MISCELLANEOUS EQUIPMENT
23.1431 Electronic equipment Original Issue and Subsequent Mercury cell battery packs for use in Emergency Locator Transmitters (ELT) should be manufactured by controlled processes. Service experience has shown that ELT mercury cell battery packs fabricated by individuals without a controlled process can result in the following:
a. Degradation of the cell seal causing leaks and a shorter shelf life.
b. Creation of internal shorts.
c. Internal corrosion.
d. Creation of highly explosive mercury fulminate.
The possibility of adverse interaction between communication and navigation equipment should be evaluated. Momentary indicator deflection or flicker is acceptable. However, loss of a required function due to interaction of assignable frequencies in the National Airspace System is not acceptable.
Interim guidance for TCAS I installations is given in AC 20-TCAS, Airworthiness Approval and Operational Use of Traffic Alert and Collision Avoidance System (TCAS I) (in draft).
Guidance for TCAS II installations is given in AC 20-131A, Airworthiness and Operational Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) and Mode S Transponders.
Automatic NAVAID selection tuning (Auto-tune) of Very High Frequency Omnirange Station/Distance Measuring Equipment (VOR/DME) for flight management or multisensor navigation systems is designed to enhance the navigation accuracy for enroute flight. Under certain conditions, and depending on the particular implementation, the auto-tune function can cause a hazard if auto-tune remains operative during VOR and ILS operations. In this case, automatic selection of a NAVAID different than that wanted by the flight crew is a possibility. Visual cues indicating the auto-tune is still active may be quite subtle and may go unnoticed during a high workload period. If the auto-tune NAVAID is reasonably in line with the projected track, the anomaly can go undetected—causing the airplane to fly an erroneous track based on the auto-tune NAVAID. This may occur either when steering manually or when the flight guidance system has been engaged. System installations that
218 employ auto-tune should be mechanized in a manner that addresses these safety issues. An acceptable method of auto-tune implementation is to automatically inhibit the auto-tune feature when a navigation function other than the one utilizing auto-tune has been selected for display on the Horizontal Situation Indicator/Electronic Horizontal Situation Indicator (HSI/EHSI).
Moving Map Displays (MMD) used for primary command guidance during IFR flight should be evaluated with the particular navigation receiver (GPS, LORAN-C, etc.) to be used. It should also be restricted to use with that particular type of receiver on that particular airplane. If a separate command or deviation indicator is used to certify the system for IFR use, the MMD should be placarded “For Reference Only” and used only if it can be shown that failure of the MMD would not fail the navigation system.
An MMD to be used for and placarded for “VFR Only” guidance would need verification that it performs its intended function when used with a particular navigation receiver. It could then be used on any other airplane with the same type navigation receiver.
JAA ACJ 23.1431(e) is acceptable for FAA certification.
23.1435 Hydraulic systems No policy available as of June 30, 2001.
23.1437 Accessories for multiengine airplanes No policy available as of June 30, 2001.
23.1438 Pressurization and pneumatic systems Amendment 23-20 and Subsequent Burst and proof tests are required at multiples of the Maximum Normal Operating Pressure.
Temperature effects are not required as part of these tests if pressurization and pneumatic system elements are constructed of materials that can withstand the operational pressures and temperatures. If sufficiently overstrength material elements are part of a design, then reduced material strength due to temperature variations is not a concern and testing may be performed at ambient temperature. The “sufficiently overstrength” determination must consider temperature cycles/extremes for materials that may exhibit structural property phenomenon and structural strength changes due to temperature changes. Certain composite materials may be characteristic of adverse performance in certain temperature environments.
Furthermore, the “sufficiently overstrength” determination must consider both the duct system and its attach/clamping/stabilization devices. This advice is consistent with §§ 23.1301, Function and Installation; 23.307, Proof of Structure; and 23.603(a), Materials and Workmanship.
23.1441 Oxygen equipment and supply Amendment 23-9 and Subsequent Plastic lines (nylon, polyvinyl chloride (PVC) and Teflon) are not acceptable for use in continuously pressurized, non-portable oxygen systems.
Plastic lines can be used in non-portable oxygen systems that are pressurized only when cabin decompression occurs with the following precautions:
a. Swaged metal type end fittings should be used to prevent leakage from cold flow.
b. Lines should be protected from abrasion by use of a reinforcing sleeve of fabric braid.
c. Lines should be routed away from areas where they might be subjected to elevated temperatures, electrical arcing (relays and switches), and flammable fluids.
d. Refer to AC 43.13-2A, Acceptable Methods, Techniques, and Practices Aircraft Alterations, Chapter 6; and NASA Safety Standard for Oxygen and Oxygen Systems, NSS 1740.15, dated January 1996, for additional guidance material.
Design and install oxygen tubes/hoses in such a manner that the hoses are stable during all phases of flight. It is not adequate to require the applicant to design tube/hose routings and chaffing protection without ensuring (by design) that the installed tubes/hoses will not vibrate/flap in a manner that would defeat the chaffing prevention wrap, or to impact other system elements such as sensors, wires, mechanisms.
Part 23 is unique in that it allows oxygen system requirements to be met with portable systems. For those portable systems, information should be provided to the flight crew in the form of limitations stating which portable system is approved, which components constitute the system, and any operating limitations.
Part 23 airplanes may be certified with or without an oxygen system. The necessity for supplemental oxygen is a function of the operational altitude not the airplane design.
Therefore, the requirements for when supplemental oxygen is required can be found in General Operating and Flight Rules. If installed, the system should meet the following part 23 airworthiness requirements: (a) §§ 23.1441 through 23.1449 (and § 23.1450 if chemical oxygen generators are used), and (b) it may be a basic part of the airplane or a portable system. Section 23.1525 requires the airplane operational limits be established in accordance with the installed equipment or lack thereof. If an airplane is delivered without
223 an oxygen system, its Airplane Flight Manual should have a limitation or there should be a placard prohibiting flight above 14,000 feet mean sea level (MSL).
Amendment 23-43 and Subsequent Under the previous amendment, certification of an oxygen system was at the discretion of the applicant. Under this amendment, an oxygen system “must be provided” if an airplane is certificated to operate at altitudes where the operational rules require oxygen use. This rule is applicable to any airplane with a certification basis of Amendment 23-43 or later.
The rule permits portable systems to be designed by a type certificate holder subject to actions to prevent the portable system from being a hazard by not being properly secured in an emergency landing (per § 23.561). The precise requirement regarding portable systems should be determined in reference to the specifics of the airplane type (i.e., its service ceiling, number of seats, etc.). The rulemaking history does not state a safety deficiency in current methods of providing supplemental oxygen by the use of operator-provided, portable, constant flow oxygen systems either attached to the seatback or restrained by a seatbelt.
If a type certificate holder does not plan to provide an oxygen system, it must specify a maximum weight and size of portable oxygen bottle and a specific means of restraining the bottle in an emergency landing per § 23.561 either by attachment to a seatback or a seatbelt.
This could be commercially available or produced by the type certificate holder and available with the airplane as standard equipment or as an option.
If an applicant does not provide the oxygen system or restraint information for portable bottles, the airplane will be limited to operational altitudes where oxygen is not required.
23.1443 Minimum mass flow of supplemental oxygen Original Issue and Subsequent When there is full compliance to this regulation, there is no need to consider the probability of a pressurization failure or to require an immediate descent in altitude in the event of a failure. Compliance should include the consideration of a rapid/explosive decompression to ambient pressure with a pilot recognition and reaction time of 17 seconds to initiate a descent.
(a) The airplane may be altitude-limited to meet this requirement, or
(b) The applicant may provide an equivalent level of safety finding.
23.1445 Oxygen distribution system Amendment 23-43 and Subsequent The guidance in this AC for § 23.1441, Amendment 23-9 and subsequent, for plastic lines is applicable to this regulation.
23.1447 Equipment standards for oxygen dispensing units Amendment 23-9 and Subsequent The Small Airplane Directorate was recently asked for applicable policy regarding the requirements for (1) operation above 25,000 feet, dispensing units be immediately available to each occupant wherever seated, and for (2) operation above 30,000 feet, dispensing units be automatically presented to each occupant before the cabin pressure altitude exceeds 15,000 feet. Item (1) above came into part 23 in Amendment 23-9 and item (2) above came in at Amendment 23-20. These rules were based on seats that were fixed in location and orientation. The question arises from the use of swiveling and tracked seats where it is possible for some occupants to move their seat into an orientation where an automatically presented dispensing unit will not be in view.
The following guidance is applicable to an airplane with a certification basis of Amendment 23-9 or subsequent. This guidance is taken from Advisory Circular 25-17, Section 25.1447, where the issue of tracked and swiveled seats has been addressed.
Automatic presentation is acceptable if the dispensing unit (mask) is presented in front of the eyes when the person’s head is resting on the seat back cushion with the seat in any position, such as upright, reclined, swiveled or tracked. The mask need not be presented in front of all persons if there is sufficient “crowd awareness,” i.e., the vast majority have proper presentation and the others can readily see that the masks have been presented. These latter persons should have a preflight briefing clearly showing them the location of their mask. The mask should be reachable with the seat belt fastened. In some seating arrangements, such as executive interiors, the various seat positions result in many different combinations of person groupings. Each combination should have an adequate number of masks reachable by every person. Consideration should be given to minimizing the likelihood of persons taking the wrong masks, thus depriving another person of their mask. If the mask must be pulled to initiate oxygen flow, the mask should be presented so that the person must pull the mask to don it. The fifth percentile female and ninety-fifth percentile male should be considered. For such as sleeper seats, bunks or lavatories, a streamer of webbing attached to the mask is acceptable to enable the person to pull the mask down to them.
Amendment 23-30 and Subsequent This amendment allows the use of nasal cannulas for operation up to an altitude of 18,000 feet Mean Sea Level (MSL). These are simple devices with no known service problems, and the FAA has not developed a design standard for them.
227 Section 23.1447(e) requires that oxygen masks be automatically presented to each occupant before the cabin pressure exceeds 15,000 feet for airplanes certificated for operation above 30,000 feet MSL. So, just before the cabin pressure altitude exceeds 15,000 feet, the oxygen mask should fall down automatically and present itself to a 95th percentile human occupant at mouth level within the visual periphery. All the occupant should have to do is pull the mask from the hanging position, don the mask, and start breathing.
23.1449 Means for determining use of oxygen No policy available as of June 30, 2001.