Casey Childers

It is my opinion that the statistical odds of an in flight APU enclosure fire are very low and exponentially lower that one would spread outside the enclosure. I believe these odds could be demonstrated to be greater than the acceptable designed failure rate for flight critical systems. This opinion is based on the fact that in the history of the Gulfstream Large cabin fleet with the thousands, perhaps millions, of flight hours logged it is my understanding that there has not been one occurrence of an in flight APU fire. In the highly unlikely event that a fire was to start the enclosure is designed in such a way as to snuff a fire due to the venture effect of the air movement in the chamber created by the exhaust duct assembly. This design quality causes an exchange of the entire volume of air in the chamber at a rate of approximately 5 times a min. Additionally the enclosure is equipped with its own dedicated Halon Fire Bottle suppression system. The relatively few APU fires that I am aware of were typically Maintenance related, on the ground, during a ground run leak check, and they were quickly extinguished by shutting down, removing fuel, or releasing the dedicated fire retardant agent. Additionally, I have seen numerous instances of items with less than desirable flammable qualities in very close proximity to or sometimes attached to a fire enclosure or fire wall in applications across the industry at large. If we apply a standard to this application, we will have to apply it to the entire industry. Doing that would be inconceivable and unwarranted. My suggestion is that we correct the situation going forward on new aircraft, but due to the issues raised above and the varied impact on operations, leave the existing structures alone.