as part of a continuing program on
aviation safety the lewis flank
propulsion laboratory of the national
advisory committee for aeronautics has
been engaged in research on the start of
fires that sometimes follow airplane
crashes the work was undertaken at the
recommendation of the naca committee on
operating problems and the subcommittee
on aircraft fire prevention these groups
are made up of leading representatives
of civil and military aviation it was
the purpose of this research to provide
a better understanding of the important
factors involved in the start and spread
of crash fires as a necessary first step
leading to significant reduction in the
crash fire hazard
the work reported in this film covers
only the research completed on airplanes
powered with reciprocating engines
a thorough review of civil and military
crash fire records emphasize the need
for well-defined information on how
crash fires start
this review showed this information can
only be provided by full-scale crash
study
findings of this study were published in
an naca research memorandum entitled
analysis of multi-engine transport
airplane fire records
the need for a full-scale crash fire
program established the united states
air force provided a group of service
weary aircraft marked for decommission
with which to conduct the research a
landing or takeoff accident was chosen
for study because the chance for
passenger survival of crash impact is
highest in this type of crash which
occurs at reduced airplane speed the
airplanes were carefully instrumented to
collect detailed information during the
crash
72 vapor detectors located in the engine
the cell wings and fuselage registered
the presence of combustible vapors over
100 flame detectors similarly located
recorded the origin and spread of fire
throughout the aircraft structure
all the main electrical circuits were
monitored at the locations shown on this
chart to indicate the presence of short
circuits
instrumentation was also provided to
indicate the time at which fuel lines
ruptured in a crash
such detailed information is registered
on this instrument panel inside a
fireproof box carried in the airplane
the instrument panel is photographed by
motion picture cameras within the box
in a crash operation the airplane is
accelerated from rest under full power
and is guided into a crash barrier by a
slipper in sliding contact with a rail
this barrier is composed of an abutment
in the path of each landing gear wheel
the abutment strip the landing gear from
the airplane
if propellers strike the abutment at
full engine power to produce extensive
damage to the engine the cell
the pair of poles on each side of the
abutment cut into the wing fuel tanks
causing spillage of the fuel at the
moment of crash impact the airplane is
moving at about 90 miles an hour the
airplane carries a thousand gallons of
fuel in the tanks outboard of the
nacelles the fuel is sometimes dyed red
for photographic purposes
a detailed description of the method of
conducting these crashes was published
in the naca research memorandum entitled
facilities and methods used in
full-scale airplane crash fire
investigation
to understand how crash fires begin it
is necessary to learn where and when
ignition sources exist and how the
combustibles move from the spillage
zones to the ignition sources while
these sources are still potent many
ignition sources are carried on the
airplane others are generated in the
crash area
a large number of ignition sources are
located in the engine nacelle which
contains the engine and hot metal parts
of the exhaust system
flames appear at the engine intake in
the familiar backfire
likewise flames appear at the exhaust
outlet
the electrical system of the airplane
represents the most widely distributed
ignition source it extends from the
nacelles into the wings to power fuel
pumps and lights into the fuselage for
lights navigational instruments and
airplane controls
of the combustibles carried in an
airplane only those in liquid form are
likely to contact ignition sources in a
crash these combustibles are fuel
hydraulic fluid
lubricating oil and alcohol
the crash fire threatens human survival
only when the fuel becomes involved in
the fire because the other combustibles
are present in small quantities however
the other liquid combustibles may be the
first to ignite and in turn set fire to
the fuel
in the conventional airplane most of the
fuel is stored in wing tanks the tanks
are interconnected by pipes so that fuel
from any tank can serve all the engines
through main lines which run to the
engine carburetor
in a crash fuel often is spilled in
liquid form from broken fuel lines
likewise liquid spillage occurs from
damaged tanks
pre-mixed fuel vapor and air spills from
the damaged engine induction system and
a combustible fuel mist sometimes forms
around the airplane the airplanes were
crashed in ways that resulted in all
these forms of fuel spillage
in studying how the fires are started it
is necessary to consider the ignition
sources along with the fuel spillage the
following discussion will take up the
various forms of fuel spillage and how
the fuel moves to the ignition sources
the characteristics of the ignition
sources will be discussed at the same
time
because the fuel in the mist form played
such an important role in the crash
fires experienced in this study fires
involving fuel mist will be discussed
first when the liquid fuel spills into
the open air while the airplane is in
motion it is atomized into a mist
in this scene shown at one-fifth normal
speed watch how the fuel dyed red for
visual clarity develops into mist during
a crash as the fuel pours from the tanks
breached by the poles at the barrier the
fuel is atomized to mist a part of which
remains suspended in the air
the plume of the fuel mist streams
directly rearward from the break in the
tanks if the damage to the airplane in
the crash results in only moderate
deceleration and the airplane continues
forward at high speed when the airplane
moves at low speed with high
deceleration the fuel surges forward out
of the break in the tank this results in
a broad fuel mist pattern in the forward
portions of the airplane under such
conditions contact between fuel and
ignition sources at the nacelle is
likely
now watch in the next crash the
transition of the fuel mist development
from the high speed low deceleration
pattern to the low speed high
deceleration pattern
here comes the airplane at about 90
miles an hour the motion is reduced to
one-fifth normal speed the impact of the
barrier will produce momentary moderate
airplane decelerations observe that the
fuel died red streams directly back from
the leading edge when the airplane
strikes the ground with high
deceleration the fuel mist develops well
forward of the wing leading edge and
spreads span wise as the airplane slows
in view of these effects the fuel mist
can be expected to contact an ignition
source which lies span wise from the
point of fuel spillage as the airplane
slows down
in the motion pictures of the crash
illustrating this effect look for a
continuing series of flames at the
engine exhaust following crash impacted
the barrier as the airplane skids along
the ground the fuel spilling from the
wing at this location moves span wise in
mist form until it reaches an exhaust
flame just before the airplane stops
now let us observe this method of fuel
movement to the engine tailpipe the
action here is reduced to one-fifth
normal
speed notice the flames at the tailpipe
contact of the fuel mist with an exhaust
flame occurs just as the airplane comes
to a stop
ignition of the fuel mist occurred on
the same airplane on the hot exhaust
collector ring of the engine on your
left at this location
under impact at the barrier the engine
the cell breaks down and exposes the
exhaust collector ring as the airplane
slows the fuel mist moves span wise and
forward to the exposed collector ring
here comes the same airplane watch how
the nacelle on your left tips downward
as the propeller hits the barrier
exposing the exhaust collector ring the
flame first appears at the top of the
nacelle where the fuel mist contacts the
exhaust collector ring
in the time between initial fuel
spillage and ignition and explosive fuel
air mixture accumulated in the wing
explosion of the mixture produced this
distribution of flaming fuel
fuels of low volatility and mist form
ignite readily in spite of the fact they
are safe in liquid form in the presence
of open flames a wick saturated with
this fuel can be ignited by the steady
application of a flame the lighted match
held above the surface of this low
volatility fuel produces no ignition
observe in the next crash the ignition
of the mist of low volatility fuel by a
tailpipe flame
note also the backfire flame at the
engine inlet that follows the main fuel
ignition
the tanks of the oncoming plane are
filled with low volatility fuel this
action is reduced to one-fifth normal
speed
here is the ignition by the tailpipe
flame
now watch for the backfire at the engine
inlet
this aerial view of the crash with the
action slowed to one third normal speed
shows the flames traveling through the
fuel mist at a rate comparable to that
of gasoline
the flames at the engine exhaust that
were observed igniting these mists may
occur in a crash as long as the engine
is rotating and drawing fuel even impact
of the propellers with an obstacle does
not ensure that the engine will stop
running
in this crash shown at normal speed the
damaged engines continues to operate for
several minutes after crash impact watch
how the propellers now in slow rotation
accelerate this alternation of slow and
fast rotation continues through several
cycles one of which is shown here
another ignition source in the engine
cell which may ignite the fuel mist is
provided by lubricating oil burning
within the nacelle
the next crash you will see shows how
the lubricating oil can set fire to the
fuel
on the low wing airplane used in this
crash the nacelle strike the ground when
the landing gear is sheared off the oil
cooler located at the bottom of the
nacelle is ripped open when the cell
strikes the ground the released oil is
ignited on contact with the hot engine
exhaust collector ring close by
now we shall see how this fire setting
process acts in a crash of a low wing
airplane having the nacelle arrangements
shown previously the action is reduced
to 1 12 normal speed
after passing through the crash barrier
the unsupported airplane strikes the
ground the cells foremost causing the
oil cooler in the nacelle to break back
and release oil onto the hot exhaust
collector ring
now condensed oil vapor generated on the
exhaust system can be seen issuing from
the nacelle
as the airplane slows the fuel spilling
from the wing moves out ahead of the
leading edge and spreads toward the
nacelle
two seconds after crash impact ignition
of the oil is indicated by the fire
detectors a marked increase in the rate
of formation of oil vapors follows
ignition of the oil
three seconds after crash impact the
entire engine exhaust collector ring is
enveloped in fire
as the airplane comes to a stop the fuel
mist and oil vapors form a continuous
combustible atmosphere in a cell oil
fire spreading through the oil mist will
now appear outside of the nacelle and
move rapidly to the fuel
watch how the fire moves to the breach
in the wing and then to the rear of the
airplane as it follows the fuel spilled
in the slide path of the crashed
airplane
finally it is necessary to consider the
time during which the mist is a hazard
this is a rear view at one third normal
speed which places the fuel mist between
the airplane and the camera the
developing fuel mist obscures the
airplane from view but it reappears
shortly as the large mist droplets rain
to the ground and the small droplets are
swept from the area by the wind as they
evaporate these mists seldom remain
around the crashed airplane for more
than 15 seconds
analysis of the photographic data shows
that this fuel missed hazard time varies
inversely with the wind speed around the
crashed airplane
to sum up it has been shown that
airborne fuel mist can move considerable
distance forward and span wise from the
fuel spillage point to reach remote
ignition sources
when the fuel is dispersed as missed it
ignites readily even though its
volatility is low
contact between the mist and an ignition
source far from the fuel spillage zones
is most likely to occur as the airplane
slows down
because of the short duration time of
the mist the ignition source must be
present while the airplane is in motion
or shortly after it stops if a fire is
to occur
now let us see how crash fires are
started with fuel spillage in liquid
form fuel in liquid form appears on the
outside of the airplane pouring to the
ground from the broken fuel tank and
fuel lines
the steam that is issuing from the
nacelle will be discussed later liquid
fuel also collects on the airplane
surfaces by interception of the fuel
mist droplets while the streams of
liquid fuel pouring to the ground are
formed as the airplane comes to a stop
and mist formation subsides
spreading of the liquid fuel within the
airplane structure begins as soon as the
tanks are damaged regardless of the
state of motion of the airplane
when liquid fuel is spilled inside the
airplane structure such as the wing
interior combustible concentrations of
fuel vapor accumulate readily and spread
within the structure as an example of
the ignition of fuel spilled within the
wing observe the wing fire set by
damaged landing lights on the leading
edge of the wing
the poles that rip open the fuel tanks
also smash the landing lights and drive
them into the wing where the
incandescent filaments set fire to the
fuel almost at once
the next motion picture sequence
projected at one-fifth normal speed
shows ignition by the damaged landing
lights the pole at the barrier drives
the landing light into the fuel tanks
the resulting fire spreads rapidly
through the fuel mist to produce this
wall of flame
the mass of fuel mist rises as it burns
out the fuel evaporating from liquid
spillage on the ground and the wetted
surfaces of the airplane continues the
fire on a reduced scale
the fuel that spills in the wing can
also move through channels within the
wing to ignition sources contained in
other parts of the airplane
one path this fuel may take is through
the duct in the wing leading edge this
duct carries hot air to warm the wing
and prevent the accumulation of ice in
flight
the duck leads to a heat exchanger at
the engine exhaust tailpipe which
provides the necessary heat
when this duct is ripped open as the
poles tear through the wing some of the
fuel issuing from the torn tanks is
diverted into the duct
this fuel flows by gravity to the hot
heat exchanger
upon ignition the flame flashes back
through the hot air duct to the fuel in
the wing
here is a crash in which these events
occurred because the wing slopes
gradually toward the nacelle a fuel
flowing through the hot air duct
requires 14 seconds to reach the cell
since the action on film is reduced to
one-fifth normal speed about one minute
will pass before this ignition appears
the steam which is issuing from the
nacelle will be discussed shortly
the fire will show first at the engine
tailpipe heat exchanger on your right
note the spread of the fire back to the
wing and the wing explosion that results
in addition to the flow of liquid fuel
through the internal channels of the
airplane fuel and rivulets and sheets
flows by gravity along the underside of
inclined airplane services this will be
called wetting conduction fuel which
spills inside the wing can seep through
seams in the wing's skin and cling to
the under surface of the wing this fuel
may then flow to other parts of the
airplane where ignition sources exist
the resulting fire travels back along
the fuel path to the fuel source the
wetting conduction of the fuel along the
under surface of the inclined wing is
illustrated by a simple experiment in
which fuel issuing from an opening in a
tube at the raised end wets and moves
along the under surface to the low end
the normal wing arrangement of airplanes
may place the wingtips higher than the
wing at the engine the cells for these
airplanes the wetting conduction flow is
toward the nacelle where ignition
sources exist
sometimes in a crash the wing
inclination is even higher which
increases the fuel movement by wetting
conduction distribution of fuel by
wetting conduction is shown on the
underside of this wing of a crashed
airplane which did not burn the fuel dye
indicates the path of the fuel the
continuous fuel wetted path extends from
the break in the wing to the nacelle and
the engine exhaust pipe
here is how the wetting conduction flow
looks immediately after a crash the fuel
on the underside of the wing clings and
flows by gravity along the wing span
some of the fuel dripping off along the
way
fuel sometimes runs into the wheel well
from broken tanks through channels in
the wing structure
here you see how it dripped and ran
along various parts of the landing gear
actuating system and along the strut
toward the wheel
any marked change in the surface along
which wetting conduction of fuel is
taking place may interrupt this fuel
flow here we see how a sharp edged
projection intercepts the wetting
conduction fuel flow and prevents
further flow along the rod
a slot in the rod provides the same
interception of the wetting conduction
flow
in cases where wetting conduction or
fuel flow through structural channels
results in prolonged contact between an
igniter and the fuel in liquid form the
use of fuels of low volatility would not
materially reduce the likelihood of fire
where vaporization of the fuel across an
air gap is required for the fuel to
reach an igniter low volatility fuel
provides a safety advantage consider
next fuel spilling in the open air that
wets the ground along the slide path of
the airplane and around the crashed
airplane at rest the pools of liquid
fuel close to the nacelles are not large
since most of the spilled fuel flows
away from the spillage point ignitable
fuel vapor from ground spillage is
carried in a thin layer close to the
ground the ignition hazard distance
which extends only a few feet from the
spillage decreases with increasing wind
velocity this short hazard distance is
illustrated by the ignition of gasoline
vapors from pans by a lighted taper
approaching from the downwind end
when ignition occurs the lighted taper
lies within two inches of the surface of
the gasoline contained in the pans the
wind speed is 10 miles an hour movement
of combustible concentrations of fuel
vapors from fuels filled in the open air
to ignition sources above the ground is
considered unlikely
however when the fuel is spilled into
wind protected areas provided by the
crashed airplane heavy ground vegetation
or ground channels the combustible
concentration of fuel vapors may travel
a considerable distance the ignition
source must appear close to the ground
in order to contact these fuel vapors
such ignition sources may be droplets of
burning oil hydraulic fluid or pieces of
hot metal broken from the engine exhaust
disposal system
friction sparks generated by the
scraping of airplane metals on concrete
runways or stony ground provide one type
of ignition source which appears close
to the ground these sparks may ignite
fuel on the ground in order to study
this type of ignition a concrete strip
was built along the slide path of the
crashed airplane
selected samples of airplane metals were
fastened to protruding ends of pneumatic
wheel struts salvaged from airplanes
crashed in this study upon crash these
metal samples bear on the concrete strip
with a contact force great enough to
produce sparks of sufficient size and
temperature to ignite aviation grade
gasoline sparks from this portion of a
steel propeller blade and this steel
wheel strut produced fires
a braided particles of this portion of
an aluminum propeller blade did not
produce ignition in order to ensure an
ignitable mixture close to the ground
near the sparks secondary fuel spillage
was provided by the spray bar at the
nose of the fuselage and these spray
nozzles along the side of the fuselage
ignition will appear at this point on
the fuselage where a portion of a steel
propeller blade is located
here we see the airplane sliding along
the concrete strip after undergoing the
usual crash damage at the barrier the
action is slowed to one-fifth normal
speed
the ignition will appear at the bottom
of the fuselage this is the first
ignition and here is the second friction
sparks obtained from steel and normal
steel grinding operations seldom have
enough size and temperature to ignite
gasoline but these studies show that
friction sparks of sufficient energy for
ignition of gasoline can occur under the
conditions of high friction loads which
exist in some crashes
to summarize these results show that the
ignitable vapor zones arising from
liquid spilling in the open air are
small except in wind protected areas
liquid fuel spilled in the wings moves
as liquid and vapor through the
structural channels
widespread distribution of a fuel in
liquid form can occur by wetting
conduction
in contrast with a fuel mist which
persists for only a few seconds in the
crash area the fuel and liquid form on
the ground and the wetted surfaces of
the airplane and in the channels of the
airplane structure are present for long
periods
these are the forms of fuel spillage
that are inflamed by ignition sources
which appear late in the crash event
the ignition of fuel pre-mixed with air
in combustible proportions is another
way in which a crash fire may begin
such fuel air mixtures appear in the
engine air induction system comprising
the supercharger and engine intake
manifold a rupture of the engine
induction system is followed at once by
release of the fuel air mixture
contained under pressure by the engine
supercharger
ignition may occur by contact of this
released fuel air mixture with the hot
elements of the exhaust disposal system
or exposed exhaust pipes by arcs and
sparks of the electrical system or by
backfire from the engine cylinders
because of the high air flow rates
through the engine the cell in the early
phases of a crash when the airplane is
moving at high speed ignition of this
released fuel air mixture must occur
shortly after engine induction system
failure otherwise the fuel air mixture
is quickly swept from the nacelle by the
airflow although the fire produced by
the ignition of the engine induction
system fuel is not serious in itself
because of the small amount of fuel
involved this fire can extend to other
fuel being spilled and so set off the
major fire in the next crash to be shown
the engine on your right breaks out of
its nacelle at the moment of impact the
engine fractures along the line passing
through the case of the supercharger the
released fuel air mixture is ignited at
once by exhaust flame issuing from the
adjacent broken engine exhaust
here the airplane approaches the crash
barrier the action is shown at 1 12
normal speed watch the engine in full
view snap from its mounts ignition of
the fuel air mixture occurs at once the
fuel being spilled adjacent to the
nacelle is then ignited from this flash
fire
another crash fire involving ignition of
the engine induction system fuel
occurred in the following sequence
damage to the engine induction system on
crash impact resulted in a fire at the
nacelle in a manner similar to that
shown in a previous crash
fuel spilling from the broken main fuel
line at the nacelle firewall was ignited
by the flash fire of the engine
induction system fuel the resulting
flames streamed rearward over the
nacelle and wing
afterwards the fuel spilling from the
wings through the ruptures cut by the
poles at the crash barrier fanned out
into the wake of the wing contact
between the flames and the fuel took
place to the rear of the trailing edge
of the wing
the flames moved forward to the wing
through the trailing fuel as the
airplane speed fell below the flame
propagation speed
now watch this fire setting mechanism in
the next movie sequence at normal speed
watch the nacelle and note the forward
movement of the flame
the research up to this point resulted
in an understanding of the ignition
sources involved in a series of crash
fires and also how the fuel in the mist
liquid and vapor forms moved from the
spillage point to the ignition sources
however these ignition sources revealed
so far usually produced fires within a
few seconds after crash impact
because it was felt these early fires
might mask other ways in which fire can
occur the known ignition sources were
inerted by experimental means
the parts of the inerting system used in
this investigation are shown
diagrammatically on this chart
here are the main parts of a typical
engine nacelle to prevent the appearance
of flames at the engine inlet and
exhaust outlet fuel system shutoff
valves are installed at the engine
and the firewall to stop the fuel flow
following crash impact
one valve stops the fuel flow to the
engine the other prevents the fuel
spillage into the nacelle several pounds
of suitable fire extinguishing agent
discharged uniformly in the engine inlet
air to inert the contents of the engine
during the period of time required for
the valves to stop the fuel flow
electrical system switch shuts down the
airplane battery and generator circuits
the ignition system continues to
function so that fuel passing into the
engine will be burned in the normal
manner in case the fuel shut off valves
and the fire extinguishing agent system
at the engine inlet are slow to function
normal engine exhaust is less likely to
start a fire than tail pipe flame which
forms that when the fuel charge passes
through the engine cylinder unburned and
is later ignited in the hot exhaust
system
in order to prevent ignition on the hot
metal of the exhaust system a water
spray is used to cool all of the exposed
metal which is hot enough to ignite the
combustible in a few seconds needed to
cool the metal to safe temperatures and
inert atmosphere of steam generated by
the water evaporating from the metal
itself shrouds this potential ignition
source to render it impotent the portion
of the water spray system which services
the exhaust collector ring is this
three-quarter inch diameter tubing bent
to conform approximately to the shape of
the collector ring the exhaust system
receives water over its entire surface
from its spray nozzle
the effectiveness of the water spray in
preventing ignition on the hot exhaust
is demonstrated by the rapidity with
which a continuously fed oil fire
burning from the exhaust system is
extinguished by the water spray
notice how the application of the water
spray extinguishes the fire almost at
once
this crash is typical of the results
obtained with five aircraft equipped
with the experimental inerting system
just described which is arranged to be
actuated as soon as possible after a
crash impacted the barrier
the only visible sign of the functioning
of the inerting system is the steam
evaporating from the hot exhaust system
this is the steam which was visible in
some of the preceding pictures the fuel
here has been dyed red
see the dust being raised by the
airplane fuselage skidding along the
ground this dust plays an important part
in starting fires to be described
shortly
this experimental inerting system used
in this crash was devised solely for
studies of this kind and does not
incorporate the considerations of weight
and bulk which would be involved in
inerting equipment for operating
aircraft
in this phase of the research in which
aircraft carrying the experimental
inerting system were subjected to
moderate damage upon crash impact no new
ignition sources were revealed
after five crashes in which no fires
were obtained and no new ignition
sources were observed the crash
circumstances were modified in an effort
to learn other ways in which fires may
occur in order to learn whether ignition
sources may be created by the tearing
and twisting of the airplane structure
in a severe crash
the forward portion of the fuselage
structure was crushed along this
inclined line in one crash as before the
nacelles carried the experimental
inerting system in the pictures which
follow note the complete collapse of
this fuselage force structure bringing
the wings to ground level and the
resulting wetting of this structure by
the released fuel
while no fire occurred around the
crushed structure ignition of the fuel
did occur in the fuel wetted wake of the
airplane the ignition source was an
electric spark discharging to the ground
from the landing gear strut which broke
off in the crash and tumbled in the wake
of the airplane
here the airplane approaches the crash
barrier upon impact with the ground the
forward structure collapses the action
here is slowed to one-fifth normal speed
now watch the wheel strut tumbling in
the wake of the airplane and observe the
ignition which occurs when the metal end
of the strut approaches the ground the
fire spreads through the fuel in the
airplane wake there is no evidence of
other ignition resulting from the
destruction of the fuselage structure or
the inerted engine the cells the igniter
in this instance proved to be an
electric spark discharging from the
landing gear strut to the ground the
necessary electrical potential on the
strut was generated in its passage
through the dust and fuel mist in the
wake of the crashed airplane
ground studies were conducted by blowing
dust and fuel over a landing gear strut
and measuring the electrical potential
built up on the surface of the landing
gear here is the landing gear strut
electrically insulated from its supports
when dust is introduced into the air
blowing over the strut at speeds equal
to that of the strut moving through the
air in the crash potentials in excess of
twenty thousand volts are generated on
the strut almost at once
this voltage applied across a spark gap
located in this small pan containing a
pool of gasoline produces ignition of
the gasoline
here is the flaming gasoline
in the last crash of this series the
effect of an airplane ground loop on the
distribution of the spill fuel was
studied watch how the airplane ground
loops as one landing gear is torn away
the ground loop places the airplane and
the fuel spray the fuselage wing and the
cell on the right side of the airplane
are wetted heavily with fuel because the
inerting system carried on this airplane
functioned properly and no new ignition
sources appeared no fires occurred
and now here's a summary of the crash
fire research from two lewis flight
propulsion laboratory scientists irving
pinkel associate chief of the physics
division and merit preston chief of the
flight research branch mr pinkle
the results of this work indicate that
significant reduction in crash fire
hazard can be realized by design
measures
that increase the span wise and forward
distance and the elevation of the
engines with respect to the fuel storage
this trend in airplane component
arrangement decreases the likelihood of
contact between the fuel mist
and the many ignition sources located at
the engine in the
cell fuel stored in wingtip tanks or in
pods suspended below the wing represent
current design trends
which decrease the likelihood of contact
between the fuel
and the ignition sources devices or
design features
which act to intercept spilled fuel
flowing within the airplane structure
are also valuable
provisions for the drainage of this
intercepted fuel
into the open air at spillage points
away from the engine the cells
would enhance the effectiveness of these
arrangements
location of landing lights away from
cordwise positions
in front of the fuel storage is
indicated as well
because these studies show how readily
combustibles spilled in the cell are
ignited it is desirable that the
components of the fuel lubricating and
hydraulic systems should be located high
in the cell where crash damage to these
compounds is least likely
tubing containing combustibles should be
designed to accommodate the cell
distortions accompanying propeller and
the cell impact
preliminary data suggests the value of
employing special paints which reduce
the tendency toward the formation of
electrostatic sparks on parts of the
airplane likely to be detached in the
crash
and trail in the dust and fuel in the
wake of the crashed airplane
in an approach to an indicated price
landing
the pilot should de-energize all of the
electrical system not required for the
landing
engine operation that provides the
coolest exhaust disposal system should
be practiced consistent with other
safety considerations
just before touchdown the fuel flow to
the engine should be cut off to allow
the engine to be purged with clean air
in view of the effectiveness of the
experimental ignition source alerting
system in preventing crash fires
experienced in this research
further study of this system for special
airplane application is desirable
material covered in this motion picture
has been published in an naca research
memorandum entitled mechanism of start
and development of aircraft crash fires