Aircraft Fire Detection system Automatic systems can detect aircraft fires or potential ignition which might not be apparent to the crew until they have developed to an extent which makes their successful control difficult, or impossible. These systems are based upon both heat and smoke sensing. Heat sensing is used for cargo holds, engines/APUs, toilet waste bins, high temperature bleed air leaks and landing gear bays. Smoke detection is used in toilet compartments, avionics bays and cargo holds. Alerts or Cautions are activated either locally in the case of toilet smoke detectors (for cabin crew investigation) or centrally annunciated in the flight deck in all other cases. Abnormal Heat detection in an engine or APU copmpartment when airborne will require remote manual activation of locally sited extinguishers. The ground case is the same for operating engines but triggers automatic shutdown and extinguisher discharge in the case of an operating APU. Heat detection in a landing gear bay is likely to require recycling of the landing gear to facilitate airflow cooling of brake units; heat or smoke detection in a hold is likely to require remote manual activation of extinguishing systems. Flight crew response to Avionics Bay smoke detection has in the past been based initially on the isolation of defective equipment by a process of systematic de-selection. Current practice is to ‘land as soon as possible’ rather than get involved in potentially time-consuming identification of the source when it may not necessarily be possible to satisfactorily control the hazard even if the source is successfully identified. Larger jet and heavy turboprop transport aircraft usually have a system of engine bleed air in addition to that for air conditioning and pressurisation which is used to provide wing and empennage anti icing. Since this air must be maintained at high temperatures during distribution, any leaks of such air at high relative pressure could cause a structural fire. If the leak is in an engine pylon close to the point of bleed from the engine, it may not be possible to stop the leak by isolating the applicable engine air system and engine shutdown may be necessary. For all other cases, the temperature of the leaking air will determine whether sensor activation triggers a warning or a caution and the corresponding flight crew response drill, which will be designed to achieve leak isolation. Finally, it is impossible to review aircraft fire detection without considering the question of fumes. Unlike heat and smoke, detection of fumes is not automated and there is consequently considerable variation both in their detection and the description of fumes by air crew. Also, with the imposition of the locked flight deck door, the language of descriptive communication from cabin crew to flight crew about detected fumes in the passenger cabin has become particularly important. The origin of fumes may be local to the source, as in the case of faulty electrical equipment, the overheated contents of a galley oven, or a failed cabin florescent light fitting; or it may be distributed from source through the cabin air conditioning system. In the latter case, it can be extremely difficult to be sure of the cause, or whether the fumes could be in any way related to a fire hazard. Of course, when assessing ‘fumes’ aircrew also have to decide if they may be hazardous to crew or passengers in their own right regardless of source, and it may be prudent for one or both pilots to fit oxygen masks (100% Oxygen).
Posted on: Sat, 25 Jan 2014 06:21:43 +0000