Conflicting Inspection Intervals: Reading a Directive Chain
Maintenance Directive 4.2, dated 3 March, states in paragraph 5: 'Corrosion inspections shall be performed at intervals not to exceed 90 days.' Change 1 to Directive 4.2, dated 19 May, states in full: 'Paragraph 5 is amended to read: 120 days for aircraft kept in indoor storage; 90 days for all other aircraft. No other paragraph is affected.' A base supplement dated 2 June states: 'This supplement governs base-level practice. Where it differs from a wing instruction, the more restrictive requirement applies.' The supplement sets no corrosion interval of its own. On 12 June a technician finds an aircraft in indoor storage whose last documented corrosion inspection was 4 February. She notes that the previous sign-off, in January, was recorded at 118 days and cites Change 1 as authority for it.
1. Which interval governs this aircraft, and how far overdue is it on 12 June?
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The competing intervals: Directive 4.2 as amended by Change 1 gives 120 days for indoor-stored aircraft. The directive's own base value is 90 days.
Which controls: The 2 June supplement claims governance of base-level practice and directs that, where documents differ, the more restrictive requirement applies. It sets no interval itself, so it cannot independently create one - but it does resolve the 90-versus-120 difference in favour of 90 days. The later date of the supplement reinforces this.
Counting from 4 February (non-leap year):
- 90 days: 24 days left in February + 31 (March) + 30 (April) = 85 days at 30 April; 5 more days lands on 5 May.
- 12 June is 24 + 31 + 30 + 31 + 12 = 128 days after 4 February.
So the aircraft is roughly 38 days overdue against the 90-day interval (8 days overdue even on the 120-day reading). Either way it is not compliant, which matters because the 120-day argument changes only the size of the violation, not its existence.
2. What does the technician's note about the January sign-off reveal?
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It is internally inconsistent. Change 1 is dated 19 May; a sign-off made in January cannot have relied on a document issued four months later. Only two readings survive:
- The January date is recorded wrongly and the sign-off actually occurred on or after 19 May; or
- The sign-off was made in January under the original 90-day rule and is 28 days late (118 - 90), with Change 1 cited after the fact as cover.
Either way, the note is not evidence that the aircraft's inspection history is sound. A 118-day interval was never compliant before 19 May, and under the supplement's restrictive clause it is not compliant after it either.
The reading lesson: a document citation must postdate the action it justifies. When a record cites authority that did not yet exist, the record's dates are suspect, and a records discrepancy is itself a finding - not a detail to be smoothed over.
3. What may the technician properly conclude and do, and what may she not conclude from these documents alone?
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Supported conclusions
- The inspection is overdue under either interval.
- The supplement's restrictive clause points to 90 days as the governing number.
- The January record contains a discrepancy that must be documented, not simply annotated.
Not supported by the text
- That the aircraft is grounded, prohibited from flight, or requires a specific corrective action. The directive establishes intervals only; it is silent on airworthiness authority. Assuming a grounding power she does not have is as much an error as assuming none applies.
- That the supplement 'sets' a 120- or 90-day rule of its own - it explicitly does not.
Reasonable action: record the aircraft as overdue, flag the January entry as an unresolved discrepancy, perform the inspection as soon as practicable, and route the scope question (does the supplement's restrictive clause reach an interval it does not itself set?) to quality assurance in writing. The judgement being tested is resisting the urge to pick the reading that clears the aircraft today without inventing authority the documents never granted.