Question:

For emergencies due to cargo smoke detector activation, will the flight crew always activate the fire suppression system in the cargo hold? Will the flight crew advise ARFF that the system has been activated?

Answer:

If the cargo fire detectors activate, the pilots should always activate the fire suppression system. Flight crews should advise ATC that the system has been activated, but rest assured if you have been called out for a cargo fire detectors activation, the pilots have activated the suppression system.

This question brings up a few important points about the cargo fire system.

The question was about “a smoke detector”, but I answered “fire detectors”. The most important part is that no single detector will provide a fire warning. It takes two detectors being activated from the same area of the cargo compartment to get a fire warning. This greatly reduces the chance of a false fire detection. In the attached diagram look at the “and logic” on fire detection. The “or logic” only comes into play if a fire detector is INOP.

Some aircraft have a combination smoke/heat detectors and others have just smoke detectors.

The fire suppression system, when activated, deluges halon into the selected cargo compartment, often from a single halon tank. (some aircraft use multiple smaller tanks plumbed together to act like a single tank) A second halon tank then starts a slow metered discharge of halon into the same cargo compartment. Once the system is activated, the pilots (and ARFF) cannot stop the halon discharge. How long the discharge takes place depends on the aircraft. Aircraft designed for domestic service have a much shorter discharge time, since these aircraft can make an emergency landing at a nearby airport shortly after activation of the system. Long range international aircraft that are designed to fly across the ocean and/or the north pole need a fire suppression system designed for a much longer time since it may be over three hours before they can get to an emergency airport. These aircraft have fire suppression systems designed to provide Halon into the cargo compartment for four hours. It does not matter if that aircraft is being operating domestically at the time, it will always provide halon for the rated time, and in this example, four hours. On some of the newest aircraft the system will dump the remaining halon when the aircraft lands.

I kept this information general and not specific to each aircraft, but keep in mind the following:

* It takes two fire detections to get a fire warning.

* Halon may be discharged into a cargo compartment for up to four hours after the system is activated.

*There is only one fire suppression system for all the cargo compartments, the pilots select which cargo compartment the system will be used on. You cannot use one bottle for one cargo compartment and then try to use the other halon bottle for a different cargo compartment.

 

About the Author:

John McLoughlin has been a commercial pilot for over 30 years. He is currently a B-767 Captain with Boeing 787 and Airbus A-330 type ratings for a major U.S airline. He also holds a position on the Airline Pilots Association (APA) Union Safety Committee. Both John and his father Jack also served as volunteer firefighters.