Jet Engine Fire Detection Systems: Technical Specifications and DIY

Jet engine fire detection systems are critical safety mechanisms that alert pilots and crew to potential fire conditions in aircraft engines. These systems are designed with redundancy and precision to ensure the highest levels of reliability and responsiveness. In this comprehensive guide, we will delve into the technical specifications, components, and operational principles of jet engine fire detection systems, providing a detailed DIY manual for understanding and maintaining these vital systems.

Dual-Loop Configuration

The engine fire detection system typically consists of a dual-loop configuration, with one element mounted on the pylon and two elements mounted on each core cowl. This redundant design ensures that the system can continue to function even if one loop is compromised. The two loops, designated as loop A and loop B, are connected to separate control unit channels, providing an additional layer of redundancy.

Pylon-Mounted Element

The pylon-mounted element is strategically positioned to detect fires that may originate in the engine’s external areas, such as the engine mounts or the pylon structure. This element is designed to withstand the harsh environmental conditions and vibrations experienced in the pylon region.

Core Cowl-Mounted Elements

The two core cowl-mounted elements are responsible for detecting fires within the engine core, where the majority of the combustion process takes place. These elements are positioned to provide comprehensive coverage of the engine’s internal fire zones, ensuring rapid detection and response.

Fire Detection and Alerting

jet engine fire detection systems

The jet engine fire detection system alerts the crew to an engine fire through a combination of visual and auditory cues. These include:

  1. L or R ENG FIRE Push Button Illumination: The illumination of the left or right engine fire push button on the cockpit panel indicates the specific engine experiencing a fire.
  2. FIRE Light on Engine Start Panel: A dedicated FIRE light on the engine start panel provides a clear visual indication of the fire condition.
  3. Crew Alerting System (CAS) Message: The CAS generates a message on the cockpit display, informing the crew of the engine fire.
  4. Audio Warning: An audio warning, such as a chime or siren, alerts the crew to the engine fire, ensuring immediate attention and response.

Engine Fire Extinguishing System

The engine fire extinguishing system provides the necessary capabilities to suppress and extinguish fires in the left and right engines. This system typically consists of two fire extinguisher bottles mounted on the aft spar, just forward of the main landing gear bay. Each extinguisher has two discharge heads, allowing for the selective discharge of the extinguishing agent into either engine.

Extinguishing Agent Delivery

The extinguishing agent is directed into the engines through a network of check tees and discharge nozzles. The check tees ensure the proper distribution of the agent, while the discharge nozzles direct the agent to the specific fire zones within the engines.

Extinguisher Discharge

The fire extinguishers are discharged using the appropriate engine FIRE push button annunciator (PBA) and bottle (BTL) PBAs located on the ENGINE and APU FIRE panel. Pressing the FIRE PBA shuts down the engine, isolates it from the airframe systems, and arms the fire extinguishers for discharge. When the BTL PBA is pressed, the corresponding bottle discharges its contents into the engine.

Extinguishing Agent Effectiveness

The effectiveness of various types of fire fighting agents in extinguishing the kinds of fires anticipated in aviation engine test facilities (AETF) has been extensively studied. The agents considered include Aqueous Film-Forming Foam (AFFF), Halon 1301, Halon 1211, and water.

Fire Scenarios and Extinguishment Criteria

Previous test work has shown the rapidity with which aircraft, especially high-performance aircraft, can be damaged by fire. Based on this, tentative criteria for the evaluation of extinguishing agents included a maximum time of 20 seconds from fire detection to extinguishment for the following fire scenarios:

  1. Underframe fire
  2. Major engine fire
  3. Engine disintegration fire
  4. High-volume pool fire with simultaneous spill fire
  5. Internal electrical fire
  6. Runaway engine fire

Extinguishing Agent Performance

The studies have analyzed the performance of these fire fighting agents in terms of their ability to quickly and effectively extinguish the various fire scenarios. The results of these analyses have provided valuable insights into the selection and deployment of the most suitable extinguishing agents for jet engine fire protection.

Failure Scenarios and Troubleshooting

In certain failure scenarios, the jet engine fire detection system may not function as expected. One such case involved the engine fire detector loops being severed by rotor disk debris, resulting in no fire warning in the cockpit. However, the EICAS (Engine Indication and Crew Alerting System) generated several warnings as the engine spooled down, including an “L ENG FIRE DET FAIL” indication on the cockpit EICAS screen.

When such an indication appears, the recommended procedure is to closely monitor the engine instruments and take appropriate actions to ensure the safety of the aircraft and its occupants.

Conclusion

Jet engine fire detection systems are a critical component of aircraft safety, providing rapid and reliable detection and alerting of engine fires. By understanding the technical specifications, components, and operational principles of these systems, pilots, maintenance crews, and aviation enthusiasts can better appreciate the engineering and redundancy built into these vital safety mechanisms. This comprehensive guide has provided a detailed DIY manual for exploring the intricacies of jet engine fire detection systems, empowering readers to enhance their knowledge and appreciation of these essential aviation technologies.

References

  1. Engine Fire Protection Systems – Federal Aviation Administration
    https://www.faa.gov/sites/faa.gov/files/11_amtp_ch9.pdf
  2. Aviation Engine Test Facilities (AETF) Fire Protection Study – DTIC
    https://apps.dtic.mil/sti/tr/pdf/ADA211483.pdf
  3. Air transportation safety investigation A14Q0068
    https://www.tsb.gc.ca/eng/rapports-reports/aviation/2014/a14q0068/a14q0068.html