Do aircraft manufacturers have the authority to either approve or disapprove the maintenance procedures of its customers?

Question

Having currently read this article in Wikipedia, linked through Reddit, regarding American Airlines Flight 191, which crashed due to maintenance issues.

Inside the article, it says

McDonnell-Douglas, however, "does not have the authority to either approve or disapprove the maintenance procedures of its customers."

Is that the scenario in the current aviation industry, or has it changed. Why would airline companies not listen to the manufacturer and carry out non-approved procedures.

Answer 1

For N-Registered Planes Under FAA regulations... (this may differ elsewhere in the world)

The short answer is No (although some service bulletins may be legally required), the manufacturer can not legally enforce anything per say, however here's how it plays out.

Most makers are at least in some capacity always testing their aircraft and aircraft procedures (at least the models in service). This may be as simple as inspecting the ones out there and looking at used parts for fatigue and what not. This in turn can lead to the company issuing a Service Bulletin which is basically a document that says: "hey here's something we found, you should look at it". This can apply to a any part of the aircraft as well as inspection and maintenance procedures. However service bulletins are not legally required to be complied with when issued by the company (although many may choose to comply).

On the other hand the Service Bulletins may trigger the FAA to issue an Airworthiness Directive which is a legally enforceable document. In this case the owner/operator of the aircraft is legally required to comply and alter their procedures.

In this case of the accident in question I think this is the AD that was issued as a result. You can find a full list of MD-10 AD's Here.

On to the question of why an airline may not listen. This is most likely a cost related issue. If the airlines insurance does not change and the cost to inspect or possibly replace a part that they don't legally need to replace is simply to high, they wont do so until its legally required. Again since every thing in aviation has two sides, manufactures may have the courtesy to replace the part at no cost to the owner. For example, when Porsche dropped the FAA Type Certification for the 3.2 motor in the Mooney M20PFM leaving all the owners somewhat high and dry, Mooney was kind enough to have the 40 odd aircraft updated with Continental motors (although many were destroyed in a hurricane while under going the change). The crux of it also comes down to the fact that only the government and its various organizations (here in US) can legally impose anything on an individual or company. So while it may be a good idea to heed the advice of the maker you may not be required to do so.

--Edit--

To answer the comment below which is somewhat relevant to the original question. My understanding is that yes the FAR's may require you to refer to the manufacturer procedure but at the same time you only must refer to the procedures required (associated with the current certification of the airframe) for your airframe an SB with out an accompanying AD is a manufacturer procedure but is not legally required. So you may refer to it but you may not have to comply with it. Ill dig into the regulations and see if I can find the letter of the law on it.

Answer 2

Short Answer:

Generally, no, but in at least one notable exception, Yes.

Longer Answer:

@Dave has given a good answer that covers much of the industry. However, there is an industry sector for which the answer is, "Yes": FAA certified Special Light Sport Aircraft (S-LSA). These maintenance requirements are found in part 91, not—curiously enough—in part 43.

Firstly, the FAA gives manufacturers of S-LSA the authority to prescribe what must be done for routine maintenance and inspections. This authority is not absolute, as part 43 also applies and the role is also open to "a person acceptable to the FAA".

See 14 CFR 91.327 (b) (1) and (2):

(b) No person may operate an aircraft that has a special airworthiness certificate in the light-sport category unless—

(1) The aircraft is maintained by a certificated repairman with a light-sport aircraft maintenance rating, an appropriately rated mechanic, or an appropriately rated repair station in accordance with the applicable provisions of part 43 of this chapter and maintenance and inspection procedures developed by the aircraft manufacturer or a person acceptable to the FAA;

(2) A condition inspection is performed once every 12 calendar months by a certificated repairman (light-sport aircraft) with a maintenance rating, an appropriately rated mechanic, or an appropriately rated repair station in accordance with inspection procedures developed by the aircraft manufacturer or a person acceptable to the FAA;

In addition to this, manufacturers of S-LSA can issue Safety Directives, which are generally mandatory and can be thought of as roughly equivalent to Airworthiness Directives (ADs). Again, this power is not absolute.

See 14 CFR 91.327 (b) (4):

(4) The owner or operator complies with each safety directive applicable to the aircraft that corrects an existing unsafe condition. In lieu of complying with a safety directive an owner or operator may—

(i) Correct the unsafe condition in a manner different from that specified in the safety directive provided the person issuing the directive¹ concurs with the action; or

(ii) Obtain an FAA waiver from the provisions of the safety directive based on a conclusion that the safety directive was issued without adhering to the applicable consensus standard;

¹ _{That is, the S-LSA manufacturer.}

Furthermore, any repairs or alterations must be approved by the manufacturer, either by the existing manufacturer supplied Maintenance Manual, or on a case by case basis for those falling outside the scope of the Maintenance Manual. Once again, this power is not absolute; the FAA has to retain some authority.

See 14 CFR 91.327 (b) (5) and (6):

(5) Each alteration accomplished after the aircraft's date of manufacture meets the applicable and current consensus standard and has been authorized by either the manufacturer or a person acceptable to the FAA;

(6) Each major alteration to an aircraft product produced under a consensus standard is authorized, performed and inspected in accordance with maintenance and inspection procedures developed by the manufacturer or a person acceptable to the FAA; and

See also this article by D. Martino: Work Books: A flight instructor’s guide to S-LSA maintenance regulations, which gives a good interpretation of these rules with less legalese.