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Development of Aircraft Maintenance Programme


1.0 Introduction.

The aircraft maintenance scheduling process is very detailed and encompasses the inputs of various departments of an airline. The maintenance programme needs to be efficient and cost effective. To establish a good maintenance programme there needs to be a liaison with the marketing, flight operations, engineering and finance departments so that the regulatory requirements of the airworthiness of the aircraft can be maintained.

The objective of this paper is to produce a cost effective and efficient maintenance programme for KalAir. This will be based on one aircraft type operating on the domestic route and another aircraft type operating on the regional/international routes. The study will cover

  1. A 10 year maintenance plan.
  2. A suitable type of maintenance programme.
  3. In-house or outsourcing decisions.
  4. Type of skills required and the number of staff

The aircraft chosen to operate the domestic route will be the ATR 72-500. The aircraft has the capability to use a propeller brake hence there is no need for an Auxiliary Power Unit (APU) when the aircraft is on ground. This will save weight on the aircraft and there will be less component maintenance costs and less spares will be required. The ATR 72 powered by the PW127F engines provides outstanding short field performance even on difficult hot and high airfields and this will be very useful for KalAir as most of its domestic destinations have short fields which are both hot and high.

The A318 aircraft is chosen for the regional/international routes because fewer aircraft is required in the first 5 years compared to the E190 and this would save KalAir some money with its upfront capital outlay. Also similar type of aircraft in the A320 family is used in the region, hence more maintenance options and expertise will be available and higher spares availability can be achieved through spares pooling.

2.0 Purpose of Maintenance

Maintenance is defined as ‘the action necessary to sustain or restore the integrity and performance of the airplane’ (Hessburg 2001). This will be achieved by carrying out the necessary inspections, repair, overhaul and the replacement of parts. Maintenance processes can be divided into three different categories namely hard time, on condition and condition monitoring. The hard time process requires the item to be removed and overhauled or discarded before exceeding a set time interval. This time interval can be based on calendar time, flight hours, flight cycles or at check intervals. The on condition process is where the item will be checked and tested periodically to see whether it meets the test standards and deterioration limits before deciding to replace the item. The condition monitoring process can either be a failure based or a predictive maintenance process if there is a trend analysis of the failure rates recorded. Generally condition monitoring components are usually operated until failure occurs and replaced as an unscheduled maintenance item until enough operator and industry experience is built.

Maintenance is carried out on aircraft to ensure the aircraft can operate safely at all times. Maintenance is in place to ensure there is aircraft availability at all times to keep the fleet in service. If an aircraft is taken out of service the whole flight schedule will be disrupted and passengers need to be put on alternate carriers or be provided with accommodation to cope with the delay. The airline has to maximise the value of the aircraft by keeping the airframe, engine and components in good working condition by carrying out effective maintenance.

Provision has to be made for chance failures like tyre bursts, hard landings and also for deterioration due to the environment and age which might cause corrosion problems, fatigue failure and wear and tear.

2.1 Types of maintenance checks

Pre-flight checks are usually done before the first flight of the day and transit checks are carried out when the aircraft is on ground at its destination before the next take-off. These are cursory inspections of the aircraft to look for obvious damage, fluid leaks, and loose panels and to also ensure that oil levels are correct.

The letter checks start of with the A check where it involves the opening of some access panels to conduct checks and servicing. Some special equipment will be required to carry out some of the checks like engine boroscope inspections.

The C check is a detailed inspection of individual systems and components for functionality and serviceability like flight controls and engine inspections. In this phase of check extensive inspections will be carried out to check for fatigue failure and corrosion. As this check requires a hangar visit for about five to fifteen days this opportunity will be used to clear deferred defects and carry out the embodiment of service bulletins and airworthiness directives.

The D check is an extensive structural check of the aircraft where both visual and non destructive test inspections are carried out to check for deformation, corrosion and cracking. As structural checks require a lot of disassembly to gain access for inspection it is very labour intensive and takes about twenty to thirty days on average. Table 1 is an example of the block maintenance and intervals for the different checks that will be used for the A318 aircraft in KalAir’s fleet.

Type Interval Downtime Main Purpose
Daily 36h 2 to 3h General visual inspection (GVI)
A Check 600 FH Overnight Servicing, Engine boroscope, GVI
C Check 18 Mths 3 to 5 days Operational Check
1C/3C 2 days
2C 3 days
4C Check 5/6 Yrs 14 to 21 days Structural Inspection (Corrosion)
4C & 5Y HMV 21 days
5Y only 14 days
8C Check 10/12 Yrs 24 to 51 days Structural Inspection (Corrosion+ fatigue)

Table 1: A318 Block Maintenance

Source: ATE Lecture notes 2008

Table 2 is an example of the block maintenance and intervals for the different checks that will be used for the ATR 72 aircraft in KalAir’s fleet.

Type Interval Downtime Main Purpose
Daily 24h 2 to 3h Checks and zonal visual inspections
A Check 500 FH Overnight Zonal visual inspections, lubrication, servicing and operational checks
C Check 4000 FH 3 to 5 days Operational and functional checks on aircraft and powerplant systems
Propeller Inspection 8000 FH 3 to 5 days

(part of C check)

Based on, on wing engine monitoring
Structural Inspections & 4C Check *2/4/8 Yrs 13 to 27 days Structural Inspection (Corrosion+ fatigue)

* based on estimated 5.5FH daily utilisation

Table 2: ATR 72 Block Maintenance

Source: Adapted from ATE Lecture notes 2008

2.2 Maintenance Systems

To carry out the maintenance on the KalAir fleet of aircraft there are two kinds of maintenance systems available. One is the pyramidal system where a set of jobs is planned for a particular interval and another set of jobs is added at the next multiple of this basic interval. The benefits of this system are that a fixed set of tasks are allocated and it can be completed within the time frame without much variation. However in this system the aircraft will be out of service for a long period of time and the workload for the maintenance staff will be subjected to cyclical variations leaving them idle at times till the next aircraft comes for maintenance. The other option available is a progressive or equalised maintenance system where large checks are broken down into smaller checks of equal size and carried out more frequently. The checks can be small enough to be carried out overnight and this will allow the workload for the maintenance personnel to be more constant. Therefore to meet KalAir’s tight flight schedule and to maximise the workforce an equalised maintenance programme will be adopted.

3.0 In-house or outsourcing decisions

The decision to conduct the maintenance in-house or to outsource the maintenance for KalAir that operates a fleet of three A318 aircraft in the first five years and four A318 aircraft in the next five years together with four ATR 72 aircraft for the whole ten year period is not an easy one. KalAir has not previous experience of operating either of these aircraft types and neither have they operated aircraft that were produced by these aircraft manufacturers. Moreover it would not make economic sense to acquire all the necessary tooling and equipment to maintain three A318 aircraft for the first five years. The capital investment to carry out heavy maintenance cannot be justified but, KalAir needs to ensure that it has adequate capability to handle line maintenance. As KalAir is operating in a region that is in close proximity to the Gulf and Indian sub-continent outsourcing the maintenance for the A318 aircraft would be the best solution. The heavy maintenance, engine overhaul and component repair can be out sourced to maintenance organisations in India as there are about five airlines operating a total of about hundred A320 family aircraft (ATI). An alternative option of sending the A318 aircraft for maintenance in the Gulf is also available but the maintenance costs might not be as competitive as in India and the number of spares available in the Gulf region might be lower considering that less A320 family aircraft operate in that region.

KalAir has some experience operating turboprop aircraft like the Antonov An 24 and Fokker F-27 and this experience can be credited towards carrying out maintenance on the ATR 72 aircraft. The systems architecture on turboprop aircraft that are western built and Russian built do not vary very much because of the use of more mechanical systems. Unlike western built modern jet aircraft which have a large amount of avionics introduced. Hence consideration can be made to carry out a larger portion of maintenance of the ATR 72 aircraft in-house. Also the hangar space required would not be very much and the equipment acquired to maintain the ATR 72 would not be a high investment compared to acquiring maintenance equipment for the A318 aircraft.

Also the availability of the ATR 72 aircraft is very important as the airfields in the domestic sector are not very well developed and do not have navigation aids. Hence having in-house maintenance capability is quite important. KalAir can establish an in-house maintenance program together with a packaged deal where provisions for engine off wing maintenance, component and line replaceable units can be outsourced to the maintenance organisation in exchange for replacement parts thereby ensuring that the ATR 72 aircraft can carry on with its normal flying schedule as soon as possible with minimal down time.

4.0 Maintenance & Engineering Organisation Structure

The maintenance and engineering organisation structure of KalAir will be established according to the following areas covering these job responsibilities. The assumption here is based on the previous operating experience of KalAir and that there is already some maintenance capability with adequate hangar space.

Technical Services

Engineering, publications, planning and training (for both A318 & ATR 72 fleet)

Aircraft Maintenance

  • Hangar
  • Line (for both A318 & ATR 72 fleet)
  • Maintenance Control Centre (for both A318 & ATR 72 fleet)

Shop Maintenance

Structures, mechanical and instrument (for ATR 72 fleet)


  • Purchasing and receiving
  • Stores and inventory


  • Quality Assurance & Quality control
  • Safety & reliability

The organisation has to be structured this way so as to ensure that it has maximum capability of handling the ATR 72 maintenance and the ability to handle an adequate amount of maintenance on the A318 so that it would not jeopardise the flight schedule. To ensure this KalAir will need to hold a large inventory of spares. This list of spares to be held will be based on the Minimum Equipment List of both the A318 and ATR 72 aircraft and also ‘AOG’ spares so that it would not render these aircraft on ground (AOG). Spare engines for both aircraft need to be kept by KalAir so that a Quick Engine Change (QEC) can be carried out and the aircraft replaced with a new engine. The engine that is removed can then be sent to the engine repair facility for repairs to be carried out.

The materials planning needs to be done well in advance and the availability of spares and tooling needs to be ensured before the aircraft goes into the hangar for maintenance.

4.1 Manpower management

As two aircraft types are operated by KalAir engineers will be type rated on both aircraft. Provisions will have to be made such that maintenance staff are trained to Part 66 standards with certification for Category A, B1, B2 and C for both the ATR 72 and A318 aircraft. KalAir needs to ensure that there is at least one staff with a Category C rating for the A318 and ATR 72 aircraft so that he can sign the certificate of release to service for these aircraft after the necessary maintenance. Though heavy maintenance of the A318 will not be carried out in-house the certification of staff at Category C level might be required for two purposes. One reason is if an AOG team is dispatched to recover an aircraft for a collapsed landing gear for example and the other is for ensuring the continuing airworthiness management of the aircraft during the airworthiness review.

The line maintenance team will comprise of two groups of staff on duty one the ATR 72 team and the other the A318 team during the day. Each team will have three to four staff and one of whom will act as the team leader. KalAir will operate a three shift pattern operating twenty four hours. Table 3 shows the shift pattern and the manpower allocation. There is an overlap in the shifts so as to allow a proper handing and taking over between each shift.

Shift Time A318 staff ATR staff Manpower
1 0630-1530 4 8 12
2 1500-2330 4 6 10
3 2300-0700 6 6 12

Table 3: Shift pattern and manpower

Though maintenance staff will be cross trained on both aircraft types to meet manpower requirements for unexpected incidents a clear distinction between the two teams will be maintained during the normal operations. A higher provision for ATR staff is made for shift 1 because of the increased activity of aircraft at 1000hras and 1400hrs. A consistent number of staff will be maintained for the night shift as the work packages will not vary considerably, if it does the staff strength can be increased or overtime can be introduced.

At the maintenance control centre two staff will be present during shift 1 and 2 as that is when all the flying activity takes place and the flight schedule needs to be maintained and the unexpected maintenance will be scheduled for the night shift. The line stations will be manned by Part 66 certified Category A staff to certify the aircraft after transit checks.

5.0 KalAir Maintenance Programme

The KalAir flight schedule for an A318 and ATR 72 aircraft combination for year 1 and year 5 onwards is attached in Appendix 1. Based on this flight schedule the flight hours and the flight cycles can be calculated for both the fleets and is shown in Table 4.

Year 1 to 4 Year 5 to 10
Aircraft Daily FH Daily Cycles Daily FH Daily Cycles
A318 1 15 3 15 3
A318 2 15 3 15 3
A318 3 11.5 2 11.5 2
[A318 4] NA NA 8 2
A318 Average 14 3 12.5 3
ATR7 1 14.3 4 14.3 4
ATR7 2 14 5 14 5
ATR7 3 9.5 3 9.5 3
ATR7 4 3 1 10 3
ATR7 Average 10.5 4 12 4

Table 4: Aircraft cycles and flight hours

The scheduling of the aircraft will be planned according to the average flight hours and cycles. Since the flight hours and cycles over time have been obtained, the calendar based and usage based inspections can be scheduled. The hard time maintenance intervals will be designed to be incorporated in the scheduled checks to allow for less down time. The aircraft that has the highest daily flight hours in each fleet will be the first in the sequence when the maintenance is planned. The maintenance schedule for the A318 aircraft will be based on the data available in Table 1 and the maintenance schedule for the ATR 72 will be based on the data in Table 2.

The calculations for the A318 aircraft give about 7 A checks in a year. This can be scheduled such that an A check together with a split C check is done at a one and a half month interval carried out throughout the night over six days. Hence the C checks will be similar to a single task oriented maintenance concept except that it would be carried out over a longer time period with less aircraft visits. The 4C check and the 8C check come together with structural checks and heavy maintenance. For year 5 when the new A318 aircraft arrives it can be used as a replacement aircraft over the period of time when the existing A318 aircraft go through their heavy maintenance. A request for an earlier delivery for the A318 aircraft can be made so that the heavy maintenance can be carried out earlier. This will cause a delay in implementing the new flight schedule but it will definitely save KalAir the costs of leasing an aircraft in the interim and it will not disrupt the existing flight schedule. The 8C check can be scheduled anytime after 10 years but as this will be a heavy maintenance combined with a C check it will take about 21 days. This will leave no alternative for KalAir but to schedule this heavy maintenance back to back for all the three older A318 aircraft after the newest A318 aircraft that came in year 5 completes its 4C check and heavy maintenance. For example A318 1 will undergo maintenance first because it has the highest utilisation, followed by A318 2 and so on from March to May during the period of heavy maintenance.

The 4C checks will commence after receiving the fourth A318 aircraft if possible. The other aircraft will then be sent to a third party maintenance organisation for heavy maintenance. This 4C checks for the A318 will be scheduled from March to May of Year 5. This is to allow for stability of the flight schedule and the balance of work load for the maintenance staff as the ATR 72 fleet will return from their heavy maintenance beginning in October in Year 4 till January in Year 5. This is to give an allowance because it has been seen from past experience that when aircraft return from heavy maintenance there is an increased occurrence of maintenance snags.

In Year 10 the 8C checks require restoration of main gear and can commence from March to May of Year 10 to synchronise all A318 heavy maintenance during this period. As this can be planned ahead provisions for a leased A318 can be made without being affected by the peak summer periods. If an A318 is unavailable KalAir can wet lease another type of aircraft that has similar capacity and operating capabilities.

For the ATR 72 as the maintenance is planned to be carried out in-house. Based on a 500FH interval for an A check it works out to about one check in one and a half months. A C check will be at about a 15 month interval based on the flight hours of the flying schedule. It would not be productive for the ATR maintenance staff to remain idle between the inspection intervals hence the C1 and C3 checks in the first five years will be equalised before the first heavy maintenance in Year 4 which will allow it to be carried out in a shorter time. The C check intervals will be shortened such that each ATR 72 aircraft will undergo a check in a year. The maintenance will be scheduled such that the ATR7 1 has the highest utilisation will undergo maintenance first followed by ATR7 2 and so on.

The heavy C checks for the ATR 72s will commence every year in October and last till January the following year. In the first five years it is possible to make a minor change to the flight schedule to free one aircraft so that the other aircraft can spend some time in the hangar for the heavy checks. Moreover this will last during the October to January time frame which is long enough for passengers not to be affected by the minor change in the flight schedule. With reference to the flight schedule in Appendix 1 the third ATR72, AT7 3 can operate to SUZ instead of TOZ at 1400hrs and operate another flight to TOZ departing for TOZ at 1800hrs as TOZ has capability to handle aircraft at night. This amendment to the flight schedule can be done during the October to January time period.

From Year 6 onwards it would not be possible to use a block concept for the ATR 72 C checks because it would not be possible to take an aircraft out of the flight schedule. It would be possible to use a single task oriented maintenance concept for the C checks but the aircraft will still have to be out of service during the periods of heavy maintenance where structural inspections need to be carried out. For example the 8C check comprises structural inspections, landing gear replacements and propeller inspections which are huge job packages to be completed over a period of night stops. Hence it would be better to ground the aircraft to carry out this heavy maintenance and the necessary modifications and embodiment of Airworthiness Directives. During this period from October to January another ATR 72 aircraft can be leased to operate the schedule. It is also possible to operate an ATR 42 aircraft if an ATR 72 is unavailable because of the spare parts commonality and cross crew qualification.

The assumptions made in creating the maintenance schedule for the A318 and ATR 72 fleet of aircraft are.

  • Aircraft maintenance is performed during the night at KKV
  • The C checks for the ATR 72 from Year 1 to 4 will be performed during the day and night.
  • The maintenance base is located within the vicinity of KKV airport.
  • The heavy maintenance for the A318 is outsourced.
  • The experienced gained on the first aircraft for the checks will allow maintenance staff to complete the same type of work on the other aircraft in a shorter time frame.
  • The scheduled overhaul of engines and components with will be planned to synchronise with the scheduled checks.

5.1 Maintenance Costs

The maintenance costs for the A318 and ATR 72 aircrafts are calculated and attached in Appendix 2A to 2D. The average flight hours and cycles from Table 3 are used to calculate the maintenance costs based on these utilisation rates. The assumptions made here are that the average distance travelled by the A318 aircraft is 1000nm and 200nm for the ATR 72, both the aircraft will depreciate to 30% of its original value after 12years and the cost of investment will include spares which amount to about 19% of the aircraft price.

The annual maintenance costs for the A318 aircraft is about two million a year. From Year 5 the maintenance costs per aircraft is slightly less because an extra A318 has been acquired and the flight hours per aircraft are slightly lower giving rise to a lower cost per aircraft trip. The maintenance costs for the ATR 72 aircraft is about one million a year and it works out to about one thousand dollars per aircraft trip. The maintenance costs from Year 5 onwards has shown an increase because more flights are undertaken with the existing fleet of ATR 72 aircraft giving rise to a fifty cents increase per aircraft mile.

6.0 Issues to overcome

There is a strong need to lease an aircraft for both the A318 and ATR 72 fleet when these aircraft undergo heavy maintenance. This is due to the high utilisation of the aircrafts in the normal flight schedule. There is a need to have an ‘AOG’ team and necessary spares inventory stationed at KKV in the event that an aircraft becomes stranded at one of the overseas stations. Supplementary work force can be employed from within the region or the Indian sub continent when the ATR 72s undergo heavy maintenance or the situation warrants it. If difficulties arise in carrying out the work in-house KalAir should establish strong relationships with maintenance organisations in India to outsource work as both the aircraft types operate in India and manpower will not be an issue.

7.0 Conclusion

Due to its unique location and surroundings KalAir has to build up substantial maintenance capability. It can outsource maintenance work but has to hold sufficient inventory of spares to keep its fleet flying. KalAir cannot afford to have an ‘AOG’ and keep the aircraft on ground due to the unavailability of spares because of the very tight flight schedule it is operating. As all domestic traffic needs to be carried it also cannot afford to cancel flights and cannot remove aircraft from service to carry out maintenance. As the lessor requires that all aircraft return to base and no night flights can be conducted it gives a good opportunity to schedule all maintenance at night and clear all faults before the first flight the next day. Due to the constraints that KalAir faces it would be more prudent to lease aircrafts in the short term period when the A318 and ATR 72 aircraft undergo heavy maintenance to meet the flight schedule.


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Hessburg, Jack. Air carrier MRO handbook. New York : McGraw-Hill, 2001.

Kinnison, Harry A. Aviation maintenance management. New York: McGraw-Hill, 2004.

S.Yan et al. Airline short-term maintenance manpower supply planning. Transportation Research Part A (38), 2004

1.0 Introduction

This paper will look into the regulatory requirements laid down by the European Aviation Safety Agency (EASA) for Continuing Airworthiness Management Organisations and then the procedures that need to be taken for a commercial airline based in the EU to meet these requirements.

The European Aviation Safety Agency (EASA) was created on 28th September 2003 and endowed with the regulatory and executive tasks in civil aviation safety. EASA has jurisdiction over new aircraft type certificates, design related airworthiness approvals for aircraft, engines and parts. EASA has also developed regulations for air operations, flight crew licensing and has also established common technical requirements and administrative procedures for ensuring the continuing airworthiness of aircraft.

European Commission Regulation 1702/2003 of 24th September 2003 is on the airworthiness and environmental certification of aircraft and related products, parts and appliances, as well as for the certification of design and production organisations. European Commission Regulation 2042/2003 of 20th November 2003 is on the continuing airworthiness of aircraft and aeronautical products, parts and appliances, and on the approval of organisations and personnel involved in these tasks.

Annex I of EC 2042/2003 is on Part M Continuing Airworthiness, which lays down the measures to be taken to ensure that maintenance and airworthiness is maintained. It also specifies the conditions to be met by the persons and organisations involved in continuing airworthiness management (De Florio 2006). Annex II of EC 2042/2003 is on Part 145 Maintenance Organisation Approval, this establishes the requirements to be met by a maintenance organisation to qualify for the issue or continuation of an approval for the maintenance of aircraft and components (De Florio 2006). Annex III of EC 2042/2003 is on Part 66 Certifying Staff, this establ

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