ARTICLES RESEARCH & TECHNOLOGY

Airbus A320: Aircraft Condition Monitoring Systems

acms

CHAPTER 4


Introduce the Aircraft Condition Monitoring Systems

ACMS report approach is being developed by Airbus with the cooperation of A320 Family operators. China eastern’s engineers are working together with Honeywell and airbus for this ACMS project, some initial achievement has been applied to help engineer monitoring the aircraft condition. Aircraft Condition Monitoring Systems (ACMS) are used by commercial airlines to provide flight performance data for aircraft to monitor aircraft engine performance.

the-current-communication-scheme-of-acms

A Flight Data Acquisition Unit (FDAU) collects CAAC parameters for maintenance and engineering. The FDAU includes an ACMS that records flight performance data from a plurality of acquisition equipment, such as sensors on an aircraft.

The acquisition equipment monitor signals supplied from a variety of transducers distributed throughout the aircraft and provide digital data representative of the aircraft’s flight performance based upon such transducer inputs.

The ACMS use the flight performance data to generate real-time ACMS reports based on required parameters. As flight performance is obtained by the acquisition equipment, the flight performance data is stored in a Flight Data Recorder (FDR).

The flight performance data may be the transmitter to an Aircraft Communication and Reporting System (ACARS) management unit for real-time transmission of, for example, snapshot position parameters, to the ground. The flight performance data is also provided to a pilot’s interface, such as a Multifunction Condition and Display unit (MCDU). The MCDU can display real-time parameters for maintenance and piloting.

The flight performance data is also provided to a pilot’s interface, such as a Multifunction Condition and Display unit (MCDU). The MCDU can display real-time parameters for maintenance and piloting.

The flight performance data is then typically recorded back to a Quick Access Recorder (QAR) .The QAR records the flight performance data on a data media such as a PCMCIA card. The PCMCIA can be plugged into a slot on the ACMS.

The PCMCIA card is then taken to a ground station for engine performance analysis. The ground station includes a Ground Support Equipment (GSE) and an Analysis Ground Station (AGS). A data loader uses a disk to load software upgrades onto the ACMS from the GSE. An Ethernet connection may be provided to the FDAU to connect the ACMS to the aircraft network.

To improve aircraft safety, CAAC recommends that the airlines check the information provided by the FDAU at regular intervals. One approach is to allow aircraft safety personnel to gain access to the flight performance data by physically removing the PCMCIA card. In other words, the mechanic needs to go on board an aircraft to load new software or to retrieve flight performance data from ACMS.

Therefore, communication of the flight performance data is deferred because no remote real-time access is possible. In addition, with the large volume of aircraft traffic, manual retrieval, and replacement of PCMCIA card is very time and manpower intensive. In addition, this approach is prone to substantial misidentification and aircraft association errors.

The aim of ACMS system

A Personal Computer Memory Card International Association (PCMCIA) card can be used to remotely communicate and interface with flight performance data on an aircraft.

The PCMCIA card can be plugged into an Aircraft Condition Monitoring System (ACMS) using a card interface. The ACMS generates an ACMS report after one or more exclusive conditions are fulfilled. The PCMCIA card includes Central Processing Unit (CPU) providing processing power and wireless transmission functionality. The PCMCIA card uses the CPU to detect whether the ACMS report is generated.

In another embodiment, the PCMCIA card remotely communicates and interfaces with flight performance data of an aircraft through the wire. The PCMCIA card can be plugged into an ACMS using a card interface. The ACMS generates an ACMS report after one or more exclusive conditions are fulfilled.

The PCMCIA card includes a CPU providing processing power and wired transmission functionality. The PCMCIA card uses the CPU to detect whether or not the ACMS report is generated. The PCMCIA card further includes an Ethernet interface coupled to the CPU.

The Ethernet interface connects the CPU to a wired network on the aircraft. The PCMCIA card further includes a memory coupled to the CPU through a communication bus. The memory stores flight performance data. The CPU transmits the flight performance data stored in the memory to the wired network after the one or more exclusive conditions are fulfilled and the ACMS reported is generated. The wired network then transmits the flight performance data to a ground station.

In order to launch preventive maintenance action, an ACMS report can be customized. For example, when the bleed temperature reaches 220°C, an ACMS report can be triggered which can be seen on the ground, through the remotely diagnostic service system of engineering and technology Company. Preventive troubleshooting can be launched before the bleed failure or overload or pilot report.

Examples of Bleed Parameters List

Parameters Name

Flight Phase
Altitude
ENG1 Pre-cooler Outlet Temperature
ENG2 Pre-cooler Outlet Temperature
ENG1 Pre-cooler Inlet Pressure
ENG2 Pre-cooler Inlet Pressure
ENG1 TRANSFERRED PRESSURE
ENG2 TRANSFERRED PRESSURE
ENG1 Pack Flow
ENG2 Pack Flow
Pack 1 Position
Pack 2 Position
ENG1 Wing AI/V
ENG2 Wing AI/V
ENG1 PRV Position
ENG2 PRV Position
ENG1 HPV Position
ENG2 HPV Position
ENG1 FAV Position
ENG2 FAV Position
Cross Feed Valve Position
Cabin Pressure
ENG1 %N1
ENG2 %N1

The remotely diagnostic service system in china eastern based on ACMS, which can supply the engineer the detailed flight information, the PFR (Post Flight Report), the warning and fault message in the ECAM on one special aircraft together with the flight phrase and associating AMM (Aircraft Maintenance Manual) chapter.

Increased interaction with Material supply department

As we know, what we have done above needs the material supply department’s substantial support. Something must be mentioned about aviation material’s repair quality in daily maintenance work. The component was sent back as a usable part while the fault still remains. Once the component of this kind is installed on the airplane during fault isolation, it can’t pass the installation test.

If there is any remaining fault in the component, it is impossible to correct the fault. What’s worse is that it will puzzle the technicians and lead them to make a wrong judgment. At this time, the mistaken replacement occurs. Therefore, the repair quality of the component is very important to the reduction of the mistaken replacement rate.

According to the repair station audit reports, which are finished by quality assurance division, the main reasons leading to bad repair quality are showed as followings:

(1) The environment of the airplane was so different from the shop environment that the test of the component in the shop cannot detect the fault.

(2) The repair station without enough capability and the limit of the equipment in the repair station has led personals not being able to find out the problems with the component completely.

(3) The fault description of the component offered by the customer was inaccurate or incomplete to help the repair station do the necessary test and check.

For the reduction of the mistaken replacement, the material supply department must emphasize on the quality and enhance the supervision on the repair stations and suppliers to ensure the quality of the part. In addition, material supply department should order the new material and test tools suggested by airbus.

new-revised-fav

The FAV was frequently updated by Liebherr to prevent the FAV inner leak (LIEBHERR is a GERMAN company which supplies china eastern‘s main aircraft parts in pneumatic systems, such as FAV, PRV, TCT.)

Airbus recommended applying these improvements in order to avoid early FAV leakage. From 2007-10-6, china eastern’s CMP (Customer Maintenance Plan) 36-CES-0005 was asked to do a pneumatic system‘s performance check in the interval of 2A check. It was made sure that the real temperature of the engine bleed when the engines were started was written down, so the FAV which was not operating normally can be checked.

new-revised-TCT

the-test-set

New TCT 342B050000 covered by SB 36-1062 (VSB 342-36-08) was made available from May 2008, the part was updated from 342B020000 to 342B030000 and 342B040000 , but the performance of TCT did not change better, According to Liebherr’s Service Bulletin,

  1. Airbus Test set PN 98L36103002: (catalog price 3.350US$)
  2. Both tools enable efficient components testing as per AMM procedures
  3. Liebherr BTS PN 99127B03 enabled to perform Health check procedures (Integration in
  4. Airbus documentation in progress: Expected available Mid-2009).
  5. In line maintenance work, it is very necessary for help the engineer‘s troubleshooting, to know if the FAV works normally or if there is the leak in sense line which connects the FAV and TCT.

Something else must be mentioned about material supply department; Through unifying the plan, storage, and control of aviation material supply resource and building up efficient distribution process, the material supply department can run more efficiently under lower cost.

As mentioned in chapter 1.2, the workload A320 workshop in the Pudong line maintenance department accounts for 25% of the entire engineering technology company. So the hub maintenance’s ensuring and line maintenance supporting capability should be improved, like the typical engine bleed fault mentioned above i.e. the aircraft with engine bleed fault diverted to Pudong airport of Shanghai whose material supply was sufficient. The Pudong line maintenance department is experienced in dealing with engine bleed fault. Thus the fault source can found in time and the delay time can be shorter.

The line maintenance department offered the works information about what had been done in dealing with the engine bleed fault to the material supply department. The material supply department must mention the frequency of the parts changed and the engine bleed fault’s seasonal feature, such as: in the summer, the TCT, the FAV should be prepared enough, especially in the main base of A320.

Base on the material supply department’s strong support, maintenance works can be carried out more successfully.

Use of Ultrasonic Technology as NDT

Ultrasonic testing is a type of Non-Destructive Testing (NDT) method used in order to find the defects in a structure. Ultrasonic technology refers to the use of ultrasonic waves in order to detect any anomalies in a structure or its functions basically cracks that can cause any type of leakage in different aircraft systems including the bleed system.

Ultrasonic waves are generally high-frequency sound waves which have a frequency range between 0.5 and 15 MHZ (for ultrasonic NDT testing). Its main applications include finding hidden cracks, different other flaws, leakage etc like abnormalities as well as to figure out dimensional measurements, material characteristics etc.

Ultrasound for crack detection in Bleed system components

Ultrasonic waves are emitted from a transducer into an object (ducts, valves, etc) and the returning waves are analyzed. If an impurity or a crack is present, the sound will bounce off of them and be seen in the returned signal. In order to create ultrasonic waves, a transducer contains a thin disk made of a crystalline material with piezoelectric properties, such as quartz.

When electricity is applied to piezoelectric materials, they begin to vibrate, using the electrical energy to create movement. Remember that waves travel in every direction from the source. To keep the waves from going backward into the transducer and interfering with its reception of returning waves, an absorptive material is layered behind the crystal. Thus, the ultrasound waves only travel outward.

ultrasonic-test-unit

One type of ultrasonic testing places the transducer in contact with the test object. If the transducer is placed flat on a surface to locate defects, the waves will go straight into the material, bounce off a flat back wall and return straight to the transducer.

Sound waves propagate into an object being tested and reflected waves return from discontinuities along the sonic path. Some of the energy will be absorbed by the material, but some of it will return to the transducer. There are many devices used to carry out ultrasonic testing in research laboratories. An example of such a device is the Krautkramer USM33 which is shown in the figure below.

krautkramer-usm-33

Ultrasonic measurements can be used to determine the thickness of materials and determine the location of a discontinuity within a part or structure by accurately measuring the time required for an ultrasonic pulse to travel through the material and reflect from the back surface or the discontinuity.

When the mechanical sound energy comes back to the transducer, it is converted into electrical energy. Just as the piezoelectric crystal converted electrical energy into sound energy, it can also do the reverse. The mechanical vibrations in the material coupled to the piezoelectric crystal which, in turn, generates electrical current.

In case of a defect, it will reflect energy sooner also. Another peak would then appear from the defect. Since it reflected energy sooner than the back wall, the defect’s energy would be received sooner. This causes the defect peak to appear before the backwall peak. Since some of the energy is absorbed and reflected by the defect, less will reach the backwall.

Thus the peak of the backwall will be lower than had there been no defect interrupting the sound wave. When the wave returns to the transducer, some of its energy bounces back into the test object and heads towards the back wall again.

This second reflection will produce peaks similar to the first set of backwall peaks. Some of the energy, however, has been lost, so the height of all the peaks will be lower. These reflections, called multiples, will continue until all the sound energy has been absorbed or lost through transmission across the interfaces.

Detecting leaks by listening to the ultrasound they produce

Leaks in the different part of the system themselves emit ultrasounds. Compared with the diffuse emission of sounds, ultrasounds spread in a concentrated fashion in one direction. They can be compared with a beam of light whose intensity decreases depending on the distance. Ultrasounds are generated naturally by fluid turbulence phenomena caused by pneumatic or hydraulic problems (leaks) or by friction phenomena caused by mechanical problems.

air-leakage

Electrical problems, such as arcs, corona effects, etc. also generate ultrasounds. In the event of a leak from a compressed air system, the air friction that escapes generates ultrasounds on the sides of the perforation. And it does this whatever the size of the leak, its flow rate and the dimension of the hole, however, small it is.

Different devices are available today; for example, The SDT 170 ultrasound detector, which detects ultrasound signals, converts them into audible frequencies and amplifies them. The aim is to transpose the signal received into an interpretable audible signal using heterodyne technology. This solution extends human hearing capacity beyond the audible range into the ultrasound band.

basic-working-principle-of-sdt170-ultrasound-detector

It must be noted that the detector’s central frequency band can be adjusted to a specific frequency between 15.1 and 190.7 kHz,; the default frequency being 38.4 kHz.

Conclusion

It has been realized that the Optimization of the maintenance procedure is very important for reduction of failure rate of bleed system, the airline flight delay rate, and the AOG (Aircraft on Ground) time in china eastern airline. The following is the conclusion of the measures for dealing with engine bleed fault.

(1) The measures taken in line maintenance:

  • Improvement in dispatch procedure
  • Strengthen the monitoring of engine bleed status
  • Perfect the communication with the crew

(2) The measures further taken in line maintenance:

  • Introduce the ACMS (Aircraft Condition Monitoring System)Increased interaction with Material supply department
  • Increased interaction with Material supply department Use of ultrasonic technology as NDT
  • Use of ultrasonic technology as NDT

All the measures taken gave good effect, which can be shown in the below:

operation-interruption-caused-by-engine-bleed-problem

As to flight abnormal data from the reliability system of the engineering and technology Company of China Eastern Airlines, this article carried out the collections, statistics, and analyses. All data withdrawn were all from the flight delays at the company’s stations all over the world, which were caused by engine bleed reasons, the same time, the number of china eastern’ s A320 fleet is given in the above graph.

The data between 2002 and 2007 when no optimization work was done are prior to the data from 2008 when optimization work was being carried out. Although other reasons like shortage of money or the flight plan of the A320 fleet, optimization work has played an important role.

From 2002 to 2008, the aircraft numbers serviced by the engineering and technology Company of China Eastern Airlines has gone through a big change, and about 8 planes were added every year during this period. In the meantime, flight delays caused by engine bleed problem were increased.

In 2007, five more aircrafts were added and thus the flight delays at stations were higher, flight delays caused by engine bleed problem had a 33% rise. Soon after a year, because of optimization work, flight delays caused by engine bleed problem happened in the year 2008 was 10% lower than the year 2007 even when the A320 fleet had a 25% growth .Considering the change of aircraft number overall, optimization work could reduce the flight delay times effectively.

operation-interruptions-by-engine-bleed-problem-in-every-1000-landings

The above graph shows the operation interruptions by engine bleed problems in 2008 and before 2008, the horizontal axis shows the operation interruption types, including flight delays, flight cancellation, flight interruption and ground interruption. The vertical axis shows the number of operation interruption in 1000 landings.

In 2008, the average delay time was 10% lower than that before 2008. Thus optimization work obviously contributed to the reduction of flight delay time greatly.

Meantime other operation interruptions’ numbers in 1000 landings decreased obviously. The detailed number has been shown below: (the situation before 2008 used the average numbers in 2005, 2006 and 2007).

Operational-interruption-in-1000-landings-before-and-after-2008

In this article, we mainly talked about engine bleed overheat problems. Through improvement, the flight interruptions caused by engine bleed overheat is less, but other engine bleed problems such as HPV faults, PRV fault, bleed over pressure happens very often. The pneumatic system still contributes a lot to the company’s flight interruption.

The engineering and technology Company of China Eastern Airlines faces unprecedented challenges, engine bleed problem will still be the main problems for a long time in the future. Therefore, it is very important to reference the advanced experience from the foreign country and the help of aircraft manufacturer (airbus) to perfect the processes and enhance the management, engineering, and technology level of the engineering and technology Company of China Eastern Airlines.

The advanced management philosophy and approach, which always comes from practice, are more operable and effective than many other theories.

The daily work of a manager in line maintenance division not only includes the administration of production but also includes the innovation of the creative management approaches and procedure. The engineering and technology Company of China Eastern Airlines will develop rapidly with the efforts of all the staff.

The paper also discusses about basic principles of leak detection. Generally analyzing the presence of leaks in engine bleed system has created many problems in the past as well as is bound to create more in the coming years.

The improvement in detection of these leaks, may it be through cracks or misfittings should be discovered to prevent catastrophic events. The presence of different types of thermostats in the aircrafts nowadays has aided in detecting leakage during flight and report it to the pilot in charge of the flight.

Ultrasonic technology and its uses in detecting cracks on structures that may cause leakage or detecting present leaks in the system is also discussed briefly in this paper. Ultrasonic technology is one of the most modernized modes of NDT available nowadays to maintenance personals and thus can be used to aid in the process of leak detection.

Either by detecting cracks or reading the ultrasound emitted by leaks the problems in the system can be detected quicker or even small deformations can be found using ultrasound. Thus its extensive use in this field can help minimizing the consequences of leakages in a system by aiding in its quick and efficient detection.