Introduction

The acquisition of a used aircraft is fundamentally different from the purchase of an ordinary high-value movable asset. An attractive purchase price, a valid Certificate of Airworthiness, or the fact that the aircraft is currently flying does not necessarily mean that the aircraft represents a legally and economically sound investment.

A substantial part of an aircraft’s value lies beyond the physical airframe. Its chain of title, registry status, mortgages and financing interests, engine condition, life-limited parts, completeness of maintenance records, structural repair history, Airworthiness Directive compliance, modifications and eligibility for registration in the intended State of Registry may materially affect its real value.

This is particularly important where a foreign-registered used aircraft is intended to be imported into Türkiye. Under the current Turkish SHT-21 regime, a used aircraft arriving from a foreign registry may require evidence from the competent authority of the previous State of Registry reflecting its airworthiness status at transfer, together with weight-and-balance information, the flight manual where applicable, historical production/modification/maintenance records and documentation supporting the relevant airworthiness review process.

For investors, the appropriate transaction sequence is therefore straightforward:

due diligence first, acquisition and closing second.

1. What Exactly Is Being Purchased?

An aircraft transaction does not necessarily involve only an airframe.

Depending upon the structure of the deal, the acquisition package may include engines, an auxiliary power unit, landing gear, loose equipment, spare parts, cabin equipment, technical records and certain associated software or data rights.

The issue is particularly important for engines.

An engine physically installed on an aircraft should never automatically be assumed to be legally owned by the aircraft seller. It may be leased from a third party, financed separately or subject to an independent security arrangement.

Accordingly, the definition of “Aircraft” in the Aircraft Purchase Agreement should precisely identify the airframe manufacturer serial number, engine serial numbers, APU and other material assets included in the transaction.

Otherwise, an investor may pay the agreed aircraft price without actually acquiring title to every high-value asset physically installed on the aircraft.

2. Title Due Diligence

The first stage of legal due diligence is a comprehensive title investigation.

The buyer should establish the registered owner, the seller’s authority to transfer title, the relevant chain of ownership and the existence of any security interests or other claims.

For aircraft entering the Turkish Civil Aircraft Registry through a purchase transaction, the DGCA requires documentation including the underlying sale agreement and original Bill of Sale. Where an aircraft comes from a foreign registry, documentation evidencing de-registration from the previous State is also central to the Turkish registration process.

A Bill of Sale delivered by the seller should therefore not be treated as the entire title due diligence exercise.

The aircraft registry should be independently reviewed and, where relevant, the historical title chain should also be investigated.

Particular attention should be paid to discrepancies between the seller and registered owner, prior financing arrangements, leasing structures, liens, attachments and other interests that could prevent the buyer from receiving clean title.

3. Mortgages, Liens and Encumbrances

Aircraft are frequently financed assets.

The fact that an aircraft has previously been subject to a mortgage or financing arrangement is not unusual. The critical question is whether all relevant security interests will be properly discharged at closing.

The Turkish Civil Aircraft Registry has a dedicated procedure for the registration and discharge of aircraft mortgages, and Turkish registry checks may reveal mortgages, attachments and other legal restrictions affecting an aircraft.

Accordingly, payment of the purchase price should be coordinated with the delivery of all necessary releases.

Where an existing lender must be repaid from the purchase proceeds, the closing arrangement should establish precisely how funds will flow and when the lender’s mortgage or security interest will be released.

A mere contractual statement that “the seller will discharge the financing after closing” may expose the buyer to unacceptable title risk.

4. Cape Town Convention and International Registry Searches

In cross-border aircraft transactions, a national aircraft registry search may not be sufficient.

The Cape Town Convention and its Aircraft Protocol establish an international regime for certain interests in aircraft objects, including qualifying airframes, aircraft engines and helicopters, supported by an International Registry and priority system.

Türkiye has made a number of declarations under the Convention. Among other matters, its declarations address certain non-consensual rights that may have priority under Turkish law, registrable rights relating to attachments and tax or governmental claims, and rights to arrest or detain aircraft objects for specified public-service charges.

A cross-border acquisition should therefore distinguish between two separate questions:

What interests appear on the relevant national registry, and what registered international interests affect the relevant aircraft objects under the Cape Town system?

This becomes particularly important where aircraft engines are separately financed or owned.

5. Eligibility for Turkish Registration Must Be Assessed Before Acquisition

One of the costliest mistakes an investor can make is to acquire an aircraft first and investigate its eligibility for Turkish registration afterwards.

The Turkish DGCA administers the first registration of aircraft intended to be temporarily or permanently imported into Türkiye. In purchase transactions, documents required in the registration process include the sale agreement, Bill of Sale, translations and evidence of signatory authority. De-registration documentation from the previous State and relevant export documentation also form part of the process.

The DGCA additionally administers airworthiness certificates, airworthiness review documentation, Export Certificates of Airworthiness and technical import conformity procedures for aircraft.

Certain imports of used or renewed civil aviation goods may additionally require a DGCA conformity letter under the applicable Turkish import regime.

Accordingly, the aircraft type, model and variant should be assessed for Turkish certification, registration and intended operational use before the buyer becomes unconditionally committed to the purchase.

6. A Valid Certificate of Airworthiness Is Not a Substitute for Due Diligence

A seller may understandably emphasise that an aircraft has a valid Certificate of Airworthiness.

For an investor, however, this should be treated as the beginning of the inquiry rather than the conclusion.

Under the current Turkish SHT-21 framework, continued validity of an airworthiness certificate depends, among other things, upon continuing conformity with applicable type-design and continuing-airworthiness requirements. Registry status and the continuing validity of the underlying type certification are also relevant.

For used aircraft arriving from a foreign registry, historical production, modification and maintenance records form an important part of the Turkish airworthiness process.

A valid Certificate of Airworthiness therefore does not replace a full technical records review.

7. Technical Records Are the Aircraft’s Second Passport

The physical condition of the aircraft and the quality of its records are inseparable from a valuation perspective.

An aircraft may visually appear to be in excellent condition while suffering significant commercial impairment because the history of a high-value component cannot be adequately established.

A proper records review should reconcile the aircraft logbooks, engine records, APU records, component status, modification and repair data, shop-visit documentation, weight-and-balance information and relevant maintenance releases.

The current Turkish SHT-21 provisions expressly require historical records capable of establishing the production, modification and maintenance standard of a foreign-registered used aircraft. They also require information identifying modifications and repairs and their approval and implementation references.

Missing records are therefore not merely an administrative inconvenience.

They may create airworthiness, registration, financing and residual-value consequences.

8. Airworthiness Directives and Service Bulletins

An independent AD status review is essential.

Airworthiness Directives are mandatory requirements issued to address identified unsafe conditions. The FAA, for example, expressly describes its ADs as legally enforceable regulations, while the Turkish DGCA also maintains its own Airworthiness Directive system.

The buyer’s technical adviser should therefore independently reconcile applicable ADs for the airframe, engines, APU and relevant components rather than relying exclusively on the seller’s summary.

EASA’s Safety Publications Tool also provides a central source for researching current mandatory continuing-airworthiness information relevant to numerous aircraft and engine types.

Service Bulletins require a more nuanced analysis. They do not necessarily carry the same mandatory status as an AD in every case. Nevertheless, an outstanding SB may represent future cost, may have become mandatory through another regulatory mechanism, or may matter because of the applicable maintenance programme, lease return requirements or the intended operation.

The investor should therefore ask not only:

“Is the aircraft legally compliant today?”

but also:

“Which currently outstanding items are likely to become expensive during the investment period?”

9. Engine Due Diligence

The engines can be among the most economically significant elements of a used-aircraft transaction.

Two aircraft of the same model, vintage and apparent condition may have materially different values because of engine status.

Engine due diligence should therefore go beyond total hours and cycles.

The investigation should consider shop-visit history, Life Limited Part status, remaining cycles, module condition, performance deterioration, prior removals and repairs, and the timing and expected cost of the next major maintenance event.

Traceability of Life Limited Parts is particularly important.

An engine that is physically operating properly may nevertheless have poor economic value where an expensive shop visit or LLP replacement is imminent.

The buyer is effectively acquiring not only the engine itself but also its accumulated future maintenance exposure.

10. The Maintenance Cliff

Aircraft valuation should never be based solely on present airworthiness.

An aircraft may be fully operational on the delivery date but only months away from a heavy maintenance event, landing-gear overhaul, engine shop visit, APU overhaul or replacement of significant time-controlled components.

This produces what may be described commercially as a maintenance cliff.

If an aircraft purchased for USD 20 million requires several million dollars of scheduled maintenance shortly after acquisition, its economic acquisition cost is not realistically limited to USD 20 million.

The technical due diligence team should therefore prepare a forward-looking maintenance forecast.

The results may justify a purchase-price reduction, seller contribution, retention or escrow arrangement.

11. Damage and Structural Repair History

The description “accident-free aircraft” should not be treated as a complete representation of structural condition.

An aircraft may previously have suffered a hard landing, tail strike, bird strike, lightning event, ground collision, hail damage or other material occurrence.

Not every such event will necessarily be described in marketing materials as an “accident.”

The more relevant question is whether the airframe has suffered material damage, how it was repaired and whether the repair was performed using properly approved data.

The current Turkish SHT-21 regime emphasises historical production, modification and maintenance records and requires identification of applied modifications and repairs with their relevant approval and implementation references.

The due diligence should therefore examine not only whether a structural repair exists but also whether it is adequately documented and traceable.

12. Physical Pre-Purchase Inspection

A records review should be complemented by a physical Pre-Purchase Inspection, normally performed by experienced technical personnel independent from the seller.

Its scope will depend upon aircraft type, age, utilisation, maintenance history and transaction value.

The inspection may cover the airframe, cabin and cockpit, signs of corrosion, engines and APU, landing gear and other systems. Where justified, the parties may agree on more detailed inspections such as engine borescope examinations.

Findings should be separated conceptually into three categories:

issues that must be rectified to preserve airworthiness, failures to comply with the contractual delivery condition, and matters that do not make the aircraft unairworthy but justify an economic price adjustment.

This distinction is important because an airworthy aircraft is not necessarily an aircraft that complies with the negotiated delivery condition.

13. Modifications and Operational Suitability

The fact that an aircraft is operating successfully in one jurisdiction does not automatically mean that it is appropriately configured for the buyer’s planned operations.

Avionics and modification status should be assessed against the intended routes, airspace and operational approvals.

Depending on the intended use, capabilities relating to RVSM, PBN, ADS-B, TCAS, EGPWS, data link or other systems may be relevant.

Cabin configuration, emergency equipment, placarding and other operational features should similarly be reviewed from the perspective of the new operator and State of Registry.

Current Turkish SHT-21 requirements also address bilingual Turkish/English placarding in designated passenger areas and documentation of aircraft modifications.

14. Aircraft Purchase Agreement Protection

The results of technical and legal due diligence must ultimately be translated into contractual protection.

A well-drafted Aircraft Purchase Agreement should address far more than the identity of the aircraft and purchase price.

Material provisions ordinarily need to allocate risk relating to the aircraft definition, deposit, inspection rights, technical acceptance, delivery condition, title and absence of liens, records, disclosed damage, conditions precedent, closing mechanics, risk of loss, insurance, delivery, governing law and dispute resolution.

Particular care is required where the seller seeks to transfer the aircraft on an extensive “as is, where is” basis.

If the buyer accepts broad disclaimers without corresponding inspection rights and title protections, subsequent claims concerning records or technical condition may become substantially more difficult.

15. Conditions Precedent and Closing Mechanics

Aircraft purchase funds should not be released merely because the aircraft has physically arrived at the agreed delivery location.

The objective of the closing process is that:

payment, clean title and control of the aircraft move through the transaction in a coordinated sequence.

Depending upon the transaction, de-registration documents, the Bill of Sale, releases of mortgages or international interests, export or airworthiness documentation and other delivery documents should be linked directly to the payment mechanics.

The Turkish DGCA’s own first-registration requirements reflect the importance of de-registration, export documentation and acquisition documents in the registration process.

For high-value aircraft transactions, an escrow or professional closing arrangement may significantly reduce simultaneous-performance risk.

16. Delivery Acceptance Certificate

The Delivery Acceptance Certificate is one of the most important documents at closing.

It records when and where the aircraft was delivered, the condition in which it was accepted and the documentation or equipment delivered with it.

It may also be central to determining the point at which risk of loss, insurance responsibility and operational responsibility shift from seller to buyer.

It should therefore not be treated as a routine administrative document.

It is the contractual bridge between the negotiated delivery condition and the actual physical delivery.

17. Tax, Customs and Financing Structure

The headline purchase price does not represent the entire acquisition cost.

Tax and customs consequences may vary depending upon the seller and buyer jurisdictions, delivery location, permanent or temporary import structure, operator status, and whether financing or leasing is incorporated into the transaction.

Even within the Turkish registration process, DGCA guidance refers in relevant purchase cases to documentation concerning stamp tax arising from the agreement and, in certain ownership changes, tax-clearance documentation.

Tax and customs structuring should therefore occur before the transaction documents are finalised rather than after the aircraft has been acquired.

18. The Investor’s Due Diligence Output

A professionally managed due diligence should not merely conclude that an aircraft is “acceptable” or “unacceptable.”

The investor should receive three interconnected outputs.

A Legal Risk Report should address title, mortgages and security interests, ownership, contracts and registration.

A Technical Due Diligence Report should address the airframe, engines, APU, components, maintenance status, AD/SB position, records and physical inspection.

A Financial Exposure Model should convert impending maintenance and technical deficiencies into monetary consequences.

Only when those three analyses are combined can the investor identify the aircraft’s genuine risk-adjusted acquisition value.

19. Major Red Flags

Material warning signs include missing or internally inconsistent historical records, unverified engine or LLP traceability, unresolved AD obligations, undocumented structural repairs, outstanding mortgages or international interests, inconsistencies between the seller and registered owner, third-party ownership of installed engines, uncertainty as to de-registration from the existing registry and doubts about acceptance into the intended new registry.

None of those issues is cured merely because the aircraft is presently capable of flight.

In many transactions, the greatest financial loss does not arise because the aircraft cannot fly.

It arises because, after closing, the buyer discovers that the aircraft is far more expensive to own and maintain than the acquisition analysis suggested.

Conclusion

The acquisition of a used aircraft is an investment transaction in which law, engineering and finance must operate together.

Effective due diligence asks far more than whether the seller owns an aircraft and whether the aircraft is currently flying.

It asks:

Is clean title available?

Are there national or international security interests?

Can the aircraft be registered and certified in the intended State of Registry?

Are the technical records complete and reliable?

What is the true remaining economic life of the engines and LLPs?

What maintenance expenditure is approaching?

Are structural repairs and modifications properly approved and documented?

And, critically, who bears each of those risks under the Aircraft Purchase Agreement?

These questions become especially important when a foreign-registered used aircraft is being acquired for operation in Türkiye. The current 2026 Turkish SHT-21 regime expressly places significance on the previous airworthiness status of foreign-registered used aircraft, their historical production, modification and maintenance records and the documentation required for the Turkish airworthiness-review process.

A sophisticated acquisition process should therefore generally proceed from:

term sheet → legal due diligence → technical records review → physical pre-purchase inspection → valuation adjustment → definitive Aircraft Purchase Agreement → coordinated closing → registration and airworthiness

rather than committing the investment first and investigating the aircraft later.

When purchasing a used aircraft, paying too much is not necessarily the most expensive mistake.

The most expensive mistake is closing the transaction without fully understanding, both legally and technically, what has actually been purchased.