After the primary/secondary fuselage structure and floor support structure modification stress issues have been addressed, along with any required control relocation modifications, consideration must be given to what type of fire detection and fire suppression/extinguishing systems that are going to be installed. The FAA established a cargo and baggage compartment classification system for transport category aircraft in 1946. Since then, the requirements have been tweaked after several in-flight catastrophes have occurred; the most recent was the Valujet/Sabretech disaster.
The classification system includes Class A, Class B, Class C, Class D, and Class E. In simplified terms, the Class A compartment does not require any additional fire detection or suppression/ extinguishing systems to be installed. The Class B compartment must have a fire or smoke detection system installed. The Class C compartment must have a fire detection and a fire extinguishing system along with a compartment liner installed. The Class D compartment does not require any additional fire detection or suppression/extinguishing systems to be installed; however, a compartment liner must be installed. Finally, the Class E compartment (most common on all dedicated cargo aircraft) must have a fire or smoke detection system along with a compartment liner installed.
After all of this, there are two major issues left to deal with to complete the modification design. These are: the crew smoke barrier bulkhead and the cargo net installation. As part of the compartment classification requirements, some compartments require that you have a means of controlling the ventilation into the cargo compartment during a fire situation. With this in mind, it will also be necessary to separate the crew from any smoke or fumes that are generated by a fire in the cargo compartment.
This separation can be accomplished by designing and building a sealed metal bulkhead, with a working door, between the cockpit and the cargo compartment. Ultimately, this arrangement will protect the crew's normal working environment and allow them to concentrate on flying the aircraft when a fire emergency occurs. If the pallet hold-down straps failed and the cargo shifted forward, the payload must be prevented from moving forward into the crew compartment area.
This crew protection is normally accomplished by the installation of a solid bulkhead or cargo restraining net. The cargo restraining net or bulkhead has to be able to withstand a 9g load without failing. If a net is installed, it must have enough room allowed ahead for it to flex and deflect while arresting the load.
By Jeremy R.C. Cox
An actual conversion
Now that we have briefly touched on the design requirements, let's discuss an example of an actual conversion program that Avtec has designed for the Falcon 20. The Avtec modification process is broken down into 14 separate and manageable processes.
•Incoming Inspection and Component Removal
• Door Opening and Surrounding Structure, including Cargo Restraining Net Installation
• Build Door - Latching Mechanism
• Cargo Floor and Floor Support Structure
• Emergency Control Relocation
• Window Plug Installation
• Relocation of Oxygen System and Rate Gyros
• Installation of all Cargo Door Control Wiring
• Installation of all Cargo Compartment Lighting Systems
• Installation of all Cargo Compartment Smoke Detection Systems
• Crew Escape Hatch
• Aft and Forward Bulkheads
• Cargo Compartment Liner
• Aircraft Delivery
Before the aircraft arrives for the modification, a deposit has been paid and a complete modification parts kit is fabricated for the aircraft. When the aircraft arrives at the Avtec facility, it is put through a comprehensive incoming inspection. Particular attention is given to the correct function and operation of the avionics and pressurization systems. All interior items, equipment, and loose items are inventoried, documented, and removed from the aircraft. All of the original plastic cabin windows are removed. Usually, the auxiliary power unit (APU) and the thrust reversers (T/R) are removed at this stage of the process, to gain a weight saving.
Most cargo operators who use the Falcon 20 dispense with these units as they consider them as deadweight. The main entrance door is removed and then the outline of the cargo door opening and the escape hatch opening is measured and drawn on the outside skin of the aircraft.
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