Role of Aviation Accident Pathology in
Fatal Aircrash Investigation
by
AVM SK Adaval AVSM VSM (Retd)

ABSTRACT

AVIATION ACCIDENT PATHOLOGY
Pathology, in its wider perspective, entails the study of mechanism of suffering and, therefore, Aviation Pathology should technically embrace all aspects of stresses encountered in aviation. However, this will enlarge the scope to such an extent that even studies on adverse effects of heat, vibrations, gravitational forces etc will come under the realms of Aviation Pathology making it too unwieldy. Mason has, therefore, designated this field as ‘Aviation Accident Pathology’ and defined it as “A comprehensive study of aviation fatalities whereby medical history of the individual and findings at autopsy can be correlated with environmental factors, structural or other damage to aircraft and use or abuse of the safety equipment, so that a complete picture of the accident may be formed.”

DEVELOPMENT OF CONCEPT OF AVIATION ACCIDENT PATHOLOGY
It will be interesting to recall that in 1908, Lt. Thomas Selfridge of US Army was killed while flying with one of the famous Wright brothers. Autopsy revealed that death was due to fractured skull. Taking this into account, Lt. Henry Arnold, who was entrusted with further flying wore a football helmet as a precautionary measure. This was the first instance in history of Aviation Pathology that the knowledge gathered by medical investigation was used for preventive purpose.

In the years to come there was no major role played by the medicals in this field, except some sporadic but useful reports by workers like Gilsen, Hass and Teare etc who recommended correlation of injuries with crash factors to suggest preventive measures. However, little was achieved beyond describing and tabulation of the injuries in great details.

Contribution, a Pathologist could make was dramatically demonstrated during the investigation of British Comet disasters over Mediterranean in 1954. As the wreckage of aircraft was not available, investigating doctors inferred from the autopsies and other simulating experiments, that occupants suffered a violent upward and forward motion and deduced that injuries could be due to explosive decompression. They also showed experimentally the mechanism of injuries due to impact on sea. This, finally, established the role of Aviation Accident Pathology and logical outcome was formation of Joint Committee of Aviation Pathology (JCAP) between USA, UK and Canada. Soon, departments of Aviation Accident Pathology were established in other countries too. In India, an Aviation Pathology Cell was set up at AFMC Pune in 1950 which moved to Air Force School of Aviation Medicine, Bangalore, in 1968. A Department of Aviation Toxicology was added in 1971. Autopsies, histological and other investigation were centralised here and correlation with crash factors was undertaken.

ROLE OF PATHOLOGIST
Aim of autopsy as required by international bodies is not only to ascertain the cause of death but also to evaluate the effects of environmental stress of flight on the fatalities, to sequence the injuries for correlation with events during accident and to look for any pre-existing diseases or factors which could cause sudden incapacitation.

Certain guidelines for pathologist were laid down viz., he should familiarize himself with the type of aircraft involved in the accident, should acquaint himself with the information on circumstances of accident, health status of aircrew and state of safety equipment. He should also be aware of ‘recurring themes of injuries’ which are characteristic of aviation, so that he can specifically look for them.

AUTOPSY
Autopsy must be performed as soon as possible. As many aircrashes occur at difficult terrains, it may not be possible to remove the bodies to a suitable mortuary. It is, therefore, advisable to take the autopsy to the body - rather than taking body to the autopsy. Suitable portable autopsy kits help in performing ‘on the spot autopsy’, which must be done on all deceased aircrew members believed to be involved in the essential flying activities. In passenger aircraft accidents, autopsy must be performed on all casualties as this will give some idea about the events prior to or during the accident and also help in identification. Liberal photographic cover must be used to record the position of body, state of clothing, relation with aircraft parts and to document the autopsy findings.

With medical history of aircrew in background, Aviation Pathologist undertakes a comprehensive and meticulous autopsy. Though there is nothing spectacular about this, it is a matter of ‘what one knows - one sees’. There are certain injuries peculiar to aviation which have repetitive pattern. Pathologist must look for them.

Radiological examination of the body must be undertaken to detect unidentified fractures and to visualise any metallic / foreign bodies embedded in the soft tissues especially when blast is suspected. They also help in establishing the age in case of unidentified bodies.

Toxicological examination of biological samples for routine detection of Carbon Monoxide & alcohol is undertaken in addition to detection of drug metabolites if suspected.

Histopathological examination must be undertaken irrespective of paucity of tissue or state of decomposition. It is seen that many a times, useful information is forthcoming from these findings.

Special investigations like detection of diatoms especially in cases of suspected drowning are to be undertaken as and when required.

CORRELATION
Conforming with Mason’s definition, medical history of aircrew findings at autopsy must be correlated with environmental factors, structural and other damage to aircraft and use or abuse of the safety equipment to try and form a picture of the accident.

At the time of crash or just prior to it, the pilot has an internal environment inside his body which may be vitiated by presence of any organic disease to cause sudden incapacitation or may have toxic substances like drugs or alcohol in his body. The external environment surrounding his body may act adversely like presence of fumes, fire, hypoxia and hostile `G’ forces.

Evidence of structural damage comes through technical examination of wreckage and factors relevant to human performance are taken into consideration. Safety equipment consists of complete oxygen system, flying clothing helmet and even ejection seat. An appraisal of this equipment is pathologist’s duty to detect any snags in it or to ascertain the reason as to why the pilot failed to use this.

RECURRING THEMES OF INJURY
There is a long list of recurring themes of injuries encountered in aviation accidents. In the external appearance of the body, punctate marks, burns, chemical coagulation and pigmentation have to be seen in detail. There is typical laceration at angles of the mouth and eyes which is characteristic of wind blast effect especially during escape. In the internal organs, contusion of bowel wall and mesentry indicates lap-belt injury, soot particles in trachea and lungs show survival in smoke or fire, rib-marking on the lungs suggest sudden blast effect and rupture of diaphragm may result during escape. There are certain vulnerable spots in the heart and aorta where laceration can result due to decelerative forces. Explosive fracture of skull occurs due to fire which can be distinguished from traumatic fracture - as in case of former, the skull bones separate from lines of sutures. When there is sudden deceleration the forward movement of head (whiplash) causes typical radiating fracture lines from foramen magnum. In sudden forward jack-knifing movement of body due to intense forward deceleration, there is ‘greenstick’ like fracture on the posterior table of sternum, while anteriorly there is no injury. Fracture of vertebrae and condition of intervertebral discs provide useful information of the direction of the forces operating in relation to bodies. Fracture of ischial tuberosities should be seen in cases of escape. Separation of pubic symphysis occur due to pull of harness. Presence of haemorrhagic and bloodless fractures in the same body indicate that some injuries were sustained when the circulation was intact.

HISTOPATHOLOGICAL EXAMINATION
While highlighting some of the recurring themes of aviation injuries it is emphasised that histological examination has time and again proved its importance. This exercise must be undertaken irrespective of paucity of tissue or state of decomposition. It is unwise to dismiss this investigation by calling it a futile academic exercise especially in cases when cause of accident is obvious. We have grouped histological findings according to whether they throw any light on causation of accident or not. They are :-

Group 1 - Consists of those features which more or less establish cause of accident, as encountered in a pilot who collapsed on the controls and histologically haemorrhage in the totally occluded left coronary artery was found.

Group 2 - Where histological findings give strong suggestion of human failure due to sudden incapacitation but have to be assessed in the light of circumstantial evidence.

Group 3 - Findings which do not give a direct indication of cause of accident, death or human failure - but help in reconstruction of the accident, and

Group 4 - Findings which are purely of an academic nature and provide an insight into traumatic pathology.

NEW AREAS OF RESEARCH
Research in this field is unending. More work is being done on timings of the injuries espcially electron microscopic changes in the cells during early death. Time since death, antemortem vs postmortem changes and Pathology of Fear are other areas. However, if we restrict ourselves to applied aspects, more efforts are needed to develop computer software for injury analysis vis-a-vis crash factors, develop the facilities to detect various drug metabolites in the tissues, special analytic procedure for soot particles, phase contrast microscopy to detect diatoms and to undertake DNA typing for differentiating between human and avian blood - and also for purposes of identification.