Airworthiness of Aircraft – the Basics

In a previous post, I explained the very basic concept of airworthiness in general. In this article, I will focus specifically on the airworthiness of aircraft and I’ll try to go through the most important airworthiness data that is required to keep an aircraft airworthy at all times.

As I mentioned in the post on the basic concept of airworthiness, the main purpose of a continuous airworthiness department of an airline is to make sure that the airworthiness of aircraft is maintained at all times when the aircraft is airborne with passengers or cargo. Yes, there are certain rare situations in which some deviation from the overall airworthiness requirements is allowed, but this never happens during commercial flights and will be the subject of a much later article.

To make a long story short, an aircraft is airworthy if all required maintenance tasks have been performed on time, all additional requirements (such as airworthiness directives) have been complied with and all defects have been rectified in an acceptable manner. There’s a bit more to it, but for now we can leave it at that. The question remains: how does an airworthiness manager know what needs to be done to the aircraft? Does she or he come up with the maintenance tasks by themselves? Or if not, where can you get that information?

There is a whole set of documents which defines the tasks needed to preserve the airworthiness of aircraft, and those documents are generally called airworthiness data. Here are the main and most important ones:

• A Maintenance Program developed for the particular aircraft exemplar, generally based on a Maintenance Planning Document (MPD) or Maintenance Schedule (MS) which can be obtained from the aircraft manufacturer (or, more accurately, the aircraft type certificate holder, but we don’t need to expand on that for the moment).
• Service Bulletins, which can be thought of as an update (or maybe more of an extension) to the MPD or MS, also developed by the aircraft manufacturer. Those are most often sent to operators when a technical issue of the aircraft becomes known to the manufacturer and requires aircraft operators to perform specific tasks.
• Airworthiness directives, which are being issued by the Civil Aviation Authority of the country where the airline is based (certified) as well as from the country of origin of the aircraft manufacturer.
• Selected chapters of the Aircraft Maintenance Manual (AMM) – this would be generally Chapter 5 – provided this manual does contain airworthiness specific information which is not included in the MPD/MS. Those would generally be so-called airworthiness limitations, but again, we won’t getting into that level of detail quite yet.
• Additional airworthiness data derived from what’s called Supplemental Type Certificate’s (if your aircraft has been modified and the modification requires additional maintenance tasks to be performed, for example) or caused by national regulations.

So, as you can see, there’s quite a bit of information to consider, especially that documents such as the directives, bulletins and maintenance manuals are separate for the airframe, engines, propellers and landing gear. There’s a general tendency (and in some cases even a requirement) to put all that additional data into the aircraft’s maintenance program which is developed by the airworthiness manager for each aircraft on a case by case basis. As much as this improves the clarity of the data, it does not alter the amount that’s required to keep an aircraft airworthy.

I will write a more detailed overview of all the documents above in later posts, so keep checking. For now, let’s just say that the development of the aircraft’s maintenance program is a crucial task not only to properly manage the airworthiness of aircraft but also to take care of the airline’s economics. As much as all regulations must be clearly observed, if you overdo it or make mistakes which are non-crucial from the safety perspective, you may end up having the aircraft in the hangar for much more time than is actually necessary. Therefore, creating a proper, tailor made maintenance program is of a lot of importance.