Part 91

When we take the time to lay out all of the maintenance requirements for an aircraft we will find some interesting scenarios that, when encountered, can cause lots of confusion and discussion. What is legal? What is right? Does it make sense? Why not? In the end as maintenance personnel we have got to be able to move forward and keep working with little or no delay in the delivery of the aircraft. On-time delivery is critical in maintaining our customer base. This is only possible if a clear set of guidelines is established and followed regarding what makes up the maintenance requirements for an aircraft. In this article we will cover inspection and maintenance requirements, where they come from, and the different weights that those requirements carry relative to severity.

To start with, the focus here is on Part 91, multi-turbine powered aircraft which are not subject to annual inspections but instead are to be inspected as outlined in the manufacturer’s recommended inspection and maintenance program or a program compiled by the owner or operator and submitted to the FAA for approval. Regardless, the inspection program consists of five major components:

• Look phase and special inspections
• Lubrication and servicing requirements
• Overhaul and replacement requirements
• Airworthiness limitations
• Service information and Airworthiness Directives

Let’s take a moment to examine each of these five components of an inspection and maintenance program.

Look phase and special inspections consist of any requirement in the recommended inspection and maintenance program that must be looked at to determine that the aircraft continues to be in airworthy condition. In order for the manufacturer to obtain a type certificate for the aircraft it must consider all stresses and strains that the aircraft will be subjected to when operated in accordance with its normal operating limitations. Considering these stresses and strains provides the engineers and technical writers with the data necessary to compile the list of required inspections and the corresponding frequency of inspection. In many cases the list is quite long, hundreds and sometimes over a thousand line items. The manufacturer provides both general instructions on what to look for and, in some cases, specific tooling and explicit instructions on what to look for to ensure that the aircraft continues to be safe to operate. Completion of these inspection items can generate a list of discrepancies that need to be handled prior to returning the aircraft to service. Once the discrepancies are listed and need to be worked, the inspection item itself can be bought off. Further inspection following the correction of the discrepancy provides an adequate method of coming full circle on the inspection.

Lubrication and servicing requirements are somewhat self-explanatory, obviously. These are the items or areas of the aircraft that carry some sort of fluid or are subject to wear due to friction or exposure to the elements. The manufacturing engineers have identified and set forth the time frequencies for these items as well. Great effort is put forth to ensure that the lubricant or other fluid used in the aircraft in these specific areas is the appropriate material for its specified use. Too often an unlikely substitute is used that can compromise the safety of the aircraft. As an inspector it is critical to verify if at all possible that the last person to touch the aircraft used the appropriate lubricant and or fluids. Many of these areas are also subject to inspection and must be thoroughly cleaned as part of the inspection process prior to applying the specified lubrication material.

Overhaul and replacement requirements consist of components of the aircraft that are simply replaced at a certain time rather than simply inspected and returned to the aircraft. Many overhaul and replacement components also have periodic inspection requirements up to the time they are replaced, but in the end they are consumable or include consumable parts. An overhaul component for example will include pieces that are always replaced during the overhaul process as well as pieces that are thoroughly inspected (to a specified standard) and reassembled with the overhauled assembly prior to return to service. Replacement items are simply removed and replaced with new regardless of their condition. The engineers have determined that these components are subject to wear and tear that may not be obviously visible to the naked eye and that replacement or disassembly and overhaul are the only adequate means of ensuring the safe continued operation of the aircraft.

Airworthiness limitation is a specific term used in our industry to identify items whose overhaul or replacement is critical to the airworthiness of the aircraft. These items are specifically identified during the type certification process of the aircraft due to the critical nature of their purpose in the operation of the aircraft and are listed in a document specifically called an Airworthiness limitations listing. In most cases, little or no wear is acceptable and the replacement or in some cases overhaul, is critical.

We group service information and Airworthiness Directives together because they are very similar in nature. However, Airworthiness Directives are much more critical because they are literally regulations themselves. Both service information and Airworthiness Directives are issued to resolve some safety, quality, or configuration issue that has been found, generally after the type certification of the aircraft. Most commonly a specific problem is identified by issuance of a Service Bulletin by the aircraft manufacturer. When the problem is most critical in nature, the FAA will subsequently issue an Airworthiness Directive that echoes the Service Bulletin and in most cases refers directly to the Service Bulletin.

Weighing the inspection components

Those are the basic components of the aircraft inspection and maintenance program, now lets talk about the weight of each component. When we refer to “weight” what we are talking about is this. We are working in a regulated industry with specific guidelines that create levels of severity, or criticality when it comes to the components of an inspection program. Like it or not, some things simply matter more that others.

Part 91.409 (e) requires that the aircraft be inspected as outlined in the inspection program regardless of whether the inspection program is the one specifically recommended by the manufacturer or one submitted by the owner operator to the FAA and approved. The rule tells us to inspect the aircraft in accordance with that program and correct discrepancies found or it is not airworthy. As most of us know, that inspection program can consist of hundreds and sometimes thousands of specific items. Because that aircraft must be inspected in order to maintain its airworthy status, inspection items carry the same weight as the regulation itself.

Lubrication and servicing requirements are not specifically called out by the regulation and therefore carry a little less weight than inspections. We have discussed several times the fact that the inspection program includes lubrication and servicing references.

Some are of the mindset that simply because the lubrication or servicing requirement is included in the inspection program it carries the weight of the inspection program. Not so. FAA Order 8300.10 specifically addresses this issue in an effort to eliminate the confusion.

Obviously we must properly lubricate and service the aircraft, the idea here is that when a scheduled lubrication requirement comes due ahead of an inspection, we have the latitude to wait until the aircraft is down for the inspection to accomplish the lubrication.

Similarly, the overhaul and replacement items are not considered inspections and can be scheduled to coincide with the next inspection. When the manufacturer considers an overhaul or replacement item as critical, it simply calls it an Airworthiness limitation. Again, looking at Part 91.409 (e) we see that the term inspection is used specifically and that the regulation also calls out Airworthiness limitations specifically. This is not to say that we don’t need to overhaul or replace items that the manufacturer suggests. Again, we believe they are listed because the component is subject to wear that may not be visible to the naked eye. If that is the case, not replacing these components or not overhauling them as scheduled could be cause for concern as an inspector. But we do have a little latitude here for scheduling the aircraft down.

As mentioned before, the Airworthiness Directives are actually regulations themselves and therefore carry the weight of the regulation. Service information is a little different. If the service information that is issued by the manufacturer is considered an inspection item, then that service information can became part of the inspection program, literally. Generally manufacturers will have several levels of bulletins ranging from informational to mandatory. They will let us know what level of bulletin is most critical and it is that level that will be considered mandatory when it involves an inspection.

The two most costly expenses the owner operator has is maintenance costs and downtime. We are wise to properly track maintenance to allow for planning and scheduling that will result in the least amount of downtime as possible as well as ensure efficient completion of the maintenance. Understanding the regulations and how these maintenance items weigh in will help you provide the best service possible to your customers, thus keeping them coming back.