Is It 10 or More or 9 or Less?

Feb. 1, 2005
Passenger seats available defines maintenacne requirements.

When it comes to operating an aircraft under 14 CFR Part 135, the number of passenger seats available is the distinguishing factor chosen by the FAA to define maintenance requirements. The FAA recently issued a controversial piece of guidance material that has resulted in tons of industry attention as well as FAA safety inspector confusion. This month we will review the regulation and guidance material that frame up the issue and attempt to provide some direction for those who need some help in interpreting how it may affect their operation.

The regulation in question is 14 CFR Part 135.411:

Sec. 135.411 applicability

(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 Secs. 135.415, 135.416, 135.417, 135.421, and 135.423. An approved aircraft inspection program may be used under Sec. 135.419.

(2) Aircraft that are type certificated for a passenger seating configuration, excluding any pilot seat, of 10 seats or more, shall be maintained under a maintenance program in Secs. 135.415, 135.416, 135.417, 135.422, and 135.424 through 135.443.

(b) A certificate holder who is not otherwise required, may elect to maintain its aircraft under paragraph (a)(2) of this section.

(c) Single engine aircraft used in passenger-carrying IFR operations shall also be maintained in accordance with Sec. 135.421 (c), (d), and (e).

The purpose of this regulation is to define the applicability of Subpart J, titled Maintenance, Preventive Maintenance, and Alterations, of 14 CFR Part 135 and further define the applicability of different sections of the subpart if there are any distinguishing factors. The passenger seating configuration seat count, not counting the pilot seats, is divided between the nine and 10. Hence, the common terms used throughout the industry to distinguish between (a) (1) and (a) (2) of Part 135.411 are "nine or less" vs. "10 or more".

The differences

The key difference in the applicability of the rule is found in the portion of the rule that follows the phrase "shall be maintained under" in both paragraph (a) (1) and (a) (2). Basically, an aircraft operating under 14 CFR Part 135 with nine or less passenger seats is to be maintained primarily under the requirements of 14 CFR Parts 91 and 43. In addition, the nine or less operator must comply with sections 135.421 and 135.423 of Part 135. (Notice: Sections 135.415, 135.416, and 135.417 all apply to both nine or less aircraft as well as 10 or more aircraft. So for the purposes of this discussion they are irrelevant.)

In comparison, an aircraft operating under 14 CFR Part 135 with 10 or more passenger seats is to be maintained under a maintenance program created and approved under sections 135.422, and 135.424 through 135.443 of Part 135. Here in lies the problem. The requirements contained in sections 135.424 through 135.443 include development of a maintenance organization, a maintenance program, a maintenance manual, required inspection personnel, continuing analysis and surveillance, and training programs just to name a few. These requirements can add a significant additional burden to a Part 135 operator unfamiliar with the requirement. The obvious preference then is to operate aircraft with a passenger seating configuration of nine or less.


For more than a decade now the basic requirement of 14 CFR Part 135.411 has been the same. It has really only changed since its inception due to changes deeper in the regulation like addition or deletion of sections. Because this rule has been in place for many years, there are obviously many aircraft that are operating under the requirements of both nine or less and 10 or more, (Part 135.411 (a)(1) and (a)(2) respectively.

As an industry we all experience the unfairness of multiple interpretations of certain rules by the many different FAA offices and even at times, between different FAA safety inspectors within an office. The FAA interpretation of this rule, however, has been fairly clear since I can remember. What happened that caused uproar and attention is a few operators have decided to push the limits and interpretation of the rule in an effort to minimize their administrative requirements by trying to make their 10 or more aircraft a nine or less aircraft. FAA headquarters in Washington took a look at this trend and issued guidance material (FAA handbook bulletin HBAW 04-06) in an effort to eliminate and prevent misinterpretation of the rule. Only one problem, this guidance material has itself been misunderstood and misinterpreted and thus has caused a great deal of discussion throughout the Part 135 sector of our industry.

I cannot include the entire bulletin here, but it is available online at: http//

I will however cover what I believe to be the most pivotal point in the bulletin -- the term "type-certificated passenger configuration". The question "What is the type certificate passenger configuration?" is answered in the bulletin like this:

"The aircraft's type-certificated passenger configuration is the configuration as indicated in the type certificate (TC) or STC. For the purpose of determining maintenance requirements for a particular aircraft, passenger seats are any seats in the aircraft that are not pilot seats which are certified to be used during takeoff and landing."

So what does this really mean? Well, an approved seating configuration must be approved either by means of the type certificate or a supplemental type certificate. Don't read this wrong now. It says "as indicated in the type certificate or STC". Some are reading into that statement "type certificate data sheets" rather than type certificate. Type certificate data sheets provide a "maximum" seating configuration, not the only seating configuration.

You see, an aircraft receives its certificate of airworthiness from the factory once it "conforms to the type design and is in condition for safe operation" (see your airworthiness certificate). That means that the signature on the airworthiness certificate is in itself certification that the aircraft conforms to type design which is all of the data that supports the issuance of the type certificate from the FAA to the aircraft manufacturer. This can get a little muddy when you consider some aircraft receive an airworthiness certificate before the interior has been installed. To find out if your aircraft was originally certificated without a complete interior you must dig a little deeper into the records of the aircraft. If the aircraft was sent to a completion center for installation of the interior, then the approval of the interior installation becomes the supporting means of the seating configuration. The supporting approval for that installation is likely an STC. So, if the aircraft was originally placed into service with a seating configuration of nine or less passenger seats either directly from the factory or from a completion center, the approval means for the seating configuration is very likely complete and adequate to support a nine or less operation. You may need to research a little, but you should be able to obtain adequate certification.

Stretching the rule

Following are some examples of what operators have done in trying to stretch the rule to fit their needs. First of all, it is not a major alteration to remove a seat from the aircraft, however, simply removing the seat so that you can't seat 10 passengers does not change the approved seating configuration of the aircraft. Another example, it is not a major alteration to place a placard on a seat that informs passengers that the seat must not be occupied for takeoff and landing; however, this simple placard does not change the approved seating configuration of the aircraft.

It is possible that your aircraft seating configuration was altered without an STC. Contrary to popular belief, FAA field approvals have been around for many years. This has been an acceptable means of major alteration since there was a reason to distinguish between major alterations and minor alterations. However, with the issuance of this particular guidance document (HBAW 04-06), the FAA has taken a position that any seating configuration change that was previously approved by means of an FAA Field Approved 337 Form for the purpose of reducing the passenger seating configuration to nine or less is not an approved change. I personally do not agree with this position by the FAA but with that and $1.35 you can buy a Starbucks.

To enforce the new guidance material, many FAA safety inspectors out there are taking one look at the type certificate data sheet for the aircraft in question and making a decision about your operational requirements based on that. This is another example of a complex manufacturing issue being inadequately explained to the flight standards field inspectors, and consequently poorly implemented in the field. Even with the issuance of the handbook bulletin to explain the situation, the issue is being mishandled by some field inspectors. Most operators find themselves having to choose the worse of two evils. Should I push back with the FAA and keep my nine or less status or should I develop the maintenance program required for 10 or more. Sadly, most are choosing the 10 or more path.

So, I offer this encouragement to you. If your seating configuration was not changed after the aircraft was placed into service, most likely there was an approval process that you can look to that meets the requirements of the FAA's new policy. If your seating configuration was changed later in the life of the aircraft and an STC was used to certify the alteration, your aircraft should meet the requirements of the FAA's new policy. But you may need to educate your FAA safety inspector in order to gain their acceptance. Be gentle. Thanks for reading!

About the Author

Joe Hertzler