Sistemi di emergenza negli aeromobili, Università degli Studi di Padova

Sistemi di Emergenza

Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Emergency Systems Lorenzo Olivieri Dipartimento di Ingegneria Industriale Università degli Studi di PadovaSummary Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder 1 Introduction 2 Alarm Systems 3 Firefighting Systems 4 Supplemental Oxygen System 5 Lightning Protection 6 Impact Energy Attenuation 7 Evacuation 8 Flight Data RecorderEmergency Systems Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Although aircraft are designed to operate safely, situations can still arise where the safety of the flight and, therefore, of the people on board and on the ground may be endangered. To prevent dangerous situations and limit their effects, aircraft are equipped with a series of emergency systems as dictated by regulations. Emergency systems must be available even in the event of a failure of the main onboard systems (propulsion, electrical, hydraulic), must be very reliable, and easy and immediate to use, even by untrained personnel (passengers).

Sicurezza Attiva

Active Safety Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Emergency systems are distinguished into systems for active safety and passive safety. In the first case, these are systems aimed at actively reducing the risk of a serious accident:

• alarm systems
• fire detection and suppression system
• emergency oxygen system
• emergency power sources (APU, RAT, batteries)
• ice protection
• overcurrent and electrostatic discharge protection
• anti-lock braking system for landing gear wheels

Sicurezza Passiva

Passive Safety Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Passive safety systems are used to reduce the consequences on occupants during or after landing/impact with the ground:

• lightning protection
• fire systems after emergency landing and inertia switch
• fuel tank explosion inhibitor
• crash-resistant seats and furnishings
• passenger and crew evacuation systems and procedures

Sistemi di Allarme

Alarm Systems Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder FIRE CHECK DOORS STARTER FUEL PUMP PITOT HEAT ALTERNATOR CHECK GEAR CHECK OIL LOW FUEL OXYGEN HYDRAULIC PUMP ON OVERBOOST LOW VOLTS CHECK EFIS AIRSPEED EXT POWER TEST AH500 Of fundamental importance for flight safety is the clear and timely indication of any faults or anomalies to the pilot. Alarm signals provide information about the conditions of various systems and the state of the aircraft (stall, maximum speed, altitude, presence of ice). Light signals are used with indicators organized in warning panels. Conventional color codes are used: lights off in case of nominal operation, yellow for warnings, and red for alarms that require immediate action. In modern aircraft, fault or anomaly indications are provided through displays that can give more information about the problem and instructions on actions to take. In addition to light signals, acoustic alarms with different tones or voice messages are also used.

Sistemi Antincendio

Firefighting Systems Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder A fire on board is an extremely dangerous situation for the functionality of onboard systems and the safety of people. Although systems are designed to minimize the probability of a fire, it is always possible that one may occur, and therefore detection and extinguishing systems are installed. A fire can be ignited by sources of intense heat or electrical arcs due to short circuits. The flames are fueled by the presence of solid or liquid combustible material (fuel, oil) and oxygen. To promptly detect the presence of a fire, thermal sen- sors or smoke detectors can be used. The former are mainly used in areas not visible to the crew; the latter are also used in the cabin. Smoke detectors measure the opacity of the air or the presence of particles.

Sistemi di Rilevamento Incendi

Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Fire Detection Systems Thermal sensors can be of two types: point - for example, bimetallic strips that deform and open the circuit above a certain temperature linear - conductors whose characteristics (resistan- ce) change above a certain threshold temperature In any case, the sensors of the fire detection system must be able to send the alarm signal even if damaged by the fire itself. The sensors are often redundant and signal the anomaly after detecting it for a certain period of time or if detected by multiple sensors simultaneously. The goal is to avoid false alarms that might prompt the pilot to perform potentially dangerous operations or maneuvers.

Sensori Bimetallici

Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Bimetallic Sensors Bimetallic sensors consist of a cylindrical metal ca- sing inside which two arc-shaped elements made of different metals are positioned. The arcs are com- pressed so as not to be in contact under nominal conditions. When the system overheats, the casing expands more than the arc elements, which then come into contact, closing the circuit and sending the signal to the onboard systems and the pilot. The activation temperature of the sensor must be accurately calibrated during the design phase and can be adjusted via a specific screw. These sensors are often used to detect fires in engines. 0 Connector C End cap 0 Barrel (a) Contacts (overheat condition) End cap Barrel Connector Pins Adjusting screw Spring-bow

Termistori

Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Thermistors Thermistors are linear sensors with medium sen- sitivity (continuous sensor). They are linear resi- stors consisting of a central conductive wire (nickel- chrome), an outer conductive and corrosion- resistant casing (stainless steel), and a partially in- sulating and heat-sensitive material that separates the two conductors (generally a silicon compound in fine grain form). When the system is heated, the resistance of the insulator decreases. By measuring the change in resistance, it is possible to determine the presence of a fire. If the portion of the thermi- stor affected by overheating is more extensive, the change in resistance is greater. These sensors can be three meters or more in length and are used to monitor the temperature of engine nacelles. Insulating material Outer sheath Centre wire (a) Outer sheath To control circuit Detector loop ) Centre wire (b) R1 Negative temperature coefficient Resistance R2 t1 t2 Temperature (c)

Sensori a Miscela Eutettica

Eutectic Mixture Sensors Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Eutectic mixture sensors are linear sensors particularly effective in detecting localized ove- rheating in small portions of their length (discrete sensor). Similar to thermistors, they are linear resistors consisting of a central conductive wire and an outer conductive casing, with an insulating material made of an eutectic mixture (eutectic salt). The mixture is calibrated to melt at a specific temperature. The molten material has a very low electrical resistance. It is used to detect fires in engines and overheating of air in the pneumatic system. Sheath Centre element Eutectic salt Resistance (ohms) Temperature (degrees)

Sensori Pneumatici

Pneumatic Sensors Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Pneumatic sensors consist of a thin tube filled with helium and equipped with a central core made of metal hydride. The tube is sealed at one end and connected to a device capable of measuring the pressure at the other end. The device has two pressure switches: one normally open (NO) and the other normally closed (NC). Alarm switch (N.O.) Electrical isolator/pneumatic manifold Power Seal R Signal Sensor tube Core element (metal hydride) Responder assembly Integrity switch (N.C.) Averaging gas (helium)Pneumatic Sensors Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder The first switch closes if the helium pressure increases significantly due to the overheating of large portions of the tube. If only small portions overheat, the helium pressure is not sufficient to close the switch. For this rea- son, the metal hydride core is present, relea- sing hydrogen when rapidly heated, compen- sating for the lower helium pressure in case of localized heating. The second switch is kept closed by the pre-compression pressure of the helium and provides a check on the sensor's integrity; in case of leaks, it opens indicating an abnormal operation. Alarm pressure Helium gas Resistance ohms Long length heated Short length heated Sheath Hydride core (hydrogen) Temperature

Sensori Ottici

Optical Sensors Emergency Systems Lorenzo Olivieri Introduction Alarm Firefighting Oxygen Lightning Impact Energy Attenuation Evacuation Flight Data Recorder Optical sensors detect the emission of light radiation from the fire. In particular, the combu- stion of hydrocarbons involves an emission in the IR band with a peak wavelength of 4.4 pm. This is the characteristic wavelength of the emission of CO2 molecules. The detector is equipped with a filter and an element sensitive to that wavelength, and it is characterized by a certain field of view. CO2 spike Radiated Intensity 30° 30° 80 45° 45º Detection Distance 50 (Percent) 30 20 0 1 2 3 4 5 6 7 8 4.4 Wavelength (Microns) Viewing angle 0° 15° 100 15° (b)