What Makes Up the Inspection Program for Turbine Aircraft?: Part 3 of 3

This is the third of a three part series dedicated to understanding aircraft inspection programs, primarily twin-turbine powered aircraft inspection programs. In this article we will delve into 14 CFR Part 135 inspection program requirements.

Nine or less vs ten or more
Part 135 has two major maintenance categories — one for aircraft configured for seating capacity of 9 passengers or less and the other for seating capacity of 10 passengers or more. This distinction is found in 14 CFR Part 135.411.
14 CFR Part 135.411
"(a) This subpart prescribes rules in addition to those in other parts of this chapter for the maintenance, preventive maintenance, and alterations for each certificate holder as follows:
(1) Aircraft that are type certificated for a passenger seating configuration, excluding any pilot seat, of nine seats or less, shall be maintained under parts 91 and 43 of this chapter and §§ 135.415, 135.416, 135.417, and 135.421.
(2) Aircraft that are type certificated for a passenger seating configuration, excluding any pilot seat, of ten seats or more, shall be maintained under a maintenance program in §§ 135.415. 135.416. 135.417, and 135.423 through 135.443."
In general terms, the difference between these two categories is that aircraft with 10 or more passenger seats must be maintained under a maintenance program (Ref Parts 135.423 through 135.443). Such a maintenance program must be developed as part of the air carrier certification process or when adding a 10 or more aircraft to an existing certificate.
The nine or less aircraft operating under Part 135 must be maintained just like aircraft under Part 91 with the addition of the requirements defined in 135.421.

Its more than an inspection program — it’s a maintenance program
One significant difference to point out when comparing Part 91 maintenance requirements to Part 135 maintenance requirements is found by comparing the following abbreviated rules:
14 CFR Part 91.409 (e) "Large airplanes — and emergency equipment, is inspected in accordance with an Inspection program—in lieu of an inspection option of 91.409(f)."
14 CFR Part 135.421 (a) "Each Certificate holder who operates an aircraft type certificated for a passenger seating configuration, excluding any pilot seat, of nine seats or less, must comply with the manufacturer’s recommended maintenance programs, or a program approved by the Administrator, for each aircraft engine, propeller, rotor, and each item of emergency equipment required by this chapter."
14 CFR Part 135.425 "Each Certificate Holder shall have an inspection program and a program covering other maintenance, preventive maintenance, and alterations—"
In this comparison, we see Part 91.409 (e) states that an aircraft must be "Inspected," whereas Part 135 states that aircraft operated under that Part shall be maintained in accordance with a "Maintenance Program."

So what is the big difference?
The definition of maintenance in 14 CFR Part 1 is: "Maintenance – means inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance."
You see, inspection is a subpart of maintenance and maintenance also includes overhaul, repair, preservation etc. We discussed in detail the requirements of the inspection program under Part 91 last issue so this month we will focus our attention on the maintenance program under Part 135.
Part 135 states that for an aircraft with nine or less passenger seats, the maintenance program must include the maintenance program recommended for the "aircraft engine, propeller, rotor, and each item of emergency equipment—", so the scope of the maintenance program is not limited to just the aircraft manufacturer.
In part two of this series, we showed that some of the manufacturer’s maintenance recommendations are optional under Part 91 because they are not inspections, but, they are still part of the recommended maintenance program. Under Part 135, those recommendations become mandatory.
Examples of maintenance items which are not specifically called inspections may include overhauls, lubrications, and servicing. These are the types of items that become mandatory under Part 135. Nevertheless, they should always be accomplished as recommended even when operating under Part 91.
Reading further into 14 CFR Part 135.421, paragraph (b) we find a definition of the "manufacturer’s maintenance program"
14 CFR Part 135.421 (b) – "For the purpose of this section, a manufacturer’s maintenance program is one which is contained in the maintenance manual or maintenance instructions set forth by the manufacturer as required by this chapter for the aircraft, aircraft engine, propeller, rotor or item of emergency equipment."
One thing to point out and discuss at this time is that paragraph (a) of Part 135.421 does not include the term "aircraft," just before "aircraft engine," whereas, paragraph (b) does.
Some FAA inspectors interpret this to be a purposeful omission by the rule makers. They believe that when operating under Part 135, you are not required to perform recommended maintenance, other than inspection, for the aircraft.
We believe, however, that the aircraft manufacturer’s maintenance requirements are included as mandatory maintenance requirements under Part 135.421 for two reasons:
1. The title of Part 135.421 is "Additional Maintenance Requirements" and is referenced by Part 135.411 (a)(1) which uses the term "shall be maintained" when referring to the aircraft.
2. Part 135.421 (b) includes the term "aircraft" when defining the manufacturer’s maintenance program.
I mention this merely because the difference in interpretation is very obvious between FAA offices and regions. One FAA FSDO will require that all maintenance items be accomplished along with normal Part 91 inspection requirements, while another will "let you in on a little secret" that in Part 135.421 (a) "they left out aircraft." It is very important that you understand your FAA’s position regarding this rule to prevent a violation.

The Operation Specification (Op Spec)
The Air Carrier Operation Specification (Op Spec) contains information that is particular to the air carrier and its aircraft as defined by the air carrier during certification and approved by the FAA as signified by approval signature on the operation specification. One of the many specifications contained in the Op Spec is "additional maintenance requirements." There are specific sections in each operation specifications under Part D dealing with additional maintenance requirements. Those sections of the Op Spec cover emergency equipment, engines, propellers and prop governors. (Notice the relationship between 135.421 and the additional maintenance requirements section of the Op Spec.)
Because the Op Spec is specific to the air carrier, each air carrier is required to define the maintenance document by which the additional maintenance requirement will be governed. This includes time between overhauls for the equipment, as well as specific inspection limitations and guidelines. If an air carrier wants the time interval to be greater that that recommended by the manufacture, they must justify the extension to the FAA and produce their own document to follow for that maintenance.

The Approved Aircraft Inspection Program (AAIP)
We were involved in a pre-purchase a few years ago of an aircraft (9 or less passenger seats) that had been operated under an air carrier certificate issued under Part 135. The operator had created, and the FAA had approved, an AAIP for his aircraft. We found out later that the FAA had mandated the creation of the AAIP as criteria for the air carrier certification and had supported that decision with Part 135.419. In this particular case, the inspection program recommended by the manufacturer had changed so much during the time the aircraft was operated under the air carrier certificate, that the cost to get the aircraft back up to the manufacturers standard was prohibitive.
14 CFR Part 135.419 states that the FAA can decide that the manufacturers maintenance program is not adequate for the Air Carrier’s operation. In that case ,the air carrier is required to create an inspection program and have it approved.
In summary, the difference between aircraft operated under Part 91 and those operated under Part 135 is inspection vs maintenance. The manufacturer’s maintenance program includes non-inspection items such as servicing, overhaul, and recommended replacements, and the manufacturer does not differentiate between Part 91 and Part 135. However, because Part 135 requires the aircraft be maintained in accordance with a "maintenance program," the non-inspection items that are recommended and optional under Part 91 become mandatory under Part 135.
Be sure to tune in next month when we will discuss operating a repair station business and the impact of the changes to the repair station rule 14 CFR Part 145. AMT

The previous articles in this series can be viewed online in the Article Archives.