Amendment 23-43 and Subsequent
A proposed revision to NPRM 90-23 explains this amendment as follows: “This proposal is addressed in conference proposal 438. It requires that the specific colors be consistent with change in brightness over the full range of ambient light conditions in the cockpit and that the luminance difference and/or color difference be sufficient to preclude confusion or ambiguity under all probable cockpit lighting conditions.
Light color is not controlled by a lens color cathode ray tube (CRT) displays now being incorporated into airplanes. Cockpit lighting evaluations are required in Section 23.1321 and clarification if needed in this section to assure compliance with these requirements.”
This amendment clarifies Final Rule, Docket 26344 as follows: “This proposes to amend Sec. 23.1322 to require the warning, caution, and advisory lights to be effective under all probable cockpit lighting conditions. One commenter recommended the words "all probable cockpit lighting conditions" be revised to "all normal cockpit illumination." The reason given for the recommendation is that the proposed words could include the need to consider a blinding lightning flash.
The FAA disagrees. If conditions exist where a "blinding" lightning flash occurs, none of the lights will be visible while the pilot(s) are blinded and this would not be considered to be a probable light condition. The lights should be evaluated for the lighting conditions that will occur immediately after that flash to ensue that, as quickly as vision is restored after the exposure to the blinding flash, they will provide effective warnings, cautions, and advisories. As noted in the NPRM, these lights need to be consistent over a full range of ambient light conditions. The words used in this proposal describe the need to evaluate the lights over this range of light conditions.
One commenter supports the proposal. This proposal is adopted as proposed.”
See AC 23.1311-1A for additional guidance for electronic displays.
23.1323 Airspeed indicating system
The corresponding rule in CAR 3 is CAR 3.663.
The corresponding rule in the Airship Design Criteria, FAA-P-8110-2, Change 2, is section 6.9.
Original Issue and Subsequent
Part 135, Operating Requirements: Commuter and On-Demand Operations, requires that IFR airplanes have a heated pitot tube for each airspeed system. In consideration of a four-pound bird strike, the minimum distance between pitot tubes that can be accepted is 14 inches, measured in a straight line.
Amendment 23-7 and Subsequent
A proposed revision to NPRM 67-14 changed five MPH to five knots with an explanation as follows: “Nautical units of speed and distance. Consistent with the gradual transition from statute miles to nautical miles being made throughout the Federal Aviation Regulations, it is proposed, in addition to certain specific changes made in this notice, to amend Part 23 by changing all references to "miles" and "miles per hour," to "nautical miles" and "knots," respectively, wherever the former are used.”
Amendment 23-17 is additionally explained by Final Rule, Docket 8083, as follows:
“The amendments are therefore adopted as proposed, using the following criteria:
(1) Conversions from miles per hour to knots are rounded off to whole units to avoid fractions of a knot unless a more accurate measurement is necessary under the present rule, and (2) current requirements expressing extremely low airspeeds such as 5 or 10 miles per hour, are not changed numerically (such as to 4 or 9 knots, respectively) since the substantive difference in these cases is approximately 1 mile per hour and is not practically significant.”
Amendment 23-20 and Subsequent
A proposed revision to NPRM 75-23 explains this change to the amendment as follows: “Proposed Sec. 23.1545(a) would require airspeed limitation marks be located at the corresponding indicated airspeeds instead of at the calibrated airspeeds, thereby providing a more useful indicator dial for operation of the airplane. However, to ensure uniformity, it is also proposed to revise Sec. 23.1323 to require that the airspeed instrument be calibrated according to the standard relationship between pressure and airspeed. (See the proposal for Sec. 23.1323.)
The allowable airspeed system error would then include position error, but exclude the airspeed instrument calibration error, consistent with Part 25. The airspeed 231
range for calibration, as set forth in proposed Sec. 23.1323, would encompass the airspeed limitations in proposed Sec. 23.1545(a).”
Indicated airspeed was changed to calibrated airspeed in Amendment 23-20 by Final Rule, Docket 14625, based on the following: “Another commentator (who concurred with the intent of the proposal to revise Section 25.1323) questioned whether the allowable error, in proposed Section 23.1323(b), should be expressed in terms of calibrated airspeed rather than indicated airspeed and whether the airspeed ranges specified in proposed Section 23.1323(b)(1) and (b)(2) were unnecessarily severe accuracy requirements. The FAA agrees that the error allowed by proposed Section
23.1323(b) should be expressed in terms of calibrated airspeed to be in accord with normal practices. However, the FAA believes that the airspeed ranges in proposed Secs. 23.1323(b)(1) and (b)(2) are needed to encompass the airspeed limitations in proposed Section 23.1545. The FAA also believes that, as a practical matter, the accuracy requirements in proposed Section 23.1323 are not significantly more restrictive than the current requirements.”
Amendment 23-34 and Subsequent
See AC 23-8B, “Flight Test Guide for Certification of Part 23 Airplanes,” for additional guidance.
A proposed revision to NPRM 83-17 added commuter category rules based on the following: “Part 135, App. A., Sec. 13(b) and (d).”
Amendment 23-42 and Subsequent
This amendment added the requirement for a heated pitot tube when a plane is approved for flight in instrument meteorological conditions or flight into known icing conditions. The NPRM states the following: “Maintaining a functional and accurate airspeed system is essential to safe and reliable control of an airplane in instrument meteorological conditions and flight in icing conditions.” The proposal was considered necessary as a minimum airworthiness standard when operations in the airplane are to be approved. Therefore, the use of a drain trap/sump in meeting the requirement for a positive means of drainage is allowable, but an applicant must consider a failure condition of an overflowing trap/sump that causes misleading readings of airspeed. Waiting for an airspeed error to occur from excess moisture is not acceptable for an airplane approved for flight in instrument meteorological conditions or flight in icing conditions.
Amendment 23-49 and Subsequent
A proposed revision to NPRM 94-21 explains this change to this amendment as follows: “The proposed new Sec. 23.1323(c) would add a requirement that each 232
airspeed indicating system design and installation should provide positive drainage of moisture from the system. This proposal is consistent with the provisions required for a static system by Sec. 23.1325(b).
If moisture enters, or accumulates in, an airspeed indicating system, that moisture could cause erroneous airspeed indications or the complete loss of airspeed information. The resulting loss of accurate airspeed information would be hazardous to the operation of the airplane; therefore, to assure the safety of the airplane, the FAA would need to apply the more general airworthiness requirements of Secs.
23.1301 and 23.1309 to such a system and require provisions for drainage of moisture. Accordingly, this proposed revision of the airspeed indicating systems requirements only clarifies the criteria that must be applied to airspeed indicating systems.
To better organize the requirements that are applicable to the airspeed systems on all airplane categories and those that would be additional requirements for the airspeed systems of commuter category airplanes, the FAA proposes to redesignate existing paragraphs (c) and (e), respectively, as paragraphs (e) and (d). By this redesignation, paragraphs (a), (b), (c), and (d) would apply to all airplanes, and paragraphs (e) and (f) would include additional requirements applicable to commuter category airplanes.
The proposal for redesignated paragraph (e) would also remove the words "in flight and" from the first sentence of that paragraph. This would remove the requirement for the airspeed indicating system to be calibrated in flight. The requirement for an in flight calibration is provided in paragraph (b). Proposed redesignated paragraph
(e) would apply to the calibration needed to determine the system error during the accelerate-takeoff ground run.
As identified in the background section of this notice, the FAA is issuing additional notices that address proposed changes to the requirement for powerplant, flight, and airframe. Proposed revisions to subpart G in the flight NPRM include placing all of the requirements for what must appear in the AFM in that subpart. With the proposals to revise the AFM requirements, the flight NPRM also proposes that the requirement in existing Sec. 23.1323(d) (to show the relationship between IAS and CAS in the AFM) be added to Sec. 23.1587 as proposed new paragraph (d)(10).
Because the AFM requirement would be added Sec. 23.1587, it no longer needs to appear in Sec. 23.1323. Accordingly, this notice proposes to remove the text of existing Sec. 23.1323(d).
Proposed new Sec. 23.1323(f) would provide that, on those commuter airplanes where duplicate airspeed indicators are required, the airspeed pitot tubes must be located far enough apart so that both tubes will not be damaged by a single bird strike.”
23.1325 Static pressure system
The corresponding rule in CAR 3 is CAR 3.665.
The corresponding rule in the Airship Design Criteria, FAA-P-8110-2, Change 2, is section 6.10.
Amendment 23-1 and Subsequent
This amendment is explained by Final Rule, Docket 1186, as follows: “The notice of proposed rule making provided that the influence of airplane characteristics not seriously affect the accuracy of instruments having static pressure connections, further specified certain static system design and installation details, required a system proof test, and made provision for countering icing conditions.
Section 23.1325(a) has been amended to specify that static pressure connections be vented so that external forces least affect instrument accuracy. This change relaxes the requirement of the notice and parallels the wording in the comparable section of Part 25.
Two commentators objected to proof testing the static pressure system in each production airplane. The rule, however, does not require test of each production airplane although that would be one way to demonstrate conformity to the approved type design. As suggested by another commentator, sample testing and production flight check could be another acceptable means of showing conformity if there were a showing of an adequate quality control system and compliance with the equipment function and installation requirements of Section 23.1301.
The Agency does not concur with various comments recommending that it adopt the Air Force static system leakage rate at an arbitrary specified altitude with associated instruments disconnected. Since many static system leaks occur at instrument disconnect points, it is considered that a realistic test for Part 23 airplanes should be made with the instruments connected. Section 23.1325(b)(2) has been amended, however, to allow a reasonable leakage loss tolerance with associated instruments connected at the airplane maximum operating altitude.
With regard to negating the effect of icing conditions, one commentator recommended deleting the requirement altogether in low-performance airplanes operating under VFR conditions. Two other commentators recommended that a protected alternate source of static pressure be allowed, while a fourth recommended use of an optional ice-free static pressure source of less accuracy where calibration is given the pilot.
Since static vent icing may occur during both VFR and IFR conditions with hazardous consequences, the Agency believes there is ample justification for antiicing as a certification requirement on all airplanes employing a static pressure 234
system for required instruments. In response to the comments, the proposed rule has been expanded to permit the use of an alternate static source having a prescribed accuracy tolerance, and, where needed, a correction card.”
Both VFR and IFR airplanes should meet the requirements of § 23.1325 in paragraph
(b)(3) of this regulation because static vent icing can occur during both VFR and IFR conditions with hazardous results. The rule provides for either an anti-icing means or an alternate static source as follows:
a. If installed, the alternate static source is not restricted to emergency conditions but may be used to monitor the primary static system.
b. We suggest marking the secondary static source with the word “Alternate.”
c. This rule also requires a correction card in the cockpit if the altimeter changes by more than 50 feet on the alternate source. The correction card does not need to be in clear view of the pilot as long as it is available to a pilot seated in the flight position. An acceptable means for alternate-static-source correction data is located in the performance section of AFMs with other airspeed and altimeter calibration graphs. A placard that the correction data is available in the performance section, which is noted in the limitations section of the AFM, may be provided for additional clarification. The alternate static source is separate, and its correction card should provide correction data for the alternate source only.
d. The alternate static source is subject to all parts of § 23.1325, as is the primary static source, except it may have reduced accuracy with compensation from a correction card.
See AC 20-124, “Water Ingestion Testing for Turbine Powered Airplanes,” for guidance on testing the airspeed and static systems for water ingestion susceptibility.
Amendment 23-6 and Subsequent
A proposed revision to the NPRM 66-44 explains this rule as follows: “One of the major objections to the current requirements is the 100-foot per minute leak rate specified in Secs. 23.1325(b)(2) and 25.1325(c)(2). In this connection, representatives of industry recognized that a 100-foot per minute leak rate at maximum cabin differential pressure would result in altitude errors of from 0 to 3 feet on most aircraft. Furthermore, on many aircraft, the altitude error resulting from leak rates as high as 3,000 feet per minute at maximum cabin differential pressure would not exceed 20 feet. It was recommended that a leak rate equivalent to 2 percent of the maximum cabin differential pressure at the maximum cabin differential pressure is considered an adequate performance criteria for pressurized aircraft, while aircraft without cabin pressurization should have static systems with leak rates 235
that do not exceed 100 feet per minute at a test pressure equivalent to 1,000 feet pressure differential. It was pointed out that the leak test should be considered a convenient and simple method of proving the integrity of the static pressure system and not a quantitative test of the system error. The Agency agrees with these comments and changes to the leak rate requirements of Secs. 23.1325 and 25.1325 consistent with the recommendations are proposed herein.
In addition to the foregoing, it is also proposed to change the requirements of Sec.
23.1325 to require that a correction card be provided if the altimeter indication on the alternate system differs by more than 50 feet from the altimeter indication on the normal system. The present requirement permits the use of a correction card if the reading of an altimeter on the alternate static pressure system exceeds a 2-percent tolerance. The Agency considers that this latter value is too small at low altitudes and too large at high altitudes.”
The proposed rule was changed by Final Rule, Docket 7831, as follows: “One commentator pointed out that the requirement that the proof tests of the static pressure systems on unpressurized aircraft be conducted with the static pressure system evacuated to a pressure differential based on an altimeter reading of 1,000 feet at sea level could be confusing to people located at elevations above 1,000 feet mean sea level. The FAA agrees and Secs. 23.1325(b) (2) (i) and 25.1325 (c) (2) (i) have been further amended to permit the proof test of unpressurized aircraft with the static pressure system evacuated to an altimeter reading of 1,000 feet above the airplane elevation at the time of the test. One commenter stated that the proposed Sec. 23.1325(b)(3) requirement for a correction card where altimeter readings on primary and alternate static systems differ by more than 50 feet, is too restrictive at high altitudes and high Mach numbers and suggested clarification as to the range of altitude and Mach numbers applying to this tolerance. However, the FAA believes that the proposed requirement is necessary to assure proper vertical separation considering the entire altitude-speed range. In the high Mach-high altitude regime, the static system accuracy may be marginal at best and errors introduced while on the alternate system could lead to hazardous operation if the pilot is not informed of the magnitude of the error. In the low speed-low altitude regime, static system errors are minimized so that correspondence between the two systems should pose no problem.”
Amendment 23-20 and Subsequent
A proposed revision to NPRM 75-10 explains this amendment as follows: “The proposal would provide more complete duality of static pressure sources if both primary and alternate sources are installed. Service experience, however, indicates no need for an additional requirement that the selector be secured in the primary source position.”
Amendment 23-34 and Subsequent
See AC 23-8B, “Flight Test Guide for Certification of Part 23 Airplanes,” for additional guidance.
This amendment added commuter category requirements from “Part 135, Appendix A., section 14.”
Amendment 23-42
Paragraph (g) was added. For airplanes specifically prohibited from flight in instrument meteorological conditions and icing conditions according to § 23.1559(b) of this part, paragraph (b)(3) of this section does not apply.
This proposal would allow airplanes that are specifically prohibited from flight in instrument meteorological conditions and IFR icing conditions to be certificated without an alternate static air source.
A proposed revision to NPRM 89-5 explains Amendment 23-42 as follows: “The FAA reviewed the rationale supporting the requirements in Sec. 23.1325(b)(3) that "each static pressure port must be designed or located in such a manner that the correlation between air pressure in the static pressure system and true ambient pressure is not altered when the airplane encounters icing condition," and "an antiicing means or an alternate source of static pressure may be used in showing compliance with this requirement." The primary concern was that airframe ice accumulation would disturb airflow in the vicinity of static port(s) causing errors in the static pressure systems and altimeter indications.
The need for such a requirement, as stated in Notice 64-14 (29 FR 3310, March 12, 1964) was based on IFR operations at higher airspeeds and altitudes above 14,500 feet. The purpose was "to increase safety and improve airspace utilization" (vertical separation of air traffic).
In an airplane certificated for flight in IFR conditions, an applicant can show compliance without flying the airplane in icing conditions. For example, if the airplane were equipped with a pitot-static probe, anti-icing would be appropriate. If the airplane had static pressure ports installed on the fuselage an alternate static pressure source would suffice.
Under the present requirements, an airplane limited to approval for flight in VFR conditions must meet a requirement intended to provide better vertical separation for airplanes flying in IFR conditions or icing conditions at altitudes above 14,500 feet.
Section 23.1325(b)(3) requires that all small airplanes, including an airplane, which isn't required to have a sensitive altimeter or a heated pitot, must either be tested in 237
icing conditions or show compliance by a heated static pressure source or an alternate static pressure source.
Therefore, it is considered inappropriate to continue to impose a requirement for an alternate static source or a means for anti-icing the static source on airplanes specifically prohibited from flight in IFR or icing conditions. It is considered unlikely that a midair collision could be caused by the altitude error in an airplane flying VFR that accidentally enters icing conditions. Continued flight in such conditions cannot be sustained for long periods of airplanes without anti-icing or deicing equipment and most airplanes certificated for VFR only do not fly above 14,500 feet. Also, an FAA review of incidents of static system malfunction in VFR icing conditions for the past five years showed no reported incidents or accidents.”
Amendment 23-49 and Subsequent
Static pressure system icing was addressed in Amendment 23-49 as follows: “Current Sec. 23.1325(b)(3) establishes certain static pressure system requirements for airplanes that encounter icy conditions. Current Sec. 23.1325(g) exempts from the requirements of (b)(3) airplanes that are prohibited from flight in instrument meteorological conditions in accordance with Sec. 23.1559(b). After the adoption of Sec. 23.1325(g), it came to the FAAs attention that there are conditions other than instrument meteorological conditions where icing may be encountered and, therefore, that this paragraph should also exempt from the provisions of Sec. 23.1325(b)(3) airplanes that are prohibited from flight in icing conditions. Accordingly, Sec.
23.1325(g) would be revised to read, "For airplanes prohibited from flight in instrument meteorological or icing conditions."
Amendment 23-50 and Subsequent
A proposed revision to NPRM 94-22 explains this amendment as follows: “This proposal would revise Sec. 23.1325 (e) to clarify that the calibration must be conducted in flight, which is standard practice. The text of Sec. 23.1325 (f) would be removed and the paragraph would be reserved. The text of paragraph (g) would be moved to paragraph (f) in a future rulemaking action. The results of the calibration would be required in the proposed Sec. 23.1587.”
23.1326 Pitot heat indication systems
There is no corresponding rule in CAR 3 or the Airship Design Criteria.
Amendment 23-49 and Subsequent
A proposed revision to NPRM 94-21 explains this rule as follows: “Due to advancements in technology, many part 23 airplane installations now utilize equipment whose data sources are critical to the accurate and dependable operation of that equipment. The heated pitot tube is one such data source. The pitot heat indicating system will advise the pilots of any inoperative heating element in the pitot tube and that subsequent inaccuracies may result.
Part 23 airplanes certificated for flight under instrument flight rules or for flight in icing conditions are required by current Sec. 23.1323(e) to have a heated pitot system or an equivalent means of preventing an airspeed indicating system malfunction due to ice accumulation. This proposal would require such airplanes equipped with a heated pitot tube to be equipped with a pitot tube heat indicating system. This requirement will provide greater assurance that the pilots will not be dangerously misled by faulty flight instrument indications caused by pitot tube icing.
When pitot tube heat indicating system requirements were added to part 25, the FAA noted the occurrence of at least one accident and several incidents in which an airspeed indicating error occurred that might have been avoided if a pitot tube heat indicating system had been installed. Part 23 airplanes operate at lower airspeeds and over shorter distances that do part 25 airplanes; therefore, their exposure to moisture and temperature conditions where icing may occur is higher than it is for transport category airplanes. Because of this environmental exposure, the potential for an inoperative heated pitot tube becoming a hazard to part 23 airplanes is greater.”
This rule requires a caution annunciation whenever the pitot heat is off or there is a failed heating circuit in the pitot tube heater. The second annunciation cause is fully justified in that it represents a failure condition. The first can have a positive safety effect if it causes pilots to activate the pitot heat in all environmental conditions. This eliminates the loss of the pitot static system because of the pilot error of failing to operate pitot heat when conditions warrant it.
A caution annunciation when the pitot heat is off has two negative issues as follows:
(1) It violates the “dark cockpit” where caution and warning lights only represent failure conditions; and
(2) Adherence to a “dark cockpit” will cause pitot heat operation in all environmental conditions, which will shorten the life of the system.
The Small Airplane Directorate is proposing rulemaking to delete § 23.1326(b)(1) (the requirement for a caution annunciation when the pitot heat is off). An aircraft design that does not include a caution annunciation when the pitot heat is off may be eligible for an ELOS finding that preserves a “dark cockpit” provided a placard or flight manual prescribes when to operate the pitot heat.
23.1327 Magnetic direction indicator
The corresponding rule in CAR 3 is CAR 3.666.
The corresponding rule in the Airship Design Criteria, FAA-P-8110-2, Change 2, is section 6.11.
Original Issue and Subsequent
If the magnetic compass that is required by § 23.1303 is the only heading instrument, then it should meet the requirements of this section. With an approved secondary system such as a directional gyro, and an appropriate placard to dictate which electrical devices should be switched off when reading the magnetic compass, according to § 23.1547, equivalent safety under part 21, § 21.21(b)(1) may be shown.
On magnetic direction indicators, heading information is considered an essential flight instrument function because its loss could result in reduced capability of the flight crew to cope with adverse operating conditions, especially for IFR flights. The indicator specified in this rule was intended to be a magnetic compass (nonstabilized). The requirement for a magnetic direction indicator existed before remote indicating compasses were available. If a magnetic stabilized direction indicator is installed as an additional instrument, the magnetic non-stabilized direction indicator (magnetic compass) is still required as the primary source of magnetic direction.
a. A magnetic direction indicator with remote magnetic sensor can be approved under § 21.21 of part 21 if it can be confirmed that it provides a level of safety equal to that provided by the magnetic compass required by § 23.1303(c). The reliability of the system should consider the effects of loss of the airplanes electrical system, the performance of the equipment under environmental conditions that may be encountered by the airplane, the integrity of the interface wiring, and the reliability of the components.
b. For a magnetically stabilized direction indicator approved under an ELOS finding, the system should be powered from a source that is independent of a single electrical generating system. This other source should be installed so it is operative without manual selection after total failure of a single electrical generating system. Dual independent stabilized indicator installations with split electrical bus systems may also be approved on multiengine airplanes under an ELOS finding. The airplanes battery is not considered an acceptable source unless the state of charge of the battery is displayed to the pilot.
c. The following installation requirements of §§ 23.1327 and 23.1547 are also directly related to approval of either type of magnetic indicator: