Who Pays When a Maintenance Error Becomes a Multi-Million-Dollar Problem?

The safe operation of a commercial aircraft does not depend solely on decisions made by pilots in the cockpit. Thousands of components—from engines and landing gear to braking systems and avionics—must be inspected, maintained, repaired and replaced in accordance with highly detailed technical and regulatory requirements.

But what happens if a relatively small maintenance error causes an aircraft to remain grounded for several days?

More importantly, what happens if an incorrectly installed component fails during flight and contributes to a serious incident or accident?

Who bears legal responsibility?

The airline?

The aircraft owner?

The Continuing Airworthiness Management Organisation?

The Maintenance, Repair and Overhaul – MRO provider?

Or the certifying staff who signed the release to service?

These questions explain why aircraft maintenance agreements are fundamentally different from ordinary service contracts.

A few provisions dealing with warranty, limitation of liability, consequential loss and indemnification may ultimately determine which party bears millions of dollars in losses following a maintenance failure.

In Turkey, the legal framework must be considered particularly in light of the Continuing Airworthiness Regulation (SHY-CA), SHT-145 Approved Aircraft Maintenance Organisations Instruction, SHT-CAM and the Turkish Code of Obligations.

The Turkish Directorate General of Civil Aviation republished SHT-145 on 16 September 2025. The updated framework regulates the approval and activities of aircraft maintenance organisations under SHY-CA and reflects developments in the European continuous-airworthiness and EASA regulatory framework.

1. What Is an MRO?

MRO – Maintenance, Repair and Overhaul is the general term used for maintenance, repair and overhaul services performed on aircraft and aircraft components.

These activities may include:

• line maintenance,
• base maintenance,
• scheduled checks,
• heavy maintenance,
• engine maintenance and overhaul,
• landing gear overhaul,
• component repair,
• structural repair,
• cabin modification,
• avionics maintenance,
• non-destructive testing,
• defect rectification.

The Turkish civil aviation authority describes authorised maintenance organisations as entities performing servicing, inspection, maintenance, repair, modification and overhaul activities required to maintain aircraft in an airworthy condition throughout their operational life.

An MRO therefore provides much more than technical labour.

Its activities are directly connected to aviation safety.

2. Can Any Company Perform Aircraft Maintenance?

No.

Aircraft maintenance is a heavily regulated activity.

Organisations providing maintenance services for civil aircraft or aircraft components must operate within the appropriate regulatory approval framework.

Under the Turkish system, SHT-145 approved organisations are organisations authorised to provide maintenance services for civil aircraft and components.

It is therefore essential to identify:

• which aircraft types the organisation is approved for,
• which components it may maintain,
• what categories of work it may perform,
• at which approved facilities the work may be conducted.

The fact that a company describes itself commercially as an “MRO provider” does not mean that it may carry out unrestricted maintenance on every Airbus, Boeing, engine or component.

The contracted work must fall within the organisation’s approved scope of work.

3. What Is the Legal Nature of an Aircraft Maintenance Agreement?

An aircraft maintenance agreement should not automatically be characterised as one single type of contract under Turkish law.

Depending on the services involved, the agreement may contain elements of:

• a contract for work,
• service obligations,
• mandate-type obligations,
• sale or supply of components,
• storage and redelivery obligations.

Where an MRO undertakes to complete a defined maintenance task, rectify a defect or overhaul a component and return it in a specified technical condition, the obligation to achieve a defined result becomes particularly important.

For example:

“Engine No. X shall be overhauled and redelivered in accordance with the applicable maintenance data.”

This goes beyond merely undertaking to provide labour for a particular number of hours.

The MRO is expected to deliver a defined technical result.

Long-term line maintenance arrangements, however, may contain stronger continuing-service elements.

The legal characterisation matters when analysing defective performance, warranty rights, notice requirements and damages.

4. Why Is the Scope of Work So Important?

One of the first questions in any maintenance dispute is:

“What exactly did the MRO agree to do?”

For that reason, the Scope of Work is one of the most important parts of an Aircraft Maintenance Agreement.

It may identify:

• the applicable maintenance programme,
• work package,
• task cards,
• service bulletins,
• airworthiness directives,
• engine workscope,
• structural inspections,
• component replacements,
• modifications,
• testing requirements,
• certification requirements.

Before liability can be determined, the contractual scope of the MRO’s obligation must first be established.

Failure to inspect a system that was never included within the agreed scope is legally very different from incorrectly performing a critical inspection that the MRO expressly undertook to complete.

5. What Constitutes a Maintenance Error?

A maintenance error does not simply mean installing the wrong component.

Potential maintenance failures may include:

• use of an incorrect component,
• incorrect torque application,
• failure to perform a required inspection,
• deviation from an aircraft maintenance manual,
• incorrect wiring,
• improper installation,
• failure to detect a fatigue crack,
• omission of a mandatory inspection,
• inaccurate maintenance records,
• work performed by unauthorised personnel,
• failure to conduct an independent inspection following critical maintenance.

The current SHT-145 framework includes procedures intended to minimise maintenance errors and omissions and provides for independent or repeated inspections in appropriate cases involving safety-critical maintenance.

Accordingly, MRO liability may involve not only an individual technical mistake but also failures in the organisation’s maintenance processes and control system.

6. What Does a Certificate of Release to Service Mean?

Once maintenance has been completed, one of the most important aviation documents may be issued:

Certificate of Release to Service – CRS.

Under SHT-145, an authorised certifying person issues the maintenance release after verifying that the relevant maintenance has been carried out in accordance with the applicable maintenance data and approved procedures and that no known non-compliance endangering flight safety remains in relation to that work.

There is, however, an extremely important legal distinction.

A maintenance release does not constitute an unlimited certification that the entire aircraft is airworthy in every respect.

The current SHT-145 guidance expressly distinguishes between certification of the maintenance work performed and the overall continuing airworthiness of the aircraft. A release certifies the maintenance covered by the relevant work order or contract; it does not necessarily mean that the aircraft, taken as a whole, is airworthy.

This distinction is central to MRO liability disputes.

7. Who Is Responsible for Airworthiness?

Outsourcing maintenance to an independent MRO does not automatically transfer all continuing-airworthiness responsibility away from the airline or aircraft owner.

Under the Turkish continuous-airworthiness system, the owner or relevant operator retains defined responsibilities concerning continuing airworthiness, while the individual or organisation performing maintenance remains responsible for the maintenance activities it actually performs. Commercial air transport operators also have specific responsibilities to maintain the required continuing-airworthiness and approved-maintenance arrangements.

Liability therefore should not be approached as a simple choice between:

“the airline or the MRO.”

Different responsibilities may coexist.

Airline / Owner / CAMO
→ management of continuing airworthiness.

MRO
→ proper performance of the maintenance entrusted to it.

Certifying Staff
→ proper certification of maintenance within the scope of their authorisation.

A serious technical occurrence may therefore require an investigation into the conduct of several different actors.

8. What Losses May Arise When an Aircraft Is Grounded?

A maintenance error does not always cause an accident.

One of the most commercially significant consequences is an:

Aircraft on Ground – AOG

event.

When a commercial aircraft remains grounded for days or weeks, the financial consequences may extend well beyond the cost of repeating the defective maintenance.

Depending on the circumstances, claimed losses may include:

• corrective maintenance costs,
• replacement components,
• engine or component replacement,
• ferry flight costs,
• parking and hangar fees,
• inspection expenses,
• engineering and expert costs,
• substitute aircraft or wet-lease costs,
• flight disruption costs,
• passenger rerouting costs,
• operational revenue losses.

This does not mean that every such amount will automatically be recoverable from the MRO.

The claimant must still address issues such as causation, proof of loss, fault, contractual risk allocation and limitation-of-liability provisions.

9. The Consequential Loss Problem

One of the most heavily negotiated provisions in international aircraft maintenance contracts is the:

Consequential Loss Exclusion.

MRO providers frequently seek to exclude claims relating to:

• loss of profit,
• loss of revenue,
• loss of use,
• loss of business,
• schedule disruption,
• consequential or indirect damages.

The commercial reason is obvious.

The cost of correcting a maintenance error may be relatively limited, while grounding a commercially valuable aircraft may generate losses many times greater than the value of the maintenance work itself.

From the airline’s perspective, however, loss of use may be the principal economic consequence of defective maintenance.

One of the central questions in MRO negotiations is therefore:

“If the aircraft remains grounded for 20 days because of defective maintenance, who bears the commercial loss associated with those 20 days?”

10. What Is a Liability Cap?

MRO providers frequently seek to impose an aggregate monetary limit on their liability.

For example:

“The aggregate liability of the MRO shall not exceed the total fees paid under the relevant Work Order.”

This is a:

Liability Cap.

Other formulations may limit liability to:

• the value of the maintenance contract,
• a multiple of the relevant work-order value,
• a specified USD or EUR amount,
• available insurance limits.

However, where Turkish law applies, including such language in an English-language contract does not necessarily guarantee its enforceability.

11. Can an MRO Completely Exclude Its Liability Under Turkish Law?

This is where the Turkish Code of Obligations becomes particularly important.

Under Article 115 of the Turkish Code of Obligations, a prior agreement excluding liability for gross negligence is invalid.

The provision goes further where a specialised service, profession or activity may lawfully be conducted only with permission from a competent authority: an advance agreement excluding liability even for ordinary negligence is also invalid.

This has significant implications for aircraft maintenance.

Approved aircraft maintenance is a highly specialised activity conducted within a regulatory authorisation framework.

Consequently, a broadly drafted clause stating:

“The MRO shall have no liability whatsoever for negligence.”

should not simply be assumed enforceable where Turkish mandatory law applies.

Similarly, a liability cap that effectively eliminates meaningful liability may itself require scrutiny under the mandatory rules governing exemption clauses.

12. Is the MRO Responsible for the Technician’s Error?

Aircraft maintenance is physically performed by technicians, engineers and certifying personnel.

An MRO may therefore attempt to argue:

“The mistake was made by an employee, not by the company itself.”

That distinction does not necessarily remove contractual liability.

Under Article 116 of the Turkish Code of Obligations, where performance is entrusted to assistants or employees, the debtor is generally responsible for damage caused by those persons while performing the obligation.

Turkish law also imposes additional restrictions on contractual exclusions relating to acts of assistants where the relevant specialised activity may only be performed under public authorisation.

The use of:

• technicians,
• certifying staff,
• engineers,
• subcontracted personnel

therefore does not automatically remove the MRO’s responsibility towards its contractual counterparty.

13. How Do Maintenance Warranties Work?

One of the central contractual protections in an MRO agreement is the:

Maintenance Warranty / Workmanship Warranty.

The MRO may warrant that the maintenance has been performed in accordance with:

• applicable maintenance data,
• agreed specifications,
• applicable airworthiness requirements,
• agreed workmanship standards.

The warranty period may begin on the date of release or redelivery.

If a warranty defect appears, the MRO’s primary contractual remedy may be limited to:

repair, rectification or re-performance.

This sounds straightforward until the aircraft remains grounded while the rectification is carried out.

The real commercial dispute then becomes:

“Who pays for five days of aircraft downtime?”

That issue will frequently depend on the interaction between the warranty clause, consequential-loss exclusion and liability cap.

14. When May Warranty Coverage Be Excluded?

MRO providers commonly seek exclusions for circumstances such as:

• normal wear and tear,
• improper operation,
• foreign object damage,
• accident damage,
• unauthorised third-party maintenance,
• subsequent modification,
• component failure outside the MRO’s control,
• original manufacturing defects.

These exclusions should be drafted precisely.

Otherwise the parties may later dispute whether a failure resulted from:

maintenance defect, operational defect or manufacturing defect.

15. Who Is Responsible for a Defective Component?

An MRO does not manufacture every component installed during maintenance.

A part may have been supplied by:

• the aircraft manufacturer,
• engine manufacturer,
• OEM,
• independent component supplier.

Where the loss originates from a defective component, liability may need to be allocated between the MRO, manufacturer and supplier.

Relevant questions may include whether the MRO:

• obtained the component from an approved source,
• verified the required documentation,
• complied with installation requirements,
• correctly installed and tested the component.

A component failure therefore does not automatically establish MRO negligence.

16. What Happens When the MRO Uses Subcontractors?

Major maintenance projects frequently involve specialist subcontractors.

Activities such as:

• NDT,
• component repair,
• engine module work,
• specialist inspections,
• painting

may be outsourced.

For this reason, the Aircraft Maintenance Agreement should contain detailed:

Subcontracting Provisions.

From the airline’s perspective, subcontracting should not automatically release the principal MRO from its contractual responsibility.

From the MRO’s perspective, the subcontractor should hold the necessary approvals and remain subject to appropriate audit and compliance procedures.

17. Why Are Maintenance Records Critical Evidence?

Following a serious defect or accident, one of the most important sources of evidence is the maintenance record.

Relevant documents may include:

• work cards,
• task cards,
• technical logs,
• defect reports,
• inspection sheets,
• NDT reports,
• torque records,
• component history records,
• SHGM Form 1 documentation,
• release certificates,
• engineer sign-offs,
• electronic maintenance data.

SHT-145 contains detailed requirements relating to maintenance records, certification and occurrence reporting.

Accordingly, immediate document preservation can become one of the first legal priorities after a major maintenance incident.

18. What Happens If a Maintenance Error Causes an Accident?

The most serious scenario is where defective maintenance contributes to an in-flight technical failure or accident.

At that stage, the matter moves beyond a simple contractual dispute between airline and MRO.

Potentially affected parties may include:

• passengers,
• passengers’ families,
• the airline,
• aircraft owner,
• lessor,
• hull insurers,
• liability insurers,
• manufacturer,
• component supplier,
• MRO,
• subcontractors.

Passengers themselves have no maintenance contract with the MRO.

Nevertheless, if negligent maintenance causes injury or loss to third parties, tort liability may arise independently of the MRO agreement.

An airline that becomes liable under the applicable passenger-carriage regime may also consider recourse against the MRO or other responsible parties where the underlying accident can be attributed to defective maintenance.

19. Can Maintenance Errors Lead to Criminal Liability?

Where a maintenance failure results in death or bodily injury, the matter may extend beyond civil liability.

Depending on the facts, individuals such as:

• technicians,
• certifying staff,
• engineers,
• maintenance managers,
• other responsible personnel

may become subject to criminal investigation based on their specific duties, conduct and degree of fault.

The critical questions will generally be:

What technical duty was breached?

and

Did that breach have a legally relevant causal connection with the accident?

The same event may also trigger regulatory investigation and administrative action by the civil aviation authority.

20. Safety Management Is Now a Legal Liability Issue

Modern maintenance regulation does not focus solely on identifying the individual technician who made a mistake.

The current SHT-145 framework requires the organisation to operate an integrated management and safety system.

This includes processes dealing with:

• hazard identification,
• safety risk management,
• internal investigation,
• safety-performance monitoring,
• management of change,
• continuous improvement.

Accordingly, after a serious maintenance event, the investigation may not stop at:

“Which technician made the mistake?”

It may also ask:

“Why did the organisation’s system fail to prevent that mistake?”

That second question is increasingly important in modern aviation liability.

21. Why Is MRO Insurance Important?

Potential losses arising from aircraft maintenance can be substantial.

Depending on the activity, relevant insurance structures may include:

• aviation products liability,
• premises liability,
• hangarkeepers liability,
• completed operations coverage,
• professional liability.

An airline may therefore require the MRO to maintain insurance at specified minimum limits and provide evidence that the policies remain in force.

In a major maintenance agreement, the insurance clause can be almost as important as the liability clause.

A multi-million-dollar contractual claim offers limited protection if the liable party has neither the financial capacity nor adequate insurance to satisfy it.

22. Why Does Redelivery Documentation Matter?

Following heavy maintenance or overhaul, the aircraft or component is redelivered to the customer.

The parties should clearly document:

• work performed,
• outstanding defects,
• deferred items,
• components replaced,
• technical records delivered,
• test results.

Redelivery documentation may later become a critical evidentiary reference point.

Acceptance of the aircraft by the airline does not necessarily release the MRO from liability for a hidden maintenance defect that could not reasonably have been discovered during ordinary acceptance procedures.

23. Turnaround Time and Delay Liability

One of the most commercially important provisions in an MRO contract is:

Turnaround Time – TAT.

Every additional day that a commercial aircraft remains in maintenance can represent a day during which an extremely valuable asset is not generating scheduled operational revenue.

The contract may therefore require maintenance to be completed within, for example:

30 calendar days.

Heavy maintenance, however, often reveals unexpected findings such as corrosion or structural defects.

The agreement should therefore address the effect of:

• additional findings,
• customer approval delays,
• shortage of parts,
• manufacturer-support delays,
• force majeure,
• regulatory requirements

on the agreed TAT.

Without clear provisions, delay risk can become a major source of dispute.

24. Can the Parties Use Liquidated Damages?

An airline may prefer not to prove its actual losses for every day of delay.

The contract may instead establish a predetermined amount payable for each day of delay.

International contracts frequently refer to such mechanisms as:

Liquidated Damages.

Where Turkish law applies, however, the legal character of such a provision may need to be assessed under Turkish rules governing contractual penalties.

An English-law liquidated-damages clause should therefore not automatically be assumed to produce an identical legal result under Turkish law.

25. What Law Applies When a Foreign Airline Uses a Turkish MRO?

A Turkish MRO may provide maintenance services to airlines from many different jurisdictions.

A foreign airline may, for example, send an Airbus A330 or Boeing 777 to a maintenance facility in Turkey.

The maintenance agreement might provide:

Governing Law: English Law

and submit disputes to:

• ICC arbitration,
• LCIA arbitration,
• ISTAC arbitration,
• English courts,
• Turkish courts.

However, selecting foreign law for the commercial contract does not automatically displace mandatory Turkish aviation-safety and regulatory rules governing maintenance performed within the Turkish approval framework.

The transaction therefore requires both:

contract-law analysis and aviation-regulatory analysis.

26. What Should a Well-Drafted Aircraft Maintenance Agreement Contain?

A comprehensive Aircraft Maintenance Agreement should address at least the following areas:

Scope of Work
What maintenance is actually being performed?

Applicable Maintenance Data
Which manuals and technical standards apply?

Turnaround Time
When must the work be completed?

Additional Findings
What happens when new defects are discovered?

Parts and Components
Who supplies replacement parts?

Certification
Who issues the CRS and other release documentation?

Warranty
What workmanship warranty is provided?

Liability
When is the MRO responsible?

Liability Cap
Is there an aggregate monetary limit?

Consequential Loss
Are loss of use and loss of profit recoverable?

Insurance
What insurance must the MRO maintain?

Indemnities
Who bears defined third-party claims?

Subcontracting
May specialist work be outsourced?

Records
How are maintenance records retained?

Audit Rights
May the airline inspect the MRO’s compliance?

Force Majeure
What events excuse delay?

Governing Law
Which law governs the contract?

Dispute Resolution
Will disputes be litigated or arbitrated?

27. Where Is the Real Legal Risk in an MRO Contract?

A common mistake when reviewing Aircraft Maintenance Agreements is to focus almost exclusively on the technical schedules.

The economic allocation of risk may actually be determined by only a few provisions.

The parties should ask:

How long does the warranty last?

Is the MRO’s only obligation to re-perform the defective work?

Is loss of use excluded?

What is the liability cap?

Does the cap apply to gross negligence?

Who is responsible for subcontractor errors?

Can the airline’s own conduct reduce recovery?

Are the MRO’s insurance limits sufficient?

Without answering these questions, the true commercial risk allocation within the MRO agreement cannot be understood.

Conclusion: Signing a Maintenance Release Is Both a Technical and a Legal Act

Aircraft maintenance agreements represent one of the clearest intersections between highly technical aviation regulation and private-law liability.

An MRO provider is not merely engaged to repair mechanical parts.

It must operate within its regulatory approval, use the correct maintenance data, employ appropriately qualified personnel, maintain systems designed to prevent maintenance errors, preserve technical records and properly certify the work it performs.

At the same time, a maintenance release is not an unlimited guarantee that the aircraft is airworthy in every conceivable respect. The current SHT-145 framework distinguishes certification of the maintenance actually performed from the broader responsibility for continuing airworthiness.

Perhaps the most commercially significant part of an Aircraft Maintenance Agreement is therefore the allocation of liability.

Warranty provisions, consequential-loss exclusions, indemnities and liability caps can determine whether a multi-million-dollar loss ultimately remains with the MRO provider or with the airline.

Under Turkish law, however, freedom of contract is not unlimited. Articles 115 and 116 of the Turkish Code of Obligations impose important restrictions on advance exclusions of liability, particularly in specialised activities that may only lawfully be performed under public authorisation. An MRO should therefore not assume that broad contractual language can eliminate all liability arising from defective maintenance by itself or its personnel.

For this reason, the key question when negotiating an international Aircraft Maintenance Agreement is not merely:

“How much will the maintenance cost?”

The more important question is:

“If a maintenance error grounds a USD 100 million aircraft—or contributes to a serious aviation occurrence—who will ultimately bear the legal and financial consequences?”

A properly drafted MRO agreement should answer that question before the aircraft enters the hangar, not after something goes wrong.