ADs, SBs and SLs: what is mandatory and what is advisory

“The manufacturer has issued a bulletin — do we have to do it?” The question comes up in every organisation and the honest answer is unsatisfying: it depends on who issued it and whether anything has made it mandatory. What follows is a map that lets you settle it in minutes rather than during an airworthiness review.

One distinction that settles everything

Technical documents fall into two categories with entirely different legal standing:

• Airworthiness directives (ADs) are issued by an aviation authority. They are mandatory by force of regulation — ML.A.303 requires compliance within the period the directive states. There is no room to assess whether the directive is justified; there is only the assessment of applicability to your individual aircraft (serial number, configuration, previous modifications).
• Manufacturer bulletins (SB, SL, SI, SN) are issued by the type certificate holder. A manufacturer has no power to impose obligations on an operator. A bulletin is a recommendation and a set of maintenance data — until something gives it a different status.

Everything else follows from that.

When a bulletin becomes mandatory

There are four routes, and three of them depend on decisions the organisation makes itself:

1. An authority makes it mandatory. A directive cites the bulletin as the means of compliance (“in accordance with SB 300-1-91-B”). From that point the bulletin binds you, in the revision the directive names.
2. The maintenance programme adopts it. Once a bulletin enters the aircraft maintenance programme as a task with a limit, it becomes an obligation — not because a manufacturer wrote it, but because that is what the approved or declared programme says (ML.A.302).
3. The manufacturer marks it mandatory. Labels such as Mandatory Service Bulletin or Alert Service Bulletin have no independent legal force against an operator, but they are frequently a warranty condition and very often precede a directive by a few weeks. Treating them as ordinary advice usually means doing the same work later and more expensively.
4. Contract or insurance terms. Less common, but real — particularly for rented aircraft and training fleets.

The practical conclusion: the status of a bulletin is the result of a CAMO decision, and that decision has to leave a trace. A record reading “reviewed, not applicable to our serial number, date, name” is what a reviewer is looking for. No record at all looks exactly like no review at all.

Where to source documents

One source per manufacturer, and it has to be the original. A copy from a forum or from correspondence with another operator tells you nothing about currency.

Issuer	Where	Note
EASA	the Agency’s AD tool (ad.easa.europa.eu)	the only reliable AD status source for an aircraft on an EU Member State register
Robinson	the publications section of the manufacturer’s site	separate SB, SL and Safety Notice lists per model (R22, R44, R66)
Extra Aircraft	the tech service section	numbering such as SB 300-1-91-B; some documents require registration
Bell	the manufacturer’s bulletin portal	UH-1H ASBs are public; revisions carry -RA, -RB suffixes in the filename
Guimbal	customer portal (behind a login)	no public source — documents arrive by mail or portal and are filed manually

That last row matters more than it looks. A manufacturer without a public repository does not relieve you of holding current maintenance data (ML.A.304, ML.A.401) — it merely changes the way you obtain it into one that depends on human discipline. This is precisely where an electronic system should display a coverage gap rather than quietly implying that nothing has been issued for that type.

What not to confuse

Three mix-ups that regularly end either in wasted work or in an unmet obligation:

• An SIB is not an AD. A Safety Information Bulletin is safety information published by the Agency. It imposes no obligation. It is numbered similarly and turns up in the same search results.
• A PAD is not an AD. A Proposed AD is a draft issued for consultation. It does not apply. Acting on a draft can be sensible, but a record saying “PAD complied with” does not close the eventual directive, which may differ in deadline, scope or the revision of the document it references.
• A foreign authority’s directive is not automatically yours. For an aircraft on an EU Member State register, the binding directives are those issued or adopted by EASA. A publication by the state of design authority (for example the American one, for an American-designed helicopter) is source material; the version that binds you is the one in the Agency’s tool. The reverse applies to aircraft on a non-EU register, where the state of registry decides — worth checking explicitly in mixed fleets, which are common in training and charter.

A separate category is the Emergency AD, recognisable by the -E suffix in the number. Compliance times are sometimes counted in flight hours or days rather than months — and this is the only class of document for which checking the source daily has a practical, rather than merely tidy, justification.

Revisions, supersedure and numbering traps

A document number is not the same thing as its identity. Three schemes to handle deliberately:

• Revision inside the number. SB-45A is revision A of bulletin SB-45, not a separate bulletin. Holding both as independent entries gives you a catalogue where “done” and “outstanding” point at the same document.
• Revision as a directive suffix. 2026-0095R1 is revision R1 of directive 2026-0095. But 2024-0007-E is a different directive (an emergency one), not a revision — the -E belongs to its identity.
• Corrections. A corrected publication of the same number is often flagged separately (C1). Without that distinction the corrected file never enters the catalogue, because “the number is already there”.

Plus one housekeeping rule: a newer revision supersedes the previous one, so the previous one should be marked superseded automatically, with a pointer to its successor. A catalogue where that is done by hand accumulates a dozen entries of unclear status within a year — and every one of them is a question waiting at the next review.

A workflow that holds up

Four steps, repeatable for every document:

1. Arrival. The document enters the catalogue as “new”, with an acquisition date and a source. Automated fetching from manufacturer sites saves time but changes nothing about the steps that follow.
2. Applicability assessment. Performed by a person in the CAMO — against serial number, configuration and modification history. No system should decide this for the organisation; at most it can narrow the candidates by aircraft type.
3. Decision and its record. Status “not applicable” or “applicable”, with a name and a date. This is where the evidence of review is created.
4. Entry into the maintenance programme. For “applicable”, a task is raised with the right limit and a reference to the document number. Only then does the item reach the due list and the AD/SB status — and only then is it tracked like any other life limit.

Step four is the one most often skipped. A bulletin assessed as “applicable” and left in the catalogue is neither done nor planned — it is merely noted. The difference becomes visible during the airworthiness review, where AD/SB status is among the first things the reviewer asks for.

Three control questions

To audit your own document workflow, three questions are enough:

1. When was the source of every manufacturer in your fleet last checked — including the one without a public website?
2. Does every directive touching your types have a record: applicable or not applicable, with a justification and a date?
3. Does every document marked “applicable” have a corresponding task in the maintenance programme, with a due point?

Three answers of “yes” mean AD/SB status can be produced in a minute. Every “no” is work that will have to be done anyway — only under deadline pressure.