# US 10,504,305 B2 · Statistically equivalent level of safety modeling for aircraft fleets

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- Number: US 10,504,305 B2
- Document ID: US10504305B2
- Status: Granted
- Kind: B2
- Application number: 16/103,861
- Filed: 2018-08-14
- Published: 2018-12-27
- Granted: 2019-12-10
- Earliest claimed: 2016-06-14
- Assignees: Textron Innovations Inc.
- Applicants: Bell Helicopter Textron Inc.
- Inventors: Brian Edward Tucker; Richard Marcos Muñiz
- Web page: https://patentgrep.com/patent/US10504305B2

## CPC

- G07C 5/0808: {Diagnosing performance data (testing of vehicles G01M17/00; testing of electrical installation on vehicles G01R31/005)}
- B64F 5/40: Maintaining or repairing aircraft
- B64F 5/60: Testing or inspecting aircraft components or systems
- G05B 23/0283: {Predictive maintenance, e.g. involving the monitoring of a system and, based on the monitoring results, taking decisions on the maintenance schedule of the monitored system; Estimating remaining useful life [RUL] (preventive maintenance, i.e. planning maintenance according to the available resources without monitoring the system G06Q10/06)}
- G06F 30/15: Vehicle, aircraft or watercraft design
- B64D 45/00: Aircraft indicators or protectors not otherwise provided for
- G07C: TIME OR ATTENDANCE REGISTERS; REGISTERING OR INDICATING THE WORKING OF MACHINES; GENERATING RANDOM NUMBERS; VOTING OR LOTTERY APPARATUS; ARRANGEMENTS, SYSTEMS OR APPARATUS FOR CHECKING NOT PROVIDED FOR ELSEWHERE
- B64F: GROUND OR AIRCRAFT-CARRIER-DECK INSTALLATIONS SPECIALLY ADAPTED FOR USE IN CONNECTION WITH AIRCRAFT; DESIGNING, MANUFACTURING, ASSEMBLING, CLEANING, MAINTAINING OR REPAIRING AIRCRAFT, NOT OTHERWISE PROVIDED FOR; HANDLING, TRANSPORTING, TESTING OR INSPECTING AIRCRAFT COMPONENTS, NOT OTHERWISE PROVIDED FOR
- G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- B64D: EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT

## Abstract

Systems and methods are provided for statistically equivalent level of safety modeling. One method includes identifying sub-fleets within a fleet based upon usage profiles, determining a sub-fleet reliability value for each sub-fleet, determining a baseline fleet reliability for the fleet by combining the sub-fleet reliability values on a weighted basis, applying at least one credit to at least one sub-fleet, determining a post-credit sub-fleet reliability value for each sub-fleet based upon the at least one credit, determining a post-credit fleet reliability for the fleet by combining the post-credit sub-fleet reliability values on a weighted basis, comparing the baseline fleet reliability with the post-credit fleet reliability to identify a change in fleet reliability and determining whether the change in fleet reliability is within a predetermined threshold to validate the at least one credit.

## Claims

### Claim 1

A method for safely extending scheduled maintenance intervals for structural components of aircraft within an aircraft fleet, the structural components subject to scheduled maintenance based upon component life limits, the method comprising:
(A). identifying aircraft sub-fleets within the aircraft fleet based upon aircraft usage profiles, each aircraft sub-fleet having a sub-fleet population;
(B). determining a sub-fleet reliability value for each aircraft sub-fleet based upon a component life limit of a structural component;
(C). determining a baseline fleet reliability for the aircraft fleet by multiplying together the sub-fleet reliability values raised to the sub-fleet population for each aircraft sub-fleet;
(D). applying at least one credit to the component life limit of the structural component of the aircraft in at least one aircraft sub-fleet;
(E). determining a post-credit sub-fleet reliability value for each aircraft sub-fleet based upon the component life limit with the at least one credit;
(F). determining a post-credit fleet reliability for the aircraft fleet by multiplying together the post-credit sub-fleet reliability values raised to the sub-fleet population for each aircraft sub-fleet;
(G). comparing the baseline fleet reliability with the post-credit fleet reliability to identify a change in fleet reliability;
(H). determining whether the change in fleet reliability is within a predetermined threshold to validate the at least one credit applied to the component life limit of the structural component of the aircraft in the at least one aircraft sub-fleet; and
(I). when at least one credit is validated, extending the scheduled maintenance interval for the structural component of the aircraft in the at least one aircraft sub-fleet such that maintenance is carried out on the structural component of the aircraft in the at least one aircraft sub-fleet according to an extended scheduled maintenance interval.

### Claim 2 (depends on 1)

The method as recited in claim 1 wherein the usage profiles are based upon measured usage levels.

### Claim 3 (depends on 1)

The method as recited in claim 1 wherein the reliability values further comprise time dependent probability distribution functions.

### Claim 4 (depends on 1)

The method as recited in claim 1 wherein the reliability values further comprise probability distribution functions selected from the group consisting of probability distribution functions of discrete random variables, probability distribution functions of continuous random variables, normal distribution functions, lognormal distribution functions and Poisson distribution functions.

### Claim 5 (depends on 1)

The method as recited in claim 1 wherein the reliability values relate to one or more structural components of the aircraft of the aircraft sub-fleets.

### Claim 6 (depends on 1)

The method as recited in claim 1 wherein the reliability values further comprise probability distribution functions based upon strength, loads and usage of the aircraft of the aircraft sub-fleets.

### Claim 7 (depends on 1)

The method as recited in claim 1 wherein the at least one credit is selected from the group consisting of life limit shifts, life factors and combination thereof.

### Claim 8 (depends on 1)

The method as recited in claim 1 further comprising applying at least one revised credit to the at least one aircraft sub-fleet when change in fleet reliability is not within the predetermined threshold and repeating steps (E)-(H).

### Claim 9

A system for safely extending scheduled maintenance intervals for structural components of aircraft within an aircraft fleet, the structural components subject to scheduled maintenance based upon component life limits, the system comprising:
a computing system having logic stored within a non-transitory computer readable medium, the logic executable by a processor, wherein the computing system is configured to:
(A). identify aircraft sub-fleets within the aircraft fleet based upon aircraft usage profiles, each aircraft sub-fleet having a sub-fleet population;
(B). determine a sub-fleet reliability value for each aircraft sub-fleet based upon a component life limit of a structural component;
(C). determine a baseline fleet reliability for the aircraft fleet by multiplying together the sub-fleet reliability values raised to the sub-fleet population for each aircraft sub-fleet;
(D). apply at least one credit to the component life limit of the structural component of the aircraft in at least one aircraft sub-fleet;
(E). determine a post-credit sub-fleet reliability value for each aircraft sub-fleet based upon the component life limit with the at least one credit;
(F). determine a post-credit fleet reliability for the aircraft fleet by multiplying together the post-credit sub-fleet reliability values raised to the sub-fleet population for each aircraft sub-fleet;
(G). compare the baseline fleet reliability with the post-credit fleet reliability to identify a change in fleet reliability; and
(H). determine whether the change in fleet reliability is within a predetermined threshold to validate the at least one credit applied to the component life limit of the structural component of the aircraft in the at least one aircraft sub-fleet;
wherein, when at least one credit is validated, the scheduled maintenance interval for the structural component of the aircraft in the at least one aircraft sub-fleet is extended such that maintenance is carried out on the structural component of the aircraft in the at least one aircraft sub-fleet according to an extended scheduled maintenance interval.

### Claim 10 (depends on 9)

The system as recited in claim 9 wherein the usage profiles are based upon measured usage levels.

### Claim 11 (depends on 9)

The system as recited in claim 9 wherein the reliability values further comprise time dependent probability distribution functions.

### Claim 12 (depends on 9)

The system as recited in claim 9 wherein the reliability values further comprise probability distribution functions selected from the group consisting of probability distribution functions of discrete random variables, probability distribution functions of continuous random variables, normal distribution functions, lognormal distribution functions and Poisson distribution functions.

### Claim 13 (depends on 9)

The system as recited in claim 9 wherein the reliability values relate to one or more structural components of the aircraft of the aircraft sub-fleets.

### Claim 14 (depends on 9)

The system as recited in claim 9 wherein the reliability values further comprise probability distribution functions based upon strength, loads and usage of the aircraft of the aircraft sub-fleets.

### Claim 15 (depends on 9)

The system as recited in claim 9 wherein the at least one credit is selected from the group consisting of life limit shifts, life factors and combination thereof.

### Claim 16 (depends on 9)

The system as recited in claim 9 wherein the computing system is further configured to apply at least one revised credit to the at least one aircraft sub-fleet when change in fleet reliability is not within the predetermined threshold and to repeat processes (E)-(H).

### Claim 17

A non-transitory computer readable storage medium comprising a set of computer instructions executable by a processor for operating a safety modeling computing system for safely extending scheduled maintenance intervals for structural components of aircraft within an aircraft fleet, the structural components subject to scheduled maintenance based upon component life limits, the computer instructions configured to:
(A). identify aircraft sub-fleets within the aircraft fleet based upon aircraft usage profiles, each aircraft sub-fleet having a sub-fleet population;
(B). determine a sub-fleet reliability value for each aircraft sub-fleet based upon a component life limit of a structural component;
(C). determine a baseline fleet reliability for the aircraft fleet by multiplying together the sub-fleet reliability values raised to the sub-fleet population for each aircraft sub-fleet;
(D). apply at least one credit to the component life limit of the structural component of the aircraft in at least one aircraft sub-fleet;
(E). determine a post-credit sub-fleet reliability value for each aircraft sub-fleet based upon the component life limit with the at least one credit;
(F). determine a post-credit fleet reliability for the aircraft fleet by multiplying together the post-credit sub-fleet reliability values raised to the sub-fleet population for each aircraft sub-fleet;
(G). compare the baseline fleet reliability with the post-credit fleet reliability to identify a change in fleet reliability; and
(H). determine whether the change in fleet reliability is within a predetermined threshold to validate the at least one credit applied to the component life limit of the structural component of the aircraft in the at least one aircraft sub-fleet;
wherein, when at least one credit is validated, the scheduled maintenance interval for the structural component of the aircraft in the at least one aircraft sub-fleet is extended such that maintenance is carried out on the structural component of the aircraft in the at least one aircraft sub-fleet according to an extended scheduled maintenance interval.

### Claim 18 (depends on 17)

The non-transitory computer readable storage medium as recited in claim 17 wherein the computer instructions are further configured to apply at least one revised credit to the at least one aircraft sub-fleet when change in fleet reliability is not within the predetermined threshold and repeat processes (E)-(H).