aircraft are provided with a pressurized oxygen supply in the form of cylinders or bottles. The magnitude of the supply depends on the size of the plane. For example a B-757 jet plane has a single 115 cubic foot oxygen bottle installed thereon which when full has a gas pressure of 1850 psi. On the other hand a B-747 plane has seven such bottles installed thereon. And on a Falcon 50 jet plane there is only one 76.6 cubic foot bottle of oxygen which when the bottle is full has a pressure of 1850 psi. Oxygen canisters (bottles) for aviation are typically cited in pounds per square inch (gauge) of pressure (“psi”), at NTPD (National Temperature Pressure Dry), while oxygen flows for breathing are typically measured volumetrically, usually liters per minute. The oxygen in the canister is supplied to one or more manifolds from where it is distributed to the pilots, crew, and passengers.
The present practice in a jet plane is to provide the oxygen supply installed therein with a pressure gauge coupled to an indicator which informs the pilot in the cockpit of the prevailing pressure of the supply; some systems also compensate for the temperature of the oxygen canister. If when the flight starts and there is 1850 psi in the canister, and sometime later there the reading is 1300 psi, the pilot knows there is less oxygen but does not have a clear indication of the duration of oxygen remaining. What the pressure gauge does not inform the pilot, yet is important that he know, is exactly how much time remains before the oxygen supply is insufficient to meet the oxygen demand of the particular flight. This demand depends not only on the size of the plane and its passenger capacity, but on the actual number of passengers and crew in the flight, and on the type of oxygen masks being used. For example, those used in emergencies when a cabin depressurizes (the yellow-colored drop down masks) are activated by pulling on the mask and the flow is through a fixed valve; thus, the flow through the mask is a function solely of the differential between the oxygen pressure in the manifold and ambient pressure (so more flows as the altitude increases). One the other hand, pilots' masks have demand regulators, so that often the pilots must use reverse breathing (that is, the oxygen is forced under pressure through the mask into the pilot's lungs, and he must force out his exhalation). Accordingly, a pressure gauge reading does not inform the pilot of a jet plane as to the duration of the oxygen supply. It is therefore the present practice to furnish a jet plane pilot with a printed chart or table which he can on occasion consult to determine for a given number of passengers and crew on a particular flight and for a given full supply of oxygen, how much time remains before this supply of oxygen runs out. In fact, each jet plane will have a different oxygen supply system, with different numbers or configurations of manifolds, and different types of regulator masks for pilots.
Pilots, for each flight, are required to plan for sufficient oxygen on board for a worse case scenario. For example, for a flight from New York City to London, most of the trip is over the Atlantic ocean, and the “worst case” is a depressurization at the Equal Time Point (ETP), the point at which the Estimated Time Enroute (ETE) returning to the nearest diversion airport or continuing to the nearest diversion airport is the same. Based on actual wind and weather conditions, the plane has an effective Ground Speed Return (GSR, returning to the last diversion airport passed) and an effective Ground Speed Continue (GSC, continuing to the nearest diversion airport). ETP can be calculated as
Fortunately, the problem of sudden cabin depressurization, to extent of oxygen requirements, is less problematic in a commercial airliner. Oxygen is only required, by FAA regulations, for flight levels above 10,000 ft. (FL 100). Commercial airliners typically carry sufficient fuel so that, after a catastrophic depressurization, they can make an emergency descent to 10,000 ft. and continue or return at that level, avoiding the need for oxygen during the entire ETE to the diversion airport.
The real problem occurs with private (e.g., corporate) jets, where the luxury of uploading sufficient fuel to fly at 10,000 ft. to a diversion airport is lacking. If there is a sudden depressurization and after emergency descent to FL 100 there is sufficient fuel to travel to a diversion airport at FL 100, the problem is averted. Otherwise, the plane must climb to increase the Specific Range (SR). Accordingly, the pilot(s) must calculate, based on the performance charts for the specific aircraft being flown, the minimum altitude at which the SR is sufficient to reach the diversion airport. The higher the altitude, the farther the SR; however, fuel usage increases slightly as altitude increases. Most importantly, at FL greater than 100, oxygen is required for the crew and passengers. Also, wind speed varies as a function of altitude, so a higher altitude may encounter a higher head (or tail) wind speed. Accordingly, in an emergency situation there is a tradeoff among fuel available, altitude (SR), and oxygen available. Unfortunately, determining the altitude for a sufficient SR and the oxygen available is an iterative process, and the time for these calculations is not during a catastrophic depressurization in the middle of the night over water. Additionally, after the decompression, the pilot(s) must determine an operating window to fly to one or two preplanned diversion airports (or, perhaps, an unplanned diversion airport); while the pilot(s) regains control of the aircraft and stabilizes the situation, the jet is still continuing on its flight path, and so is using fuel, oxygen, and changing the distances between it and the diversion airports, further effecting calculations of the operating window.
Ruder, U.S. Pat. No. 3,922,149, is directed to eliminating tanks of stored oxygen by providing an oxygen enrichment system that uses a molecular sieve that absorbs oxygen the least, and hence enriches the oxygen content of the sieve effluent stream.
Bishaf, U.S. Pat. No. 3,875,801 which discloses a pressurized gas tank to supply oxygen to a scuba diver, the gas being depleted at a variable rate. In Bishaf, the amount of gas remaining in the tank is displayed “in terms of the amount of time until depletion.” In the Bishaf system, a transducer placed within the gas tank produces an electrical signal indicative of the instantaneous gas pressure. The signal is applied to an integrated circuit chip what develops a signal proportional to, the rate of change of the instantaneous pressure.
Schmitt, U.S. Pat. No. 4,485,669, is directed to a device for determining the timely delivery of compressed gas from compressed gas canisters, and especially for the ejection of weapons in a submarine, to assure proper ejection velocity at all depths at which the submarine may be operating.
Erickson, U.S. Pat. No. 4,408,484, discloses a temperature compensated gauge for pressurized gas, especially for natural gas fuel for vehicles or homes.
In view of the foregoing one object of this invention is to provide, in association with a supply of pressurized gas, a system adapted to monitor the drain of the gas from the supply and to indicate the time which remains before the supply is depleted. More particularly, an object of this invention is to provide a system of the above type which is useable in connection with an oxygen supply installed on a jet aircraft to feed oxygen into the interior of the plane when it flies at high altitudes. The system indicates the time remaining before the supply is depleted whereby the pilot has time to take the plane to a lower altitude at which there is no need for oxygen.
Also an object of the invention is to provide a system of the above type in which on the flight deck of the jet plane there are displayed the prevailing pressure of oxygen in the supply, the number of liters of oxygen remaining in the supply, and the time remaining before the supply is depleted.
Yet another object of the invention is to provide a computerized system of the above type which is reliable in operation and affords correct readings.
Still a further object of the invention is to provide a system by which, after an emergency or catastrophic depressurization of a jet cabin, a window of operation is provided to the pilot(s) based on fuel, flight level, and oxygen stores, to reach the nearest diversion airport. In various embodiments, the pilot(s) can be provided with a readout of suitable parameters to continue the flight, and/or can be provided with a graphical display based on the foregoing parameters.
Briefly stated, these objects are attained in a system useable in a jet aircraft having installed therein a pressurized oxygen supply which feeds oxygen into the interior of the plane when it flies at high cabin altitudes, the system indicating the changing status of the supply as oxygen is drained therefrom. The system includes a pressure transducer coupled to the supply and means associated with the transducer to determine the lapse rate at which the pressure of the supply is reduced as oxygen is drained therefrom to yield a first signal representing this pressure lapse rate, and to concurrently determine the lapse rate at which the number of liters of oxygen in the supply is reduced as oxygen is drained therefrom to yield a second signal representing the liters lapse rate. These signals are applied to a microprocessor in whose data base is entered the total oxygen inventory of the supply and the oxygen demand on the plane in which the supply is installed. When oxygen is being drained from the supply, the microprocessor calculates and reads out the prevailing supply pressure, the number of liters remaining in the supply, and the time in hours and minutes remaining before the supply is exhausted based on the current rate of oxygen consumption. The amount of oxygen can be corrected for temperature. The fuel remaining and the distances to the diversion airports can be included in the calculations.
The system described herein is by no means limited to this particular application, for it is applicable to any pressurized gas supply whose operator must monitor the supply and know how much time remains before the supply is depleted. Thus oxygen supplies used in hospitals and helium supplies used in dental offices can be monitored by a system in accordance with the invention, as well as oxygen-acetylene supplies used by welders, air/oxygen tanks used by divers (in which depth monitoring (analogous to SR) and depressurization time (analogous to fuel) are input to the system), and the like systems.
For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawings, wherein:
Before addressing the present invention, it is useful to understand how a pilot should determine, the total amount of oxygen that should be carried on board, including planning for an emergency/catastrophic cabin decompression, to have a suitable operating window (fuel, SR, and oxygen) to safely divert to an alternate airport. The following procedure is not necessarily done, and does form in integral part of this invention because typically the pilot only estimates the amount of oxygen that should be required for the flight, and then not always assuming a worst case emergency scenario.
Prior to departing, the pilot must first calculate the amount of oxygen that would normally be required for the flight.
As noted above, FAR (federal aviation regulations) require that a commercial flight above 410 FL have a pilot breathing oxygen at all times. At flight levels above FL 100, each plane is designed to have an effective cabin altitude somewhere between FL 50 and FL 100 regardless of the altitude.
During an unevenful flight, the oxygen requirement will be the sum of that required above FL 410 (as shown in FIG. 3), any therapeutic oxygen required (i.e., a passenger requiring oxygen during the entire trip), and any needed for an emergency descent to FL 100 (at which level oxygen is not required; see the bottoms of FIGS. 5A/5B and 6A/6B, which include the emergency descent oxygen for the listed passengers plus a crew of two, and are discussed in more detail below). This is then the minimum amount of oxygen that should be carried onboard. For example, a flight having two pilots and an effective cabin pressure of 7000 ft. for 3 hrs, no passengers on therapeutic oxygen, and six passengers, would require about 1260 liters (
Additionally, the pilot must plan for an emergency at the ETP. The flight plan provides (and the pilot can always determine later, prior to departure) the actual wind conditions, and typically provides the ETP (or it can be derived) and the amount of fuel remaining at the ETP. Based on the amount of fuel remaining at the ETP and the known time (via ETP) to reach a diversion airport, the pilot must determine the altitude at which the jet must fly to have an SR sufficient to reach either diversion airport at the ETP. Knowing the altitude required to have a sufficient SR to reach the diversion airport, the oxygen requirement will be defined. This oxygen requirement should then be added to that determined for an unevenful flight.
In reality, after an emergency descent, the jet will climb to an altitude sufficient to provide an SR effective to reach a diversion airport. The charts shown in
Thus, the total calculated oxygen is 2330 (normal operations plus emergency descent) plus 770 plus 1549, for a total of 4649 liters. Also, under 200 psi there is no useful amount of oxygen supplied, so at 70° F. an additional 350 liters of oxygen must be added. Hence, the total oxygen required, including that for “expected” emergencies is about 5000 liters. Looking at
After a real emergency while in flight, the crew would have to manually redo the calculations based on an ETP where the emergency actually occurred. If there is a sole pilot, this can present significant problems, having to both control the jet and make iterative calculations. For example,
A system in accordance with the invention, when associated with a pressurized gas supply having a predetermined initial gas pressure defining a predetermined initial number of liters of gas, preferably corrected for temperature as gas is being drained from the supply acts determines the estimated time existing for use of the gas. The system updates the data, preferably in real time, to provide an indication to the pilot(s) of the oxygen remaining. A more preferred system determines a suitable operating window for flying after emergency decompression of the jet cabin.
For a known quantity of oxygen in the supply, the time remaining until the supply is depleted (hereinafter referred to as “oxygen duration”) is computed by dividing the initial quantity of oxygen expressed in liters by its rate of depletion in a unit of time consumption rate in (liters per minute). This computation affords a direct reading of time remaining before the oxygen supply is exhausted. Signal S1 from temperature compensator 15 is applied to a pressure lapse rate module 17. Module 17 periodically samples pressure signal to yield a pressure lapse-rate signal L1. By lapse rate is meant the rate, per unit of time, (one minute) at which the pressure of oxygen in the supply decreases as oxygen is drained from the supply. Obviously the rate of drain is greatest when a given plane is filled to its capacity by passengers. Signal S2 from temperature compensator 16 is applied to a lapse rate module 18 which determines the rate, per unit time, at which liters of oxygen in the supply are being drained therefrom. Module 18 periodically samples this rate to yield a liters lapse rate signal L2. The pressure lapse rate signal L1 and the concurrently produced liters lapse rate signal L2 are applied to the input of a microprocessor 19 in which the signals are digitalized and then processed to provide the following readouts which are displayed in the cockpit or flight deck 20 of the plane so that they can be seen by the pilot and the flight crew.
Readout P presents the existing pressure of oxygen as oxygen is drained from supply 10 when the plane is flying at high cabin altitudes. Thus when the supply is full, it typically will have a pressure of 1850 psi, and in the course of the flight, it will drop progressively until the oxygen supply is depleted and meter P reads zero psi. Readout L indicates the number of liters of oxygen remaining in the supply. If therefore when the supply is fill, it has 2168 liters of oxygen, readout L will so indicate, and as the oxygen is being drained, readout L will decrease until the oxygen is exhausted and no liters remain in the supply. In reality, usefull oxygen supply ends when the pressure decreases below 200 psi. The indications to the pilot of P and/or L can be biased to provide a more accurate reading (e.g., rather than the pilot, during an emergency, having to subtract 200 psi from a pressure reading to determine the useful oxygen available).
But as noted previously, the prevailing pressure of the supply and the number of liters of oxygen therein do not indicate “oxygen duration,” the time remaining before the oxygen is depleted, for this depends on the rate per unit time at which the oxygen is being drained, which rate is a function of the number of passengers and crew being supplied with oxygen. Hence the number of passengers and crew must be factored into the computation to produce the third readout D which is the Oxygen Duration (which can likewise be compensated for the 200 psi minimum).
Microprocessor 19 is provided with a keyboard 21 by which is entered into the data base of the computer the identification of the plane, the number of liters of oxygen in the supply when full, and the internal pressure of the supply initially.
To make it possible for the same system to provide readings of oxygen duration, prevailing pressure and remaining liters readings for a broad spectrum of different commercial jet planes, the computer may be provided with software 22 in the form of a CD-ROM, ROM, EPROM, EEPROM, hard disk or the like, in which is digitally stored a plurality of charts, the data on each chart being appropriate to a respective jet plane and being entered into the data base. From software 22 the system will derive information for producing a static display. For example, if passenger seats are added or removed, or if the pilots' masked are changed to one having different flow characteristics, the ROM-type memory can be changed, or the information can be modified from the keyboard using a removable medium (e.g., the CD-ROM) with the correct data. Preferably, data stored on a rotatable median (e.g., CD-ROM, hard drive) is loaded into working memory (RAM) for normal operation to avoid problems with the storage device effecting calculations.
When no oxygen is being consumed, it is then desirable that the system present a static display based on a predetermined projection or forecast which takes into account the number of passengers and crew on board the plane, and an estimated oxygen consumption rate for the particular system. Thus when no oxygen is being consumed, the display is in its “static” mode, while when oxygen is being actually drained from the supply, the system is then in a “dynamic” mode. Alternatively, the system may only have a dynamic mode; for example, indicating oxygen usage when neither the crew nor passengers is using oxygen, as an indication of a leak (e.g, in the manifold, or a faulty regulator for the canister).
It must be borne in mind that the system is not limited to use when oxygen is being drained from the supply at high cabin altitudes, for it is applicable to whenover oxygen is being consumed. For any particular flight it is important that the supply of oxygen for that flight not run out.
A more preferable system uses the aforementioned microprocessor and includes additional inputs and provides a graphical readout to the pilot(s).
Prior to departing on such a flight, the pilot should enter into the system the characteristics required for the two diversion airports at ETP; preferably, the system database will maintain a list of airports and, together with existing instrumentation, calculate the proper course for diversion flight.
As seen, the present invention greatly simplifies the pilots' decisions in an emergency situation and eliminates the time-consuming, error-prone, iterative and interpolative calculations pilots would normally have to perform to safely alter their flight plan. Because a person can become unconscious immediately upon sudden depressurization (the “expected” five to eight seconds of aware activity may not be sufficient and is not a safety margin due to the individual-specific reaction upon such an event), the present system can be integrated with an autopilot: a pressure sensor, such as activates passengers' emergency oxygen, can determine when sudden depressurization has occurred and the plan can descend automatically to a desired flight level within the operating window (because descent to FL 100 and ascent to a desired flight level can waste fuel, which may be a limiting resource).
For new aircraft, the present system is preferably built in with a non-volatile memory having the pre-programmed therein the characteristics of the engine and the oxygen system. For existing aircraft the present system can be integrated with a CD-ROM reader to input information for that particular aircraft. All systems can include the capability to read removable media to facilitate inputting changes to the engines and/or oxygen system.
In another preferred embodiment, the performance charts (e.g., FIGS. 7A/B) are also displayed. On the left hand portion of each figure is a table labelled “Specific Range vs. Wind Component” and is based on the International B.O.W. (basic operating weight). Of course, a jet may have additional supplies (ranging from a collapsible tow bar for smaller airports not accustomed to receiving jets, to deicing fluid for winter travel) to emergency equipment (life rafts, flares, water, food) to additional normal rations (food, liquor). This additional equipment must be added to the B.O.W. to arrive at the weight (in pounds) shown in the table. The table shows that at a given weight, the TAS (true air speed) and fuel flow expected for a given weight; the decimal value is the distance (in nautical miles) that would be expected per pound of fuel for a given wind speed (head/tail wind or no wind); multiplied by the amount of fuel, this value provides the SR of the jet. Thus, in one instance, the chart and the graph can be displayed (simultaneously or alternately) to the pilot, and the pilot can check that data with the actual TAS and fuel flow to evaluate the existing characteristics of the jet. Also, preferably the chart listings for a given wind speed are provided in the same color as the lines on the graph for the same wind speed.
The foregoing description is meant to be illustrative and not limiting. Various changes, modifications, and additions may become apparent to the skilled artisan upon a perusal of this specification, and such are meant to be within the scope and spirit of the invention as defined by the claims.