Deferral diligence
Deferred maintenance records reviewed in the transaction data room
A deferred maintenance source review reads the deferral log a seller uploads and verifies, from the same room, that each sampled deferral was raised, controlled, and cleared the way the log claims. It covers MEL and CDL items, deferred defects out of checks, and carried-forward tasks, following each to its authorization and its clearing work record. Buyers and lessors run it during pre-purchase or pre-lease diligence. It closes with a sourced exception list sized for the deal schedule.
When this review is needed
- The current deferral log is short and the buyer wants confidence it reflects the aircraft rather than housekeeping before the sale.
- Check handover documents mention carried-forward items the posted log no longer shows.
- MEL deferrals recur on the same system, hinting at a chronic defect the summary conceals.
- Redelivery conditions require zero open deferrals and the clearance evidence must exist before acceptance.
The problem
Deferral records live between two systems, the operations side that raises MEL items and the maintenance side that clears them, and data rooms reliably capture only one. A cleared deferral needs a work record proving rectification; a closed log line with no work order behind it proves nothing. Recurring deferrals scatter across months of log pages, so the pattern that matters most is the hardest to see in a folder of PDFs.
What gets reviewed
- The posted deferral log reconciled against check handover documents and technical log extracts in the room
- Sampled deferrals traced from raising through authorization, extensions, and clearance
- MEL items checked against category time limits and any extension approvals
- Clearance entries matched to the work records that performed the rectification
- Recurring deferrals on the same system grouped and assessed as reliability signals
- Open items at the review date listed with their remaining time and required actions
Scope this review
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What gets validated
- Each sampled deferral cites an authorization consistent with the operator's MEL or deferral procedure
- Category time limits were respected, or extensions carry the required approvals
- Every cleared line connects to a dated work record describing the rectification
- Items carried out of checks reappear in the log rather than vanishing at the check boundary
- The current open list agrees with the most recent technical log states available in the room
Evidence normally required
- All deferral and deferred defect logs for the period in scope
- Technical log pages or extracts posted in the uploads
- Work orders and task cards cited by clearance entries
- The operator's MEL and deferral procedure references, where uploaded
- Check handover and carried-forward item lists
Common discrepancies
- Clearances recorded in the log with no rectification work order anywhere in the room
- A category B item that ran past its limit with no extension paper posted
- The same system deferred repeatedly across months, invisible until the log is read as a series
- Carried-forward items from a check that never re-enter any posted log
What is at stake
Deferrals cleared without rectification evidence resurface as open defects at induction, and chronic items that diligence missed become the new operator's dispatch problem from day one. Where redelivery or delivery conditions demand a clean aircraft, unevidenced clearances turn acceptance day into a standoff, with hangar time and lease rent burning while the paper is chased.
Move from findings to resolution
Move from findings to a documented resolution path.
How the work runs
Assemble the deferral picture
Combine the posted log with technical log extracts and check handover lists to reconstruct the true population.
Trace raising and control
Verify authorization, category limits, and extensions for the sampled items.
Prove the clearances
Match every sampled cleared line to the work record that rectified it.
Summarize and flag
Deliver the exception list, the open-item table, and the chronic-item summary for induction planning.
What the buyer receives
- A deferral-trail report covering raising, control, and clearance for the sample
- Exceptions referenced to log lines and folders for the diligence schedule
- A chronic-item summary for the buyer's reliability and induction planning
Who uses the output
- Diligence leads negotiating open-item conditions into the deal
- The incoming operator's maintenance control planning day-one dispatch
- Records teams verifying clean-aircraft conditions at delivery or redelivery
How the work fits into the transaction or program
Deferral history connects condition to compliance: the non-routine review shows what checks found, and this review shows what the operation lived with in between. Its chronic-item summary often shapes the physical survey scope, and its open-item list feeds directly into delivery-condition drafting.
Jurisdiction-specific considerations
MEL frameworks under FAA operations specifications and EASA operator rules both categorize deferrals with time limits, but extension authority and documentation conventions differ between regimes and between operator types. ICAO Annex 6 principles sit behind both, which helps when a mixed history must be read against more than one rulebook.
Regulatory limits
The review neither approves deferrals nor judges dispatch decisions. It makes no airworthiness determination, does not validate the operator's MEL against its master document, and leaves all certification and enforcement matters with the operator and its authority; it reports what the posted evidence supports.
What this review does not cover
- Physical verification that deferred items were rectified on the aircraft
- Revising or approving the MEL
- Reliability engineering beyond flagging recurrence patterns
Specific to this review
- Deferral logs are the record class most exposed to pre-sale housekeeping, which is why the reconciliation against technical log extracts matters more than the log itself.
- A clearance without a work record is the single most common deferral finding, and it is usually a filing failure that Q&A can fix while the room is still open.
- Recurrence is invisible line by line; only reading the log as a time series exposes the rotable swapped four times for the same symptom.
- Open deferrals at closing are negotiable; unevidenced cleared deferrals are harder, because nobody can price what might sit behind them.
Sources
U.S. Government (eCFR). Maintenance recordkeeping content and approval-for-return-to-service requirements, including 43.9, 43.11, and Appendix B.
U.S. Government (eCFR). Records an owner or operator must keep, including total time in service, current status of life-limited parts, and AD compliance.
European Union / EASA. Continuing airworthiness, maintenance records, CAMO responsibilities, and the airworthiness review process in the EASA system.
International Civil Aviation Organization. International standards for aircraft operation, including maintenance program and recordkeeping expectations.
Frequently asked questions
The open deferral list is empty. Does the review still add anything?
An empty list raises the question of how it got empty. Clearances recorded shortly before a sale deserve their work records checked, and the recurrence analysis still reveals chronic systems the next operator will inherit. Clean logs are verified, never assumed.
Relevant glossary terms
Related pages
Where this fits
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