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Business Aircraft MRO: What is Aircraft Maintenance?

Every aircraft, regardless of the mission or use, periodically faces Maintenance, Repair and Overhaul (MRO). It’s a common enough industry term not to warrant much thought – but what exactly does each element cover? Dave Higdon explores business aircraft ‘Maintenance’.

Dave Higdon   |   1st February 2020
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Dave Higdon Dave Higdon

Dave Higdon is a highly respected, NBAA Gold Wing award-winning aviation journalist who has...
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Business aircraft maintenance is an unavoidable part of a business aircraft’s life. Regularly scheduled aircraft maintenance stands as a necessary element of continued airworthiness of any aircraft.
 
Fortunately, manufacturers of modern business jets and turboprops all provide guidance and instructions regarding periodic and preventive maintenance. Every aircraft comes from its manufacturer with a specific set of maintenance instructions, and a timeline for their observance. These instructions detail when certain inspections and work packages must be undertaken.
 
The OEM develops those instructions through in-house groups. Typically, these include a Maintenance Review Board at the aircraft manufacturer, and, in the US, the Federal Aviation Administration (FAA).
 
Other national or regional airworthiness authorities play the same role for aircraft built within their jurisdictions or imported there under national airworthiness approvals.
 
Why is Aircraft Maintenance Important?

Maintenance is important to uphold an aircraft’s highest safety standards. It also optimizes the comfort of its passengers. Moreover, a well maintained business aircraft commands a better resale price than a poorly maintained one.
 
Aircraft can quickly become non-airworthy (and legally grounded) if maintenance rules are neglected, or an inspection is skipped, or a mandated airworthiness directive is missed.
 
In such situations, the operator or maintenance provider would need to apply to the regulatory authority and obtain what's called a ‘ferry permit’ to allow the aircraft to be flown from its current location to a site where the required maintenance work can be performed.
 
The rules and standards for aircraft maintenance by the OEM and governing authority help ensure maintenance standards are uniformly implemented. Operators are obliged to observe the maintenance requirements concomitant with the type of operation they fly.
 
An individual or company operating their aircraft solely for their own benefits (i.e. not for hire and not for profit) falls under Part 91 of the Federal Air Regulations (FARs).
 
A Part 91 operator must follow regulations defined by the FAA for operations of small non-commercial aircraft within the US and other nations which choose to use FAA rules as their own standard. Part 91 regulations set conditions in which the aircraft may fly (e.g. weather conditions).
 
Aircraft Mechanic Stands in Front of Cessna Citation Private Jet
 
For commercial airlines and charter operators the rules are either Part 121 (scheduled carriers with nine or more seats), or Part 135, for on-demand charter and unscheduled commercial, for-hire operations.
 
What are the basic differences in maintenance rules for each?
 
  • Private aircraft operations (Part 91) face some basic maintenance rules and must undergo an annual inspection within a 12-month period since the last cycle.
  • Commercial operators (Part 135 and 121) must subject their aircraft to 100-hour inspections.
What’s the Difference between Aircraft Maintenance Inspections?
 
The difference between an annual inspection and a 100-hour inspection essentially comes down to the time period, since the inspections themselves are identical. There are, however, differences in who can perform these inspections.
 
An annual inspection can be performed only by an Airframe & Powerplant (A&P) mechanic who holds an Inspection Authorization (IA). By comparison, a 100-hour inspection can be performed by any A&P, with or without an IA.
 
And there are other so-called ‘phase inspections’ set by the manufacturer; period checks (labeled ‘A-Check’ through ‘D-Check’). An A-Check is essentially performed with every crew change or before every flight, when the aircraft pilot or co-pilot performs the basic walkaround pre-flight inspection.
 
Each phase is progressively more detailed, with the C- and D-Checks being lengthy, involved procedures requiring a deeper examination of the aircraft and its systems and condition.
 
D-Checks are usually the longest and most expensive inspections, requiring a detailed and complete review of every part of the airframe.
 
What Areas of Maintenance are Usual for an Aircraft?

Beyond the airframe, the aircraft’s engines and avionics also face periodic, repetitive and preventive maintenance. Modern turbine engines enjoy lengthy times between required inspections and overhauls (known as Time Between Overhaul).
 
The interim inspections and overhauls are normally well defined by the powerplant manufacturers. The interim (or ‘hot section’ inspection) looks at parts subject to the extreme heat and pressures of engine operations, i.e. the compressor sections, combustion chambers or burner cans; and the turbine wheels driven by hot exhaust gases to power the compressor section and accessories.
 
As for the avionics, the main point of their maintenance is to ensure that navigators and communications radios function properly, and that software used by the avionics is updated in accordance with the device’s function.
 
For today's modern software-driven avionics, that means routine updates of navigation databases and other software changes periodically required by the manufacturer.
 
Aircraft Mechanics Work on Helicopter Rotor
 
Who is Responsible for Maintenance Compliance of an Aircraft?

Though the various maintenance items may require a licensed A&P to perform the work, the responsibility for ensuring completion of that work belongs to the operator or owner.
 
The FAA looks at manufacturers' recommended TBO differently for private, Part 91 operators than it does for commercial operators. Under Part 91, TBO is a recommendation – a suggestion with factory backing. For commercial operators, a TBO is a mandate which must be met for continued use of the aircraft for profit-making flight.
 
How Much Does Aircraft Maintenance Cost?

To make aircraft maintenance costs predictable, enrolment of the aircraft in a per-hour maintenance program is advisable. These programs levy a per-hour fee that is banked against the inevitability of maintenance needs. They are proven to help operators budget their maintenance costs more effectively.
 
Since business aircraft type and use varies widely, an estimate for standard costs is difficult to confine to this article. Many variables exist that will cause the average cost to change, including aircraft size and age.
 
Phase inspections naturally cost more than 100-hour and annual inspections, while engine overhauls cost more than hot-section inspections do.
 
Closing Thought…

Many systems and businesses exist to help operators follow and adhere to the FARs covering aircraft maintenance, but the best hedge against making a mistake is a qualified mechanic or technician who is experienced in your aircraft make and model.
 
The best maintenance safety system available is that devoted A&P who knows everything about the operation.
 
 
Read the AvBuyer Maintenance Special Edition

Read more about: Aircraft Maintenance | Business Jet Maintenance | MRO

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