By John McHale
BELLINGHAM, Wash. - U.S. Navy and civil aviation officials are investigating the use of a new microprocessor- and reflectant sensor-based fire detection and suppression system designed to keep aircraft cargo bay fires in check for however long is necessary to land the plane safely.
The system, Air Fire And Security Package (Air FASPAK), from scientists at Microsafe Industries Inc. of Bellingham, Wash., employs several sensors located throughout the aircraft that interface with microprocessors.
Microsafe engineers are working with officials from China Lake Naval Air Warfare Station in Ridgecrest, Calif., to develop a military version of Air FASPAK.
Officials from the U.S. Federal Aviation Administration are expected to require fire detection and suppression systems in cargo holds within the next two or three years, says Greg Juen, president of the Flight Safety Systems Division of Microsafe. That should make for a billion-dollar market for these types of systems, he says.
Made up of primarily commercial-off-the-shelf (COTS) equipment, Air FASPAK uses smoke and photoelectric rate-of-rise temperature sensors; a tuned, solid-state flame detector; and radio receiver, transmitter, and antenna, Juen says.
"The suppliers of the batteries, sensors, and processors are to be determined, but they will be COTS and we will have multiple supplier agreements within each sub- assembly to reduce cost and schedule risk," he says.
Each sensor has redundant microprocessors to control the device and reduce the number of false alarms. When ones sensor goes off, the system alerts, and goes to full alarm status when a second sensor triggers.
Each sensor acts as a check and balance to the other, thereby helping to lower the false alarm rate, Juen says. "The sensors continuously communicate with each other."
Also helping lower false alarm rate is the reflectant smoke sensor, Juen explains. The sensor`s LED emitter and detector are tuned towards the reflective characteristics of smoke, thereby eliminating any other materials that would blind a less-precise sensor, he says.
"Current predictions for the false alarm rate are somewhere between 1.5 and 2.5 false alarms per billion hours of flight operation," Juen says. Within 10 milliseconds of when sensors detect a flame or a large change in cargo bay temperature, on-board microprocessors initiate audible and visual alarms, and the system starts suppressing the fire 10 seconds later, Juen explains. The aircraft crew have 30 seconds to adjust the system manually before it releases the fire-suppressing chemical Halon.
A two-stage solenoid valve monitors the Halon tank, Juen says. While most systems pump out 44pounds of Halon when they detect a fire, Air FASPAK pumps only enough of the chemical to keep the fire suppressed until the aircraft lands, he adds. Halon is an ozone-destroying chemical, and the federal government is limiting its use.
"The reason for a two stage valve is that you want to make absolutely sure it opens when we blow the diaphragm on the halon tank," Juen explains "The two-stage valve uses a pilot valve which with just a little pressure on the load side of the tank will move the main valve to the position we desire."
To make the system useful for military aircraft "we have to achieve a quicker reaction time in the dry bay," to give the pilot time to make a decision when he is hit by an enemy weapon, Juen says.
Advanced sensors help a new system suppress aircraft fires before they burn out of control.
