BFOD: Big Fod
F.O.D. stands for Foreign Object Debris or Foreign Object Damage. According
to the National Aerospace Standard 412, maintained by the National Association
of FOD Prevention, Inc, Foreign Object Debris is a substance, debris or article
alien to the vehicle or system which would potentially cause damage. Foreign
Object Damage is any damage attributed to a foreign object that can be expressed
in physical or economic terms that may or may not degrade the product's required
safety and/or performance characteristics. Typically, FOD is an aviation term
used to describe debris on or around an aircraft or damage done to an aircraft.
"Internal FOD" is used to refer to damage or hazards caused by foreign objects
inside the aircraft. For example, "Cockpit FOD" might be used to describe a
situation where a clipboard, water bottle, or other item gets loose in the
cockpit and jams or restricts the operation of the controls. "Tool FOD" is a
serious hazard caused by tools left inside the aircraft after servicing. Tools
or other items can get tangled in control cables, jam moving parts, short out
electrical connections, or otherwise interfere with safe flight. Aircraft
maintenance teams usually have strict tool control procedures including toolbox
inventories to make sure all tools have been removed from an aircraft before it
is released for flight.
FOD costs the aerospace industry $4 billion USD per year and causes expensive,
significant damage every year to aircraft and parts and may cause death and
injury to workers, pilots and passengers.
Examples
Examples of FOD include:
Bird strikes: when an aeroplane flies into a bird, the impact can cause severe
damage to the fuselage or engine, or even directly injure those aboard the
aircraft if the bird strikes the aircraft in such a way as to enter the cockpit
and/or cabin.
Rock or other metal parts: Usually occurs when the aircraft is taking off or
landing. The intake suction from a jet engine is often powerful enough to suck
up loose material lying on the runway, and the winds created by a helicopter or
prop-driven aircraft's rotors can send such objects airborne, creating hazards
to nearby personnel.
Hail: can break windshields and damage or stop engines.
Ice on the wings
Dust or ash clogging the air intakes (as in sandstorms in desert operating
conditions or ash clouds in volcanic eruptions). For helicopters, this is also a
major problem during a Brownout.
Tools, bolts, metal shavings, etc. mistakenly left inside aircraft during the
manufacturing process.
All aircraft occasionally lose small metal parts during takeoff and landing.
These parts remain on the runway and can cause damage to tyres of other
aircraft, hit the fuselage or windshield ("canopy"), or be sucked up into an
engine. Although airport ground crews regularly clean up runways, the crash of
Air France Flight 4590 demonstrated that accidents can still occur: in that
case, the crash was caused by debris left by a flight that had departed only
four minutes earlier.
On aircraft carriers, "FOD walkdowns" are conducted before flight operations
begin. A line of crewmen walk shoulder to shoulder along the full length of the
flight deck, searching for and removing any foreign objects. The objects removed
are often also referred to as "FOD" although they haven't caused any damage. In
this context a more appropriate translation of the acronym would be "Foreign
Objects and Debris".
Jet engine design and FOD
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Modern jet engines suffer major damage due to even small birds being sucked into
the engine. The FAA (Federal Aviation Administration) requires that all engine
types pass a test which includes throwing a fresh chicken (dead, but not frozen)
into a running jet engine. The engine does not have to remain functional after
the test, but it must not cause significant damage to the rest of the aircraft.
Thus, if the bird strike causes it to "throw a blade" (break apart in a way
where parts fly off at high speed), doing so must not cause loss of the
aircraft. It is reputed that the chicken used in the tests is known in aviation
circles to be a specific size and is thus known as an "aviation standard bird".
Engine design that avoids FOD
Some Military aircraft have a unique design to prevent FOD from damaging the
engine. The design consisted of an S-shaped bend in the airflow so that air
entered the inlet, was bent back towards the front of the plane, and bent back
again towards the back before entering the engine. At the back of the first bend
a strong spring held a door shut. Any foreign object flying in the intake flew
in, hit the door, opened it, flew through, and then exited the aircraft. Thus,
only small objects swept up by the air could enter the engine. This design did
indeed prevent FOD problems, but the constriction and drag induced by the
bending of the airflow reduced the engine's effective power, and thus the design
was not repeated. However, many consider it an innovative solution to a
challenging engineering problem.
The Russian MiG-29 fighter has a special engine design to prevent injestion of
FOD during take-off from rough airfields. The front air intakes could be closed
and special inlets on the top of the plane temporarily opened. This would allow
enough airflow to the engine for take-off but reduced the chances of the engine
sucking up objects from the ground.
FOD damage examples
Air France Flight 4590
The crash of a Concorde, Air France Flight 4590, at Charles de Gaulle
International Airport near Paris was caused by FOD, in this case a piece of
titanium debris on the runway which had been part of a thrust reverser and which
fell from a Continental Airlines DC-10 that had taken off about four minutes
earlier. All 100 passengers and ten crew on board the flight, as well as four
people on the ground, were killed.
B-1A crash
In the late 1970s, the B-1A bomber began production and the military began
flight testing to determine its capabilities and limitations. Very shortly after
the aircraft was accepted by the military, there was at least one very high
profile crash, shortly after takeoff, from an airfield in North Dakota. The
cause of the crash was determined to be FOD. Specifically, the aircraft flew
into a flock of geese moments after it lifted from the ground. Many geese struck
the leading edge of the wings. Unfortunately, the primary, secondary, and backup
hydraulic system lines were all positioned within inches of each other in that
section of the wing. The bird strikes dented the aircraft skin, which in turn
dented the hydraulic lines and caused loss of pressure in all three systems. The
aircraft became uncontrollable and crashed.
It was determined that the aircraft design was the major factor in this crash,
not the birds. Any military jet should be expected to operate in unimproved
conditions and probably incur FOD during normal operation. Thus, the design
decisions were faulty in that (a) all three hydraulic systems were too close
together, (b) they were very close to the outer skin of the aircraft, and (c)
they had no extra shielding on the skin nearest this juncture point. The B-1A
was a short lived model. The B-1B incorporated many changes including rerouting,
separating, and shielding the hydraulics.
British Airways Flight 9
On 24 June 1982, British Airways Flight 9 on route to Perth, Australia flew into
a volcanic ash cloud over the Indian Ocean. The Boeing 747-236B suffered engine
surges in all four engines until they all failed. The passengers and crew could
see a phenomenon known as St. Elmo's fire around the plane. Flight 9 dived down
until it exited the cloud allowing the ash clogging the engines to come out. The
cockpit window was badly scratched by the ash particles but the plane landed at
Jakarta, Indonesia safely. The 747's paint had been scratched off at the leading
edges.
Wildlife and wetlands near airports
Significant problems occur with airports where the grounds were or have become
nesting areas for birds. While fences can prevent a moose or deer from wandering
onto a runway, birds are more difficult to control. Often airports employ a type
of bird scarer that operates on propane to cause a loud enough noise to scare
away any birds that might be in the vicinity. Airport managers use any means
available (including trained falcons) to reduce bird populations. While this may
seem cruel, the loss of human life from just one bird-related aircraft crash
could be significant. As such, it is necessary to take all possible precautions
to prevent such an accident from occurring. In other words, if such an accident
occurred, the major (likely 100+) loss of human life would greatly overshadow
the death of a single bird that happened to be sucked into the engine of an
airplane.
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