Week 4: Fire Investigation and AD 14

       For this week I want to look more into Fire Invesigation and AD #14. While most Aviation crashes either are a result of a crash or the cause of a crash we need to understand more of determining when the fire happened. Controlld flight into terrain as we discussed previously is flying an airworthy aircraft into a terrain, water or an object. Now a crash due to a fire would eliminate CFIT do due the airworthinies being eliminated fires due happen during crashes and we need to dicuse the investigation portion of it.

Definitions

 

       During this section you will see words used, so lets look at a few definitions.

 

• Fire: is a oxidation reaction producing heat and light
• Open Flame: A rapid oxidation reaction with the production of heat and light.
• Deflagration: Subsonic gaseous combustion resulting in intense heat and light and possibly a low level shock wave. ( Most aircraft impact are deflagratons)
• Detonation: A Supersonic combustion process occurring in a confined or open space characterized by a shock wave preceding the flame front
• Explosion: Detonation within a condined space resulting in a rapid build up a pressure and rupture of the confining vessel.
• Flash Point: The lowest temperature at which material will produce a flamable vapor
• Auto-Ignition Temperature: Also called ignition temperature o Auto ignition temperature. Temperature at which material will ignite on its own without any outside source of ignition
• Flammabilty limits: General list of upper and lower flammablity or explosive limits.
• Flash over: Term used to describe the situation where an area  or its contents is heated to above its auto ignition temperature, but does not ignite due to shortage of oxygen.
• (Woods & Sweginnis, 2006)

 

 

FIRE Chemistry

 

     Fire is a result of an oxidaton reaction. There are four essental condition that must be present for a fire to occur. Will discuse these is further detail later on in this chapter/ 

 

• Combustible Material
• Oxidizer
• Ignition
• Enough hear or engergy to sustain the reaction

 

1. Combustible Material: Airplanes carry alot of flamiable material when ever its flying or on the ground, Fuel and hydrolic fluid do not burn on an aircraft however their vapors due. (Woods & Sweginnis, 2006). With that being said an airplane with more fuel is less flamable then an aircraft with less fuel since its the vapors the ignite and not the fluid. Flamable vapors can also be created in the form of mist. Inside a jet engine the fuel is sprayed into the compustion chamber as a fine mist. That mist can ignite at a lower temperature than the fluids vapor flast point (Woods & Sweginnis, 2006.) During investigation of fires involving solids, its well to remember that almost any substance on an airplane will react somehow to heat.

 

     2.   Oxidizer: Since air is 20% oxygen, ordinary air is sufficent enough to support most fires. If a

           fire occurs during flight and the fire is exposed to the relative wind, oxygen is added and the

           fire will burn hotter and spread faster (Woods & Sweginnis, 2006). Due to the pressure being

           different at different altitudes the partial pressure is not. The reduction of atmospheric   

           pressure there is also a reduction in the quality of oxygen. At some point depending on the

           quality of fuel and temperature the quality of the oxygen becomes insufficient to support the

           oxidation reaction (Woods & Sweginnis, 2006).

 

     3.   Ignition: As we all know for a fire to ignite, the ignition source must first rase the temperature

           of the combustible vapors.(Woods & Sweginnis, 2006)

 

 

     4.   Heat or energy to sustain the reaction: If the ignition process provides this energy, the fire

           will be self- sustaining. If not the fire will go out when the source of ignition is removed.

           (Woods & Sweginnis, 2006) Once properly ignited the fire will continue until one of the four

           events occur.

• The combustible material is consumed or removed.
• The oxidizing agent concentration is lowered to below that necessary to support combustion
• The combustible material is cooled to below its ignigtion temperature.
• The fire is cheicallyinhibited

 

Level of Burning Reaction

 

       There are serveral types or levels of burning. These term must be understood to determine what level of burning is occuring.(Woods & Sweginnis, 2006)

• Diffusion or open flame: The lowest level of burning reaction and is analogous to a candle flame
• Deflagration: Most "Fireballs" seen immediately after an aircraft crash impacts are deflagration
• Detonation: This is the third level of burning reaction and it diffirs from an explosion only in that it is confined.
• Explosion: This is the form of detonation occuring in a confined space and may either be mechanical of chemical
• (Woods & Sweginnis, 2006)

 

 

Characteristics of Aircraft Fluids and Material

 



1. Fluids: Characteritics of common aircraft fluids included fuel, oil, hydraulic fluid, battery gases. Figure 8-2 in (Woods & Sweginnis, 2006) shows the flash point and ignition temperature for fluids associated with aviation.
2. Aircraft Material:  In firgures 8-3 in (Woods & Sweginnis, 2006) you can see certain aircraft material and the temperature at whcih the will ignite.
3. Compsite Material: The principal composite material used in airplanes today are composed of fiberglass or carbon fiber. they also may be sandwhiched between metalic or non metallic core.
4. Aluminum Alloys:  Most aircraft are made of about 95% pure aluminum alloyed with other elemnts.
5. Melting: Aluminum alloy becomes plastic around 850 degrees and begins to sag.
6. (Woods & Sweginnis, 2006)

 

 

Source of Fuel

 

1. Aircraft Fuel: Aircraft fuel is the most obvious source of ignition.(Woods & Sweginnis, 2006)when an aircraft crashes fuel tanks can rupture and can form most that can be ignited by friction sparks, engine exhaults or hot engine parts. (Woods & Sweginnis, 2006)
2. Oil:  Aircraft oil is not a common source of fuel for a fire as it is confined to the engine and seperated from the rest of the aircraft by a firewall.(Woods & Sweginnis, 2006)
3. Hydraulic Fluids: All hydaulic fluid can be ignited and will sustain cumbustion if the temperature is hot enough.(Woods & Sweginnis, 2006)
4. Battery Gases: All aircraft has a battery that uses hydrogen. If the battery is not properly vented hydrogen can accumulate in the battery compartment and be ignited.(Woods & Sweginnis, 2006)
5. Cargo: If the fire comes from the fuselage with cargo on board, the cargo is always suspected.

 

Source of ignition

 

      The ignition of fire depends on the flammability of the fuel and th temperature or energy level of the ignigtion source. Some sources are

• Engine Hot sections
• Exhaults
• Over heated equipment
• Static Discharge
• Lightning
• Hot Brakes
• Aircraft Heaters
• (Woods & Sweginnis, 2006)

So What does this Mean?

 

       So the main question we are asking our self is how do this effict controlled flight into terrain. Well in order to determine if the fire started before the aircraft made contact with the ground or if the fire stated while in flight we must look at a few things investigators will look at to determaine if this is CFIT. First thing is

 

1. Indirect Evidence: First thing investigators will review the flight through radio transmissions. Did they don they smoke mask? Did they diactivate electrical circuits.(Woods & Sweginnis, 2006)
2. Direct Evidence:  This will be determined by 4 main parts, In flight fire effects, Ground fire effects, Crash Dynamics and impact effects.

 

 



       After looking into AD14 Investigators can use this tip to determine if the fire started in flight or when it impacted the ground. While most aircraft crashes create fires its important to determine where the fire started so they can rule out CFIT if neccesary

 

 

REFERENCE

 

Wood, R. H., & Swegonnis, R. W. (2006). 22. In Aircraft Accident Investigation (2nd ed., pp. 61-75). Casper, WY: Endeavor Books.