EASA CS 25 Instrument & Electrical System: Sofema Aviation Services (SAS) considers the following codes:
- Instruments installation (§ 25.1321 à 25.1333)
- Electrical systems & equipment (§ 25.1351 à 25.1365)
INSTRUMENTS INSTALLATION – CS 25.1321 Arrangement and visibility
(a) Each flight, navigation, and powerplant instrument for use by any pilot must be plainly visible to him from his station with the minimum practicable deviation from his normal position and line of vision when he is looking forward along the flight path.
(b) The flight instruments required by CS 25.1303 must be grouped on the instrument panel and centered as nearly as practicable about the vertical plane of the pilot’s forward vision. In addition:
(1) The instrument that most effectively indicates attitude must be on the panel in the top centre position;
(2) The instrument that most effectively indicates airspeed must be adjacent to and directly to the left of the instrument in the top centre position;
(3) The instrument that most effectively indicates altitude must be adjacent to and directly to the right of the instrument in the top centre position; and
(4) The instrument that most effectively indicates direction of flight must be adjacent to and directly below the instrument in the top centre position.
(c) Required powerplant instruments must be closely grouped on the instrument panel. In addition:
(1) The location of identical powerplant instruments for the engines must prevent confusion as to which engine each instrument relates to, and
(2) Powerplant instruments vital to the safe operation of the aeroplane must be plainly visible to the appropriate crewmembers.
(d) Instrument panel vibration may not damage or impair the accuracy of any instrument.
(e) If a visual indicator is provided to indicate malfunction of an instrument, it must be effective under all probable cockpit lighting conditions.
CS 25.1333 Instrument systems
(a) For systems that operate the instruments required by CS 25.1303(b), which are located at each pilot’s station, means must be provided to connect the required instruments at the first pilot’s station to operating systems, which are independent of the operating systems at other flight crew stations, or other equipment.
(b) Equipment, systems, and installations must be designed so that sufficient information is available to assure control of the aeroplane in airspeed, altitude, direction, and attitude by one of the pilots without additional flight crew action after any single failure or combination of failures that are not assessed to be extremely improbable (see AMC 25.1333(b)); and
(c) Additional instruments, systems, or equipment may not be connected to the operating systems for the instruments required by CS 25.1303(b), unless provisions are made to ensure the continued normal functioning of the required instruments in the event of any malfunction of the additional instruments, systems, or equipment which is not shown to be extremely improbable.
ELECTRICAL SYSTEMS AND EQUIPMENT CS 25.1351 General
(a) Electrical system capacity. The required generating capacity, and number and kinds of power sources must:
(1) Be determined by an electrical load analysis; and
(2) Meet the requirements of CS 25.1309.
(b) Generating system. The generating system includes electrical power sources, main power busses, transmission cables, and associated control, regulation, and protective devices. It must be designed so that:
(1) Power sources function properly when independent and when connected in combination;
(2) No failure or malfunction of any power source can create a hazard or impair the ability of remaining sources to supply essential loads;
(3) The system voltage and frequency (as applicable) at the terminals of all essential load equipment can be maintained within the limits for which the equipment is designed, during any probable operating condition;
(4) System transients due to switching, fault clearing, or other causes do not make essential loads inoperative, and do not cause a smoke or fire hazard;
(5) There are means accessible where necessary, in flight, to appropriate crew members for the individual and rapid disconnection of each electrical power source (see AMC 25.1351(b)(5)); and
(6) There are means to indicate to appropriate crew members the generating system quantities essential for the safe operation of the system, such as the voltage and current supplied by each generator (see AMC 25.1351(b)(6)).
(c) External power. If provisions are made for connecting external power to the aeroplane, and that external power can be electrically connected to equipment other than that used for engine starting, means must be provided to ensure that no external power supply having a reverse polarity, a reverse phase sequence (including crossed phase and neutral), open circuit line, incorrect frequency or voltage, can supply power to the aeroplane’s electrical system.
(d) Operation without normal electrical power. (See AMC 25.1351(d).) The following applies:
(1) Unless it can be shown that the loss of the normal electrical power generating system(s) is Extremely Improbable, alternate high integrity electrical power system(s), independent of the normal electrical power generating system(s), must be provided to power those services necessary to complete a flight and make a safe landing.
(2) The services to be powered must include:
(i) Those required for immediate safety and which must continue to operate following the loss of the normal electrical power generating system(s), without the need for flight crew action;
(ii) Those required for continued controlled flight; and
(iii) Those required for the descent, approach, and landing.
(3) Failures, including junction box, control panel, or wire bundle fires, which would result in the loss of the normal and alternate systems must be shown to be Extremely Improbable.
CS 25.1365 Electrical appliances, motors, and transformers
(a) Domestic appliances must be so designed and installed that in the event of failures of the electrical supply or control system, the requirements of CS 25.1309(b) and (c) will be satisfied.
(b) The installation of galleys and cooking appliances must be such as to minimise the risk of overheating fire, burns, or spilled liquids to the aeroplane, passengers, and crew.
(c) Domestic appliances, particularly those in galley areas, must be so installed or protected as to prevent damage or contamination of other equipment or systems from fluids or vapours which may be present during normal operation or as a result of spillage, where such damage or contamination may hazard the aeroplane.
(d) Unless it can be shown that compliance with CS 25.1309(b) is provided by the circuit protective device required by CS 25.1357(a), electric motors and transformers, etc. (including those installed in domestic systems, such as galleys and toilet flush systems) must be provided with a suitable thermal protection device if necessary to prevent them overheating such as to create a smoke or fire hazard under normal operation and failure conditions.
In showing compliance with CS 25.1365(a), the following should be taken into consideration:
1.1 The design and installation of heated domestic appliances should be such that no single failure (e.g. welded thermostat or contactor, loss of water supply) can result in dangerous overheating and consequent risk of fire or smoke or injury to occupants.
An acceptable method of achieving this is by the provision of a means independent of the normal temperature control system, which will automatically interrupt the electrical power supply to the unit in the event of an overheating condition occurring.
The means adopted should be such that it cannot be reset in flight.
1.2 The design and installation of microwave ovens should be such that no hazard could be caused to the occupants or the equipment of the aeroplane under either normal operation or single failure conditions.
1.3 Heated liquid containers, e.g. water boilers, coffee makers should, in addition to overheat protection, be provided with an effective means to relieve overpressure, either in the equipment itself or in its installations.
1.4 When considering failures of domestic appliances, the effect of the loss of the water supply to a water heater, with the electrical supply maintained, should be taken into account.
NOTES: Due account should be taken of the possible effects of lime scale deposit both in the design and maintenance procedures of water heating equipment.
The design of galley and cooking appliance installations should be such as to facilitate cleaning to limit the accumulation of extraneous substances, which may constitute a fire risk.
- Electric Overheat Protection Equipment – In showing compliance with CS 25.1365(d), the following should be taken into consideration:
a. Failures of any automatic control systems, e.g. automatic timer systems, which may cause the motor to run continuously;
b. Short circuit failures of motor windings or transformer windings to each other or to the motor or transformer frame;
c. Open circuit of one or more phases on multi-phase motors;
d. Motor seizures;
e. The proximity of flammable materials or fluids;
f. The proximity of other aeroplane installations;
g. Spillage of fluids, such as toilet waste;
h. Accumulation of combustible material; and
i. Cooling air discharge under normal operating or failure conditions.
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