23.507 Jacking loads (Amendment 23-14)
136. Is there any policy available on paragraph (a) of this section as of January 1, 2007?
No.
137. How do I meet the intent of paragraph (b) of this rule? The intent is accomplished when structure affected by jacking loads is designed to withstand the inertial load factors in part 23, § 23.507(a)(2) and (c). Section 23.507( b), in essence, is redundant with § 23.471 General (Ground Loads).
138. Is there any policy available on paragraph (c) of this section as of January 1, 2007?
No.
23.509 Towing loads (Amendment 23-14)
139. Is there any policy available on paragraph (a), (c) or (d) of this section as of January 1, 2007? No.
140. What is an auxiliary gear? Auxiliary gear means a landing gear unit that is not part of the main landing gear.
23.511 Ground load; unsymmetrical loads on multiplewheel units (Amendment 23-7)
141. Is there any policy available on this section as of January 1, 2007? No.
WATER LOADS
23.521 Water load conditions (Amendment 23-48)
142. Is there any policy available on paragraph (a) of this section as of January 1, 2007?
No.
143. Is there any policy available on paragraph (b) of this section as of January 1, 2007?
No. See 23.603, Materials and workmanship, for information that pertains to floats.
23.523 Design weights and center of gravity positions (Amendment 23-45)
144. Is there any policy available on this section as of January 1, 2007? No.
23.525 Application of loads (Amendment 23-45)
145. Is there any policy available on this section as of January 1, 2007? No.
23.527 Hull and main float load factors (Amendment 23-45)
146. Is there any policy available on paragraph (a) or (b) of this section as of January 1, 2007? No.
147. Does the term “seaplane structure,” as used in paragraph (c), apply to the engine mounts? Yes. Therefore the factor K 1, used in the calculation of the water reaction load factor nw, may be reduced at the bow and stern to 0.8 of the value shown in figure 2 of appendix I in part 23.
23.529 Hull and main float landing conditions (Amendment 23-45)
148. Is there any policy available on this section as of January 1, 2007? No.
23.531 Hull and main float takeoff condition (Amendment 23-45)
149. Is there any policy available on this section as of January 1, 2007? No.
23.533 Hull and main float bottom pressures (Amendment 23-45)
150. Is there any policy available on this section as of January 1, 2007? No.
23.535 Auxiliary float loads (Amendment 23-45)
151. Is there any policy available on this section as of January 1, 2007? No.
23.537 Seawing loads (Amendment 23-45)
152. Is there any policy available on this section as of January 1, 2007? No.
EMERGENCY LANDING CONDITIONS
23.561 General (Amendment 23-48)
153. Is there any policy available on paragraph (a) of this section as of January 1, 2007?
No.
154. What are the historical requirements of this section in reference to Cargo Restraints?
a. Guidance information about ultimate inertial strength requirements for cargo restraint devices in part 23 airplane designs originally centered around part 135 air taxi operators who carried mail sacks in an empty cabin after passenger seats were removed. The guidance is from around 1968.
b. There is an inconsistency between Civil Air Regulations (CAR) 3.386(d) and § 23.561(e), in recodified part 23, dated February 1, 1965. The inconsistency concerns protecting occupants from mass items that might cause injury if they come loose in a minor crash landing (up to 9g’s). Another inconsistency exists between CAR 3.392 and § 23.787(c) when considering occupant protection. This inconsistency concerns the cargo compartment contents ultimate forward acceleration of 4.5g’s. Another inconsistency exists between CAR 3.392 and § 23.787(c). Section 23.787(c) sugges ts that a designer should also consider the maximum flight and ground-load factors for load conditions.
c. As originally viewed, CAR 3.392 applied to airplane configurations that contained a forward crew compartment, a center passenger compartment, and an aft bulkhead, which separated a small cargo compartment from the passenger area. In this configuration, 4.5g restraint was considered adequate since the National Aeronautics and Space Administration (NASA) data showed that, in a typical crash, the g-forces became lower as distance increased aft from the airplane nose. Thus, what would be adequate cargo restraint in the aft fuselage would probably be inadequate near the cockpit. When CAR 3.392 was adopted, the Civil Aviation Authority did not envision all-cargo CAR Part 3 aircraft.
d. For § 23.561(b) and (e), the restraining devices should meet the 9g requirement.
155. What are the historical requirements of this section in reference to Cargo Compartment Design?
a. Regulatory history about cargo compartment design practices and minimum airworthiness standards guidance is from around 1968.
b. CAR 3.392 requires a cargo restraint of 4.5g forward inertial load factor when structure separates the contents in a cargo compartment from occupants forward of the compartment. Section 23.787 requires a cargo restraint of 9.0g forward inertial load factor when structure separates the contents in a cargo compartment from occupants forward of the compartment. At Amendment 23-36, the FAA increased the mass item retention to 18.0g for occupant protection when the mass items are located in the cabin with the occupant (i.e., not located in a separated cargo compartment).
c. The emergency provisions protection, the intent of CAR 3.386, is as follows: Each acceleration specified in CAR 3.386 should be considered to act independently. If the occupants’ heads could strike sharp edges of objects within the passenger cabin under combinations of load factors less than those given in CAR 3.386(a), then the designer should use 55
the general requirement of the first paragraph of CAR 3.386 with the guidelines of CAM
3.386-1.
156. What are the historical requirements of this section in reference to Cabin Safety?
a. Airplane designers (and modifiers) and FAA Aviation Safety Engineers should pay attention to the need for increased emphasis in the design of cabin safety provisions in small airplanes. Observe the following guidelines: Strive for the highest level of occupant crash protection feasible within the state-of-the-art technology for the general emergency landing conditions and the occupant protection provisions given in §§ 23.561, 23.562 and 23.785. Do this early and frequently in the Type Certification Process.
b. Cabin safety emphasis is intended to influence an individual designer’s choices early in the conceptual phases, when safety objectives can be achieved with little or no burden on the designer and the manufacturer. The level of occupant crash protection is determined by interrelated cabin features including, but not limited to, the following:
(1) Seating configuration (considering occupant flailing characteristics);
(2) Occupant restraint devices, supports, attachments, and installations;
(3) Energy absorbing padding (thoughtfully located); and
(4) Potentially hazardous hard points.
c. To clarify confusion about static side load factors: Mass items have a 4.5g static side load factor requirement, whereas occupants have only a 1.5g condition.
d. The occupant sideward static load factor requirement of 1.5g was recodified into § 23.561(b)(2)(iii) from the Civil Air Regulations, Part 3. Twenty-three years later, part 23, Amendment 23-36, put the 4.5g mass item requirement into the seat and restraint systems dynamic test requirements. The General Aviation Safety Panel (GASP) studied and recommended these actions.
e. GASP I, as the first group was known, recognized that 26g times the SIN 10° equals
4.5g, which is the sideward dynamic emergency landing condition for an airplane impact associated with a yaw. They further recognized that it would be much more economical to conduct static tests, or analyses, than dynamic tests for mass items installed on the airplane.
Consequently, GASP I recommended the static load factor now contained in § 23.561(b)(3).
157. Is there any policy available on paragraph (c) of this section as of January 1, 2007?
No.
158. What is the background of protection of occupants in an airplane for a sliding bubble canopy and with no turnover structure? Until Amendment 23-36, effective September 14, 1988, the turnover requirement in § 23.561(d) was essentially the same as in CAR 3.386(c), which first appeared in CAR 3, as amended in November 1949.
159. What are the requirements of this section for airplane turnover?
a. Regardless of the type of landing gear installed, the inverted attitude is probable;
therefore, the emergency exit requirements of § 23.807(a) should be demonstrated unless escape means are obvious.
b. Figure 8 presents an overall relational view of turnover protection airworthiness standards.
FIGURE 8
RELATIONAL VIEW OF TURNOVER PROTECTION
c. To meet the static emergency landing conditions requirements (see § 23.561(d)), the strength of turnover structure may be shown by analysis. However, conduct tests if an analysis is questionable (see § 23.601).
160. Is there any policy available for this section on a Jettisonable Canopy?
a. The airworthiness standard for § 23.807(a), Emergency exits, requires that emergency exits be located to allow escape in any probable crash attitude. Compliance with this requirement should be demonstrated with a rollover structure installed.
b. Section 23.807(b)(4), the emergency exits regulation, requires each emergency exit to have reasonable provisions against jamming by fuselage deformation. Compliance with this requirement should be demonstrated with the airplane resting inverted after accounting for any structural collapse.
c. In an acrobatic category airplane, the occupants should be able to bail out quickly, with parachutes, at any speed between VSO and VD (see § 23.807(b)(5)). Further, § 23.807(c) requires that the proper functioning of each emergency exit be shown by tests, which are usually demonstrated on the ground rather than in flight.
d. Forward sliding, jettisoning, and hinged canopy designs were not originally envisioned by CAR 3 or part 23. Occupant protection and escape from an airplane damaged in a turnover, and in-flight emergency escape provisions, should be addressed in any certification project, since adequate emergency exit airworthiness standards exist in these regulations.
Special conditions may be required for a jettisonable canopy to address continued safe flight, inadvertent canopy opening hazards, and in-flight canopy jettison-safe trajectory. Other possible methods of showing compliance to the airworthiness standards include wind tunnel tests, sled tests, or other ground tests that simulate flight.
e. A jettisonable canopy may not jam when the airplane is resting inverted.
f. For the bail-out requirement of § 23.807(b)(5) for an acrobatic category airplane:
(1) If the canopy is not jettisonable, show that the occupants can safely exit the airplane between VSO and VD.
(2) If the canopy is jettisonable, show that the canopy trajectory will not injure the occupants while separating from the airplane between VSO and VD. Also demonstrate that the airplane can continue safe flight and landing without the canopy. Alternatively, inadvertent canopy jettison should be improbable.
161. Is there any policy available for this section on Emergency Exit requirements in an Airplane Turnover Condition?
a. The inverted attitude is a probable crash attitude for small airplanes. The occupant emergency exit requirements of § 23.807(a) should be shown. If escape from the inverted attitude airplane is not obvious, or is questionable, compliance should be by demonstration.
b. It is not acceptable to rely on an emergency procedure that requires canopy jettison immediately before an impact accident (except for an in-flight canopy jettison above a safe parachute altitude required in § 23.807(b)(5)). If the canopy is made jettisonable, to comply with § 23.807(b)(4), avoid jams with fuselage deformation when the airplane is resting inverted. If there is any doubt, the applicant should demonstrate by tests.
162. Is there any policy available on paragraph (e) of this section as of January 1, 2007?
No.
163. Do internal cabin doors have to remain operational after an emergency landing? Do not allow an internal cabin door to jam during an emergency landing and block the flight crew’s escape path. See the Systems and Equipment Guide for Certification of Part 23 Airplanes, AC 23-17B, 23.807 Emergency Exits, for further guidance.
164. What minimum occupant weight should I use? Use, at least, the following minimum occupant weights when showing compliance with the emergency landing conditions static strength airworthiness standards of § 23.561:
a. Design each seat and its supporting structure for an occupant weight of at least 170 pounds, for normal and commuter category airplanes. Use a 190-pound occupant weight, which includes a parachute, for utility and acrobatic category airplanes. (Reference § 23.25(a)(2).)
b. Also, design each seat and restraint system for at least a 215-pound occupant weight when considering maximum flight and ground-load conditions of the airplane-operating envelope.
NOTE: A 1.33 factor should be applied to all load s that affect the strength of fittings and attachment of the following:
(1) Each seat to the structure, and
(2) Each safety belt and shoulder harness to the seat or structure.
23.562 Emergency landing dynamic conditions (Amendment 23-50)
165. Is there any policy available on paragraph (a) of this section as of January 1, 2007?
No.
166. Do I have to retest the seats in my airplane if I want to change the fabric dress covers, following the conduct of dynamic certification tests per the seat dynamic performance standards? No. You may substitute typical dress fa brics for each other, including leather, without retest. The change in friction due to dress cover alone is less significant than the variation possible due to clothing, etc. However, dress covers that exhibit low friction coefficients (i.e., hard plastics, which are not in use, to our knowledge) may require some resubstantiation.
167. Are there any certification issues at all for changing the dress covers or seat cushions on seats? Yes. Dress cover and cushion changes that affect the flammability of the dress cover and seat do require resubstantiation to the respective flammability requirements. Also see the next question about cushions.
168. Do I have to retest or analyze the seats in my airplane if I want to change the seat cushions, following the conduct of dynamic certification tests per the seat dynamic performance standards? Yes. The seat cushion static and dynamic res ponse characteristics can affect the lumbar column/pelvic load measured during the seat dynamic certification tests.
Thus, a change in the seat cushion would require re-substantiation. Analysis may be used per the guidance in AC 20-146.
169. In the acquisition of data for Head Injury Criteria (HIC), are 8-bit analog to digital converters adequate? No. In accordance with Society of Automotive Engineers (SAE) recommended practice J211 “Instrumentation for Impact Tests,” the converter should be at least 10-bit in order to obtain a sufficient level of resolution.
170. Can I run a vertical drop test as an acceptable alternate means for the determination of seat/floor deformation requirements found in § 23.562(b)(2)?
a. No. The seat/floor deformation requirement is more an assessment of the airplane seat’s tolerance to structural deformations than it is an assessment of potential airframe deformations. Intolerance of seat/floor interface to deformation is deemed a major cause of structural failure of the seat/floor structural attachment. If you want to pursue this type of test for information for research only (but not for certification), the following are the kind of items that you should consider.
(1) Drop tests are typically a simulation of the vertical impact velocity only; an actual airplane accident possesses both vertical and longitudinal impact velocity vectors. While the measured impact acceleration levels may provide some insight into the overall vertical impact characteristics of the airframe, the test condition does not simulate the combined vertical and longitudinal (and potentially lateral) loads on the airplane seat, its attachments, and interface structure.
(2) An actual airplane accident frequently occurs on an irregular impact surface that may also contain local obstructions, which can cause significant local loading, structural fractures, and deformations. A vertical drop test on a flat surface does not address the common and more critical impact case that may occur on irregular and obstructed surfaces.
(3) Large, significant, dynamic, structural deformations can occur during an impact test, or airplane accident that are not readily detectable for measure after the impact condition.
These results have been demonstrated during the general aviation airplane impact test series.
Consider this if you plan to measure the residual static floor deformation after the impact test.
(4) Choose accelerometers with an amplitude class that is adequate for the g-loads expected during your particular drop test.
b. The above paragraphs attempt to address the kinds of considerations that the 10 degree pitch and 10-degree roll in part 23, § 23.562, already account for.
171. Can I use static ultimate load tests as an alternate means of showing compliance to the dynamic seat test requirements of § 23.562? No. One of the key requirements of part 23, § 23.562 is to assure that an occupant’s vertical lumbar load is limited to 1,500 pounds or less during the 30 degree incline test. In addition, the HIC and upper torso restraint maximum loads can only be demonstrated by dynamic testing. The FAA is unaware of any analytical (except computer modeling techniques, discussed below) or static test procedure that will meet the dynamic seat test requirements.
172. Is there any policy available on paragraph (c) of this section as of January 1, 2007?
No.
173. Is there any policy available on paragraph (d) of this section as of January 1, 2007?
No.
174. Is analysis alone an acceptable alternative approach as stated in paragraph (e)?
a. Yes, per the guidance in AC 20-146.
b. The following two SAE papers provide helpful, related, information:
(1) SAE Paper No. 850853, “The Development of Dynamic Performance Standards for General Aviation Aircraft Seats,” Stephen J. Soltis and John W. Olcott.
(2) SAE Paper No. 851847, “Human Injury Criteria Relative to Civil Aircraft Seat and Restraint System,” Richard F. Chandler.
c. AC 23.562-1, Dynamic Testing of Part 23 Airplane Seat/Restraint Systems and Occupant Protection, contains useful guidance about this airworthiness standard topic.
175. How are the minimum safety standards determined for restricted category airplanes?
The FAA issues type certificates under the regulatory procedures of part 21, Certification Procedures for Products and Parts. The Small Airplane Directorate decides the appropriateness of part 23 airworthiness standards as they apply to the special purpose restricted category airplane. If a regulation is found inappropriate, the FAA excludes that regulation from the certification basis of that airplane.
NOTE: A finding of equivalent level of safe ty or the need for an exemption is unnecessary for that specific airworthiness standard.
176. How are the minimum safety standards determined for agricultural or special purpose airplanes?
a. The FAA has allowed the certification of restricted category aircraft since Civil Air Regulations (CAR) Part 8 was introduced (around 1950). The preamble to CAR 8 recognized that, for restricted category aircraft where the public was not endangered, it was unnecessary to provide an equivalent level of safety to the standard airworthiness requirements.
b. Policy: As of December 1, 1997, for emergency landing dynamic conditions, evaluate the airplane using at least the following considerations:
(1) The placement of the chemical hopper forward of the cockpit so that there is no large item of mass that threatens to collapse the cockpit should a crash occur.
(2) The elimination of any protruding knobs, handles, or other rigid structures from the cockpit that the pilot or crew member may contact in a crash. Approved Department of Transportation or Mil-Spec protective headgear is mandatory.
(3) The installation of a military type lap belt and shoulder harness having a 5,000 pound rating or greater or approved equivalent.
(4) Special purpose crew members who assist in the aerial application operation,
i.e., flaggers, loaders, may be carried in ferry flights provided certain conditions are met. First, each crew member must have a seat, a lap belt and shoulder harness comparable in strength to that of the pilots. Second, the crew seat must not be in the cockpit. Third, the crew seat must be located behind the pilot seat. Special purpose crew members that are carried for any other purpose will be afforded the same protection as that of the pilot.
c. Dynamic seat airworthiness standards used in part 23 were developed for normal, utility, and acrobatic category airplanes only. These standards were never intended for use on restricted category airplanes. When NASA, the general aviation industry, NTSB, and the FAA examined survivability envelopes, they did not consider restricted category airplanes in the database because there were notable differences in the crash scenarios.
d. The Small Airplane Directorate decides whether dynamic seat test requirements are appropriate or not, after reviewing crashworthiness design features of the specific make and model airplane. Service experience shows that agricultural airplane operators have a lower accident fatality rate than general aviation operators. Certain make and model agricultural airplane designs contain increasingly effective crashworthy features throughout recent development history, which are the obvious reasons for the fatality rate differences.
e. Policy: The FAA will not automatically exclude the emergency landing dynamic conditions requirement (§ 23.562) for any applicant who is seeking a type certificate for an agricultural airplane. Instead, the Small Airplane Directorate reviews the design for compensating features to the dynamic seat airworthiness standards and decides whether the dynamic seat test requirements are appropriate or not on a case-by-case basis.
f. For useful guidance, refer to AC 21.25-1, Issuance of Type Certificate: Restricted Category Agricultural Airplanes.
177. I would like to use ejection seats for emergency egress. Can I get my part 23 airplane certificated with ejection seats installed? Yes.
178. What are the criteria or minimum safety standards for approving ejection seats for use in an airplane certificated to part 23? Part 23 does not have any minimum safety standards for ejection seats, and the FAA does not have the expertise to evaluate ejection seat testing. However, the military has been develo ping ejection seat technology for 40 to 50 years.
Therefore, the applicable sections of the Air Force Systems Requirement Document (SRD) are used as the minimum safety standards. The SRD provides specific criteria for crew escape, and for ejection seat testing and verification. The Air Force is used as a consultant. We only approve the ejection seat data after the Air Force has reviewed the data and concurs that the ejection seat satisfies the SRD crew escape, testing, and evaluation requirements.
179. Do I have to show literal compliance to the emergency landing dynamic conditions of this rule (23.562) for ejection seats?
a. No. You may show literal compliance if you choose to, or you may pursue an Equivalent Level of Safety (ELOS) finding for compliance to this rule. An ELOS is allowed instead of literal compliance to a rule, by part 21, § 21.21(b)(1). You may use the Air Force SRD as the basis for this finding.
b. The lower limits of the ejection seat operating envelope must be zero altitude above ground level and zero airspeed if you choose to pursue an ELOS for this rule.
180. Are there other rules relevant to ejection seats that I may pursue an ELOS for? Yes.
You may also pursue an ELOS for the applicable portions of § 23.807 and § 23.1309.
181. The original certification basis of my airplane is before Amendment 23-36 and was manufactured on, or before, December 12, 1986. I wo uld like to install side-facing seats.
Do I have to comply with the emergency landing dynamic conditions of this rule (23.562)?
a. Yes. You must comply with the emergency landing dynamic conditions of this rule if you want approval by a Supplemental Type Certificate (STC), an amended Supplemental Type Certificate (ASTC), or an amended Type Certificate (ATC) for the installation of side-facing seats.
b. Earlier regulations were written with forward or aft-facing seats in mind, and they do not provide adequate standards for protection of occupants in side-facing seats. Therefore, in accordance with part 21, § 21.101, an applicant must comply with the current standards, including the emergency landing dynamic conditions contained in this rule (23.562), before any side-facing seat installation (to be occupied during takeoff or landing) can be approved.
c. An alternative to compliance with the current regulations is to prohibit occupation of side-facing seats during takeoff and landing through the use of a flight manual supplement and clearly visible placards. This t ype of installation should include a restraint system that keeps the occupant securely seated during turbulence or maneuvering.
d. This policy is applicable to airplanes whose original certification basis was before Amendment 23-36 to part 23, and the airplanes that were manufactured on, or before 62
December 12, 1986. This includes normal, utility, acrobatic, and commuter category airplanes with earlier amendments to part 23, Civil Air Regulations 3 (CAR-3), or airplanes with any previous airworthiness regulations as their original certification basis.
e. The one exception to this policy is an airplane that had side-facing seats as part of its original certification basis and with a certification basis that falls within the scope of paragraph d, above. In this instance, an application for an STC, ASTC, or ATC for side-facing seats does not need to meet the requirements of emergency landing dynamic conditions of this rule
(23.562).
f. Also see § 23.785 in AC “Systems and Equipment Guide for Certification of Part 23 Airplanes and Airplanes”.