FLOATS AND HULLS
23.751 Main float buoyancy Original Issue and Subsequent For a twin float seaplane or amphibian aircraft, the 80 percent excess buoyancy requirement should be applied to both rather than each float.
The rules for twin float aircraft do not address water stability or capsizing. They only require that the aircraft remain afloat with any two compartments of the main floats flooded.
The history does not support the position that the aircraft will remain afloat indefinitely without capsizing with two compartments flooded. However, if an unsafe condition exists, certification should be denied under the provisions of part 21, § 21.21(b)(2). An example of an unsafe condition could be capsizing so rapidly that the occupants could not safely exit. Capsizing that is delayed long enough to permit taxi to the shore or dock is not an unsafe condition. The time to capsize should be listed in the Emergency Procedures Section of the Airplane Flight Manual.
23.753 Main float design No policy available as of June 30, 2001.
23.755 Hulls Original Issue The discussion on capsizing and unsafe conditions in 23.751 applies to this rule also.
Amendment 23-45 and Subsequent This amendment changed the rule to prohibit capsizing in fresh water for planes over 5,000 pounds with two adjacent compartments flooded, and those between 1,500 and 5,000 pounds with any single compartment flooded.
23.757 Auxiliary floats No policy available as of June 30, 2001.
PERSONNEL AND CARGO ACCOMMODATIONS
23.771 Pilot compartment No policy available as of June 30, 2001.
23.773 Pilot compartment view Amendment 23-14 and Subsequent See AC 23-8A, Flight Test Guide for Certification of Part 23 Airplanes, for guidance on this regulation.
23.775 Windshields and windows Original Issue and Subsequent The rule requires the luminous transmittance (LT) be no less than 70 percent when the pilot is seated in a normal flight position. This rule does not specify how the LT is to be measured. Industry, federal practices, standards and airframe manufacturer specifications have specified a minimum LT measurement per Federal Standard 406, Method 3022 or equivalent.
On the basis of available data, we cannot determine that an LT of 70 percent is in itself an unsafe condition. There are other factors such as windshield/window inclination from vertical. The criteria to determine an unsafe condition is a qualitative pilot evaluation.
Nonsplintering material in this section refers to materials such as safety glass, which shatter into small fragments that can cause superficial injuries. Splintering materials are those that shatter into slivers, which can result in serious injuries.
Policy for 14 CFR part 23, § 23.775, Temperature and Temperature Gradient Requirement Certification:
Section 23.775 requires the following:
- “The design of windshields, windows, and canopies in pressurized airplanes must be based on factors peculiar to high altitude operation, including – The effects of temperatures and temperature gradients;” and
- “If certification for operation above 25,000 feet is requested, the windshield, window panels, and canopies must be strong enough to withstand the maximum cabin differential loads combined with critical aerodynamic pressure and temperature effects, after failure of any load-carrying element of the windshield, window panel, or canopy.”
On-airplane testing is one acceptable Means of Compliance (MOC) to these requirements.
Other acceptable MOC’s are component level testing, a combination of tests and analyses, or an analysis based on known temperature and temperature gradient effects for a specific material and installation. Qualification by similarity is also acceptable.
Note: At this time, we are not aware of any case where an applicant has used an analysis without testing, but we should consider this if it is proposed by an applicant.
80 The testing or analysis would have to consider pressurization loads or fail-safe loads with the temperature and temperature gradient effects. These would be in addition to the cyclic or fail-safe testing of the complete pressure cabin at ambient temperature.
Current practice is to superimpose the pressure loading and the thermal gradients in a test.
The testing and conditions vary from full-scale test articles with environmental chambers around the windows and windshields to component tests. For fail safe requirements, most manufacturers are using a “failed” article (cut before test) while running a test to fail-safe loads or better.
If the bird strike requirements in § 23.775(h)(1) are applicable (Amendment 23-49), the applicant should consider the effects of temperature and temperature gradients when showing compliance to the two-pound bird strike.
JAA ACJ’s 23.775(f) and 23.775(g), which apply to § 23.775(g) and (h) in 14 CFR part 23, are acceptable for FAA certification.
23.777 Cockpit controls Original Issue and Subsequent The FAA has no rule preventing placement of non-flight controls on control wheels, but we consider such installations to be marginal since a switch could easily be confused with microphone or autopilot switches. Approval would require special crew training and AFM guidance to ensure it was used properly.
We strongly recommend that all redundant cockpit controls be symmetrical from one side of the cockpit to the other.
Amendment 23-33 and Subsequent Section 23.777(c)(4) was added by this amendment. It requires that airplanes with sideby-side pilot seats and two sets of powerplant controls, have one set on the left console and one set on the right console. We will consider an Equivalent Level of Safety Finding for airplanes with one set on the left hand side and one on or near the cockpit center line.
The preamble to the 23-33 Amendment shows that floor mounted, mechanical flap controls are acceptable.
14 CFR part 23/CAR 3 Airplanes; Clarification of Type Certification Process of Single Lever Power Controls The purpose of this guidance is to provide recommendations for certification of single lever power controls (SLPC) installed in part 23/CAR 3 airplanes.
There are airplanes certificated or currently undergoing certification that have combined the features of two or more of the cockpit powerplant controls for power (thrust), propeller (rpm control), and mixture control (condition lever and fuel cutoff for turbine powered airplanes) into a single power lever. The design feature of an SLPC was not envisioned by part 23/CAR 3. Further, an SLPC cannot meet the standards imposed by §§ 23.777(d) and 23.781(b) as amended by Amendment 23-33. The current amendment level of part 23 (Amendment 23-53) contains regulations that allow evaluation of an SLPC without the need for Special Conditions (e.g., §§ 23.777(a)(b),
23.779(b)(1), 23.1309). However, since an SLPC was not envisioned at the time Amendment 23-33 was adopted, the question of compliance with §§ 23.777(d) and
23.781(b) as amended by Amendment 23-33 still exists.
82 Due to recommendations made by the NTSB, Amendment 23-33 provided specific location, height, and shape requirements for a number of cockpit controls, including power, propeller, and mixture controls. With the design feature of an SLPC integrating the functions of multiple controls into a single cockpit control, a nonstandardized design approach for the affected powerplant cockpit controls is used. Additionally, § 23.1141(a) states: “Powerplant controls must be located and arranged under § 23.777. . . .” However, an SLPC, as described earlier, cannot be arranged in accordance with § 23.777; therefore, compliance with § 23.1141(a) is not possible.
Notice No. 84-12, which was the basis for Amendment 23-33, described the intent of §§ 23.777 (d) and 23.781 (b). As stated in the notice:
"An effective means of enhancing pilot experience and training would be to require complete standardization in cockpit design. While such action may initially improve the level of safety, it might ultimately inhibit design advancement and result in lower levels of safety than would have evolved without such a total standardization.
An effective and practical means of enhancing the effectiveness of pilot training and enhancing safety would be to require standardization of location, shape, color, and direction of movement of those cockpit controls. This would have minimal adverse effect on design advancement."
From the preceding, it is obvious that the FAA and industry did not envision or address the future use of an SLPC when drafting this rulemaking, but it was intended to allow design advancements that would enhance safety. An SLPC is a design advancement in the public interest and does not adversely affect safety. Therefore, an SLPC will meet the intent, but not literal compliance, of §§ 23.777(d) and 23.781(b) as amended by Amendment 23-33.
We, therefore, recommend use of an Equivalent Level of Safety finding for airplanes with a certification basis of Amendment 23-33 or later when making compliance determinations for §§ 23.777(d) and 23.781(b). For these airplanes, Special Conditions are usually unnecessary. In some cases, however, the applicable airworthiness standards may not be adequate due to other novel or unusual features of the aircraft, and Special Conditions may be warranted.
For airplanes with a certification basis prior to Amendment 23-33, no special considerations will be needed unless they involve other novel or unusual design features not covered by the applicable regulations.
83 We have initiated regulatory action to revise part 23 to allow incorporation of an SLPC without special considerations. However, until these actions have been completed, the recommendations in this advisory circular may be used for certification of an SLPC on part 23/CAR 3 airplanes.
23.779 Motion and effect of cockpit controls Original Issue—Reserved The original rule only specified primary aerodynamic and throttle motion.
Amendment 23-33 and Subsequent This amendment requires that the propeller control should move forward to increase rpm.
Therefore, a propeller pitch control on the vertical instrument panel does not comply. A switch located in a horizontal position with forward motion to increase rpm does comply.
Other designs would have to be considered by an Equivalent Level of Safety Finding. We would consider a propeller pitch control switch that would increase propeller rpm when moved to the “UP” position with a placard to denote rpm change to be eligible as an equivalent.
We have no objection to the propeller pitch control switch being spring loaded against the fine and coarse propeller blade angles. The airplane should be evaluated to ensure no unsafe operating condition occurs with a propeller switch in each critical blade position.
See § 23.777 for guidance applicable to single power lever controls.