The effect of condition based maintenance on engine maintenance effectiveness and reliability

Durum izlemeye dayalı bakımın uçak motor güvenilirliğine ve bakım etkinliğine etkisi

Abstract

As the worldwide commercial airline operation has been becoming more and more competitive environment while profit margins are dropping, airlines try to find ways to reduce maintenance costs and aircraft downtime. Aircraft maintenance downtimes and man-hour/material expenditure associated maintenance activities are two main factors affecting aircraft performance. Airlines want to increase aircraft availability and reliability to minimize the operational interruptions and the customer satisfaction with an effective maintenance. The effective maintenance would be performed just before the failure is impending. But, in practice, this can only be done if thert' is any possibility to detect the component deterioration before its failure. So, airlines try to find out methods to move from reactive maintenance to predictive maintenance. The preventive maintenance task intervals are established initially by the working groups and steering committee personnel using good judgment and operating experience. Since maintenance programs may include ineffective maintenance items for a specific airline working and environmental conditions, every airline operator should have a system to analyze the effectiveness of the maintenance program to periodically validate that individual tasks in program are effective and their intervals are adequate based on operator reliability data.Engine Health monitoring (EHM) has been very popular subject to increase aircraft availability with the minimum maintenance cost. Health monitoring provides earlier indication for future maintenance requirements to allow maintenance planners to more proactively and accurately plan mechanics, spares, tools and equipment. This study is aimed at providing a method to monitor the aircraft engine health during the flight with the aim ofproviding an opportunity for early fault detection to improve airline maintenance effectiveness and reliability. Since the impending engine failures may cause to change the engine parameters such as Fuel Flow (FF), Exhaust Gas Temperature (EGT), engine compressor speed (N2), etc., engine deteriorations or faults may be identified before they occur by monitoring them.Engine data are typically collected once or twice per flight and transferred to a ground monitoring sys-tem. In the study, the snapshot data collected from engines during the cruise entered into SAGE program are used. Since the observed values are recorded in different altitudes and environmental conditions, the data should be corrected to the sea level or to a fixed altitude for the same atmosphere condition. In EHM analysis, these values are put in time series such as cycles and flight hours. The Delta measurements used are deviations in EGT, N2 and FF from a base line 'good engineFor ideal engine conditions, A value should be zero. The value increases or decreases depending on the engine system fault or deterioration. EHM is performed by monitoring the As (AEGT, AFF and AN2) trend changes together to detect and isolate any fault. Similar to human body, in an aircraft engine has N2 in place of pulse, FF in place of blood pressure and EGT in place of body temperature. EGT is an excellent indicator of engine health just as blood pressure is a common indicator for health of human heart. Troubleshooting check is replaced with the interview in a patient check.Many researchers have emphasized that current health monitoring systems need more improvement in terms of automation and more accurate predictions. So as to monitor engine health in flight, the automation of current work for EHM done manually by airlines is developed by using fuzzy logic (FL) model. FL is selected to develop automated EHM system (AEHMS), since it is a very useful method for automation health monitoring. The fuzzy rule inference system for different engine faults is based on the expert knowledge and real life data in Turkish Airlines fleet. The method is utilized to run for monitoring the engines in Turkish Airlines fleet. This study has shown that AEHMS can be used by airlines or engine manufacturers efficiently to simplify the EHM system and minimize the drawbacks of it, such as extra labor hour, human error and requirement for engineering expertise.Finally, it was shown that health monitoring based maintenance is very effective to increase reliability and reduce maintenance cost. This method may also be applicable other than aircraft engines such as auxiliary power unit, structures. Since every engine type has different characters, it is required to revise the fuzzy rules for the concerning engine types.

Özet

Minimum bakım maliyeti ile uçakların kullanılabilirliğini artırmak için, Motor Durumunu İzleme (MDI) çok rağbet görür hale gelmiştir. Bu çalışmada, uçak bakım etkinliği ve güvenilirliğini artırmak için, arızaların olmadan önce saptanmasına imkan sağlayacak MDÎ için bir metod geliştirmek ve durum izlemeye dayalı bakımın maliyete ve güvenilirliğe etkisi incelecektir. Yaklaşan motor arızaları, yakıt akışı (FF), egzoz gaz sıcaklığı (EGT), motor kompressör devri (N2) vb. motor parametrelerinin değişmesine sebep olduğundan, motor kötüleşmeleri veya bozulmaları, bu parametrelerin zamanla değişimleri izlenerek tespit edilebilir. Bu çalışmada, motor durumunu uçuşta izlemek içinr bulanık mantık kullanılarak, havayolları tarafından yapılan mevcut elle yapılan MDİ'nin otomasyonu geliştirilmiştir. Farklı motor arızaları için, Türk Hava Yolları 'ndaki gerçek veriler ve uzman bilgilerine dayanarak bulanık mantık kural tabanı oluşturulmuştur. MDÎ'nin tüm çevrimi MATLAB'teki bulanık mantık modülü kullanılarak otomatikleştirilmiştir. Sonuçta, bu metod Türk Hava Yollarındaki motorların izlenmesinde kullanılabilmesi için çalıştırılmıştır. Sonuçlar, bu metodun ekstra adam-saat, insan hatası ve mühendislik uzmanlığı gerekliliği gibi dezavantajları en az seviyeye indirerek geliştirilen MDÎ'nin, hava yolları tarafından kullanılabileceği göstermiştir. Kullanılan veriler ve elde edilen sonuçlarla, durum izlemeye dayalı bakımın maliyeti düşürdüğü ve güvenilirliği artırdığı gösterilmiştir. Bu metot, uçak motorları dışında, uçaklardaki yardımcı güç üniteleri, yapısal elemanlar vb. komponetlere uygulanabilir. Her motor tipi farklı karakterlere sahip olabileceği için, farklı motor tiplerinde bu metot kullanırken kural tabanının revize edilmesi gerekir.