ARTICLES RESEARCH & TECHNOLOGY

Bleed System Failure Analysis of Airbus A320

bleed-air-turbo-engine

CHAPTER 1


Introduction

Airbus A320 Family

The Airbus A319, A320, and A321 are the world’s most profitable single-aisle aircraft. Their advanced technology and maximum operational flexibility has resulted in lesser fuel burn, reduced maintenance costs, lower direct operating costs and higher residual values than other competing aircrafts.

The A320 Family’s excellent economics results from numerous factors that include advanced aerodynamics in the wing design, the extensive use of lighter-weight composite materials, the use of fly-by-wire controls that reduce mechanical complexity and the incorporation of centralized monitoring for avionics and aircraft systems.

Wide under-floor cargo holds allow the A320 Family to carry more weight with standard LD3 containers and in bulk and thus adding to airlines’ profit with more revenue on each flight.

Commonality within the Airbus fly-by-wire product line has also contributed to the economy of the A320 Family. The ability to use a single pool of pilots, cabin crew and maintenance personnel for the A318, A319, A320 and A321 has saved money and gives airlines maximum flexibility in scheduling and planning.

In addition to this, the A320 Family’s similarities with the fly-by-wire A330, A340 and A380 enable operators to benefit from similarity with the Airbus aircraft product line up to seating capacities of 550-plus passengers.

Airbus A320 Family has benefitted from lower maintenance costs following an increase in the intervals between scheduled maintenance tasks, which have been approved by the European Aviation Safety Agency (EASA), the US Federal Aviation Administration (FAA) and Transport Canada.

All airliners undergo maintenance at regular intervals – from simple daily checks of items such as engine oil level, up to heavy maintenance checks in which much of the aircraft structure is disassembled and then visually checked. The intervals at which such maintenance must be carried out are specified by the aircraft manufacturer and are typically based on calendar time, flights, flight hours or some combination of these.

The latest approvals for the A320 Family means that the time between A-check has been increased from 500 hours to 600 hours and that C-check has gone from every 15 months to every 20 months or 6,000 flight hours.

In addition, the 5-year heavy maintenance check interval has been extended to 6 years and 10-year heavy maintenance check to 12 years. These improvements are the result of some two years of work involving the airworthiness authorities, airlines flying Airbus A320 Family aircraft, engine-manufacturers, major suppliers, and Airbus.

As part of this improvement, the maintenance checks are now more flexibly based on flight hours and flights, giving airlines greater flexibility in planning and carrying out various maintenance tasks. In a further measure aimed at simplifying and reducing maintenance costs, Airbus has introduced standard maintenance-packages representing three common types of aircraft yearly utilization.

This allows airlines to choose a ready-made solution that is close to their yearly utilizations which, for an A320 Family operator, typically range from about 1,800 to over 3,500 flight hours a year.

A320 in China Eastern Airlines

In 1998, the first A320 (Nationality Registration Number B-2203) was introduced. Through 10 years’ development, the fleet number had increased to nearly 100 which was about 40% the whole China Eastern fleet.

fleets-operated-by-pudong-line-maintenance-department

fleets-operated-by-pudong-line-maintenance-department

Pudong line maintenance department operates more than 70 aircrafts including Airbus 300-600, Airbus 330,Airbus 340,Airbus 320 series, MD-11, B747-400F. The Airbus A320 series accounts for 33% of all the fleet operated by Pudong line maintenance department.

Between 2007 and 2009, only the number of A320 and A330 have had a high increase rate, an average of about 8 A320 a year are added in the fleet operated by the Pudong line maintenance department, another 20 A320 were introduced in next 2 years.

The analysis of pneumatic problems in line maintenance

The A320 family is welcomed by more and more customers for its highest production rate and low maintenance cost. Now it takes a big part in the short- to medium-range commercial aircraft market in china, but the problems in Pneumatic system trouble different sectors.

Problems such as overheat of engine bleed air and bleed air system leakage(which are what we are mainly talking about in this paper. These problems cause flight delay, returning and emergency landing. The graph below is about the abnormal flight(including flight delay, returning and emergency landing.)that occurred in A320 fleet in2006, 2007 and 2008.

abnormal-flight-number-caused-by-the-top-four-ata-chapter-in-recent-3-years

the-10-ata-chapters-which-cause-abnormal-flight-in-recent-3-years

In the two graphs above, we analyze the operational interruption in A320 fleet in 2006, 2007, and 2008 by ATA. We can see that the top four ATA chapters are: 70-80 engine problem (not including engine bleed problem), 32 landing gear, 36 pneumatic (besides engine bleed problem) and 27 (flight control). 10.6% of operational interruptions were caused by pneumatic problems. The pneumatic problem is a source of a headache not just for A320 fleet, but also for A330 and A340.

Its troubleshooting is always time-consuming and causes operational interruption. The airbus has kept on update the system parts as well as introduced new troubleshooting procedure but the fault in this system has been troubling the maintenance department a great deal. So in this article, the fault of the pneumatic system and improvement in maintenance work is discussed.

The seasonal regularity in pneumatic problems have been shown in the graph below.

operational-interruptions-in-A320-fleet-by-month

According to the analysis from the Operational interruption rate caused by Engine bleed fault between 2006 and 2008 it is observed that the fault rate changes with the seasons. It is seen that the Engine bleed fault happens frequently in summer, especially from Jun to Oct. From Jun to Oct, it is summer in China. One of the reasons the Engine bleed fault happens is that high temperature can descend the performance of TCT, another being the fact that wet air mixed with dust can jam the filter of TCT.

From Jun to Oct, it is summer in China. One of the reasons the Engine bleed fault happens is that high temperature can descend the performance of TCT, another being the fact that wet air mixed with dust can jam the filter of TCT.

To understand why the engine fault rate changes with seasons, the climate of Shanghai will be introduced here: Standing by the East China Sea, Shanghai enjoys a comfortable climate. Shanghai has a subtropical maritime monsoon climate, with four distinct seasons.

The average annual precipitation in Shanghai is over 1,000mm, especially the time of the “Plum Flower Rain” period (frequent drizzle) starting from mid-June to July. During summer, the rainstorm and gale are frequent. Generally, Shanghai in summer is humid and hot, besides July and August are likely to be the hottest and has an average temperature of 27.6 degrees centigrade.

As to the seasonal regularity of engine bleed fault, special solutions have been put forward in line maintenance afterward.

General information about A320 pneumatic system

pneumatic-system-layouts

The pneumatic system gets compressed air from the pneumatic air sources and supplies the compressed air through ducts to other systems. The ducts are installed in the fuselage, the belly fairing, and the wings.

The aircraft engines, the APU or a ground air source can supply compressed air to the pneumatic system. The distribution system supplies the compressed air from the different sources to the user systems.

The aircraft engines are the primary source of compressed air in flight. The air is bled from the 5th (IP) or 9th stage (CFMI engines) of the engine High Pressure (HP) compressor. The engine bleed air is temperature and pressure controlled. The Auxiliary Power Unit (APU) is the primary source of compressed air on the ground.

The air is bled from the APU load-compressor module. APU can be used to supply bleed air to the user systems during flight. The APU can supply bleed air up to an altitude of 20000 ft. (6096 m). A ground air source is an alternative to the APU for the supply of compressed air on the ground. There is one High Pressure (HP) ground connector installed on the aircraft. It can be used to let the ground air source supply compressed air to the pneumatic system.

The pneumatic system feed the subsequent aircraft systems:

(1)the wing ice protection system
(2)the air conditioning system
(3)the engine starting system
(4)the hydraulic reservoir pressurizing system the
(5)pressurized water system
(6)the nacelle anti-ice valve (servo pressure)

As mentioned above, we know that there are three kinds of pneumatic resources.

As to flight abnormal data from the reliability system of the engineering and technology Company of China Eastern Airlines, most of the pneumatic problems concentrate on engine bleed, which take about 70.2%, APU (Auxiliary Power Unit) bleed take 23.2%, the ground air take only 6.6%. We can see engine bleed problems takes a big part.

Pneumatic-problems-by-different-sources

pneumatic-problems-by-different-sources_001

Next is the analysis of the engine pneumatic system in A320 family, only based on the deeply understanding the operation of engine bleed system, we can find solutions to engine bleed problems.

 

Read More: CHAPTER 2