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

• US 20150134198A1
• Filed: 05/15/2013
• Published: 05/14/2015
• Est. Priority Date: 05/16/2012
• Status: Active Grant

• Current Assignee: Safran Aircraft Engine Company
• Original Assignee: Snecma (Safran SA)
• Inventors: Masse, Jean-Remi Andre, Beauseroy, Pierre Jean, Emile, Boulet, Xavier, Grall-Maes, Edith, Hmad, Ouadie
• Granted Patent: US 9,346,558 B2
• Time in Patent Office: Days
• US Class Current: 701/34.2
• 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 23/0235 based on a comparison with predetermined threshold or range, e.g. "classical methods", carried out during normal operation; threshold adaptation or choice; when or how to compare with the threshold
• CPC Class Codes: G07C 5/0808 Diagnosing performance data testing of vehicles G01M17/00; testing of electrical installation on vehicles G01R31/005

Abstract

A method for monitoring degradation of an on-board device of an aircraft includes comparing an abnormality score obtained for a given aircraft flight to a decision threshold and emitting an alarm when the decision threshold is exceeded. The decision threshold is determined automatically for a given alarm probability Pa, corresponding to probability of an alarm being emitted during the monitoring when the on-board device is undamaged, by: calculating plural abnormality scores for plural flights of the aircraft without degradation to obtain a probability density distribution of the abnormality score, the distribution being specific to a physical nature of the on-board device; adjusting the distribution using a non-parametric estimator of the probability density to obtain a continuous adjusted distribution function; calculating a continuous adjusted allocation function from the continuous adjusted distribution function; and reading precedent of the continuous adjusted allocation function for value 1-Pa, the precedent corresponding to the decision threshold.

Claims

1-5. -5. (canceled)

6. A method for monitoring a degradation of an on-board device of an aircraft, implemented by a computer, a degree of the degradation of the on-board device being defined by an abnormality score from measurements of physical parameters of the on-board device, the monitoring method comprising:

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

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

calculating a plurality of abnormality scores for a plurality of flights of the aircraft without degradation to obtain a distribution of a probability density of the abnormality score, the distribution being specific to a physical nature of the on-board device;

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

calculating a continuous adjusted allocation function from the continuous adjusted distribution function; and

reading a precedent of the continuous adjusted allocation function for the value 1-Pa, the precedent corresponding to the decision threshold.

7. A method according to claim 6, wherein the non-parametric estimator of the probability density is a Parzen window estimator.

8. A method according to claim 7, wherein the distribution is formed from a number N of abnormality scores for a plurality of flights of the aircraft without degradation, the distribution having an estimated standard deviation 6, the Parzen window has a width h defined according to formula:

9. A method according to claim 6, wherein the alarm probability Pa is obtained using formula:

10. A method according to claim 9, further comprising:

implementing the method for monitoring a degradation of the on-board device, with the decision threshold determined in advance, for a plurality of abnormality scores formed for a plurality of flights of the aircraft with degradation to deduce therefrom a probability of detecting a degradation a posteriori (1−

β

)_{a posteriori};

determining a new alarm probability Pa on the basis of the probability of detecting a degradation a posteriori (1−

β

)_{a posteriori}; and

determining a new, refined decision threshold from the new alarm probability Pa.