Reference 4, Chapter 1, Perform Field Approval of Major Repairs and Major Alterations, Section 1, paragraph 5D(2) states: “Acceptable data that may be used on an individual basis to obtain approval are:
- ACs 43.13-1A and 43.13-2A, as amended*
- Manufacturers technical information (for example, manuals, bulletins, and kits)
- FAA Field Approvals”
*NOTE 13: AC 43.13-1B, Change 1, dated September 27, 2001 superseded AC 43.13-1A.
When using a previous field approval as acceptable data, the pull test need not be done if it can be determined that a previous pull test applied 814 pounds for normal category or 910 pounds for utility or acrobatic category. Field approvals for shoulder harness installations should not be done by referencing a previous field approval and deleting the pull test, unless the attachment parts either have a PMA, or other FAA approval. If the attachment parts have no FAA approval, the strength is not known or assured, since they have not been manufactured to an FAA approved quality control system.
Shoulder harness installations attaching to the center of an unsupported wing carry through tube, or other unsupported member, should not receive a field approval without a design approval from an ACO. Applying the test load in such cases may cause damage or permanent set to the affected structure.
Existing FAA guidance, including AC 43.13-2A and AC 21-34, recommend against attachment to the center of unsupported members. Figure 9-16 in AC 43.13-2A shows typical shoulder harness attachments to tubular members. These are all at tube intersections and not at the center of unsupported tubes.
Figure 9-12 shows a typical wing carry through member installation. This is in the center of the carry through member that is a hat section as found in metal skinned airplanes. Part of the figure shows the hat section is riveted to sheet metal skin (which would provide longitudinal support
Personnel performing the field approval must assure that both the harness and belt are compatible and have a TSO approval.
3. Minor change. Part 21, § 21.93(a), Classification of changes in type design, states as follows: “A minor change is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product.”
Information provided to us by the Anchorage ACO suggests that some shoulder harness installations that provide known safety improvements have been approved as a minor change. In these situations, the FAA certificated mechanic who installs it makes an entry in the maintenance log of the airplane.
One shoulder harness installation kit supplier uses this process (no FAA approvals) to install shoulder harnesses in PA-18 airplanes. The installation does not require modification of the airframe. The front seat harness attaches to the center of the rear wing spar carry through tube. However, it may not meet the 9.0-g forward inertia load required by CAR 3.386. The kit supplier stated that some airplane owners who had accidents reported the harness installation had saved their lives.
In general, shoulder harness installations should not use the center of an unsupported wing carry through tube or other unsupported member as an attachment point. This type of attachment may pose a risk to the structural integrity of the airplane. Although the attachment may be a clamp-on fitting that does not alter the existing airframe, the installation may result in a major change in the type design. This is because the shoulder harness attachment may introduce new loading conditions into the carry through tube.
It is acceptable for the carry through structure to be damaged in an emergency landing. However, it is unacceptable for the tube to fail in-flight. Carry through tubes, loaded in compression, may experience a beam-column buckling failure if the occupant applies a load to the shoulder harness attachment. Occasionally, small loads on the shoulder harness attachment may cause beam-column buckling failures.
Some shoulder harnesses that have been installed by minor change do not have a TSO approval. TSO-C114, Torso Restraint Systems, was issued March 27, 1987.
Torso restraint systems manufactured before that date did not have to meet the prescribed SAE standard, Aerospace Standard 8043, “Aircraft Torso Restraint System,” dated March 1986. AC 43.13-2A and AC 21-34 provide guidance for acceptable harnesses. Acceptable harnesses for minor change installations include:
- harnesses that meet TSO-C114 or Military Specification (MIL-SPEC) requirements,
- harnesses that have been produced under a PMA, or
- other harnesses appropriate to the certification basis of the aircraft.
We have studied the circumstances and legality of shoulder harness installations done by minor change. An airplane owner may wish to install shoulder harnesses, but an STC or prior field approval is not available for his airplane. In this case, it is not likely that an individual airplane owner would apply for an STC or a field approval since the owner would need to hire an engineering consultant to perform 111
the structural test and any associated structural analysis. Also, there is a possibility the airframe may be damaged during the pull test. In such installations, a pull test would not be done and there is no assurance the installation will provide occupant protection to the ultimate inertia force requirements (the 9.0-g forward force) of § 23.561 or CAR 3.386.
About the legality of shoulder harness installation by minor change, we conclude the following: Since CAR 3.386 and § 23.561(b)(1) before Amendment 23-36 (which became effective September 14, 1988) state that “proper use is made of belts or harnesses provided in the design,” the previously approved seat belt installation alone must meet the prescribed ultimate inertia forces.
CAR 3.652, Functional and installation requirements, states as follows: “Each item of equipment which is essential to the safe operation of the airplane shall be found by the Administrator to perform adequately the functions for which it is to be used, shall function properly when installed, and shall be adequately labeled either for identification, function, operational limitations, or any combination of these, whichever is applicable.”
Before Amendment 23-20 (which became effective September 1, 1977), § 23.1301 contained essentially the same requirement as CAR 3.652. Amendment 23-20 deleted the words “essential to safe operation” and made the provisions of § 23.1301 applicable to “each item of installed equipment.”
We conclude from these rules that if a shoulder harness is not required equipment, it is not essential to the safe operation of the airplane. Therefore, CAR 3.652 and § 23.1301, before Amendment 23-20, should not be used as a basis to prohibit shoulder harness installation by minor change. These rules should be applied to shoulder harness installations made by STC and field approval.
The mechanic making such installations should consult AC 43.13-2A, Chapter 9, for information on restraint systems, effective restraint angles, attachment methods, and other details of installation.
See AC 21-34, “Shoulder Harness-Safety Belt Installations,” AC 21-25A, “Approval of Modified Seats and Berths,” and AC 43.13-2A, “Acceptable Methods, Techniques, and Practices—Aircraft Alterations.”
Aft-facing and side-facing seats
For aft-facing seats, seat obliqueness should be limited to 15 degrees unless additional occupant protection for side-facing seats is installed.
Part 23 allows side-facing seats, but it does not address the crashworthiness problems of these installations. We recommend that side-facing seat installations be discouraged. If such an installation is made, the following should be applied as well as any applicable rules from the original certification basis:
a. A sideward facing seat is defined as one in which the plane of symmetry of the occupant makes more than an 18 degrees angle with the vertical plane containing the airplane centerline when viewed from above.
b. Each occupant of a sideward facing seat should be protected from serious head injury when experiencing the inertia forces of § 23.561(b)(2) by both a safety belt and energy absorbing rest that will support the head and torso or by a safety belt and shoulder harness that will prevent the head from contacting any injurious object. There should be adequate padding on any restraining bulkhead. Riding up of diagonal shoulder straps on the neck, which could cause neck injury, and location of attachments and rigidity of the seat support that could cause twisting and compression of the spine should be considered. For a multiple side-facing seat, a passenger seated immediately forward of another passenger cannot be considered an energy absorbing rest (human cushion).
c. Sideward facing seat installations that do not comply with paragraph “b” above should be placarded to prohibit occupancy during takeoff and landing. The sidefacing seats still require one seat belt for each passenger to protect against inflight turbulence, and the berth should be considered an item of mass for emergency landing conditions of § 23.561.
d. Special conditions will be required for sideward facing seats that are to be occupied during takeoff and landing when the certification basis requires compliance with § 23.562, Emergency landing dynamic conditions.
Seat Removal for Parachute Operations
This guidance is intended for engineering assistance in the field approval process, TC approval or STC approval of sport parachute modifications to small airplanes. The Small Airplane Directorate has received NTSB recommendations on the safety record of small airplanes that have been modified for use in sport parachute operations.
Most of these modifications have been approved by FAA Form 337 field approvals without engineering assistance. These modifications should either be approved by the TC process, STC process or by a field approval with engineering assistance.
ACOs should not provide engineering assistance for sport parachute 113
modifications that change the limitations of an airplane or affect primary structure, required systems and equipment, handling, crashworthiness or performance. They should be completed using an STC or TC.
The acceptability of sport parachute operations is given in operational regulations.
14 CFR, part 91, allows the use of the cabin floor for sport parachute operations and requires the operations be conducted per 14 CFR, part 105. Part 105 requires radio equipment for operations in controlled airspace, but there are no other equipment requirements other than the parachutes. AC 105-2C, “Sport Parachute Jumping,” gives information on complying with the regulations and provides a list of airplanes that may be operated with one cabin door removed. The part 91 regulation means floor seating is acceptable only for sport parachute operations, but this does not mean the crashworthiness of the airplane can be unacceptable or that an unsafe condition can be created by a modification.
The small airplane certification basis is mostly CAR 3 or early part 23. The modifications include: seating capacity increases, seat and restraint removal and replacement belt installation, door removal for airplanes not listed in AC 105-2C, step and hand holds on airplane exteriors, gross weight increases and CG changes.
Seating capacity increases can be acceptable if: 1) all people are protected in emergency landing loads per § 23.561 (3.386), 2) all persons are secured against sliding backwards in climbs to maintain an acceptable CG position, and 3) any changes in allowable CG range and increased gross weight are found acceptable. The applicant should also supply data to show that emergency exits are not crowded in a ground evacuation with the increased seating capacity per § 23.807 (3.387). This test/analysis must be done with all occupants except one representing a pilot in a parachute, and all parachutists initially restrained in place by the replacement belts/restraints.
Removal of certified seats, seat belts and shoulder harnesses, if any, is allowable per part 91, § 91.207(a)(3)(ii). This does not remove the requirement to prevent an unsafe condition in an emergency landing or normal operations. The replacement belts/restraints should, therefore, meet the requirements for emergency landing upward, forward and sideward loads, per § 23.561 (3.386), and secure all people against sliding backwards in climbs to maintain an acceptable CG position. Per § 23.785 (3.390), the attachment of the replacement belts/restraints to structure must have a factor of 1.33 times the emergency landing loads in § 23.561 (3.386). A simple belt that fastens across the lap of a person sitting on the cabin floor is not acceptable. This prevents movement only in the direction the person is facing. For instance, facing to the rear (as has been reported) prevents movement toward the tail in a climb, but it does not secure a person against uncontrolled movement toward the front in an emergency landing. The FAA and the United States Parachute Association (USPA) have tested a pair of adjustable belts attached to the parachute harness and found that they are more effective in providing restraint while the emergency-landing 114
forces dissipate. We find it acceptable, therefore, for a parachutist to use adjustable belts instead of the seat belt. Acceptable restraint systems for floor seating of sport parachutists are given by the Civil Aeromedical Institute (CAMI) of the FAA in Report DOT/FAA/AM-98/11, “Evaluation of Improved Restraint Systems for Sport Parachutists,” dated March 1998. The dual-strap restraints (5D, 6D and 7D) provided the least flailing and bending of body segments and the least forward translation of the pelvis. ACOs should require one of these restraint systems for any TC, STC or engineering assistance to a field approval. Limitations should be imposed to call out the three operational procedures on page 21 of the CAMI Report.
The dual strap restraints have been tested with floor attachments. So far, there has not been any acceptable testing of a sidewall attachment. An applicant who wants to attach a restraint system to a sidewall will need to perform sled testing by an approved procedure to verify its relevance in the emergency landing loads.
An acceptable procedure for use of the dual-strap restraints (5D, 6D and 7D) is as follows:
a. Sit on the aircraft floor between two seat rails facing aft.
b. Attach two adjustable belts to your parachute harness for the 5D, 6D, or 7D configuration. You may loop the adjustable belt through your parachute harness webbing or you may attach a quick-release clip through the ring on your harness.
c. Attach the other end of each harness to the seat rail in the aircraft floor. Make the attachment to the floor rail on the same side as the attachment to your harness.
d. Adjust the belt as snugly as possible without causing discomfort.
NOTE 14: If possible, place a lap belt attached to the floor rails around your upper legs to prevent flailing during the emergency landing.
Door removal raises issues in Subpart B of 14 CFR part 23. Performance, stability, and control must be found acceptable with the door removed in flight. If the AFM gives performance numbers such as takeoff and takeoff over a 50-foot obstacle, the applicant should verify that performance or issue a Flight Manual Supplement (FMS) with the revised numbers. Of course, the applicant does not have to present any data or do any tests for airplanes that are listed in AC 105-2C.
Steps and handholds to be installed on the exterior of a small airplane should be shown to meet the structural strength and fatigue requirements in part 23 (CAR 3).
Carriage of parachutists outside the aircraft must be shown to not be hazardous in a power loss failure in takeoff and climb flight phases.
Increases in gross weight and allowable CG range should be shown to comply with the requirements in part 23 (CAR 3) as would any other modification that affected these numbers.
Aircraft modified for sport parachute operation must include a placard or flight manual limitation that prohibits flight with doors or seats removed except in sport parachute operation.
Amendment 23-7 and Subsequent A revision to NPRM 67-14 explains this amendment as follows: “Experience indicates that a significant reduction in injuries and fatalities in small airplane accidents may be obtained by the installation and use of effective upper body restraints or by designing airplane interiors to either eliminate injurious objects within striking radius of the head or provide energy absorbing support for the upper torso. This proposal would therefore apply, to small airplanes, standards identical with those long administered for large airplanes under Sec. 25.785(c).”
AC 23-28, when issued, will provide information and guidance applicable to the static strength substantiation of the attachment points for occupant restraint system installations, which have both a safety belt and shoulder harness.
Amendment 23-36 and Subsequent A revision to NPRM 86-19 explains this amendment as follows: “The FAA is proposing a substantial revision of the current and new requirements for seats, berths, litters, safety belts, and shoulder harnesses. The revision is considered necessary to present the proposed requirements in a more logical sequence as a result of the new requirements being proposed by this rulemaking action. The new requirements are based to a large extent on the proposals submitted by the GASP to the Part 23 Airworthiness Review Program. The GASP proposals were based in large measure on FAA, NASA, and NTSB research studies and impact/accident analyses.”
See guidance for § 23.562, Emergency landing dynamic conditions.
See guidance for dynamic seat certification in AC 20-146, “Methodology for Dynamic Seat Certification by Analysis for Use in Part 23, 25, 27, and 29 Airplanes and Rotorcraft.”
Part 23 did not envision more than two seats on the flight deck, although the part does not prohibit such an installation. The airworthiness standards do not contain adequate standards for an “observer” seat (occupied by an FAA Flight Standards inspector on commuter flights). Therefore, we would expect to apply special conditions to such an installation that would address occupant restraint, emergency egress, and appropriate 116
placarding to prohibit use by a passenger under any circumstances. The special conditions should establish a level of safety equivalent to that established in the certification basis of the airplane. This is not only for the observer seat occupant but also the crewmember seated in front of the occupant.
The weight of a parachute is included in the 215-pound occupant weight if a parachute is required. The weight remains at 215 pounds when a parachute is not required.
23.787 Baggage and cargo compartments
The corresponding rule in CAR 3 is CAR 3.392.
The corresponding rule in the Airship Design Criteria, FAA-P-8110-2, Change 2, is section 4.35.
Original Issue and Subsequent
Questions have been raised about § 23.787(c), which requires an ultimate inertia forward force of 4.5g for to protect passengers from any cargo compartment. This regulation is related to the CAR, which imagined a crew compartment forward, a passenger compartment in the middle followed by a bulkhead and a small cargo/baggage compartment aft. In this concept, the 4.5g was considered satisfactory based on NASA data that showed g forces become less as distance from the nose increases in a typical crash. Our review of all cargo configurations has led to the conclusion that under § 23.561(b) and (e), the restraining devices should meet the 9g requirements. The up and side load inertia forces are not considered to be applicable in this case where the crew would not be subject to injury from upward or sideward cargo movement.
To modify a passenger plane to an all-cargo configuration, the following items should be considered:
a. The cargo compartment should meet the requirements of § 23.787. Special attention should be given to cargo loading placards and the cargo restraint system.
b. The cargo restraint system, including tie downs and the supporting structure to which they are attached, should be substantiated to the emergency landing ultimate inertia forces in § 23.561(b)(2).
c. The floor loading should be re-substantiated to assure the floor structure is not overloaded.
d. Emergency egress from an emergency exit or the entrance door should be verified accessible for the crew.
e. A supplement to the AFM weight and balance section that shows the various permissible cargo loading arrangements and cargo restraints should be furnished.
Guidance on Carriage of Hazardous Cargo for Operators of part 23 Certificated Aircraft 118
There are no 14 CFR, part 23, airworthiness standards that directly address the design of an aircraft to allow for the carriage of hazardous cargo and passengers simultaneously. We cannot, therefore, provide guidance on the issuance of ATCs or STCs specific to this operation.
However, for the carriage of cargo and baggage in general, 14 CFR, part 23, does provide certification requirements for baggage and cargo compartments. Specifically, § 23.787 “Baggage and cargo compartments,” which focuses on the design requirements of the baggage or cargo compartment and its integration with the airframe.
§ 23.855 “Cargo and baggage compartment fire protection” focuses on the shielding, insulation, and flammability requirements of cargo or baggage containers. In addition, this regulation adds additional requirements and tests on cargo and baggage compartments for use in commuter category aircraft.
Title 49, § 175.85, states that hazardous materials may be carried in a main deck cargo compartment of a passenger aircraft. This is provided the compartment meets all certification requirements for a Class B aircraft cargo compartment as defined in 14 CFR, part 25, § 25.857.
The certification requirements for Class B cargo compartments exceed the requirements identified in §§ 23.787 and 23.855. Normally, a Class B cargo compartment is not a certification requirement for a part 23 certificated airplane.
However, a cargo compartment may be certificated, using either an ATC or STC process possibly involving special conditions, if it meets the appropriate airworthiness design standards for a Class B aircraft cargo compartment. Any ATC/STC effort must be coordinated with the responsible ACO.
Once approved, a Class B cargo container installation in a part 23 certificated aircraft does not necessarily entitle the operator to carry hazardous cargo. The operator must also show compliance with the appropriate operational rules and requirements of 14 CFR, part 135, and Title 49 governing the carriage of hazardous cargo. For additional information on part 135 requirements, we recommend the operator contact their local FSDO.
Amendment 23-14 and Subsequent See AC 23-2, “Flammability Tests.”
A proposed revision to NPRM 71-13 explains this amendment as follows: “This proposal would make it clear that it is not only the cargo shifting that would affect the CG of the airplane that is covered by the rule but it is also cargo shifting which could damage essential controls, equipment etc. In addition, for airplanes in which cargo is carried in the passenger compartment the proposal would make the higher 119
inertia forces of Sec. 23.561(b)(2) applicable to the protection of the passengers.”
Amendment 23-36 and Subsequent A proposed revision to NPRM 94-21 explains the amendment as follows: “Section
23.787(c) is proposed to be revised because, as presently stated, the required ultimate forward inertia force for cargo restraint is not adequate considering the current requirements of Section 23.561. It was the consensus at the conference that cargo restraint should be at least to the ultimate inertia forces of Section 23.561 to adequately protect occupants forward of the cargo. In addition, when designs provide for cargo to be carried in the same compartment with occupants, it is proposed that means be provided to restrain the cargo, at least to the loads resulting from the emergency landing dynamic conditions being proposed in Section
23.562(b)(2). It is considered necessary to protect occupants from cargo being forced into their occupied area as a result of an emergency landing when they are otherwise being adequately protected from serious injury. The increased ultimate static load factors will achieve this objective.”
The rigid movable/removable cargo restraint bulkhead attached to seat rails and to points along the cabin sidewalls and roof is considered a structure per § 23.787(c).
Before this amendment, the loads to design this structure were not defined, but the loads for a cargo restraint system and tie downs in a cargo compartment had to withstand an ultimate inertia force of 4.5g. Even though not defined, some certification programs applied a 4.5g ultimate load factor to design a rigid movable/removable cargo restraint bulkhead in the cabin. The reason was to bring occupant protection to a 9g forward load. In this amendment, the ultimate forward load factor for any cargo restraint system and tie downs has been increased to 9g. In this case, the structure can be designed to no load since the occupant protection of 9g has been met by the cargo restraint system and tie downs.
If this structure separates the occupant compartment from the cargo compartment, only § 23.787(c) applies. Section 23.787(b) is applicable if cargo is carried aft of the occupants in the same occupant compartment. The ultimate load factor in § 23.561 has been increased to 18g by Amendment 23-36.
Amendment 23-49 and Subsequent
A proposed revision to NPRM 94-21 explains this amendment as follows: “Section
23.787 would be revised by extending the present requirements for cargo compartments to baggage compartments. As proposed, future baggage compartments on all airplane categories would be required to be placarded for their maximum weight capacity; have a means to prevent the baggage from shifting; and have a means to protect controls, wiring, lines, and equipment or accessories that are located in the compartment and whose damage or failure would affect safe operation of the airplane. These standards have been applicable to cargo compartment design 120
for same time and should be applied to baggage compartments since the same safety factors are involved. Because manufacturers recognize the need for these standards, many of these provisions have been included in the current design of baggage compartments and, therefore, the proposed requirements are not expected to create a significant burden. With this revision the commuter category requirements of Sec.
23.787(g) would be redundant and that requirement is being removed.
Proposed revisions to this section would also move the substance of paragraphs (d) and (f) to a proposed new Sec. 23.855, which will address cargo and baggage compartment fire protection.
Proposed new paragraph (c) of this section would require flight crew emergency exits on all cargo-configured airplanes to meet the requirements of Sec. 23.807. This requirement would provide increased assurance that flight crews of all cargo airplanes will have ready access to an emergency exit.”