Deferrals and MEL history
Deferred maintenance history review before an airline sale or lease return
Ahead of a sale or lease return, this review tests whether an airline's deferred maintenance history will withstand a counterparty's reading. It checks each deferral against its MEL or CDL basis, follows every cleared item to the corrective action and certifying entry that closed it, and reconciles the whole population to the deferred maintenance log the transaction will present. Records specialists run it for fleet and continuing-airworthiness teams before the data room opens. The output is an item-level findings list with the evidence needed to close each one before commercial sign-off.
When this review is needed
- A lease return is approaching and the redelivery conditions require a clean or fully evidenced open-items position.
- An aircraft is being marketed and the deferral history will be read as a proxy for how the fleet was run.
- Tech log and maintenance system deferral counts disagree and the difference has never been explained.
- MEL revisions changed rectification intervals during the operating period and old deferrals were managed against superseded categories.
The problem
Deferral records are written in the middle of operations: a tech log entry at the gate, a control-center allocation, a clearing entry days later at another station. The chain for any single item crosses the tech log, the maintenance system, and the work package that finally fixed it. Over years of operation the log accumulates items cleared with thin references, deferrals re-raised under new numbers, and category extensions whose approvals live in an email archive. A transaction reads all of it at once.
What gets reviewed
- The deferred maintenance log against tech log entries for every raise and clearance
- MEL and CDL references checked against the revision in force when each item was raised
- Rectification interval compliance, including extensions and their approval records
- Corrective action evidence behind each clearing entry
- Repeat and re-raised deferrals linked across their occurrences
- Open items at the review date verified as genuinely open and correctly categorized
Scope this review
Tell us the asset, the event, and the evidence in scope, and we will outline a focused first engagement.
Send a representative, redacted record set and we will scope the review.
What gets validated
- Every cleared item shows a corrective action and a certifying release, and the dates make operational sense
- Deferral categories and intervals match the MEL revision applicable on the raise date
- Interval extensions carry the approval the operator's procedures and authority required
- No item was closed and re-raised to reset an interval without rectification in between
- The transaction log agrees with the maintenance system and tech logs on the count and status of items
Evidence normally required
- The deferred maintenance log as it will be presented in the transaction
- Tech log pages or electronic tech log extracts for the review period
- MEL and CDL revisions in force across the operating window
- Work orders and packages containing the clearing corrective actions
- Extension approvals and the procedures governing them
Common discrepancies
- Clearing entries citing a work order that contains no rectification for the deferred defect
- Items managed under a category interval from a superseded MEL revision
- Chains of raise-clear-re-raise around the same defect with no effective repair in the sequence
- Extensions applied without the documented approval step the exposition requires
What is at stake
Counterparties treat deferral hygiene as a signal. A log with unexplained closures or interval breaches invites deeper sampling across every other record class, extends technical acceptance, and hardens negotiating positions. Genuine interval exceedances found late can trigger airworthiness questions the airline must answer to its authority as well as to the buyer.
Move from findings to resolution
Move from findings to a documented resolution path.
How the work runs
Freeze the population
Fix the deferral log at a cut date and reconcile counts across systems before item work starts.
Verify raises
Check each item's MEL basis, category, and interval against the revision in force when raised.
Prove closures
Follow every clearing entry into its work package and confirm a real corrective action.
Split and assign
Separate evidence gaps from compliance questions and assign closure ahead of acceptance.
What the buyer receives
- An item-level findings list separating evidence gaps from genuine compliance questions
- A reconciled deferral history the transaction team can present with confidence
- Closure actions assigned and sequenced ahead of technical acceptance
Who uses the output
- Fleet managers negotiating redelivery open-item positions
- Continuing-airworthiness leads resolving compliance questions before an authority hears them
- Records teams finalizing the data room's deferral chapter
How the work fits into the transaction or program
Deferral history connects the operational record to the transaction file: it proves the airplane was managed inside its MEL and that closures were real. This review runs with the logbook and AD chapters of transaction preparation, and its findings often point into work packages that the non-routine review then examines.
Jurisdiction-specific considerations
FAA operators manage deferrals under their MEL approval and 14 CFR 91.417 recordkeeping, while EASA operators answer to Regulation 1321/2014 and ICAO Annex 6 based national rules on deferred defect control. Interval arithmetic and extension authority differ between regimes, so an aircraft moving registries at sale needs its history readable under the receiving rules too.
Regulatory limits
The review evaluates records, never operations. It does not approve deferrals or extensions, judge past dispatch decisions, or determine airworthiness. Where the records suggest an interval was exceeded, the finding is documented for the operator to disposition with its authority.
What this review does not cover
- Assessment of current open defects on the aircraft
- MEL revision, approval, or dispatch procedure consulting
- Rectification planning or execution of open items
Specific to this review
- Deferral findings age poorly: the mechanics and stations behind a thin clearing entry become unreachable within a few years, so late reviews recover less.
- Raise-clear-re-raise chains are the single most scrutinized pattern in buyer reviews because they can mask an interval breach inside individually compliant entries.
- Electronic tech logs shifted the failure mode from missing pages to broken references: entries exist but point at the wrong work order more often than before.
- The deferral log is often the first record a counterparty reads in full, which makes it the cheapest place to earn or lose credibility for the rest of the file.
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
How far back should the deferral review reach?
Cover the current operator's tenure at minimum, and the full back-to-birth chain if the transaction's representations reach that far. Most negotiations concentrate on the last several years, but a single old interval breach can still surface through the maintenance system history, so the cut date should be a decision, never an accident.
Relevant glossary terms
Related pages
Where this fits
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