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 y Threshold Level Runway Threshold ILS Glide Path Origin FIGURE 1. ACCEPTABLE METHOD FOR DETERMINING
ALTITUDE LOSS IN APPROACH 254
FIGURE 1⎯CONTINUATION
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 to 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.”
Amendment 23-49 and Subsequent
A proposed revision to NPRM 94-21 clarified the quick release rule 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 rule in the Airship Design Criteria, FAA-P-8110-2, Change 2, is section 6.14.
Original Issue and Subsequent Paragraph (a) in § 23.1331 applies only to gyroscopic instruments, but paragraph (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 paragraph (b)(1) in § 23.1331 applies to either vacuum or electrically driven gyroscopic instruments.
NOTE 20: Section 23.1331 does not apply to pitot and static systems.
Electrical Systems When complying with paragraph (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 such 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 primary 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 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 to 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 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 commenters 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.”
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 batteries used in normal operations are acceptable as backup power sources only if their state of the charge can be reliably verified to the pilot.
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. The last option would:
(1) Require reliability and probability data for the aircraft battery that is acceptable to the FAA (applicants have not provided such data so far); and
(2) Require the state of charge be available to the pilot during all stages of flight and include a caution alert according to § 23.1322 when the state of charge is less than 30 minutes.
23.1335 Flight director systems
The corresponding rule in CAR 3 is CAR 3.669.
The corresponding rule in the Airship Design Criteria, FAA-P-8110-2, Change 2, is section 6.15.
Amendment 23-20 and Subsequent
A proposed revision to 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, is 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."
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 rules in the Airship Design Criteria, FAA-P-8110-2, Change 2, are sections 6.4 and 6.16.
Original Issue and Subsequent No specific criteria have been established for the minimum orifice size for fuel and oil lines. We believe 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-C55, “Fuel and Oil Quality Instruments (Reciprocating Engine Aircraft),” 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- C55 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.
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 23-8B, “Flight Test Guide for Certification of Part 23 Airplanes,” for guidance on fuel quantity indicators and auxiliary tanks.
A proposed revision to NPRM 75-19 revised paragraph (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 to NPRM 90-23 adds auxiliary power unit requirements and clarifies a fuel quantity rule in paragraph (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 to 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.
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 to 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.”
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 rules in the Airship Design Criteria, FAA-P-8110-2, Change 2, are sections 6.4 and 6.17.
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 Practices⎯Aircraft Inspection and Repair,” Section 3, for allowable wire in airplane manufacture and alteration.
Wire 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 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.