(1) In the operating limitations section, the airspeed limitations, maximum altitude for operation if different from the maximum certificated altitude of the airplane, category of ILS approaches for which approval is granted, minimum approach height, and any other applicable limitations.
(2) In the operating procedures section, the normal operating information, including navigation and glide slope intercept recommendations. For those autopilot systems, which incorporate either monitors or limiter devices, the pre-engagement procedures and the means of indicating that, the preengagement has been successfully completed.
(3) In the emergency operation procedures section
(a) A statement of the altitude loss in the cruise, climb, and descent configurations; and maneuvering flight conditions, because of possible malfunctioning of the autopilot system.
(b) A statement of the altitude loss because of malfunctions while in the approach configuration. If engine inoperative approach is approved, the altitude loss should be included.
(c) Any other procedure related to emergency procedures associated with either the autopilot or associated systems. (See Figure 1.)
Altitude Loss
1. Malfunction inducement point.
2. Malfunction recognition by pilot.
3. Initiation of manual recovery action by pilot.
4. Altitude loss with no instrumentation.
5. Altitude loss with instrumentation.
30 ILS Nominal Glide Slope Path of Airplane Wheels One Second Delay Y Malfunction Inducement Point 1:29 Slope 15.0 feet 8177 Runway Threshold ILS Glide Path Origin FIGURE 1. ACCEPTABLE METHOD FOR DETERMINING
ALTITUDE LOSS IN APPROACH 261
262 FIGURE 1CONTINUATION
Malfunction Evaluations. The airplane should be established on the ILS glide slope and localizer in the configuration(s) with the approach speed(s) specified by the applicant for approach. Simulated automatic flight control system malfunctions should be induced at critical points along the ILS taking into consideration all design variations and their limits in automatic flight control system sensitivity and authority.
The malfunctions should be induced in each axis. While the pilots may know the purpose of the flight, they should not be told when a malfunction is to be or has been applied except through a deviation of the airplane from the intended flight path, abnormal control movements, or by a reliable failure warning system. After a failure, recovery should be initiated one second after the pilot recognizes the failure.
a. A three-degree glide slope should be used for these tests to determine the malfunction effects to be expected in service.
b. For use during a coupled ILS approach, the automatic control system should not fail in such a way that it causes the airplane wheels to descend below a limit line lying below the glide slope, sloping upward at 29:l from a point 15 feet above the runway threshold. With the airplane established on the glide slope in approach configuration, at approach speed, the most critical malfunction is induced at a test altitude referenced to the runway threshold. Measure the altitude loss between the test altitude and the lowest point of the manual recovery, unless instrumentation is available to measure the vertical deviation from the intended glide path to the lowest point in the recovery maneuver. The altitude loss and the known distance to the threshold from the lowest recovery altitude are compared to the limit line.
The lowest test altitude, from which malfunction and manual recovery can be completed, without the airplane wheels descending below the limit line, is considered the minimum height for use of the automatic flight control system.
c. Recovery from all malfunctions should be shown either by overpowering or by manual use of an emergency quick disconnect device after the appropriate delay.
The pilot should be able to return the airplane to its normal flight altitude under full manual control without exceeding the defined limits.
Amendment 23-43 and Subsequent
A proposed revision in NPRM 90-23 added a requirement for a quick release explained as follows: “This proposal would standardize the location of the quick release (emergency) control for autopilot systems. Standardization permits consistency of pilot responses in preventing hazardous airplane attitudes during autopilot malfunctions. The location specified is consistent with the requirements for part 25 airplanes, except this proposal allows the control to also be located on a stick control.”
263 Amendment 23-49 and Subsequent
A proposed revision in NPRM 94-21 clarified the quick release requirement explained as follows: “New Sec. 23.1329(b), adopted by Amendment No. 23-24 (58 FR 18958, April 9, 1993), does not state clearly that stick controlled airplanes must be equipped with the same autopilot quick release controls that are required for airplanes with control wheels. This proposed revision of Sec. 23.1329(b) would clarify that a quick release control must be installed on each control stick of an airplane that can be operated from either pilot seat.”
23.1331 Instruments using a power source
The corresponding rule in CAR 3 is CAR 3.668.
The corresponding airworthiness criteria is section 6.14, Airship Design Criteria, FAA-P-8110-2, Change 2.
Original Issue and Subsequent Section 23.1331(a) applies only to gyroscopic instruments, but § 23.1331(b) in this section applies to any instrument that depends on external power or external energy for proper operation.
The requirement for two independent power sources in § 23.1331(b)(1) applies to either vacuum or electrically driven gyroscopic instruments.
NOTE: Section 23.1331 does not apply to pitot and static systems.
Electrical Systems When complying with § 23.1331(b) in this section, a single battery required for starting is acceptable if: 1) the electrical system is capable of continuous normal operation without external excitation or stability, and 2) there is no probable failure of the battery that will adversely affect the electrical system once it is operating.
However, the airplane battery cannot be accepted toward showing compliance to the power source requirements of §§ 23.1331 and 23.1351 unless the state of charge of the battery is displayed to the pilot.
A single electrical bus is unacceptable for a multiengine airplane.
The multiengine requirement is for two independent power sources. Therefore, an installation with a single primary power source for all flight instruments and a manually operated backup is not acceptable.
a. This system could conceivably fail in su ch a way that all the flight instruments could be simultaneously damaged or disabled (that is, loss of voltage regulation).
This would not be corrected by switching to the backup power source.
b. Also, an electrical system with a pr imary power source that employed a backup source with common circuitry or components is not independent.
Standby Vacuum Systems The intended function of a standby vacuum system is to provide a second vacuum source for the gyroscopic instruments after a failure of the primary vacuum system.
The standby system should either supply enough vacuum to maintain the accuracy and reliability of the gyroscopic instruments throughout the phases of flight, or there
265 should be limitations on operation in the AFM. When operating on the standby system, the pilot should predicate operations on other certified systems (partial panel) and use the gyroscopic instruments as an aid, provided the pilot determines these instruments give acceptable information. Also, the pilot should not manipulate the throttle, other than for normal flight, in an attempt to control vacuum pressure within the limitations.
If a second vacuum system were not required, the standby installation would be for non-required equipment according to this rule. In addition, § 21.21(b)(2) requires there be no feature that results in an unsafe condition. To comply with these requirements, it should be shown that neither operation nor failure of the standby vacuum system interfere with the normal operation of the primary system or result in any unsafe condition. The pilot should also be kept apprised of when the standby system is in operation either by manual source selection or by red visual annunciation (§ 23.1322) if an automatic switching system is installed. To assure that no unsafe condition will result, the standby system should be flight evaluated in each unique airplane installation. In addition, operating information, emergency procedures, and limitations should be available in an AFMS or placards, as appropriate. This information should meet the requirements of §§ 23.1583 and 23.1585 of this part, and it should emphasize the standby vacuum system is for emergency use only and should not be used for dispatch purposes.
Amendment 23-43 and Subsequent Independent Power Sources A proposed revision in NPRM 90-23 explains this amendment as follows: “This proposal requires a visual annunciation to indicate when power for gyroscopic instruments is not adequate, and two independent sources of power for all airplanes.
Requirements in current paragraphs (a)(1) and (a)(2) are being deleted because the general requirements of §§ 23.1301 and 23.1309 will adequately address these issues.”
The proposal to Amendment 23-43 by Final Rule, Docket 26344, is based on comments as follows: “Several comments were received on this proposal. One commenter supports the proposal but notes that it does not address non-gyroscopic instruments, and would result in power supply requirements for such instruments being omitted from regulations. This commenter also believes the word "adjacent" in proposed Sec. 23.1331(a) is too restrictive and requests the meaning of the word "independent" in proposed Sec. 23.1331(c) in context of sources of power for singleengine airplanes. Finally, this commenter identifies support for the provisions of proposed Sec. 23.1331(b)(2).
The FAA has reviewed this proposal and agrees that by inserting the word "gyroscopic" in the introductory text of this proposal, other types of instruments that use a power source for their function would be omitted from the regulations. To correct this omission and retain the current provision of the regulations that address
266 all instruments, the word "gyroscopic" is being removed from the introductory text.
To further clarify the applicability of these requirements, the words "that uses a power source" are being added between the words "instrument" and "the".
The FAA also reviewed this commenter's position on the word "adjacent" and agrees that its application could be too restrictive. The intent of this proposal is to require any installed separate power indicator to be located so that a pilot who is using that instrument will notice the loss of that instrument's power. To clarify and preclude restrictive application of this requirement, the word "adjacent" is removed and replaced with words similar to those used in Sec. 23.1321(a).
In regard to the commenters question on the word "independent" in context of sources of power for single-engine airplanes, this word has the same meaning for all airplanes, except that on single-engine airplanes the second source cannot be driven by a separate engine.
Adverse service experience that has resulted from power source failures and the subsequent loss of flight instrumentation has shown that it is necessary to provide a backup power source for the flight instruments. In the case of instruments that use a vacuum power source, the second source has been provided by installing a smaller electric driven vacuum pump and by arranging the vacuum system so that this pump is isolated from the normal vacuum system and so that it provides power to the instruments only after the normal engine driven pump fails.”
Guidance
This amendment adds the requirement for independent power sources for required instruments for single-engine as well as multiengine airplanes. This was considered appropriate because of the number of single-engine airplane accidents that were attributed to the loss of power to required flight instruments. Also, the reference to “gyroscopic” was removed to include both gyroscopic and non-gyroscopic instruments since non-gyroscopic flight instruments are in use.
a. Instruments that provide required flight information and use an external power source are now required to have two independent power sources. This requirement has the same intent for single-engine airplanes as for multiengine airplanes: to functionally isolate flight instruments so any failure of one power source or instrument will not cause the complete loss of a required flight instrument function. Thus, in the failure of a heading instrument, that failure may not result in the loss of the proper supply of energy to the attitude indicator powered by the same source, and loss of a single power supply may not cause loss of any required instrument function.
b. Ships starter batteries used in normal operations are acceptable as backup power sources only if they are approved per § 23.1353.
c. This regulation is not intended to apply to circuit protection devices, which are to be considered in §§ 23.1351 and 23.1357.
d. These changes are meant to apply to those instruments that rely on a power source and provide required flight information. Such instruments are those that provide information for direct control of flight that are required by the kinds of operation for which the airplane has been approved. Thus, this section applies to all flight instruments required by 14 CFR, part 23, § 23.1303 and part 91, § 91.205. So, instruments in airplanes limited to VFR operations that are not required for VFR would not have to comply with the requirements of § 23.1331. Exemptions would not be necessary or appropriate.
e. Each independent power source must provide enough power for normal operations throughout the approved flight envelope of the airplane and for any operations for which the airplane is approved. For example, an IFR approved airplane must have independent power sources for the display of attitude that are not limited to altitudes below the approved service ceiling of the airplane.
f. Section 23.1331(c) does not require installing dual alternators or vacuum systems on single engine airplanes. Other options include: 1) a dedicated battery with a 30-minute capacity for electrical instrument loads essential to continued safe flight and landing, 2) use of differently powered types of instruments for primary and standby, or 3) verifying the aircraft battery used for starting by a system safety analysis per § 23.1309.
Amendment 23-62 and Subsequent
In Docket No. FAA-2009-0738, the Discussion of the Regulatory Amendments stated: The proposed changes to § 23.1331would apply to instruments that rely on a power source to provide required flight information for IFR operations.
Consequently, this section applies to all flight instruments such as those required by parts 23, 91, 121, and 135. Airplanes limited by type design to VFRoperations would not have to comply with the requirements of proposed § 23.1331(c).
Each independent power source must provide sufficient power for normal operations throughout the approved flight envelope of the airplane and for any operations approved for the airplane. Section 23.1331(c) would not require the installation of dual alternators or vacuum systems on single engine airplanes. One option includes a dedicated battery that meets the requirements of § 23.1353(h) for electrical instrument loads essential to continued safe flight and landing. Another option includes separately powered types of instruments for primary and standby use. The last option would include performing a system safety analysis, per § 23.1309, to identify the procedures necessary to verify the charge state of any airplane starting battery that is used to power a stand-by system.
Change 1 AC 23-17C 7/16/2012
268 This amendment removes the requirement to comply with § 23.1331(c) for Day VFR and Night VFR aircraft. For IFR aircraft, this amendment clarifies that two independent power sources are acceptable if:
1. Two electrical power sources are installed for an all electric aircraft,
2. One generated electrical source and a battery that meets § 23.1353(h) is installed in an all electric aircraft, or
3. Different types of power, electrical and vacuum, are installed for primary and secondary instruments.
The Final Rule is adopted with clarification.
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.