(r) For each turbine engine, an indicator for each fuel strainer or filter to indicate the degree of contamination of the strainer or filter to the degree established as an operating limitation for the engine.
(s) For each turbine engine, a warning means for each oil strainer or filter that has no bypass, to warn the pilot of the occurrence of contamination of the strainer or filter before attainment of contamination of the degree established as an operating limitation for the engine.
(t) An indicator to indicate the functioning of any heater used to prevent ice clogging of fuel system components.
A proposed revision to NPRM 71-12 explains Amendment 23-15 as follows: “The provisions of paragraph (q) would be transferred from present Sec. 23.1093. The indicator and the means proposed in paragraphs (r) and (s) are necessary to implement the requirements of proposed Secs. 23.997 and 23.1019, respectively. The indicator proposed in paragraph (t) is necessary in the event that a mechanical means, such as a fuel heater, is used in the airplane to heat the fuel as it passes through a filter or screen in the fuel system. Such an indicator could be used in meeting the requirements of proposed Sec. 23.951.”
Amendment 23-15 is further explained by Final Rule, Docket 11010 as follows: “As a result of the issuance of Amendment 23-14 (38 FR 31816), which contains new paragraphs, Sec. 23.1305(q) and (r), the proposed paragraphs (q), (r), (s), and (t) are redesignated (s), (t), (u), and (v), respectively. The following discussion is keyed to the new designations.
One commentator questioned whether the fuel strainer or filter indicator referred to in Sec. 23.1305(t) were required on all filters, even "last chance" filters. Consistent with the requirements applicable to the strainers or filters themselves, Sec. 23.1305(t) has been revised to make clear that the indicator required is for a fuel strainer or filter required under Sec. 23.997. Similarly, Sec. 23.1305(t) and (u) have been reworded in order to be consistent with Secs. 23.997 and 23.1019, respectively, in regard to the degree of contamination that must be indicated. In response to a further comment, Sec. 23.1305(t) has been reworded to clarify that the desired indication is of the occurrence of contamination rather than the more stringent requirements of the degree of contamination as suggested in the notice. This change achieves consistency between paragraphs (t) and (u).
One commentator questioned whether other presently installed gauges for other functions could be used as "indicators" to indicate the functioning of a heater as required in paragraph (v). As discussed above, in connection with the indicators required for oil strainers or filters, the FAA anticipates that the requirement will be met by installation of gauges to indicate the functioning of heaters. However, if a clear and positive indication can be obtained from other gauges used to portray 194
functions different than direct heater functioning, the requirements of the section are met.”
Amendment 23-18
A proposed revision to this amendment added a requirement for a fire-warning indicator for those airplanes required to comply with § 23.1203.
Amendment 23-26
A proposed revision to NPRM 75-31explains this amendment as follows: “The proposal would permit up to an eight-degree movement of the propeller blade below the flight low pitch position before an indication of the movement is required for the flight crew. This would be consistent with the corresponding requirements in Part 25 and with the proposal to revise Sec. 35.23. The FAA does not believe it necessary to require immediate indication when the propeller blade moves past the flight low pitch stop.”
Amendment 23-34
A proposed revision to NPRM 83-17 added the following instruments:
(f) A cylinder head temperature indicator for -
(1) Each air-cooled engine with cowl flaps, and for each airplane for which compliance with Sec. 23.1041 is shown at a speed higher than VY; and
(2) Each reciprocating engine-powered commuter category airplane.
(h) A manifold pressure indicator for -
(1) Each altitude engine; and
(2) Each reciprocating engine-powered commuter category airplane.
(k) A fuel flowmeter for -
(1) Each turbine engine or fuel tank, if pilot action is required to maintain fuel flow within limits; and
(2) Each turbine-powered commuter category airplane.
“The source for this change was: part 135, Appendix A., § 58.”
Amendment 23-43 and Subsequent
A proposed revision to NPRM 90-23 changed Amendment 23-43 as follows: “This proposal clarifies the powerplant instrument requirements by separating the reciprocating engine, turbine engine, turbojet/turbofan, and turbopropeller requirements; and adding requirements for coolant temperature indicator, fuel lowlevel warning, manifold pressure indicator, and chip detector indicator.”
This amendment was added by Final Rule, Docket 26344 as follows: “This proposes to amend Sec. 23.1305 to clarify the powerplant instrument requirements by reorganizing the section and by defining the additional instruments that are required for the particular type of engine that is installed. Two commenters submitted comments on various paragraphs of this proposal.
One commenter suggests that the proposal for Sec. 23.1305(a)(1) cross-reference Sec. 23.1337(b)(5). The FAA does not agree that the suggested Sec. 23.1337(b)(5) is the proper reference but does agree with the intent of this suggestion. In reviewing this comment, it is noted that the intent of the words, "or for each assembly of interconnected tanks that function as one tank" in proposed Sec. 23.1305(a)(1) is provided by current Sec. 23.1337(b)(4), and that other provisions of Sec. 23.1337(b) address other applicable fuel quantity indicator requirements, such as their marking.
To clarify the fuel quantity indicator requirement of part 23, the above quoted words from the proposal for Sec. 23.1305(a)(1) are removed and replaced by the words "installed in accordance with Sec. 23.1337(b). By this change, Sec. 23.1305 will make it clear that a fuel indicator is required for each tank and Sec. 23.1337 will provide the installation requirements for those indicators.
Both commenters requested that the FAA make it clear that a dipstick is an acceptable oil quantity measuring device for meeting the requirement of proposed Sec. 23.1305(a)(4). The FAA notes that Sec. 23.1337(d) identifies an acceptable means of measuring the oil quantity and identifies a stick gauge as being one acceptable means. To provide the clarification requested by these commenters, the proposal for Sec. 23.1305(a)(4) is revised by adding the words, "which meets the requirements of Sec. 23.1337(d)" to the end of the proposal.
One commenter asks the FAA to make it clear that N1 is an acceptable parameter that can be related to the thrust indication required by proposed Sec. 23.1305(d)(1).
The FAA has reviewed this request and finds that the indication of the N1 speed is an acceptable means. For some installations, however, the applicant may be required to demonstrate that N1 is acceptable. By the discussion of this comment, the requested clarification is provided and proposed Sec. 23.1305(d)(1) is not revised.”
Amendment 23-51 and Subsequent
Amendment 23-51 was changed by a revision to NPRM 94-19 as follows: “The proposed revision to paragraph (b)(3) would delete paragraph (b)(3)(ii) which refers to compliance with Sec. 23.1041.”
Amendment 23-52 and Subsequent
A proposed revision to NPRM 94-37 explains this amendment as follows: “The intent of the fuel pressure indicator requirement for pump-fed engines is to advise the pilot of a fuel pressure deficiency before total engine failure. The term "indicator" in Sec. 23.1305 (b)(4) implies that the fuel pressure be constantly displayed.
The proposal would change the current requirements in that a fuel pressure indicator or a fuel flow indicator would be acceptable. The fuel flow indicator would constantly display information that the pilot could use to evaluate engine power, fuel mixture, and other engine performance factors. Furthermore, it is technologically possible to have a microprocessor that monitors engine operation and triggers a warning if the fuel system operation does not match the other monitored engine trends. Therefore, this proposal would also change the rule to accept a means that monitors the fuel system and warns the pilot of any trend that could lead to engine failure.
Accordingly, this proposal would adopt a performance standard, instead of a requirement for specific equipment. In this way, the designer could show compliance with paragraph (b) of the proposed by developing any design that monitors the fuel system and warns the pilot of any trend that could lead to engine failure. The Aviation Rulemaking Advisory Committee (ARAC) did not believe this would reduce the level of safety originally intended by the requirement. A warning light system could possibly alert the pilot sooner than if the pilot relied on an instrument panel scan to notice a trend in the fuel pressure indication.
Microprocessing units that monitor engine operation and warn of fuel system problems have already been incorporated in transport aircraft and automobiles.
Furthermore, pilots are not monitoring gauges like they use to; instead, they are increasingly relying on warnings to alert them. Late model automobiles, computers and other equipment are designed to protect the operators from mistakes by using built-in warnings. It is important to note that this NPRM does not propose to allow "idiot lights" to replace fuel pressure gauges. A light that comes on at the same time that the engine quits is useless. A warning light system that would comply with this proposal would be sophisticated enough to read transients and trends, and would give a useful warning to the pilot. The FAA expects this proposal to result in fuel systems that provide the pilot with useful engine operating information; thereby, it would offer more value to the operator.
Today, fuel pumps are more reliable than those built in the 1940s and 50s.
Consequently, airplane operators are more concerned about reducing engineoperating costs than they are about the probability of a fuel pump failure.
A fuel flow indicator offers additional value compared to a fuel pressure indicator. It enables the operator to monitor the engine's fuel consumption and compare it to fuel consumption listed in the airplane flight manual. If a fuel monitoring system is installed that automatically controls the engine or helps the pilot to properly lean the fuel mixture, then engine operation would be optimized and the direct operating costs would go down through reduced fuel consumption. Reciprocating engines run better if the fuel to air mixture is leaned out according to the optimum (manufacturer's) specified setting. Furthermore, fuel flow also rotates to power, and pilots can use fuel flow readings to quickly access the health of their engine during critical phases of flight, such as takeoff.
Comprehensive engine monitors and redesigned electronic engine instrument displays are also being used in experimental aircraft. The FAA should encourage airplane manufacturers to utilize new technology to improve operation and reduce operating costs. New engine monitoring systems may improve reliability and engine life resulting in increased safety.
The proposal would achieve the same safety objective as the current rule; the crew would have sufficient warning of any negative trend that could lead to partial or total engine failure. However, the proposal recognizes that this objective can be achieved by measuring fuel pressure, fuel flow, or with a "smart" fuel monitoring system.”
This proposal was further explained by Final Rule, Docket 28011 as follows:
“Transport Canada questions the ability to show compliance with the requirement in Sec. 23,1549 to identify maximum and, if applicable, minimum safe operating limits as well as the normal operating range of the instrument. This commenter points out that the typical fuel flow meter is a digital type, and it would be difficult for the applicant to provide equivalent markings. Engine manufacturers provide the information required by Sec. 23.1549, which is then usually transcribed to the installed fuel pressure gauge. It appears that this information would not be presented through the use of typical digital fuel flow meters. The commenter offers the following suggestion: "FAR 23.1549 was written with a traditional dial instrument in mind where the engine limitations could be easily displayed on the face of the unit and monitored by the crew. To allow flow meters or other fuel system monitors to satisfy the requirements of Sec. 23.1549 where such a gauge no longer exists, compliance could be shown by (1) different colors to indicate changing trends in system performance (e.g., amber color for a low pressure/flow condition, red for impending engine failure), or (2) placarding, if appropriate, to indicate the normal and abnormal operating ranges".
The FAA agrees with the commenters' suggestions as an acceptable means of compliance with § 23.1549. Suggested items (1) and (2) above offer the pilot a means to determine fuel flow limitations, which may be needed if a fuel flow meter is installed.
A commenter from Australia supports the proposal; however, the commenter feels the proposed text would require a monitoring system that provides a warning of any trend that could lead to engine failure, which is a difficult compliance requirement. The commenter further states: "The historic requirement, and the NPRM preamble, clearly addresses fuel pressure (as an indication of the availability of fuel flow) or fuel flow only. Such wording may stifle the development of monitoring instrumentation for small airplanes". The commenter suggests that, for clarification, the proposed text for Sec. 23.1305(b)(4)(ii), be amended to read as follows: "That continuously monitors the fuel system and warns the pilot of any fuel flow trend that could lead to engine failure".
The FAA agrees with the commenter the proposed wording may be too broad, making compliance difficult or the system unnecessarily complex. The FAA encourages "smart" systems; however, the intent of the proposal was to warn the pilot of any fuel flow trend and, for that reason, the final rule and the preamble adopt the commenters' language.
Section 23.1305 is adopted with the change in paragraph (b)(4)(ii) to add the words "fuel flow" before the word "trend".”
23.1307 Miscellaneous equipment
The corresponding rule in CAR 3 is CAR 3.655.
The corresponding rule in the Airship Design Criteria, FAA-P-8110-2, Change 2, is section 6.5.
Amendment 23-43 and Subsequent
A proposed revision to NPRM 90-23 explains a revision to this amendment as follows: “This proposal deletes the word "an approved" in Section 23.1307, and adds a new requirement that all equipment items necessary for the airplane to operate in the NAS to its maximum approved altitude and in all kinds of operations for which it is approved must be included in the type design.
Conference proposal 432 recommended deleting Section 23.1307(a) in its entirety, because it was redundant to Section 23.785(b). Conference proposal 433 recommended deleting only the word "approved" in Section 23.1307(a).
Both Sections 23.1307 and 23.785(b) contain seat requirements; however, Section
23.1307(a) only requires a seat or berth for each occupant, while Section 23.785(b) contains specific design requirements for each seat, berth, safety belt, and shoulder harness, but does not include requirements for a seat or berth to be provided for each occupant. The requirements of Section 23.1307(a) were added by amendment 23-23 to eliminate questions as to the maximum seating capacity and compliance with the emergency exit requirements. The FAA does not consider these requirements to be redundant and plans no further action on these recommendations.
A new paragraph (c) is added because the FAA considers it necessary to clarify the type design requirements for part 23 airplanes relative to equipment items.
Frequently, manufacturers have requested their airplanes be approved relative to structural, performance, and propulsion requirements for a specific altitude without also requesting approval of necessary equipment to operate at that altitude. The FAA considers it necessary for the type design to include all equipment necessary for the type design to include all equipment necessary for operation in accordance with the limitations required by Sections 23.1559 and 23.1583.”
Amendment 23-49 and Subsequent
A proposed revision to NPRM 94-21explains this rule as follows: “This proposal would remove the requirement of Sec. 23.1307(a) which is being added to Sec.
23.785. The discussion of sec. 23.785 covers this change. Also, the provisions of 200
Sec. 23.1307(b)(1), (b)(2), and (b)(3), are being removed from Sec. 23.1307. These requirements have been previously added to Secs. 23.1361, 23.1351, and 23.1357, respectively; therefore, they are redundant and may be removed. The designator for paragraph (c) has also been removed from the remaining text of this section.”
23.1309 Equipment, systems, and installations
There is no corresponding rule in CAR 3.
The corresponding rule in the Airship Design Criteria, FAA-P-8110-2, Change 2, is section 6.6.
Amendment 23-14 and Subsequent
A proposed revision to NPRM 71-13 explains the adoption of this rule as follows:
“Because of the increasing reliance on systems and equipment in the modern, complex, high performance airplanes, the FAA believes that the proposed amendments to Secs. 23.1301, 23.1305, and 23.1309 are necessary to insure the reliability of such systems and equipment.”
Adoption of this rule is also explained by Final Rule, Docket 11011 as follows: “The other commentator objected to the proposed section on the ground that it could be interpreted to require the complete elimination of radio interference which is impossible. That is not the intent and the FAA does not agree with that interpretation. Similarly worded requirements already exist in the Federal Aviation Regulations and have not been misinterpreted to place an undue burden on manufacturers. However, based on further review, the proposed section has been revised to require that equipment installed in single engine airplanes be designed to minimize hazards to the airplane in the event of a probable malfunction or failure.”
The FAA has reviewed the part 1 definition of the word “instrument,” and other data and has concluded as follows:
a. Where a light is sufficient, the instrument requirement should be changed to a warning means.
b. Where trend information is needed, the word “indicator” should be retained.
c. Where point information or steps in a sequence need to be shown, the words should be changed to “indicating means” (that is, the functioning of the ice protection system).
Software Order 8110.49 "Software Approval Guidelines", issued June 3, 2003, provides guidelines for the approval of software changes in legacy systems using RTCA DO-178B.
See AC 23.1309-1C, “Equipment, Systems, and Installations in Part 23 Airplanes,” for additional guidance.
Airplane Parachute Recovery Systems Use of a parachute recovery system is not covered by part 23. Applications for installing this system will require special conditions.
Amendment 23-17 A proposed revision to NPRM 75-10 had a minor editorial change in adding commas in the title.
Amendments 23-34 through 23-40 Amendment 23-34 added requirements for commuter category airplanes that were later adopted for all part 23 airplanes. A proposed revision to NPRM 83-17 “added the requirements from part 135, Appendix A., § 59”.
Amendment 23-41 and Subsequent A proposed revision to NPRM 89-6 explains this amendment as follows: “Current Part 23 airplane airworthiness requirements are based on single-fault or fail-safe concepts and, when they were promulgated, the FAA did not envision use of complex, safety-critical systems in such airplanes. This proposal will require examination of systems and equipment for their criticality for continued safe flight and will permit the continued use of the existing reliability requirements of Part 23 for airplanes whose systems are not complex and do not perform safety-critical functions. For those cases where the manufacturer finds it necessary or desirable to include complex, safety-critical systems, the proposal includes requirements for identifying those systems and defines additional requirements needed for their certification. The proposed changes to Section 23.1309 are summarized as follows:
Proposed paragraphs (a), (a)(1), (a)(2), and (a)(3) of Section 1309 are derived from current paragraphs (a), (b), and (c) of Section 23.1309. Under proposed Section
23.1309(a)(1), the systems and installations, as well as the items of equipment, will be required to meet those requirements contained in current Section 23.1309(a). Under proposed Section 23.1309(a)(2), the systems and installations, as well as the items of equipment for single-engine airplanes will be required to meet those requirements contained in current Section 23.1309(c) and proposed Section 23.1309(a)(3) will require these items on a multiengine airplane to meet the requirements contained in current Section 23.1309(b).
(2) A new Section 1309(b) is proposed which will require a detailed examination of each item of equipment, system, and installation. This examination is to determine whether a failure would effect the airplane's continued safe flight and landing. Each item of equipment, each system, and each installation identified by such an examination as being critical to the safe operation of the airplane would be required to meet additional requirements. This will permit the approval of more 203
advanced systems, that were not envisioned when Section 23.1309 was added to Part 23, without the need for special conditions.
A new Section 23.1309(c) is proposed to require identification of loads which are "essential loads" and requires the airplane power sources for these loads to meet requirements consistent with other airplane airworthiness requirements. These requirements are substantially equivalent to section 59(b) of Appendix A to Part 135.
A new Section 23.1309(d) is proposed to allow reduction of power loads when showing compliance with proposed Section 23.1309(c)(2). This provision is substantially equivalent to section 59(c)(3) of Appendix A to Part 135.
A new Section 23.1309(e) is proposed to require that the design of each electrical system, each item of equipment, and each installation take into account critical environmental conditions. Critical environmental and atmospheric conditions would include radio frequency energy and direct and indirect effects of lightning. Section
23.867 now requires the airplane structure to be protected from the effects of lightning and Section 23.954 now requires the airplane fuel system to be protected from the effects of lightning.
A new Section 23.1309(f) is proposed to provide a definition of the systems to which the requirements of this section are applicable and specifically identifies certain items to which they are not applicable.
Early in the development of minimum requirements for transport category airplanes, it was realized that more complex systems were being added to airplane designs and there was a need to include requirements which specifically addressed equipment, systems, and their installation. This was accomplished by the addition of Section 4b.606 to Part 4b of the Civil Air Regulations (CAR), Amendment 4b-6, effective March 5, 1952, in part, accomplished this objective. The preamble to that amendment included the following in regard to that addition:
An amendment clarifying the requirements for equipment, systems, and installations with regard to functioning and reliability is made in Subpart F. In addition, it specifies dual power supply for those installations the functioning of which is necessary to show compliance with the Civil Air Regulations.
This requirement, as adopted by that amendment, was retained in CAR Part 4b until that regulation was recodified to the Federal Aviation Regulations, Part 25, effective February 1, 1965. At that time, this requirement, substantially unchanged, was identified as Section 25.1309. For many years the "single fault" or "fail safe" concept of this requirement, along with experience based on service-proven designs and engineering judgment, were used to successfully evaluate most airplane systems and equipment.
However, in the late 1960's there appeared a number of safety-critical systems that were utilizing new technical complexity to accomplish safety-critical functions. Due to the increasing complexity of the technology being used to develop these systems, it was becoming increasingly difficult to apply engineering judgment as the only means of determining the effects or likelihood of failure conditions. The increasing difficulty in evaluating these complex systems, along with the potential hazards to the airplane that could result from their failure made it necessary to provide duplicate and triplicate systems to assure an acceptable level of safety.
At about this same time, the development of rational methods for safety assessment of systems led to the conclusion that an inverse relationship should exist between the probability of a failure condition and its effect on the airplane. That is, the more serious the effect, the lower the probability must be that it will occur.
The availability of this rational method for safety analysis of systems, along with the increasing difficulty in applying the then existing "single fault" or "fail safe" concept, prompted the FAA to propose an amendment to Section 25.1309 which would permit the use of this rational method as an acceptable means of accomplishing safety analysis. That proposed revision to Section 25.1309, which specified a level of safety in qualitative terms, and required assessments to be made, was adopted by Amendment 25-23 on April 1, 1970.
At that time, the FAA also realized that more complex systems were being utilized in small airplanes and that there was a need to add a reliability requirement to Part 23.
Accordingly, rulemaking action was initiated which resulted in Section 23.1309 being added to Part 23 by Amendment 23.14, effective December 20, 1973. The requirements of that new Section 23.1309 were similar to those of Section 25.1309 prior to Amendment 25-23 which were based on the "single fault" or "fail safe" concept. At that time, it was not envisioned that complex safety-critical systems, utilizing technology now available, would be used in the designs of small airplanes.
Therefore, there was no identified need to include provisions for use of the rational method of analysis in Part 23, as had been done in Part 25 by Amendment 25-23.
Experience has shown that the envisioned rate of technical growth of systems used in small airplanes was inaccurate and that safety-critical systems are now being proposed for use on Part 23 airplanes. As with the earlier experience with Part 25, the FAA is finding that it is difficult to apply "single fault" concepts to these complex systems and to utilize the application of engineering judgment as the only means of determining the effects or likelihood of certain failure conditions. Accordingly, there is now a need to revise the reliability requirements of Part 23 to allow the use of the latest available rational method for safety analysis of these complex safety-critical systems to assure continuation of the level of safety intended for airplanes certificated to Part 23. Such safety critical systems are currently being proposed for approval and there is an urgent need to accomplish this proposed rule change.