Hi Kieran,
one answer may be given in AMC1 ORO.MLR.100 (a)
quote:
(a) The operations manual (OM) may vary in detail according to the complexity of the operation and of the type and number of aircraft operated.
Obviously we must distinguish the needs of CAT, NCC and SPO-Operators...

Hi Kieran, while it's important that all the required items are included, Operators have some flexibility to organize the content in a way that best suits their operational needs and preferences, Including the possibility of adding sections that are not specified.
A good structure of the operations manual facilitates consultation by the parties, workers, and inspectors

As Axel said, it depends on the type of operation.
Per ORO.MLR.101 the main structure in terms of Parts A through D is a hard requirement for all operations (to which Part-ORO applies and) that do not only involve "single-engined propeller-driven aeroplanes with an MOPSC of 5 or less or single-engined non-complex helicopters with an MOPSC of 5 or less, taking off and landing at the same
aerodrome or operating site, under VFR by day".
That doesn't mean that the contents of these parts cannot be spread across multiple actual documents. For example, a large German CAT operator has portions of the OM-A and OM-B relevant for flight safety assembled into a "Flight Safety Manual" FSM for ease of use with flight and cabin crew members.
Part-ORO explicitly allows for additional contents to be added to the OM, such as the contents of the MSM.

Hi Kieran,
the structure and detail depends on the type of operation.
For CAT operations (AOC), it is custom to structure the operations manual (OM) iaw AMC3 ORO.MLR.100. As far as all the CAT operation I have inspected so far are concerned, I have not seen any structure other than that of AMC3 ORO.MLR.100. The code of conduct is usually that all numerical chapter elements (ie "8", "8.1", "8.1.1") make up the manual structure (and 'table of content'). All topics with alphabetic ordering ((a), (b), (c)...) may be structured to the operator's liking below the next superior numerical chapter. For exampe, the flight crew qualification requirement of a commander (which is 5, 5.2., (a)) would thus be found under
5 QUALIFICATION REQUIREMENTS
5.2 Flight crew
however it could be 5.2 or 5.2.X (where X is to the operators liking).
This standard structure facilitates, as Antonio already stated, interoperability with other entities and significantly reduces the operator conversion training for new pilots or employees that have work experience with other EU airlines.
Operators of other operations (ie NCC or CAT which only SEP operation) are a different type of animal. AMC2 ORO.MLR.100 is interpreted only to cover the subject areas and may not need to be unterstood as strucural requirement.

Hi Kieran, Hi all
It is just a good tool for harmonisation and standardisation . Truly , we must step back a little and think of it from an outside perspective. It is quite cool to be able to refer to the same paragraph number for a particular rule or procedure. From Finland to Greece , From France to Malta , or from the small guy with just one Robinson 44 to the big mega airline with one hundred 100 tonners , paragraph A 8.3.3 Altimeter setting (for example) will always describe the same matter. It is better for everyone. including a pilot transitionning from one operator to another.
These are good reasons to follow the structure of the AMC . Use all the numbers and titles. Just write "reserved" or "not applicable" when you are not impacted. (You may become one day)
If your are starting your manual from scratch make it easy on yourself and just follow the organisation of the AMC. If, like many of us around, you ve kind of inherited an old manual in 2014; then do the best to stick to the suggested order. And whenever you have time , try to re arrange the maze...
Hoping it helped . Cheers