23.781 Cockpit control knob shape Amendment 23-33 and Subsequent This rule did not envision a single power lever installation. See § 23.777 for guidance applicable to single power lever controls.
23.783 Doors Original Issue and Subsequent An Equivalent Safety Finding process for part 23, § 23.783(b), should include the following:
a. Pilot operated locks when the propeller stops turning.
b. A special operating procedure to ensure the door is opened only after the propeller has stopped turning should be provided in the flight manual and on the inside of the door.
c. If an electric lock is used, complete loss of electric power should not affect opening the door.
d. The door should be designed and placarded so it can be opened from the inside by passengers and from outside by ground personnel.
e. A railing or guard that would deploy to guide passengers away from the propeller plane should be provided as an integral part of the door.
f. If engagement of the engine starter would be an immediate hazard to a person near the propeller, an interconnection between the door and the engine starting circuit should be included in the design.
Amendment 23-34 and Subsequent The direct visual inspection of the locking mechanism by crewmembers to determine whether external doors, for which the initial opening movement is outward, are fully closed and locked may be conducted from outside the airplane. It will be necessary to provide a means to visually inspect each individual lock of the locking mechanism. Means that do not permit direct visual inspection of each lock are unacceptable unless there is no failure mode of the locking mechanism that would allow a false visual indication that each latch is properly positioned and locked. If optical devices are used from either inside or outside, it should be determined that they are not subject to fogging, to obstruction by foreign objects, or to a false indication of a locked condition.
The locking mechanism should incorporate features that provide a positive means to prevent the door from vibrating open throughout the approved operating envelope. Over center features of the mechanism are not acceptable as a locking means. Also, it should not be possible to position the locks in a locked position if any of the latches are not in the fully latched position.
87 Amendment 23-36 and Subsequent Section 23.783(c) was adopted to provide standards that would ensure the opening means of passenger and crew doors were simple, easy to locate, could be operated in darkness, and ensure the doors met particular marking requirements. Overly complex opening means had been identified as a major contributor in accident investigations. The particular marking means are those of § 23.811. Paragraph 23.783(c)(3) was adopted mainly as a measure to ensure that the opening means of passenger and crew doors were kept as simple as possible, and that these doors could be located and opened in a timely manner.
Paragraph 23.783(c)(4) was adopted in order to make the location of cabin doors more conspicuous and to facilitate emergency evacuation.
These requirements do not mandate the use of self-illuminated or electrically illuminated external markings. A reasonable and acceptable method of compliance can be found in § 23.807 by substituting “passenger or crew door” where reference is made to “emergency exit.”
This amendment added a requirement that doors be reasonably free of jamming from fuselage deformation from the ultimate load factors found in the General Requirements for Emergency Landing Conditions (23.561) and the limit Proof of Structure (23.307(a)).
Some applicants choose ultimate Proof of Structure loads as a higher level of safety than proposed here. Methods used to demonstrate compliance with these requirements should include:
A determination from tests that each emergency door can be opened from inside and outside the airplane after imposing each critical static test load condition from the following limit flight and ground design load requirements (provided they equal or exceed the Emergency landing Conditions).
FLIGHT LOADS General (§ 23.321) Symmetrical flight conditions (§ 23.331) Flight envelope (§ 23.333) Design airspeeds (§ 23.335) Limit maneuvering load factors (§ 23.337) Gust load factors (§ 23.341) Pressurized cabin loads (for flight, § 23.365(a) and (b); and for landing, § 23.365(a) and
(c))
GROUND LOADS General (§ 23.471) Ground load conditions and assumptions (§ 23.473) Landing gear arrangement (§ 23.477) Level landing conditions (§ 23.479) Tail down landing conditions (§ 23.481) One-wheel landing conditions (§ 23.483) Side load conditions (§ 23.485).
Amendment 23-49 and Subsequent This amendment adds a requirement that passenger doors not be located with respect to any other potential hazard as well as the propeller disk. These hazards could include hot anti-ice, hot de-ice surfaces, and sharp objects on the airplane structure.
23.785 Seats, berths, litters, safety belts, and shoulder harnesses Original Issue and Subsequent Methods of Approval of Retrofit Shoulder Harness Installations in Small Airplanes A retrofit shoulder harness installation in a small airplane may receive approval by Supplemental Type Certificate (STC), Field Approval, or as a minor change. An STC is the most rigorous means of approval and offers the highest assurance the installation meets all the airworthiness regulations. A Field Approval is a suitable method of approval for a shoulder harness installation that needs little or no engineering. Shoulder harness installations may receive approval as a minor change in certain cases. In such cases, the FAA certificated mechanic who installs the shoulder harness records it as a minor change by making an entry in the maintenance log of the airplane.
The FAA does not encourage the approval of retrofit shoulder harness installations as minor changes. The preferred methods of approval are Supplemental Type Certificate or Field Approval. However, the FAA should not forbid the approval of a retrofit shoulder harness installation as a minor change in: the front seats of those small airplanes manufactured before July 19, 1978, and in other seats of those small airplanes manufactured before December 13, 1986.
A retrofit shoulder harness installation may receive approval as a minor change in these small airplanes if:
The installation requires no change of the structure (such as welding or drilling holes).
The certification basis of the airplane is 14 CFR part 23 before Amendment 23-20, part 3 of the Civil Air Regulations, or a predecessor regulation.
In addition, a minor change installation should follow the guidance for hardware, restraint angles, and attachment locations provided in the following:
Advisory Circular (AC) 43.13-2A, Acceptable Methods, Techniques, and Practices Aircraft Alterations.
AC 21-34, Shoulder Harness - Safety Installations.
AC 23-4, Static Strength Substantiation of Attachment Points for Occupant Restraint System Installations.
90 Installations approved as a minor change may not provide the occupant with the protection required by regulation (Civil Air Regulation (CAR) 3.386 or 14 CFR part 23, § 23.561). However, a properly installed retrofit shoulder harness installation is a safety improvement over occupant restraint by seat belt alone.
References Advisory Circular (AC) 21-34, Shoulder Harness — Safety Belt Installations, June 4, 1993.
AC 23-4, Static Strength Substantiation of Attachment Points for Occupant Restraint System Installations, June 20, 1986.
AC 43.13-2A, Acceptable Methods, Techniques, and Practices — Aircraft Alterations, Revised 1977.
Order 8300.10, Airworthiness Inspector’s Handbook, Change 12, December 14, 1999, Volume II.
Technical Standard Order (TSO)-C114, Torso Restraint Systems, March 27, 1987.
Technical Standard Order C-22g, Safety Belts, March 5, 1993.
What are the Requirements?
1. Front seat shoulder harnesses required. Section 23.785 of 14 CFR part 23 as amended by Amendment 23-19 effective July 18, 1977, required all normal, utility, and acrobatic category airplanes for which application for type certificate was made on or after July 18, 1977, to have an approved shoulder harness for each front seat. Section 91.205(b)(14) requires all small civil airplanes manufactured after July 18, 1978, to have an approved shoulder harness for each front seat. The shoulder harness must be designed to protect the occupant from serious head injury when the occupant experiences the ultimate inertia forces specified in § 23.561(b)(2). The inertia force requirements are discussed in paragraph 3 below.
2. Shoulder harnesses required at all seats. Section 91.205(b)(16) requires all normal, utility, and acrobatic category airplanes with a seating configuration of 9 or fewer seats, excluding pilot seats, manufactured after December 12, 1986, to have a shoulder harness, for forward-facing and aft-facing seats, that meets the requirements of § 23.785(g) [which requires that the occupant be protected from the ultimate inertia forces specified in § 23.561(b)(2)]. Section 23.785(g) also
91 provides: “For other seat orientations, the seat and restraint means must be designed to provide a level of occupant protection equivalent to that provided for forward and aft-facing seats with safety belts and shoulder harnesses installed.”
The above part 91 operating rule stems from § 23.2, Special retroactive requirements, Amendment 23-32, effective December 12, 1985.
3. Belts or harnesses provided for in the design. Civil Air Regulation (CAR) 3.386 and part 23, § 23.561, Amendments 23-0 through 23-34, effective February 17, 1987, require occupant protection from serious injury during a minor crash landing when “proper use is made of belts or harnesses provided for in the design,” when the occupants are subjected to the following ultimate inertia forces:
Normal & Utility Category Acrobatic Category Forward 9.0g 9.0g Sideward 1.5g 1.5g Upward 3.0g 4.5g With Amendment 23-36, effective September 14, 1988, the text of § 23.561 quoted above was changed to read: “proper use is made of seats, safety belts, and shoulder harnesses provided for in the design.” Section 23.785(b) was also changed to read:
“Each forward-facing or aft-facing seat/restraint system in normal, utility, or acrobatic category airplanes must consist of a seat, safety belt, and shoulder harness that are designed to provide the occupant protection provisions required in § 23.562 of this part. Other seat orientations must provide the same level of occupant protection as a forward-facing or aft-facing seat with a safety belt and shoulder harness, and provide the protection provisions of § 23.562 of this part.”
The emergency landing ultimate inertia load factors have remained unchanged from Amendment 23-36 through Amendment 23-54, effective December 20, 2000.
Amendment 23-54 is the latest amendment level to part 23.
For inertia force requirements for occupant protection preceding CAR 3, refer to Table 1 in AC 21-34, which lists the requirements for the regulations dating from Bulletin 7-A to the original part 23.
What are the methods of approval for retrofit shoulder harness installations?
1. Supplemental Type Certificate (STC). An STC is the most desirable and most rigorous approval. The STC offers the highest assurance that all of the airworthiness regulations have been met. The STC approvals are issued by the FAA Aircraft Certification Offices (ACO's). STC approvals are usually obtained
92 by a shoulder harness installation kit supplier for multiple airplane installations in an airplane model or model series.
AC's 21-34 and 23-4 (References 1 and 2) provide guidance and acceptable means of compliance for shoulder harness and seat belt installations. AC 23-4 specifically addresses part 23 installations. These AC's are also applicable to installations in airplanes having a certification basis of predecessor regulations (for example, CAR 3).
An applicant for an STC may use a salvaged airplane fuselage to substantiate the strength of the fuselage and the shoulder harness attachment fittings by structural tests, since the shoulder harness attachment structural test may damage an airworthy fuselage. It may be a problem that the available test airframe may be stronger than the lowest strength production airframe. This may be a problem in steel tube airframes.
During many years of producing such airframes, various specification materials may have been used. For example, many CAR 3 (and predecessor regulations) airplanes were originally produced from 1025 steel tubing and later constructed from higher strength 4130 steel. In one case studied, two different specification 1025 steel tubes were used which may have an ultimate tensile strength (UTS) ranging from 55,000 to 79,000 pounds per square inch (psi). The UTS of 4130 steel is 90,000 to 95,000 psi.
The test article should be representative of the lowest strength production airframe. This may be accomplished by a conformity inspection using the production drawings. The strength of materials of parts affected by the modification needs to be verified by the airframe manufacturer’s process and production records. The serial number of the test article needs to be verified.
An alternative course of action would be to determine, by appropriate tests (for example, chemical analysis, hardness tests, strength tests), the strength of the parts of the test article affected by the modification. Follow with testing to a conservatively higher load that accounts for the difference in strengths of the test article and the lowest strength production article. Determination of the higher applied test load should take into account any uncertainty in the test(s) used to determine the strength of the material.
Another alternate course of action may be to conduct the harness pull test on the available test airframe. The applicant may then substantiate the strength of other tubing specifications by a combination of test results and analysis.
93 AC 23-4 provides an acceptable means of compliance for static strength substantiation of attachment points for occupant restraint system installations. A test block is described to apply the 9.0-g forward inertia load. The safety belt installation alone is tested to 100 percent of the load. The shoulder and safety belt combined load is distributed 40 percent to the shoulder harness and 60 percent to the seat belt.
In airplanes having side-by-side seats, the pull test may need to be applied simultaneously to the harness fittings for both seats. However, this depends on the type of harness and where the upper ends are anchored. Normally, this would not be necessary for a single diagonal belt shoulder harness attached to the outboard fuselage side or wing spar root end.
In the case of a pull test for a retrofit shoulder harness installation in a tandem seated tubular steel fuselage, the forward inertia load was applied simultaneously for both harnesses. This was done for convenience in applying and reacting the loads. It was found, that due to the tube geometry, the load at the aft harness attachment caused a tension in the rear spar carrythrough tube. The front seat shoulder harness upper end was attached to the rear spar carrythrough tube. This enabled the front seat harness attachment to test to a higher load than if the pull test was done to each harness individually. In such a case, the test loads for each harness should be done individually.
Part 21, § 21.50(b) requires the holder of an STC to furnish Instructions for Continued Airworthiness, prepared in accordance with § 23.1529.
An STC can not be used to modify an aircraft without the permission of the STC holder. FAA Notice 8110.69 dated June 30, 1997, requires the STC holder to provide the customer (installer or airplane owner) with a signed permission statement that includes the following:
- product (aircraft, engine, propeller, or appliance) to be altered, including serial number of the product;
- the STC number; and
- the person(s) who is being given consent to use the STC.
The permission statement needs to be kept as part of the aircraft records. The requirement for this permission statement originated in the Federal Aviation Authorization Act of 1996 (Public Law 104-264). This provision was put into law to try to stop the pirating of STC's.
2. Field Approval. A shoulder harness installation in a small airplane may receive a Field Approval (FAA Form 337) granted by a Flight Standards Aviation Safety Inspector. Field Approvals are appropriate for alterations that involve little or no engineering. If the installation requires structural modifications, an Aircraft Certification Office will need to assist in the Field Approval process by approving the structural aspects of the installation. A Field Approval constitutes a change to type design and must meet the same regulatory requirements as an STC.
AC 43.13-2A (Reference 3) contains methods, techniques, and practices acceptable to the Administrator for use in altering civil aircraft. Chapter 9 covers shoulder harness installations. Section 3 covers attachment methods. Shoulder harnesses installed under Field Approval must meet the same regulatory requirements as an STC; therefore, the applicant should demonstrate by test 9.0- g forward load capability. The test load should be 814 pounds for Normal Category or 910 pounds for Utility or Acrobatic Category, in accordance with AC 23-4.
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:
- AC's 43.13-1A and 43.13-2A, as amended*
- Manufacturer’s technical information (for example, manuals, bulletins, kits, and so on)
- FAA Field Approvals” * Note: Advisory Circular (AC) 43.13-1B, dated September 8, 1998 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 have a Parts Manufacturer Approval (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 carrythrough tube, or other unsupported member, should not receive a Field
95 Approval without a design approval from an Aircraft Certification Office.
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 carrythrough member installation. This appears to be in the center of the carrythrough member that is a hat section as found in metal skinned airplanes. Part of the figure shows that the hat section is riveted to sheet metal skin (which would provide longitudinal support).
Personnel performing the Field Approval must ensure 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: “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 indicates 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 carrythrough 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 that the harness installation had saved their lives.
In general, shoulder harness installations should not use the center of an unsupported wing carrythrough 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 carrythrough tube.
96 It is acceptable for the carrythrough structure to be damaged in an emergency landing. However, it is unacceptable for the tube to fail in-flight. Carrythrough tubes, highly loaded in compression, may experience a beam-column buckling failure if the occupant applies a load to the shoulder harness attachment. In some cases, very small loads on the shoulder harness attachment may cause beamcolumn 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 Society of Automotive Engineers 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 the following:
- harnesses that meet TSO-C114 or Military Specification (MIL-SPEC) requirements,
- harnesses that have been produced under a Parts Manufacturer Approval (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 the structural test and any associated structural analysis. Also, there is a possibility that the airframe may be damaged during the pull test. In such installations, a pull test would not be done and there is no assurance that the installation will provide occupant protection to the ultimate inertia force requirements (particularly the 9.0-g forward force) of § 23.561 or CAR 3.386.
Concerning 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.
Civil Air Regulation (CAR) 3.652, Functional and installation requirements, states:
“Each item of equipment which is essential to the safe operation of the