Method for monitoring a degradation in an on-board device of an aircraft with automatic determination of a decision threshold

• US 9,598,178 B2
• Filed: 09/05/2014
• Issued: 03/21/2017
• Est. Priority Date: 09/06/2013
• Status: Active Grant

• Current Assignee: Safran Aircraft Engine Company, Universite de Technologie de Troyes
• Original Assignee: Safran Engineering Services (Safran SA), Snecma (Safran SA), Universite de Technologie de Troyes
• Inventors: Masse, Jean-Remi Andre, Grall-Maes, Edith, Hmad, Ouadie, Beauseroy, Pierre Jean Emile
• Primary Examiner(s): Shaawat, Mussa A
• Application Number:
  US14/478,076
• Publication Number:
  US 20150073650A1
• Time in Patent Office: 928 Days
• US Class Current: 1/1
• CPC Class Codes: B64D 2045/0085 Devices for aircraft health monitoring, e.g. monitoring flutter or vibration
• CPC Class Codes: B64D 45/00 Aircraft indicators or protectors not otherwise provided for camouflage F41H3/00
• CPC Class Codes: G05B 23/024 Quantitative history assessment, e.g. mathematical relationships between available data; Functions therefor; Principal component analysis [PCA]; Partial least square [PLS]; Statistical classifiers, e.g. Bayesian networks, linear regression or correlation analysis; Neural networks

Abstract

A method for monitoring a degradation in an on-board device of an aircraft, comprising a step of comparing an abnormality score obtained for a given flight of said aircraft with a decision threshold (S) and a step of transmitting an alert in the event of said decision threshold (S) being exceeded, said decision threshold (S) being automatically determined for a given probability of alert Pa, corresponding to the probability of an alert being transmitted during the monitoring method when said on-board device is healthy, by means of a plurality of steps, including a step of reading the antecedent of the continuous adjusted division function for the value 1−Peac, said antecedent corresponding to said decision threshold (S), with Peac being the elementary probability of exceeding the threshold for confirmation per k exceedances of threshold during n consecutive flights and being a function of the probability of alert Pa.

Claims

1. A method for monitoring a degradation in an on-board device of an aircraft, implemented by a computer, the method comprising:

measuring physical parameters from a plurality of sensors on the on-board device of the aircraft;

transforming, using the computer, the measured physical parameters to obtain an abnormality score for a given flight of the aircraft;

comparing the abnormality score obtained for the given flight of the aircraft to a decision threshold; and

transmitting an alert when the decision threshold is exceeded,

wherein the decision threshold is automatically determined for a given probability of alert Pa, corresponding to a probability of an alert being transmitted during the monitoring method when the on-board device is undamaged, by;

computing a plurality of abnormality scores for a plurality of flights of the aircraft without degradation;

obtaining a distribution of a probability density of the plurality of abnormality scores, with the distribution being specific to a physical nature of the on-board device;

obtaining a continuous adjusted distribution function by adjusting the distribution using a non-parametric estimator of the probability density;

computing a continuous adjusted division function based on the continuous adjusted distribution function; and

determining the decision threshold by reading an antecedent of the continuous adjusted division function for a given value, the antecedent corresponding to the decision threshold,

wherein the given value is 1−

Peac, where Peac is an elementary probability of exceeding the decision threshold for confirmation per k exceedances of the decision threshold during n consecutive flights and is obtained by the following formula;

Peac=B<sup>−

1</sup><sub>(k, n−

k+1)</sub>(Pa)

wherein B<sup>−

1</sup><sub>(k, n−

k+1)</sub> is an inverse Beta division function of parameters k and n−

k+1 and Pa is the probability of alert.

2. The method for monitoring according to claim 1, wherein the non-parametric estimator of the probability density is a Parzen window estimator.

3. The method for monitoring according to claim 2, wherein the distribution is formed from a number N of abnormality scores for the plurality of flights of the aircraft without degradation, the distribution having an estimated standard deviation {circle around (σ

)}, and a width h of the Parzen window is defined according to the following formula;

4. The method for monitoring according to claim 1, wherein the probability of alert Pa is obtained by the following formula:

5. The method for monitoring according to claim 4, further comprising:

deducing the probability of detecting the a posteriori degradation (1β

)_{a posteriori} by implementing the method for monitoring the degradation in the on-board device with the previously determined decision threshold for the plurality of abnormality scores formed for the plurality of flights of the aircraft with degradation (1β

)_{a posteriori};

determining a new probability of alert Pa as a function of the probability of detecting the a posteriori degradation (1β

)_{a posteriori};

determining the elementary probability of exceeding the threshold Peac based on the new probability of alert Pa; and

determining a new decision threshold that is refined based on the new elementary probability of exceeding the threshold Peac.

6. The method for monitoring according to claim 1, further comprising:

predetermining values of k and n.

7. The method for monitoring according to claim 6, wherein the value of n is selected before that of k and the value of k is selected as a function of that of n.

8. The method for monitoring according to claim 7, wherein the value of n is selected in order to maximise the detection probability.