1. AIRCRAFT ACCIDENT INVESTIGATION MOOC CRASH SURVIVABILITY

2. OVERVIEW Survival Factors Survival Factors Investigation Emergency Rescue Operations

3. SURVIVABLE CRASH A crash is deemed survivable if:  Cockpit and cabin structure remains relatively intact providing sufficient living space for occupants,  Deceleration forces experienced by the occupant do not or should not exceed the survivable limits of human “G” tolerance.  Post-accident environmental factors allow egress or rescue before conditions become intolerable. If an occupant is thrown clear and survives, this does not classify the accident as survivable United 232 Crash Site, Sioux City, Iowa, July 19, 1989

4. NON-SURVIVABLE CRASH Cockpit and Cabin structure is destroyed by impact so that livable space is reduced below what is required. May occur if:  Hull is crushed, or  Projections intrude on the living space Deceleration forces exceed those of human tolerance Post-crash environment so severe that egress or rescue is impossible United 718/TWA 2 Midair Collision over Grand Canyon, June 30, 1956

5. CRASHWORTHINESS Since 1960s, investigation has focused on crash survivability NASA-Langley had aircraft drop test area to test crash survivability on general aviation aircraft and commercial aircraft up through Boeing 737 Investigations and tests led to improvements in fuel systems, seat designs, and aircraft structures NASA Langley Full Scale Aircraft Crashworthiness Test

6. CRASHWORTHINESS (CONT) Big questions: Was the crash survivable? Why or why not? If the crash was survivable, were there occupants who did not survive that should have survived? Why? If the crash was not survivable, were there occupants who did survive that should not have survived? Why? Given the dynamics of the crash, what could have been done to improve crash survivability? What improvements in aircraft or appliances should be made to enhance crash survivability?

7. CRASH DYNAMICS How the aircraft hits the ground What happens to the aircraft and its occupants upon impact. Every landing can be considered a controlled crash Crash survivability depends on the amount of the deceleration force and the amount of livable space within the cabin.

8. CRASH DYNAMICS (CONT) Pre-crash factors influencing crash dynamics:  Velocity  Impact angle  Terrain factors Given these initial conditions, it is possible to calculate the “G” forces experienced by occupants throughout the deceleration Tree and ground scarring by aircraft during descent

9. THREE DIMENSIONAL FORCES Crash loads in response to crash generated decelerations have three dimensional vectors. Structural requirements to withstand these loads are expressed in terms of longitudinal (X or parallel to the fuselage) axis, lateral (Y or parallel to the wing), and vertical (Z or up-and-down) axis requirements. The forces are not equal along these axes Deceleration injuries depend on maximum “G” loading, duration of “G” loading, and direction of “G” loading

10. FORCE VECTOR AXES Aircraft Axes Human Axes Forces exerted on the aircraft and the occupants are measured along the axes shown in the figures above. Vector analysis is used to resolve forces along each axis.

11. IMPACT ANGLE Impact angle varies as a function of terrain angle, flight path angle, and deck angle (angle of attack). Figures show variations in impact angle as these factors are varied.

12. DECELERATION FORCES Deceleration forces (G) on the aircraft depend on:  Initial velocity (V o )  Final velocity (V f )  Stopping distance (S)  Time (t) Deceleration forces felt by the occupants depend on:  G absorption characteristics of the aircraft structure  G absorption characteristics of the restraint system

13. RECTANGULAR DECELERATION PULSE Constant deceleration rate Constant G force throughout deceleration G = (Vo) 2 /64.4S t = (Vo)/32.2G

14. TRIANGULAR PULSE 1 Constantly changing deceleration rate Constantly increasing G during deceleration G = 4(Vo) 2 /96.6S t = (Vo)/32.2G

15. TRIANGULAR PULSE 2 Constantly changing deceleration rate Constantly decreasing G during deceleration G = 2(Vo) 2 /96.6S t = 2(Vo)/32.2G

16. TRIANGULAR PULSE 3 Constantly changing deceleration rate G initially increases then decreases G = (Vo) 2 /32.2S T = 2(Vo)/32.2G

17. SPEED IS NOT THE KILLER? The danger lies in how it is dissipated. A common misconception in this respect is that it takes hundreds of feet of obstacle-free terrain to make a survivable crash landing. Theoretically, it would take only 20 feet to stop a 20 -G deceleration, if the stopping force could be applied uniformly over this distance. The same uniform deceleration (20 Gs) would bring an aircraft to a stop from 60 knots in a distance of about 2.5 meters. The arresting gear of aircraft carriers and runway barriers shows how this concept can be applied under controlled conditions.

18. STRESS-STRAIN DIAGRAM Elastic range – as stress increases, strain increases, the material deforms, but will return to its original position when the stress is released Plastic range – as stress increases, strain increases, the material deforms, and will not return to its original position when stress is released – permanently deformed Yield Point – load at which deformation becomes permanent – shift from elastic to plastic deformation – usually used as maximum load factor Failure/fracture point – load at which the material fails

19. STRESS-STRAIN DIAGRAM (CONT) Metal under stress behaves according to the Stress-Strain curve for that particular metal.

20. CREEP INVESTIGATION METHOD Container Restraint Energy Absorption Environment Post Crash Factors The first 4 factors pertain to the dynamic portion of the crash itself, from the initial impact with terrain, the associated deceleration forces, and the deformation and dislocation of aircraft structure and components. Final factor deals with occupant egress and rescue.

21. CONTAINER Must provide a living space for occupants and resist penetration of objects into the living space Engineers design the hull to withstand crushing and penetration Accident investigation focuses on origin of injuries – what did the passengers impact that caused their injuries/deaths? Investigator must look for “elastic deformation”

22. CONTAINER INTACT Photo Courtesy of Jeff Jennings

23. INSUFFICIENT LIVING SPACE AND WING PENETRATION INTO LIVING SPACE Photo courtesy of Dr. Katherine Moran

24. INSUFFICIENT LIVING SPACE Photos courtesy of Jeff Jennings

25. RESTRAINTS Investigator presupposes restraints are used and maintained properly. Improper use invalidates protective qualities. Restraints must be able to prevent occupants from being thrown against the container or having objects propelled toward them. Restraints must be able to prevent injuries at force levels expected during the most severe, survivable crash. Restraint components (belts, attachments, connectors, etc.) must be matched for capability and rated load factor.

26. RESTRAINT SYSTEMS PHOTOS COURTESY OF DR. KATHERINE MORAN

27. RESTRAINTS (CONT) Shoulder Harness – Limits upper body ability to rotate forward and down – Five point harnesses are the most protective, although rarely seen outside of military aircraft. Crotch strap – not used often–resists upward movement of lap belt caused by shoulder harness pulling it and forces of body moving Web width – larger is better, because it spreads the force over a wider area –  Minimum recommended - 2.5” for lap belt  Desirable 4” for lap belts, 2” for shoulder straps

28. SEAT LEGS, CONNECTION, AND TRACK DEFORMATION

29. ENERGY ABSORPTION Deceleration force attenuated or amplified by the seat and the structure – the more energy the structure absorbs before it gets to the occupant, the less the occupant will have to absorb – increased survivability Soft deep seat cushion can amplify vertical G load Deep seat cushion that deforms only under high load can reduce vertical G load Energy absorbing structures can reduce chance of injury and increase probability of survival Rigid structures can transmit high deceleration forces directly to the point of impact to the human

30. ENVIRONMENT Flail zone-Area of the living space that may be hit by parts of the occupant’s body not secured by the restraint systems (head, arms, legs) Assume there will be violent flailing within minimum space. Delethalize the volume through which unrestrained extremities can travel (flailing envelope) Remove or pad obstructions within the flailing envelope Flying debris within the aircraft.

31. POST-CRASH CONDITIONS Survivors must be able to reach emergency exits, activate them, and get through them quickly and safely Post crash fire is the most significant hazard – fuel, oxygen, ignition sources readily available in the crash Fire can kill directly Fire also causes toxic fumes and smoke as well as heat

32. POST-CRASH CONDITIONS (CONT) Designer’s #1 priority is preventing post-crash fire  Fuel lines and tanks should be in least vulnerable location  Cabin materials  Fire retardant clothing  Smoke hoods Carry on baggage big problem  Weight and balance calculations based on 10 pound carry on per person – low estimate  Overhead bins usually stressed to hold 80-125# of baggage – overloaded – difficult to restrain  Overheads materials could contribute to a post-crash fire and may open and release contents on impact

33. POST CRASH FIRE

34. CRASH INJURIES Crash injuries, like aircraft damage, are the result of the violence generated by sudden stoppage and Two broad categories of injuries  Contact Injuries  Deceleration Injuries

35. POST CRASH COMPLICATIONS Injuries resulting from post-crash complications form a separate category. In the event of fire or during ditching, fuselage distortion and final aircraft attitude may interfere with the timely evacuation of the wreckage. Although this hazard can be controlled to some extent by the design of fuel systems and emergency exits, it is often the pilot's landing technique and his knowledge that govern the post-crash survival aspects.

36. CRASH/FIRE RESCUE FACTORS Airport Emergency Plan (AEP) outlines response to aircraft emergencies and accidents Minimum firefighting equipment required at airports established by FAR Part 139 based on average daily departures and aircraft length for scheduled air carrier operations at the airport AEP should outline fire, rescue, medical, and security responses for aircraft accidents on the airport and in the surrounding area May establish mutual aid agreements with other local agencies to provide support during accidents.

37. CRASH/FIRE RESCUE FACTORS FAR Part 139 establishes emergency response time requirements Firefighter/rescue priorities:  Rescue survivors  Control and extinguish fire  Recover human remains Rescue efforts may damage or destroy evidence Investigator must be able to differentiate between crash damage and rescue damage

38. SUMMARY Crash survival analysis and testing has improved crash survivability through enhanced aircraft and seat/restraint system design Crash survivability depends on maintaining sufficient space within the accident aircraft to support life, keeping deceleration forces below those fatal to humans, and ensuring immediate occupant egress and emergency response Crash survival investigation uses CREEP Method as a systematic means to assess all survival factors Airport Emergency Plans outline individual airport emergency operations and requirements in response to airport emergencies and accidents.