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SHORT DURATION ACCELERATION(SDA)?
- -<0.5 seconds.
- -usually unplanned
- -occur in
- extremely heavy landing
- unprepared surface,
- -ditching or Controlled Flight Into Terrain (CFIT).
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Tolerance to SDA?
- a) Magnitude and duration.
- b) Rate of onset. By decreasing the rate of onset of a deceleration, the magnitude of the rate of change of acceleration (or jolt) is decreased, thus increasing survivability.
- c) Direction of applied force. Gx is tolerated best as it provides
- the greatest area for a force to be spread over.
- d) Site of application:back and buttocks spread loads better than the limbs and head, forehead-withstand 200G,Nose/Cheeks-80G.
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If the body?s tolerances are exceeded?
- a) Tolerable: non?incapacitating eg. bruises and abrasions. These accidents are survivable.
- b) Injurious:
- c) Fatal: generally fighter/trainer accidents or CFIT where there are extremely high deceleration forces.
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CRASHWORTHINESS Injuries are therefore modified by local factors such as?
- - intrusion of objects,
- -loose objects becoming projectiles and
- -inadequate restraint.
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CRASHWORTHINESS OF AN Aircraft factors?
CREEP
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DESCRIBE CREEP PNEUMONIC?
- Container (C):
- -describes the compartment/cockpit space that surrounds the aircraft occupant.
- -perfect container would completely protect occupants from incursions of outside materials/debris during the impact. ?
- -Deformations of the container that reduce survivable space can cause injury and death,
- -typical roll-cage is designed to strengthen the container space to prevent this from occurring.
- -Penetrating bird strikes are a relatively common form of container compromise that causes accidents.
- Restraint (R):
- -Harnesses must prevent the occupants from being thrown around or ejected from the aircraft.
- -Seats must have sufficient structural integrity to hold the occupant fast, thus utilising the survival space available.
- Environment (E):
- -immediate environmental hazards.
- - Flail distance
- -chest decelerating into a restraint harness will experience a different injury force than a head decelerating into a control surface.
- During impact, poorly attached bulkhead?mounted equipment such as radar units or fire extinguishers can become detached and cause injury.
- Energy Absorption (E):
- -aircraft crushes in a controlled manner
- -absorbing energy during impact,
- -the aircraft effectively increases the distance (and time) through which the occupant decelerates,
- -decreasing the peak crash force experienced.
- Honeycomb construction,
- stroking seats,
- helmets,
- collapsible landing gear and
- landing strut systems are a few design features that can facilitate energy absorption.
- Post-crash Factors and Escape (P)
- -physical obstacles that impede escape or difficult-to-open emergency exits.
- -Toxic fumes
- -Un-stowed baggage or a direct fire threat can cut off escape.
- -life support equipment-correct use and function of
- -ejection seat
- -water survival gear
- -environment clothing
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DESCRIBE DYNAMIC OVERSHOOT?
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RESTRAINT SYSTEMS Features incorporated into the ideal restraint system include?
- a) Comfort - must fit all sizes and cater for safety equipment.
- b) Efficiency - reliably and restrain the occupant during impact.
- c) Ease of use - single hand operation for egress and no possibility of inadvertent release.
- d) Minimum restriction - able to carry out tasks and reach all controls
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HARNESSES Lap belt?
- -passenger type aircraft
- -simple operation
- - minimal restriction
- -high likelihood of flail
- -adopting the brace position (minimise the upper body flailing)
- -submarining improved with rearward facing seats.
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HARNESSES 3 Point Harnes?
- -helicopters for passengers
- -light civil aircraft
- -motor vehicles.
- -reduce upper body flail
- -limited lateral restraint.
- -allows submarining.
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HARNESSES 4 Point Harness?
- -most transport type aircraft.
- -good lateral support,
- -good crash restraint
- -still the possibility of submarining.
- -does not hold the occupant firmly on the seat under -Gz.
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5 Point Harness?
- -fighter/trainer aircraft.
- -secure during all aircraft manoeuvres, including -Gz,
- -maintain an ideal ejection position.
- -only system that effectively prevents submarining.
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Helmets will help to prevent the following problems?
- a) Skull fractures - linear, depressed or basal. Bone may flex up to 1cm without breaking but still enable brain injury. There is a much higher incidence of bleeding inside the skull and post?traumatic epilepsy if a fracture is present.
- b) Primary brain injury the brain accelerates/decelerates and rotates against bony structures and membranes.
- This results in bruising and swelling of the brain itself, often with small haemorrhages. Impact fore and aft occurs as the brain bounces off the skull, which is called a ?contre coup? injury. Direct trauma to the brain occurs if the skull is penetrated. Tearing of membranes and blood vessels leads to accumulation of blood clots within the skull increasing pressure and compression of the brain.
- c) Secondary brain injury - further damage to brain cells may occur due to swelling, loss of auto?regulation systems, hypoxia and hypercapnia (increased CO2) which often occur when consciousness is lost.
- d) Concussion - a poorly defined syndrome following head injury. There is usually no obvious structural damage but ongoing symptoms can last for weeks. There is probably disruption of function at a cellular level.
- e) Other superficial facial and scalp injuries, including lacerations, contusions etc.
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Head injuries may be minimised by using rearward facing seats, adding padding to aircraft structures, increasing survival space and wearing of helmets.
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Rearward facing seats are useful as the headrest provides head restraint in an impact situation. They also provide the best impact protection but are not as well accepted by passengers.
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The survival space (Container) can be designed to allow a flail area around the occupant minimising sharp protrusions in the area of the occupant or padding likely impact areas to improve survivability.
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Helmets offer protection in the following ways?
- a) Hard Outer Shell. A hard outer shell protects against sharp object penetration. A smooth outer surface also helps to deflect sharp objects and reduces the possibility of the helmet getting caught.
- b) Load Spreading. When the hard outer shell maintains its integrity in an impact it spreads the load over a larger area reducing the pressure exerted on any one part of the head. The suspension system inside the helmet aids to dissipate the energy.
- c) Increasing Stopping Distance. A layer of crushable material reduces the peak G by increasing the stopping distance between the object and the skull and increases the duration of any deceleration. Some helmets also dissipate impact energy by breaking up in much the same way as the ?crumple zone? of a car.
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The frontal bone of the skull (forehead) will break if subjected to an impact of?
100-200 G.
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A helmet padding?
-15mm reduce a 500G to 83G which is survivable.
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To provide maximum helmet impact protection?
- a) Attenuation of Impact Energy
- -polystyrene foam) raise tolerance 80-200G
- - stopping distance 3mm skull no protection, addinh styrofoam 25mm to 10mm extra 15mm stopping distance.
- -6x more stopping therefore 6X G force.
- b) Rotary impact forces brain rotation-shearing stress
- -should not offer a high friction surface
- -any objects attached to helmets that can catch and cause it to rotate should break off easily.
- c) Dynamic Overshoot.
- d) Protection against penetration is a function of the hard shell (and the Visor/Mask for the face). Penetration of the skull by smaller objects is possible from forces much less than required by blunt trauma from a larger smoother surface, so this is essential in the overall protection.
- e) Retention: good fit, ear cup tension, and chin straps.
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Helmets after any impact?
- -discarded
- -are ?single use? items.
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Desirable characteristics in helmet design include THE IDEAL HELMET?
- a) Weight ? lightweight helmets reduce neck strain, particularly when conducting high G manoeuvres.
- b) Size ? compact to prevent interference of movement.
- c) Shape ? a smooth exterior to prevent snagging. Helmet protrusions must break off easily to prevent whiplash
- of the neck.
- d) Comfort ? Helmets by their very nature must be a snug fit, so comfort is imperative. Wearing of helmets for long periods can result in ?hotspots? if they are not fitted or designed correctly.
- e) Good fit ? enables helmet to remain on the head during a crash or ejection.
- f) Ease of use ? it must be easy to don and doff, even in the cockpit.
- g) Visibility ? should not interfere with vision whilst providing eye protection from birdstrike/glare.
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FUNCTIONS OF A HELMET?
- a) Protects from bird strike;
- b) Protects eyes from canopy clearing mechanisms and other ejection related eye trauma (explosive cords shower the occupant in molten lead spatter and the whole process of ejection exposes the aircrew to canopy fragments either by destruction of the canopy or if that fails, as the seat penetrates the canopy. Lead in the eye can precipitate iritis and polycarbonate fragments in the eye have obvious implication as an intra ocular foreign body ? they don?t show up on X?ray either!). The soft lens cover should ALWAYS be stuffed in the gap above the visor to protect from lead spatter and canopy fragments;
- c) Protects your eyes and face from windblast injury on ejection;
- d) Protects from glare/bright light. This is both for comfort and visual performance;
- e) Protects eyes from harmful UV radiation (just like a pair of sunglasses). UV light can cause cataracts in the long term. Polycarbonate, from which the visor is made, has quite good properties for blocking UV and blue light which causes this, so even a clear visor decreases transmission of these hazards considerably. Extra filters and coats can further aid this function. Tinting increases comfort as well as protecting the eyes by reducing overall light transmission into the zone where visual performance is highest. Protection from bright light by the tinted visor also stops bleaching of photopigments which improves night vision;
- f) Provides an extra 2 or 3 dB of noise attenuation by improving the overall integrity of the outer shell of the helmet; and
- g) In conjunction with the oxygen mask will assist in face and eye protection from flash fire.
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Checking helmet fitting?
- a) at least one visor down, and two whenever possible,
- b) chin strap securely fastened,
- c) noise test for hearing protection, and
- d) ensure the helmet does not rotate on the head.
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