Unscheduled Removals Research Articles

Incidencia de retirada no programada de dispositivos invasivos en enfermos con COVID-19 en cuidados intensivos

IntroductionThe rate of unscheduled removal of invasive devices (ID) is an indicator of quality programmes in the critically ill. Our research group performed prevalence analyses since 2010 and another during the pandemic. The aim was to analyse the rates of use and non-planed removal of endotracheal tubes, catheters (central venous and arterial) and enteral catheters in the first wave of the COVID-19 pandemic comparing them with previous rates. MethodologyPrevalence study in a polyvalente ICU. After 4 prospective observational analyses (2010, 2011, 2018, 2019) a retrospective analysis was performed (8 March-8 May 2020). Variables: diagnosis, stay and reason for removal of ID (endotracheal tubes (ET), central venous catheters, arterial catheters and enteral catheters) and rate of reintubation after self-removal of ET. Variables analysed and described as accidental removal rates per 1000 device-days and rates of ID use. Results2026 patients were included (631 in 2010, 724 in 2011, 210 in 2018, 361 in 2019 and 100 in 2020). Significant differences, between all periods, in diagnoses (P<.001), ICU stay (P<.001) and mortality (P=.016) and, between 2020 and all other periods, in rates of use per 100 days-stay (P<.010) and per 100 admissions (P<.001) in all devices except arterial catheter. In 2020, there was an increase in ET obstruction (36.0%; rate 20.27 per 1000 intubation/days, P<.010), decrease in ET self-removals (2020 rate: 0.00 per 1000 intubation/days; P<.050) and enteral catheters (14.33 per 1000 catheter/days). Overall reintubation (all periods) after self-extubation: 12.5%. ConclusionsThe rate of devices self-removal in COVID-19 patients in the first wave of the pandemic was lower than that observed in the previous four periods. The high incidence rate of ET obstruction in these patients was significant and relevant.

Aircraft Engine Bleed Valve Prognostics Using Multiclass Gated Recurrent Unit

Prognostics and health management is an engineering discipline that aims to support system operation while ensuring maximum safety and performance. Prognostics is a key step of this framework, focusing on developing effective maintenance policies based on predictive methods. Traditionally, prognostics models forecast the degradation process using regression techniques that approximate a mapping function from input to continuous remaining useful life estimates. These models are typically of high complexity and low interpretability. Classification approaches are an alternative solution to these types of models. We propose a predictive classification model that translates the input into discrete output variables instead of mapping the input to a single remaining useful life estimate. Each discrete output variable corresponds to a range of remaining useful life values. In other words, each output class variable represents the likelihood or risk of failure within a specific time range. We apply this model to a real-world case study involving the unscheduled and scheduled removals of a set of engine bleed valves from a fleet of Boeing 737 aircraft. The model can reach an area under the (micro-average) receiver operating characteristic curve of 72%. Our results suggest that the proposed multiclass gated recurrent unit network can provide valuable information about the different fault stages (corresponding to intervals of residual lives) of the studied valves.

IDENTIFIKASI KEGAGALAN PADA KOMPONEN PITOT PROBE BOEING 737-900ER

Based on Boeing 737-900ER unscheduled removal data of pitot probe 0851HT-1 January, 2020 to November, 2021 found 14 removal for pitot probe with one of the defect is “pitot light on”. This indicate that there is a problem with the component and can disrupt the pilot and delay the aircraft. Knowing the result of failure identification and the type of failure be the aim of this research. Analysis using Failure Mode and Effect Analysis used to identify failure modes, causes and effects of failure, severity, occurrence, and detection ranking so that the risk priority number obtained. Based on the FMEA Worksheet, there are 8 failure modes that occur on the pitot probe with the highest Risk Priority Number is 126 on mode “IAS AND ALT DISAGREE”.

Damage Analysis of Propeller Blade P/N R815505 with Root Cause Failure Analysis Method on ATR 72 Aircraft

The propeller blade is a component that is the main source of thrust on the ATR 72 aircraft. Based on data from the Aircraft Flight Maintenance Log (AFML) for the period 2019 – 2021 ATR 72 aircraft, the propeller blade component was damaged causing the need for unscheduled removal which had impact losses to airlines such as delays and aircraft-on-ground (AOG). This study aims to find the root causes of damage to the propeller blade components. Analysis was carried out using the Root-Cause Failure Analysis (RCFA) method using fault tree analysis (FTA) and fishbone diagrams as tools so that factors related to propeller blade damage will be found. The results of analysis using fault tree analysis (FTA) and fishbone found that the root cause of damage to the propeller blade was in the area of ​​the heating element (de-icer) as the top event, while the propeller blade operation, propeller blade maintenance and the ATR 72 aircraft operating environment were the intermediate events

Catheter-related complications in onco-hematologic children: A retrospective clinical study on 227 central venous access devices.

The use of central venous access devices (CVADs) is of paramount importance to safely deliver antiblastic and support therapies in children with cancer. Though, in pediatric patients, as much as in adults, CVADs are potentially associated with severe complications which may result in unscheduled interruption of therapy, hospitalization, increased morbidity/mortality, and increased cost of care. We have reviewed retrospectively our experience with CVADs in children with solid tumors and hematologic diseases, with the purpose of verifying if the adoption of well-defined insertion and maintenance bundles might be effective in reducing catheter-related complications, and in particular catheter-related thrombosis. A total of 227 CVADs were analyzed: 175 peripherally inserted central catheters (PICCs), 50 centrally inserted central catheters (CICCs), and 2 femorally inserted central catheters. All CVADs were non-valved, non-cuffed power injectable polyurethane catheters; 81% were tunneled. Median dwelling time of CVADs was 172 days, for a total number of 39,044 catheter days. A very low incidence of both symptomatic catheter-related thrombosis (0.9%) and catheter-related blood stream infection (0.56 episodes per 1000 catheter days) was found. Unscheduled removal or guidewire replacement because of mechanic complications occurred in 15.7% of CVADs. There was no difference in terms of complications between PICCs and CICCs or between tunneled and non-tunneled catheters. Our experience with CVADs in oncologic and hematologic children suggests that catheter-related complications may be minimized by the adoption of appropriate insertion and maintenance bundles.

Scheduled removal of central venous catheters (CVC) to prevent CVC-related bloodstream infections in patients with hematological disease or autologous stem cell transplantation: a registry-based randomized simulation-study

Although not generally recommended, scheduled central venous catheter (CVC) removal is sometimes carried out in order to reduce the CVC-related bloodstream infection (CRBSI) incidence. We conducted a simulation for scheduled CVC removal within the multicenter CRBSI registry (SECRECY). Non-tunneled jugular and subclavian CVC in patients with hematological disease or with germ cell tumors (including patients receiving autologous stem cell transplantation [SCT]) were included. Cases were randomized in a 1:1:1:1 ratio to either a simulated, scheduled CVC removal after 7, 14, and 21 days, or to non-simulated, unscheduled CVC removal (control group). The primary endpoint was definitive CRBSI incidence for a scheduled CVC removal after 14 days (dCRBSI-D14rmv). Among other, secondary endpoints were definite CRBSI incidence for a scheduled removal after 7 days (dCRBSI-D7rmv) and 21 days (dCRBSI-D21rmv). Data on 2984 CVC were included. Patients’ median age was 59 (range 16–95) years, 58.8% being male. The vast majority (98.4%) were patients with hematological malignancies. Jugular veins were the main insertion site (93.2%). dCRBSI-D14rmv was 3.10/1000 CVC days as compared to 4.15/1000 CVC days in the control group (p = 0.23). There was a significant difference between dCRBSI-D7rmv (0.86/1000 CVC days) and controls (p < 0.001), but not between dCRBSI-D21rmv (4.10/1000 CVC days) and controls (p = 0.96). Our data suggest that in patients with hematological diseases or autologous SCT recipients scheduled CVC removal after 14 days does not result in a lower CRBSI incidence compared to unscheduled removal.Trial registration: DRKS00006551, 2014/09/29, retrospectively registered.

Cost-effectiveness analysis of bundled innovative devices versus standard approach in the prevention of unscheduled peripheral venous catheters removal due to complications in France.

The objective of the study was to perform a cost-effectiveness analysis of bundled devices (BDs) versus standard devices (SDs) for the prevention of unscheduled peripheral venous catheter (PVC) removal due to complication from a French investigator-initiated, open-label, single center, randomized-controlled, two-by-two factorial trial (CLEAN-3 study). A 14-day time non homogeneous semi-markovian model was performed to be fitted to longitudinal individual patient data from CLEAN-3 database. This model includes five health states and eight transitional events; a base case scenario, two scenario analyses and bootstrap sensitivity analyses were performed. The cost-effectiveness criterion was the cost per patient with unscheduled PVC removal avoided. 989 adult (age≥18 years) patients were analyzed to compare the BDs group (494 patients), and the SDs group (495 patients). The assessed intervention was a combination of closed integrated catheters, positive displacement needleless-connectors, disinfecting caps, and single-use prefilled flush syringes compared with the use of open catheters and three-way stopcocks for treatment administration. For the base case scenario, an unscheduled 1st PVC removal before discharge was significantly more frequent in the SDs group (235 patients (47.5%) in the SDs group and 172 patients (34.8%) in the BDs group, p = 0.00006). After adjustment for 1st catheter time, the number of patients with unscheduled PVC removal per day was of 16 (95%CI: 15; 18) patients (out of 100) in the BDs group and of 26 (95%CI: 24; 28) patients (out of 100) in the SDs group. The mean cost per patient (adjusted on catheter-time) was of €144 (95%CI: €135-€154) for patients in the SDs group versus €102 (95%CI: €95-€109) for patients in the BDs group; the mean saving per patient was of €42 (95%CI: €32-€54). As a consequence, the assessed BDs strategy was less costly and more effective than the SDs strategy. Trail registration: CLEAN-3 study is registered with ClinicalTrials.gov, NCT03757143.

Subcutaneous tunneling technique to improve outcomes for patients undergoing chemotherapy with peripherally inserted central catheters: a randomized controlled trial.

ObjectiveTo compare the value of the subcutaneous tunneling technique versus the normal technique in improving the outcomes of patients undergoing chemotherapy with peripherally inserted central catheters (PICCs).MethodsOne hundred thirty patients were randomly divided into an experimental group (subcutaneous tunneling technique) and control group (normal technique) according to the PICC placement technique, and clinical data were compared between the groups.ResultsIn total, 129 PICCs were successfully inserted. Compared with the control group, the experimental group had a lower occurrence of complications after placement (especially catheter dislodgement: 3.1% vs. 15.4%, venous thrombosis: 3.1% vs. 15.4%, and wound oozing: 14.1% vs. 27.7%), lower occurrence of unscheduled PICC removal (3.1% vs. 13.8%), greater comfort during placement (14.16 ± 2.21 vs. 15.09 ± 2.49 on a scale ranging from 6 to 30 points, with higher scores indicating lower degrees of comfort), and lower costs of PICC maintenance (median (interquartile range) per-day maintenance cost: 13.90 (10.99–32.83) vs. 15.69 (10.51–57.46) Yuan). The occurrence of complications and amount of bleeding during placement were not significantly different between the two groups.ConclusionsThe subcutaneous tunneling technique can improve PICC placement by reducing complications and costs of maintenance with better patient comfort during placement.

A New Method of Calculating the Attainable Life and Reliability in Aerospace Bearings

The aviation industry made significant progress improving reliability, efficiency and performance throughout the last decades. Especially aircraft engines and helicopter transmission systems contributed significantly to these improvements. The kerosene consumption decreased by 70 % and the CO2 emissions due to air transport decreased by 30 % per passenger kilometer within the last 20 years. Simultaneously, the flight safety was increased with aircraft engine in-flight-shut-downs as low as 1 ppm and „unscheduled engine removals” as low as 4 ppm. Flight safety is equal to the reliability of the systems in service. Failure of these systems directly leads to exposure of human life. Among the most critical aviation systems are aircraft engines including the rolling element bearings which support the rotors. A serious damage to the aircraft engine main shaft bearings during flight requires shout-down of the engine to avoid a further damage escalation subsequently leading to engine fire. Today, it is a requirement for aircraft to operate with one engine shut down. However, each in-flight-engine-shut-down typically is connected with flight diversion or abort and immediate landing. Inflight-shut-downs translate into increased risk for passengers and crew and substantial on cost. Therefore, rolling element bearings for aircraft engines are developed – similar to other aircraft engine components – targeting a reliability of nearly 100 % over an operation time of more than 10 000 hours prior to overhaul. To achieve this requirement despite the extreme operating conditions such as high speed and temperatures occurring in gas turbines, special high-performance materials are used for the rolling bearing components which are partially integrated in surrounding engine parts like shafts and housings. These special conditions - deviating from conventional industrial rolling element bearing applications - are currently not sufficiently considered in the standardized method of calculating the bearing life per ISO 281. A new method of calculating the attainable life of rolling elements bearing in aerospace applications is presented. This method considers the special aerospace conditions and materials and thus enables a higher reliability of the theoretical analysis and life prediction.

New Method of Calculating the Attainable Life and Reliability in Aerospace Bearings

The aviation industry made significant progress improving reliability, efficiency and performance throughout the last decades. Especially aircraft engines and helicopter transmission systems contributed significantly to these improvements. The kerosene consumption decreased by 70 % and the CO2 emissions due to air transport decreased by 30 % per passenger kilometer within the last 20 years. Simultaneously, the flight safety was increased with aircraft engine in-flight-shut-downs as low as 1 ppm and „unscheduled engine removals” as low as 4 ppm. Flight safety is equal to the reliability of the systems in service. Failure of these systems directly leads to exposure of human life. Among the most critical aviation systems are aircraft engines including the rolling element bearings which support the rotors. A serious damage to the aircraft engine main shaft bearings during flight requires shout-down of the engine to avoid a further damage escalation subsequently leading to engine fire. Today, it is a requirement for aircraft to operate with one engine shut down. However, each in-flight-engine-shut-down typically is connected with flight diversion or abort and immediate landing. Inflight-shut-downs translate into increased risk for passengers and crew and substantial on cost. Therefore, rolling element bearings for aircraft engines are developed – similar to other aircraft engine components – targeting a reliability of nearly 100 % over an operation time of more than 10 000 hours prior to overhaul. To achieve this requirement despite the extreme operating conditions such as high speed and temperatures occurring in gas turbines, special high-performance materials are used for the rolling bearing components which are partially integrated in surrounding engine parts like shafts and housings. These special conditions - deviating from conventional industrial rolling element bearing applications - are currently not sufficiently considered in the standardized method of calculating the bearing life per ISO 281. A new method of calculating the attainable life of rolling elements bearing in aerospace applications is presented. This method considers the special aerospace conditions and materials and thus enables a higher reliability of the theoretical analysis and life prediction.

A technology evaluation of Annovera: a segesterone acetate and ethinyl estradiol vaginal ring used to prevent pregnancy for up to one year

ABSTRACT Introduction The segesterone acetate and ethinyl estradiol contraceptive vaginal ring (SA/EE CVR) was FDA-approved in August 2018 and is now available in the U.S. The CVR is placed vaginally for 21 days followed by a 7-day ring-free interval, when withdrawal bleeding typically occurs. One ring can be used for up to a year (13 cycles). Areas covered This review summarizes this novel method of contraception, including the delivery system and the hormonal components. We describe the potential market, how it is used, the pharmacokinetic properties of the device, and results of clinical trials including efficacy, bleeding profile, acceptability, and safety. Expert opinion The SA/EE CVR represents the first long-lasting user-controlled hormonal contraceptive device. The bleeding pattern is highly favorable and consistent over the entire year and is associated with very low discontinuation. Efficacy and safety are similar to other methods of combined hormonal contraceptives. Unscheduled ring removals increase the risk of failure. Further studies are needed to evaluate continuous use of the ring for greater than 21 days, and potential non-contraceptive benefits of the ring such as reduced menstrual bleeding.

Evaluation and Improvement of Unscheduled Removal Component Reliability Calculation Method with No Fault Found (NFF) Shop Finding Results

The test results of the removed aircraft components are classified into No Fault Found (NFF), Real Reason Conform (RRC) and Other Defect Found (ODF). Corrective actions will be taken on findings that are classified as RRC and ODF, while for the NFF category no action will be taken. In the MRO XYZ, for the NFF category, the age of the component during the removal is included into the failure data. Moreover, the reliability calculation in the MRO XYZ uses the 2-parameters Weibull distribution. These will result in unrepresentative reliability calculation. Therefore, it is necessary to evaluate the method. The research compares the results of the reliability calculation between the 2-parameters and the 3-parameters Weibull distributions by applying them to several part numbers data. Furthermore, the reliability calculation using the 3-parameters Weibull is also applied to the data where the NFF category is not included the failure data. The location parameter, γ, is calculated using the Muralidhar method. The research also develops an excel VBA macro-based tool for reliability calculation. The results of the reliability calculation show that there is a significant difference of the failure rate between using the 2-parameters and the 3-parameters Weibull distribution. The failure rate calculated by using the 3-parameters Weibull distribution for the data where NFF category is not included into the failure data show a significant different as compared to the method used by the MRO XYZ, where the difference is affected by the percentage of NFF items in the failure data.

ROC-based Business Case Analysis for Predictive Maintenance – Applications in Aircraft Engine Monitoring

Predictive maintenance approaches leveraging integrated knowledge, fleet-wide data and machine-learning techniques allow for earlier warnings on impeding failures and for higher accuracy in remaining useful life predictions compared with traditional prognostics. However, in case relative to correctly predicted maintenance needs, missed detections or false alarms occur too often, follow-up costs, e.g. due to cascading effects or unnecessary inspection effort, can outweigh the advantages. Here, we show that a general cost-benefit analysis based on the Receiver Operating Characteristics (ROC) curve of a failure prediction algorithm allows deducing application-specific requirements on the failure prediction quality for achieving a net benefit. Moreover, various prediction algorithms can be compared and optimized regarding cost-efficiency. The value of the approach is demonstrated by an application example in aircraft engine maintenance showing that for reducing unscheduled engine removals by (more) accurate prediction of turbine blade failures, maximal cost-saving potentials of up to 16 Mio $ emerge per mature-run, widebody engine and per Mean-Time Between Removals (MTBRs). Here, realistic, literature-based assumptions on various costs, failure probability and algorithm performance were incorporated and varied within sensible limits. As a further key result, the value of data for predictive maintenance purposes is impressively demonstrated. Compared with the net benefit achievable by failure prediction of a pure physics-based damage accumulation model and by turbine operating data, an up to 6 Mio. $ higher cost-saving potential per MTBRs was shown to emerge from a literature-based hybrid approach fusing physics and further sources of data, e.g. on manufacturing, geography and environment as well as customer and inspection information by means of machine learning techniques. Generalized applications of the presented cost-benefit analysis approach e.g. to optimize costs associated with engine workscope planning or other system maintenance are discussed.

Predictive maintenance for aircraft components using proportional hazard models

Abstract Unscheduled maintenance can contribute significantly to an airline's cost outlay. Reliability analysis can help to identify and plan for maintenance events. Reliability analysis in industry is often limited to statistically based approaches that incorporate failure times as the primary stochastic variable, with additional strict assumptions regarding independence of events and underlying distributions of failure phenomena. This foregoes the complex nature of aircraft operations, where a whole range of operational factors may influence the probability of occurrence of a maintenance event. The aim of this research is to identify operational factors affecting component reliability and to assess whether these can be used to reduce the number of unscheduled occurrences (i.e. failures). To do so, a data-driven approach is adopted where historical operational and maintenance data is gathered and analysed to identify operational factors with a measurable influence on maintenance event occurrence. Both time-independent and time-dependent Proportional Hazard Models (PHMs), models which incorporate operational factors as covariates, are employed to generate reliability estimates. Results obtained from analysing historical data of a set of nine components with respect to unscheduled removals indicates that adopting new maintenance schedules, derived from the proposed reliability models, can reduce the number of unscheduled occurrences.

Maintenance Model of Digital Avionics

The cost of avionics maintenance is extremely high for modern aircraft. It can be as high as 30% of the aircraft maintenance cost. A great impact on the cost of avionics maintenance is provided by a high level of No Fault Found events (NFF). Intermittent faults are the leading cause of the NFF appearance in avionics. The NFF rate for avionics systems is between 20% and 50%. The practice of avionics operation and maintenance confirms the relevance of assessing the impact of intermittent faults on the maintenance cost and the choice of such option of the maintenance management, in which the negative impact of the intermittent faults is minimized. In this paper, a new mathematical model of digital avionics maintenance is developed. Key maintenance effectiveness indicators are selected. General mathematical expressions are obtained for the average availability, mean time between unscheduled removals (MTBUR), and expected maintenance cost of single unit and redundant avionics systems, which are subject to permanent failures and intermittent faults. The dependence of the maintenance effectiveness indicators on the rate of permanent failures and intermittent faults is investigated for the case of exponential distribution of time to failures and faults. The dependence of average availability on the number of spare units in the airline’s warehouse is also analyzed. On the base of the proposed maintenance model, different options of avionics maintenance management are considered. Numerical examples illustrate how to reduce the expected maintenance cost of avionics systems.

Evaluating diagnostic failures during system design

For the modern industry, diagnostic failures have been an area where huge sums of money is wasted through increasingly high levels of unscheduled removals. This is not only due to the continued tread in increasing system complexities and cost implications on maintenance programmes, but also attributed to design limitations associated with testability. As a result, No Fault Found (NFF) events continue to pose significant problems for achieving successful failure diagnosis within a system. This has a direct impact on the availability requirements, compromises reliability and also contributes to the cost of resolving an unknown failure. This article investigates how the diagnostic analysis of a system can be used to help recognise and reduce the number of NFF events. It is revealed that such a problem is difficult to resolve using traditional fault isolation calculations, and that Monte Carlo based methods provide a better alternative. A simulation-based evaluation is carried out on a UAV fuel system, to establish the relation between large ambiguity groups and the number of NFF events. It also demonstrates a method for estimating cumulative replacement costs due to false removals and hence, the overall system costs during the design stage. Such studies can be used for benchmarking, as well as a measure of how maintenance requirements might change over the intended lifetime of a system.

Forecasting fault events for predictive maintenance using data-driven techniques and ARMA modeling

Abstract Presently, time-based airline maintenance scheduling does not take fault predictions into account, but happens at fixed time-intervals. This may result in unnecessary maintenance interventions and also in situations where components are not taken out of service despite exceeding their designed risk of failure. To address this issue we propose a framework that can predict when a component/system will be at risk of failure in the future, and therefore, advise when maintenance actions should be taken. In order to facilitate such prediction, we employ an auto-regressive moving average (ARMA) model along with data-driven techniques, and compare the performance of multiple data-driven techniques. The ARMA model adds a new feature that is used within the data-driven model to give the final prediction. The novelty of our work is the integration of the ARMA methodology with data-driven techniques to predict fault events. This study reports on a real industrial case of unscheduled removals of a critical valve of the aircraft engine. Our results suggest that the support vector regression model can outperform the life usage model on the evaluation measures of sample standard deviation, median error, median absolute error, and percentage error. The generalized linear model provides an effective approach for predictive maintenance with comparable results to the baseline. The remaining data-driven models have a lower overall performance.

Benefits Analysis of Prognostics &amp; Health Monitoring to Aircraft Maintenance using System Dynamics

The benefits of applying Prognostics &amp; Health Monitoring (PHM) techniques to Aircraft Maintenance are evaluated using System Dynamics (SD). It is well known that a key motivation for PHM is to increase aircraft availability by reducing unscheduled removals and downtime, ultimately reducing Direct Maintenance Costs (DMC). The benefits to aircraft maintenance are tested by modelling two maintenance philosophies using SD: the traditional approach driven by scheduled &amp; reactive maintenance; and through Condition Based Maintenance (CBM) by considering PHM functionality in maintenance practice. The study is focused on an Electromechanical Actuator (EMA) for an aircraft flight control system across a fleet of 25 aircraft over an 8 year maintenance overhaul period. The study indicated there were fewer unscheduled removals as a result of CBM in comparison to the traditional approach. Further sensitivity studies on varying degradation patterns led to instability in maintenance planning with more reactive maintenance due to more abrupt failures of the EMA. The cost effectiveness of CBM as a function of PHM efficiency is demonstrated through DMC accumulation where it was found that CBM is no longer cost-beneficial when over 85% of the EMA life has been used. Overall, the SD models presented a general level of systems understanding of the causalities that are inherent within the two maintenance policies and are a useful methodology to consider PHM benefits through analysing the impact of different policies on the system behaviour.

Hyper-cylindrical micro-clustering for streaming data with unscheduled data removals

We present a streaming data clustering algorithm which allows removals of data records at any arbitrary time. Unlike other existing algorithms whose objective is to track evolving clusters by letting the weight of old data decline with time, we consider the case when all data records do not have pre-specified lifetime which is the characteristic of many real data sets such as bank accounts. A data record can be added or removed by users at any arbitrary time. The algorithm processes each datum in one-pass-throw-away fashion without storing the whole data set. A technique for merging several micro-clusters into a hyper-cylindrical micro-cluster is proposed to reduce the number of micro-clusters in feature space, and thus reduce computation. The performance of this algorithm is tested with several data sets including both synthetic and real data sets. The proposed algorithm shows better performances compared with other state-of-the-art algorithms in terms of several indices for measuring clustering performance.

METHOD FOR TECHNICAL AND ECONOMIC EVALUATION OF THE EFFECTIVENESS OF RELIABILITY IMPROVEMENT OF MILITARY AIRCRAFT GAS-TURBINE ENGINES IN THEIR AFTERSALES SUPPORT BASED ON OUTCOME PERFORMANCE MEASURES

article describes a conflict between interests of the state customer and the prime contractor on the issue of aeronautical systems and subsystems reliability improvement during its aftersales support. conflict between interests is shown to arise under the traditional approach to payment for the prime contractor’s services on a basis called “costs+”. Contractual models of public-and-private partnership which are used in the foreign countries successfully, with a payment scheme for the contractor’s services based on outcome performance measures of aeronautical systems and subsystems aftersales support, are presented as a conflict settlement mechanism. A long validity term of such contracts and independence of performance payment amounts from the contractor’s actual expenses motivate the private partner to hold some activities aiming at systems and subsystems reliability improvement. Applicability of technical and economic assessment of these activities is demonstrated. main provisions of the method for technical and economic evaluation of the effectiveness of aeronautical systems and subsystems reliability improvement are presented thorough the example of a fleet of engines operated within a group of military transport aircrafts with their aftersales support based on outcome performance measures. method is based on a simulation model of engines fleet operating which allows for the measures of technical and economic evaluation to be identified: average availability of the military transport aircrafts group during the contract validity period, state customer’s operating costs and the prime contractor’s profit. It is experimentally shown on the developed method basis that when the fleet of engines is supported aftersales based on outcome performance measures the prime contractor has an economic interest to improve engines reliability above the requirements specified in the regulatory documentation. Keywords technical and economic evaluation, simulation modeling, availability of aeronautical systems and subsystems, conflict between interests, aftersales support, outcome performance measures, gas turbine aircraft engine, gas turbine engine reliability, operating time between unscheduled removals, military transport aircraft. References