METHOD FOR MONITORING A DEGRADATION IN AN ON-BOARD DEVICE OF AN AIRCRAFT WITH AUTOMATIC DETERMINATION OF A DECISION THRESHOLD

• US 20150073650A1
• Filed: 09/05/2014
• Published: 03/12/2015
• 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, HMAD, Ouadie, GRALL-MAES, Edith, BEAUSEROY, Pierre Jean Emile
• Granted Patent: US 9,598,178 B2
• Time in Patent Office: Days
• US Class Current: 701/32.1
• 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. Method for monitoring a degradation in an on-board device of an aircraft, implemented by a computer, with the degree of the degradation of said on-board device being defined by an abnormality score formed on the basis of measurements of physical parameters of said on-board device, said monitoring method comprising a step of comparing an abnormality score obtained for a given flight of said aircraft with a decision threshold and a step of transmitting an alert in the event of said decision threshold being exceeded, with said decision threshold being automatically determined for a given probability of alert Pa, which corresponds to the probability of an alert being transmitted during said monitoring method when said on-board device is healthy, by means of the following steps:

a step of computing a plurality of abnormality scores for a plurality of flights of said aircraft without degradation so as to obtain a distribution of the probability density of the abnormality score, with the distribution being specific to the physical nature of the on-board device;

a step of adjusting the distribution using a non-parametric estimator of the probability density so as to obtain a continuous adjusted distribution function;

a step of computing a continuous adjusted division function on the basis of the continuous adjusted distribution function; and

a step of reading the antecedent of the continuous adjusted division function for a given value, said antecedent corresponding to said decision threshold, wherein said given value is 1−

Peac, with Peac being the elementary probability of exceeding the threshold for confirmation per k exceedances of threshold during n consecutive flights and being 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 said probability of alert.

2. Method according to claim 1, wherein said non-parametric estimator of the probability density is a Parzen window estimator.

3. Method according to claim 2, wherein, with the distribution being formed on the basis of a number N of abnormality scores for a plurality of flights of said aircraft without degradation, the distribution being an estimated standard deviation {circumflex over (σ

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

4. Method according to claim 1, wherein the probability of alert Pa is obtained by the following formula:

5. Method according to claim 4, comprising:

a step of implementing said method for monitoring a degradation in said on-board device, with the previously determined decision threshold (S), for a plurality of abnormality scores formed for a plurality of flights of said aircraft with degradation so as to deduce a probability of detecting an a posteriori degradation (1−

β

)_{a posteriori};

a step of determining a new probability of alert Pa as a function of the probability of detecting an a posteriori degradation (1−

β

)_{a posteriori};

a step of determining the elementary probability of exceeding the threshold Peac on the basis of the new probability of alert Pa; and

a step of determining a new decision threshold (S) that is refined on the basis of the new elementary probability of exceeding the threshold Peac.

6. Method according to claim 1, comprising a step of predetermining values of k and n.

7. Method 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. Method according to claim 7, wherein the value of n is selected in order to maximise the detection probability.