23.1335 Flight director systems
The corresponding rule in CAR 3 is CAR 3.669.
The corresponding airworthiness criteria is section 6.15, Airship Design Criteria, FAA-P-8110-2, Change 2.
Amendment 23-20 and Subsequent
A proposed revision in NPRM 75-23 explained the commonality between parts 23 and 25 as follows: “Service experience has shown that safety is compromised when the flight crew is not informed as to the current mode of operation of the flight director system. Moreover, experience has also shown that the position of the mode selector switch is not a reliable means of providing that information. This proposal would ensure that an indication entirely independent of the mode selector switch is provided.”
The proposals for both parts 23 and 25 for Amendment 23-20, of Final Rule, Docket 14625, are based on the following comment: “One commentator criticized the proposed phrase "independent of the mode selector switch" because it would tend to dictate design. Another commentator objected to the same phrase on the ground that it does not take into account modern panels, which incorporate illuminated mode indications that give positive indication of the selected mode, but are not independent of the mode selector switch since they are incorporated in it. The FAA agrees with these comments. The phrase "independent of the mode selector switch" is deleted from proposed Section 25.1335 and another sentence is added thereto reading, "Selector switch position is not acceptable as a means of indication."
TSO-C52b, Flight Director Equipment, is available.
23.1337 Powerplant instruments installation
The corresponding rules in CAR 3 are CAR 3.670, 3.671, 3.672, 3.673, and 3.674.
The corresponding airworthiness criteria are sections 6.4 and 6.16, Airship Design Criteria, FAA-P-8110-2, Change 2.
Original Issue and Subsequent No specific criteria have been established for the minimum orifice size for fuel and oil lines. FAA believes that .020 inches for fuel lines and .060 inches for oil lines can be accepted (according to Air Force Systems Command Manual 80-1, Part C, Chapter 5, paragraphs 3.1.1.3.7 and 3.1.2.3.3).
See AC 23-16A, “Powerplant Guide for Certification of Part 23 Airplanes and Airships,” § 23.959, for unusable fuel test procedures for guidance on § 23.1337(b)(1). AC 23-16 incorporated the guidance in canceled AC 23.959-1, “Unusable Fuel Test Procedures for Small Airplanes.” The quantity of unusable fuel is determined by compliance to § 23.959, and AC 23-16A provides an acceptable means of compliance.
Changes to total fuel quantity by incorporation of a fuel tank filler connection (§ 23.973) outboard of the existing connection will require changing the fuel quantity indicator to indicate the new quantity of fuel. The new indicator should meet the accuracy as specified in TSO-C55a, “Fuel and Oil Quality Instruments,” or MIL-G-9798.
The rule requires that fuel quantity be calibrated as zero when only unusable fuel (as determined under § 23.959) is left in the tank. Some fuel tank system designs can result in a lowest reading obtainable in level flight being greater than the unusable fuel supply. In this case, an ELOS is acceptable by placing a red radial at the “lowest reading obtainable in level flight,” and mounting a placard stating the amount of usable fuel remaining at the red radial.
Fuel quantity indicators are also governed by § 23.1301, as are all 14 CFR, part 23 Subpart F appliances. This regulation requires the installed indicators function as designed and not create a hazard in their operation. This precludes indicators that read higher than the actual fuel level since this would constitute a hazard. 14 CFR, part 23, does not require an applicant to install a TSO fuel quantity indicator.
However, when installed in a reciprocating engine airplane and produced under TSO- C55a authorization, the allowable error of the indicator is no more than three percent of full scale. It is believed that ground and cruise attitude(s) are the minimum attitudes required for operation within the three percent tolerance. Evaluation of the gauge function throughout the normal and expected operation of the airplane is needed to assess gauge indications outside the ground and cruise attitude conditions.
271 The purpose of this evaluation is to establish the ground and cruise attitude(s) gauge tolerance is functional and satisfactory for the airplane.
Amendment 23-7 and Subsequent
This amendment moved the requirement for cylinder head temperature indication from this section to § 23.1305.
Amendment 23-18 and Subsequent See AC 23-8C, “Flight Test Guide for Certification of Part 23 Airplanes,” for guidance on fuel quantity indicators and auxiliary tanks.
A proposed revision in NPRM 75-19 revised § 23.1337(a) and is explained as follows: “Powerplant instruments and instrument lines sometimes utilize flammable fluids. The proposal would require that those instruments and lines be installed and located so that leakage of the fluid would not create a hazard. The proposal would also editorially revise Sec. 23.1337(a) for clarity.”
Amendment 23-43 and Subsequent
A proposed revision in NPRM 90-23 adds auxiliary power unit requirements and clarifies a fuel quantity rule in § 23.1337(b)(5) as follows: “This proposal adds APU installation requirements and clarifies fuel quantity indicator requirements.
Conference Proposal 449 recommended amending this section to include APU requirements for the reason that applications have been received for approval of auxiliary power unit installations in part 23 airplanes. These installations also need protection from the escape of flammable fluids. The proposed revision to paragraph
(b)(5) will maintain compatibility with proposed changes to Section 23.955(d).”
Amendment 23-49 and Subsequent
A proposed revision in NPRM 94-21 explains this amendment as follows: “This proposal would revise the heading of this section to reflect the powerplant instrument installation requirements that it contains. The difference between this section and Sec. 23.1305 is clarified by this change.
Section 23.1337(b) would be revised by removing the wording that authorizes installation of only those fuel indicators marked in gallons and pounds. In countries that use the metric system, other acceptable units of measure for marking fuel indicators are used. This proposed revision would allow the use of any appropriate measurement unit. Section 23.1337(b) would also be revised by adding the word "usable" to the first sentence of this section. This revision is consistent with the requirements of Sec. 23.1337(b)(1), which requires the fuel quantity indicator to be calibrated to read "zero" when the fuel in the tank is equal to the unusable fuel determined under Sec. 23.959.
272 Proposed new Sec. 23.1337(b)(4) would require a "means to indicate" the amount of usable fuel in each tank when the airplane is on the ground. This requirement would ensure that a reliable means is provided for the pilot to determine before takeoff that the amount of fuel that is in the airplane is adequate for the intended flight. The ability to make this preflight determination will help reduce the number of accidents that have resulted from fuel starvation. This proposal, which is patterned after Sec. 23.1337(d) and (d)(1), would not require a separate fuel indicating system. The means to determine the amount of fuel while on the ground may be provided by a calibrated dipstick separate markings on the inflight fuel indicator, or any other acceptable means selected by the manufacturer. Accordingly, this proposal would contribute to the safe operation of the airplane and would not appreciably add to the cost of the airplane design.”
Amendment 23-51 and Subsequent
A proposed revision in NPRM 94-19 clarifies the reference to Subpart E as follows:
“Under the area of "Installation," the reference in Sec. 23.1337 (b)(1) to Sec. 23.959 would be changed to Sec. 23.959 (a), in accordance with the revision to Sec. 23.959 proposed in this notice. The revision would redesignate the existing Sec. 23.959 text as Sec. 23.959 (a); there is no change in the requirement itself.”
273 Section 3. Electrical Systems And Equipment
23.1351 General
The corresponding rules in CAR 3 are CAR 3.681, 3.682, 3.686, and 3.687.
The corresponding airworthiness criteria are sections 6.4 and 6.17, Airship Design Criteria, FAA-P-8110-2, Change 2.
Original Issue This rule does not allow a failure or malfunction of any electrical power source to impair the ability of any other source to supply essential circuits.
Amendment 23-7 and Subsequent This amendment allows one exception to the original rule. This exception would allow loss of an alternator that is dependent on a battery for initial excitation or stabilization when that battery has failed. This exception was adopted under the premise the advantages of having a battery connected for initial excitation or stabilization for alternators needing it outweighed the results of that battery failing.
This exception is only applicable to alternator installations that need a battery. Loss of an alternator because of battery failure was considered of no greater result than the intrinsic failure of the alternator itself. In single-engine airplanes, loss of the battery and alternator would result in the loss of the electrical system, which would be no worse than other single failures (that is, shorts to ground and conductor failure) that would also result in loss of the electrical system.
Wire, meeting MIL-W-5086, has been removed from the list of approved wire in AC 43.13-1B, Change 1, because of its flammability characteristics, corrosive vapors, and toxic gases of Polyvinyl Chloride (PVC) insulation. See AC 43.13-1B, Change 1, “Acceptable Methods, Techniques, and PracticesAircraft Inspection and Repair,” Section 3, for allowable wire in airplane manufacture and alteration.
Wire/Cable that is not listed in AC 43.13-1B, Change 1, should be shown by tests and analyses to meet the airworthiness requirements of §§ 23.863, 23.1351, 23.1359, and
23.1365 as applicable.
Amendment 23-14 and Subsequent
This amendment added requirements so designed that the risk of electrical shock to crew, passengers, and ground personnel is reduced to a minimum. There must also be a means to give immediate warning to the flight crew of a failure of any generator.
Fire resistance. Electrical equipment must be so designed and installed that if there is a fire in the engine compartment, during which the surface of the firewall adjacent
274 to the fire is heated to 2000 degrees F for five minutes or to a lesser temperature confirmed by the applicant, the equipment essential to continued safe operation and located behind the firewall will function satisfactorily and will not create an additional fire hazard.
Amendment 23-17 and Subsequent
A proposed revision in NPRM 75-10 requires overvoltage control of generators with the following explanation: “Complete electrical system failures on both single and twin engine aircraft continue to occur. The electrical failure that causes this problem is often the loss of voltage control in the voltage regulator. This usually results in a bus voltage well above the capabilities of the electrical equipment connected to the bus. This overvoltage condition frequently destroys electronic equipment and boils the electrolyte in the battery. The proposal is only directed at this overvoltage problem and therefore differs from Sec. 23.1351(b). The proposal would not require a specific method of overvoltage control.”
Amendment 23-20 and Subsequent
A proposed revision in NPRM 75-23 added external power requirements with the following explanation: “If an external power supply with reverse polarity or reverse phase sequence were to supply power to the airplanes electrical system extensive damage to the system could result. This proposal would require a means to prevent such an occurrence.”
Amendment 23-34 and Subsequent
A proposed revision in NPRM 83-17 added commuter category requirements from “part 135, Appendix A, sections 61 and 63”.
Amendment 23-43 and Subsequent
A proposed revision in NPRM 90-23 explains this amendment as follows: “This proposal would allow a generator to be installed and operate below its continuous rating when it has a rating higher than necessary, allow methods other than reverse current cutouts for protecting against reverse current, and would require the airplane to operate safely for 5 minutes without normal electrical power.
Conference proposal 453 recommended revising paragraphs (c)(1) and (c)(3) essentially as proposed herein. The justification given is that the generator-rated output may be higher than required for the electrical loads of the airplane and, in such case, the electrical system (generator output) is limited by its regulation system.
The consensus at the conference supported the objective of this conference proposal.
The FAA agrees with the need for changing paragraph (c)(1) to clarify its intent and to revise paragraph (c)(3) to relieve the burden to install a specific type of reverse current control where more efficient and less costly controls are now available.
275 Conference proposal 456 recommended adding paragraph (g), essentially as proposed herein except the requirement would only be applicable for airplanes operated above 25,000 feet. The justification was that part 23 airplanes that operate at high altitudes above 25,000 feet depend upon electrical power for safe operation.
Emergencies involving loss of normal electrical power at or above this altitude typically result in the loss of other systems, such as electric fuel pumps, pressurization system, warning system, navigation, communications, and instrumentation. The FAA developed special conditions for part 25 that initiated the requirement in this proposal and it was later adopted into part 25 by amendment
25.41, in 1977. Conference proposal 456 was essentially developed from the part 25 requirements except for the 25,000 foot applicability. When offered for comment at the conference, there were no objections on conference proposal 456. After further review, FAA has concluded that the proposal should not be limited to airplanes that operate above 25,000 feet since emergencies resulting in the loss of normal electrical power are critical for all airplanes. Five minutes is considered adequate time to cope with such an emergency so that pilot can operate the airplane safely and assess the reason for the loss of normal electrical power.
Conference proposal 452 recommended changing the phrase "essential for safe operation" to "essential to flight safety" for consistency in the regulations. A word search of the regulations indicated that there were other phrases such as "essential to safety of flight," and "essential to continued safe operation." All of these phrases have been interpreted to have the same meaning. Since the affected regulations have been administered effectively without significant problems, the FAA does not consider the recommended changes to be beneficial.”
Final Rule, Docket 26324, has the following clarification: “It has been brought to the FAA’s attention that many electrical generating devices that are used on part 23 are now referred to as "alternators" and that there is some confusion about such units acceptability because Sec. 23.1351(c) continues to address "generators." To provide clarifications, ten locations in Sec. 23.1351, paragraphs (c), (c)(1), (c)(2), (c)(3),
(c)(4), and (c)(5), are being revised by changing the word "generator" to "generator/alternator." This proposal is adopted with the aforementioned change.”
Amendment 23-49 and Subsequent
A proposed revision in NPRM 94-21 explains this amendment as follows: “The proposal would revise current Sec. 23.1351 by removing portions of paragraphs
(b)(2) and (b)(3) and by removing all of paragraph (b)(4). The removed requirements are applicable to alternators that depend upon the battery for initial excitation or for stabilization. This revision responds to a Joint Aviation Authority recommendation to remove the provisions that allow a battery failure to result in the loss of the alternator. Information in this recommendation showed that self-excited alternators are now available for installation on newly certificated airplanes. The FAA has verified that self-excited alternators are now available; therefore, there is
276 no longer a need for the regulations to address alternators that depend upon a battery for initial excitation and stabilization.
Revised Sec. 23.1351(c)(3) would require an automatic means for reverse current protection. Reverse current protection is accomplished by means that automatically detect changes in the current. The proposed revised wording would more accurately define this function and the equipment that would accomplish the protection.
Finally, Sec. 23.1351(f) would be revised by adding a requirement that would require the ground power receptacle to be located where its use will not result in a hazard to the airplane or to people on the ground using the receptacle.”
Final Rule, Docket 27806, has the following clarification: “The proposals are adopted as proposed, except that paragraph (c)(3) has been revised to clarify that protection for any generator/alternator and the airplane electrical system must be provided.”
EASA AMC effective February 12, 2009, AMC 23.1351(a)(2) is acceptable for FAA certification.
EASA AMC effective February 12, 2009, AMC 23.1351(b)(5)(iv) is acceptable for FAA certification to 14 CFR, part 23, § 23.1351(b)(4)(iv).
23.1353 Storage battery design and installation
The corresponding rule in CAR 3 is CAR 3.683.
The corresponding airworthiness criteria is section 6.18, Airship Design Criteria, FAA-P-8110-2, Change 2.
Original Issue and Subsequent
See AC 43.13-1B, Change 1, “Acceptable Methods, Techniques, and PracticesAircraft Inspection and Repair,” Chapter 11, Section 2, for battery installation guidance. Replacement batteries would require PMA, unless exempted by part 21, § 21.303(b), whether the replacements are lead-acid, lithium or nickelcadmium. The airworthiness standards of 14 CFR, part 23, §§ 23.1301, 23.1309,
23.1351, and 23.1353 should be considered for replacement battery installations.
Amendment 23-20 and Subsequent
A proposed revision in NPRM 75-23 explains this amendment as follows: “Proposed Sec. 23.1353(b)(1) would add "or power" to the battery recharging standard. The proposal by adding an alternative standard is intended to clarify the present rule to more appropriately include all battery charging means and parameters. In some battery charging techniques, voltage is not a controlled factor except by response of the battery. Also, power is a measure of heat input to the battery. A similar proposal is made for Secs. 25.1353(c)(1)(i), 27.1353(b)(1), and 29.1353(c)(1)(i).
Short circuits of nickel cadmium batteries (either internally or to the airplane structure through the battery caps) have occurred in service. The heat generated by such short circuits may in some circumstances damage nearby structure or essential systems. It is therefore proposed to require provisions to prevent any hazardous effect from this cause. See also proposed new Sec. 23.1353(f) in Airworthiness Review Notice No. 2 (Notice 75-10), which is aimed at reducing the occurrence of short circuits that are caused by excessive battery charging current.”
Amendment 23-21 and Subsequent
A proposed revision in NPRM 75-10 explains § 23.1353(g) as follows: “The proposal conforms to paragraph (b) of AD 72-19-4, which applies to all nickelcadmium batteries that are capable of being used to start an aircraft engine or auxiliary power unit.”
Amendment 23-49 and Subsequent
A proposed revision in NPRM 94-21 explains the 30-minute requirement in this amendment as follows: “Proposed new Sec. 23.1353(h) would require that, the event of a complete loss of the primary electrical power generating system, airplane battery
278 capacity must be sufficient to supply at least 30 minutes of electrical power to those loads essential to the continued safe flight and landing of the airplane.
This proposal is not limited to airplanes that are approved for any particular type of operation. Although the battery capacity needed for an airplane approved for day VFR operations would be much less than the capacity for an airplane approved for day/night IFR operations, the same level of safety should be provided for all airplanes. While this proposal would add an additional requirement to part 23 for normal, utility, acrobatic, and commuter category airplanes, in practice this requirement to provide a battery capacity sufficient to supply at least 30 minutes of electrical power is not new to many airplane manufacturers. Certain other countries in which part 23 airplanes have been certificated have requirements for such a 30- minute battery capacity. Manufacturers experience with these requirements has shown that the only design impact that results from complying with these requirements is the need to install a battery with greater capacity than might otherwise be installed. Experience has also shown that a load shedding procedure may be necessary for certain airplanes. No other airplane design changes would be needed.
Despite the above referenced experience record, this requirement would be new to some manufacturers and they may have questions on how it would be applied. For that reason, this notice discusses compliance considerations that have emerged from experience based on substantively equivalent requirements.
This compliance experience has shown that the rating of the battery selected for the airplane should be sufficient to cover the loss of capacity that would occur with battery age and the reduced capacity that results from a realistic state of charge, which may be less than a full charge. Using a design battery capacity that is only 75 percent of the battery nameplate rating would be an acceptable way of accounting for these losses.
In addition to determining the battery rating that would be needed, the manufacturer would also need to determine the functions that would be necessary for 30 minutes of safe flight and the landing of the airplane. Again, experience has identified several functions. For a day VFR approved airplane, no functions may require battery power; however, it may be necessary to supply power for certain communication capacities or, if the airplane has electrically powered retractable landing gear.
Providing a secondary means for lowering the gear would be an acceptable alternative to providing electrical power or battery power for this function. For other types of operating approvals, providing power for the following functions and equipment should be considered:
1. Any required flight and navigation instruments. Air driven instruments that would function over the required period can also be accepted for this function.
2. Cockpit and instrument lighting.
3. For IFR and icing approvals, power for the heated pitot tube.
4. For radio communication, usually one VHF communication system with power for three to five minutes of transmission would be acceptable.
5. Functions needed for safe night flight and night landing for the airplane.
6. Electronic engine ignition systems.
7. Any functions that cannot be readily shed following the loss of generator power.
8. Engine inlet heat or deicing protection required for normal operation of the airplane.
Although power for the listed functions may provide for the safe operation and landing of most airplanes, individual airplane designs may require the consideration of additional functions.
In applying these rules it may be assumed that airframe and engine icing protection equipment would not be operating at the time of the generator system failure. Power for icing protection would not be required if the icing protection equipment is not required for the normal operation of the airplane.
This proposal would require additional battery capacity and would not alter or supersede any other requirements in this part for separate or dedicated emergency power supplies. When requirements such as those in current Sec. 23.1331(a) or in proposed Sec. 23.1311(a)(5) are applicable to the airplane design, these power supplies are required to provide a needed level of safety for that function; therefore, that power source must be supplied.”
The requirements of § 23.1353(h) are as follows:
“In the event of a complete loss of the primary electrical power generating system, the battery must be capable of providing at least 30 minutes of electrical power to those loads that are essential to continued safe flight and landing. The 30 minute time period includes the time needed for the pilots to recognize the loss of generated power and take appropriate load shedding action.”
It should be noted that for a single engine airplane used in Part 135 operation, a battery is an acceptable means of compliance for emergency power in § 135.163. If a battery is the means of compliance, it must supply 150 percent of emergency electrical loads for at least one hour.
Previous guidance on this issue states the airplane’s primary electrical power includes the airplane’s electrical generation system and the airplane’s starter battery when only one battery is installed. The battery for the 30-minute criteria, therefore, should be an
280 independent power source from the airplane’s starter battery. If adequate monitoring and procedures are incorporated so the pilot knows the airplane’s starter battery meets the 30-minute criteria after an engine start and during all other operations, an ELOS finding may, with FAA approval, be an acceptable method for using the airplanes starter battery.
Please refer to the guidance in AC 23.1309-1E, “System Safety Analysis and Assessment for Part 23 Airplanes,” for determining the loads that are essential to continued safe flight and landing. Continued safe flight and landing is defined as follows:
“This phrase means that the airplane is capable of continued controlled flight and landing, possibly using emergency procedures, without requiring exceptional pilot skill or strength. Upon landing, some airplane damage may occur as a result of a failure condition.”
The 30-minute power bus should include all systems that could cause a catastrophic failure condition under the § 23.1309, Failure Hazard Assessment. Sometimes, it may not be practical to include all systems on the 30-minute power bus that could cause a catastrophic failure condition. For example, systems with large heating loads for ice protection may not be included on the 30-minute electrical power bus;
however, the possible hazards that could cause catastrophic failure conditions should be minimized.
To minimize the hazard either is to reduce, lessen, or diminish to the least practical amount with current technology and materials. The least practical amount is that point at which the effort to further reduce a hazard significantly exceeds any benefit in safety gained from that reduction. Additional efforts would not result in any significant improvements to safety and would inappropriately add to the cost of the product.
Assuming operations under IFR conditions for parts 91 or 135 operations, the following systems should be included on the 30-minute power bus:
1. If needed to comply with §§ 23.1323 and 23.1325, one airspeed indicator and altimeter with a heated pitot tube and heated static pressure source;
2. The magnetic compass, and any display necessary for continued safe flight and landing, sufficiently illuminated for night operation;
3. One navigation system installation appropria te to the ground facilities to be used;
4. One communication installation system;
5. One gyroscopic pitch and bank indicator;