Forty Years of Fatal Accidents -A statistical analysis by By Carl Nilsson.

Forty Years of Fatal Accidents -A statistical analysis by By Carl Nilsson.

Forty Years of Fatal Accidents -A statistical analysis by By Carl Nilsson.

August 9, 2017 By Mark Smith
This article gives a brief summary of four reports on fatal accidents from the Australian Transport Safety Bureau (ATSB) covering the years 1975 through to 2014, including some recent data...

This article gives a brief summary of four reports on fatal accidents from the Australian Transport Safety Bureau (ATSB) covering the years 1975 through to 2014, including some recent data from Recreational Aviation Administration Organizations (RAAOs).  The data were examined to seek trends in medical incapacitation, the number of fatalities per fatal accident and the number of passenger (PAX) fatalities.   Fatal accidents are defined as those in which at least one person has died.  Fatal accident rates per million flying hours are higher for the RAAOs than for fixed-wing General Aviation (GA) and the proportion attributed to medical incapacitation is higher.  However, the number of passenger or non pilot-in-command (non-PIC) fatalities, which should be of greater concern to CASA, is significantly lower for Recreational Aviation Australia (RA-Aus) aircraft due to the seating limit of two. There have been no third-party (ground) fatalities from private (GA or RA-Aus) crashes.  Table 3 gives some context for those evaluating the responses to the recent CASA AvMed discussion paper1.

 

  1. The ATSB Reports

 

Most accident statistics are reported in terms of events or accidents per so many hours flying time – e.g. accidents per 100,000 or one million flying hours.  This does not convey much to the casual reader or the General Practitioner.  Before signing off on a Recreational Aviation Medical Practitioner’s  Certificate (RAMPC) application or Ausroads certificate, the GP might be thinking along the lines “what are the chances of this person collapsing and killing themselves (and others) in the next twelve months?”    More to the point: “how many others are they likely to kill or injure?” That is what I wanted to gather from four ATSB reports covering the years 1975 through to 2014 and the recent data in the submission by RA-Aus to the AvMed discussion paper. A fatal accident can be caused by accidents of severity varying from apparently minor to catastrophic.

 

1.1     The Newman report on incapacitation accidents, 1975- 2006, ATSB B2006/0170, Jan 2007.

 

This report by Newman (2007)2 showed firstly, that the 98 inflight medical events listed over the 31 years 1975 – 2006 appeared to show a strong decline as years progressed, but many of the occurrences were airline related and were either gastrointestinal or related to smoke and fumes.  This decline may not have applied to GA.  About 60 events were associated with the GA Private+Business+Sports category (which we can call GA-PBS).  There were 10 fatal accidents (associated with medical incapacitation).  All involved single-pilot operations. In these, 24 fatalities were recorded.  There was only one survivor (the wife of the accident pilot), who sustained serious injuries.  The number of fatalities was weighted by eight deaths in one fatal accident due to pilot hypoxia, which I have omitted because it does not relate to a medical precondition.    Of the remaining nine fatal accidents, five were listed as due to heart attacks, two from loss of consciousness,  one from respiratory illness and one from neurological impairment.  The averages over this 30-year period for GA-PBS comprised about 0.3 fatal accidents per year due to medical incapacitation and a mean fatality rate of 1.8 fatalities per fatal accident.  In these nine fatals, there were 16 fatalities, all pilots-in-command (PIC) died and there was one seriously injured survivor. so the rate of fatalities per fatal accident was 1.0 for PICs and 0.8 for non-PICs.  The average number of persons on board (POB) was 1.9 and the most common (modal) value was 1.

Most importantly, Newman concluded that “The majority of pilot incapacitation events recorded by the ATSB do not involve a chronic or pre-existing medical condition. That is, they are largely unforeseeable events, often involving acute illnesses or injury.

 

1.2     “General Aviation Fatal Accidents – how do they happen?” 1991-2000, ATSB B2004/0010.

 

This review on GA fatal accidents is very comprehensive.  In the decade 1991-2000 there were 163 fixed-wing (aero) and 52 rotary-wing fatal accidents3.  Just 6 of these 163 aeroplane fatal accidents were due to pilot incapacitation. That is 3.7%, meaning 96% were due to other causes.   Of the 215 total, approximately 82 percent of fatal accidents were in the controlled flight into terrain (CFIT), managed flight into terrain (MFIT) or uncontrolled flight into terrain (UFIT) groups.  The first and obvious conclusion is that tightening medical standards cannot do much to decrease the fatal accident rate, which, overall is mostly due to pilot error (CFIT and UFIT) of one form or another.

 

The six fatal aeroplane accidents due to pilot incapacitation caused 19 fatalities.  Presumably one of these accidents involved the case of pilot hypoxia referred to above in the report by Newman (for the period 1975 – 2006) which took eight lives.  If we remove this from the statistics (because the health of the pilot at take-off was irrelevant) we have five fatal fixed wing accidents due to pilot incapacitation taking 11 lives.  This gives a ratio of 2.2 fatalities per fatal accident.   In the broader picture for this period, considering all fatal (aero) accidents, there were 331 fatalities from 163 accidents giving a figure of 2.0 fatalities per fatal accident; 162 crew and 166 PAX died and two glider pilots and one third party were killed.

 

The figures for number of POB killed and the breakdown for PAX chances of survival are not given separately for fixed-wing and rotary-wing aircraft, so these must be considered together.  The fatalities to fatal (accident) rate for rotary-wing was 82/52 = 1.6  and for both classes of aircraft together was 413/215 = 1.9.   Where there was more than one POB in single aircraft fatal accidents , 83% of POB died.  In 69% of such accidents (with more than one POB), all aboard died.  These key figures when considering policy changes regarding risk.  They do not include the solo accidents, which were 39% of the total and in which, by definition of a fatal accident, the PIC died. In all the fatal accidents, 21 crew survived from a total of 206 flight accidents, of which 125 had at least 2 POB.  This figure is generally consistent with the notion that an individual crew member has about a 10% chance of surviving an accident that is fatal for at least one crew member.  It comes about by the definition of a fatal accident.  If you consider accidents of such severity that the independent chance of each crew member being killed is 90%, then (with two crew side by side) there is a 99% chance of at least one being killed, making it a fatal accident.  For the lucky 1% (with two POB), it is not a fatal accident.  Regardless, as the ATSB observed, “the probability of coming out of a fatal accident unscathed is low.

 

Eighty per cent of fatal accidents resulted in either one or two fatalities.  39 % were solo accidents;  I estimate nearly 30% of the accidents would have had two POB.   Some fatalities would have come from accidents with more than two POB, in which there were one or more survivors.  The highest number of fatalities in a single accident was nine.  Unfortunately, none of the referenced reports list the fatality numbers according to the number of POB and it is not possible to accurately recover the POB from the published data.  A fatal accident is not one of any particular severity.  The more POB, the less severe an accident has to be to result in at least one death.

 

 

1.3     “Aircraft accidents involving private operations, 2001 to 2005”, ATSB 20070099, Final, 2007.

 

This report4 gives us the activity data for each year over a five year period, which was surprisingly (to the author) constant.  Restricting this discussion to just the fixed-wing data: from 26 fatal accidents, only two were related to medical/injury.   The number of VH- aircraft showed a 5% rise over this period, with a mean of 8955; the mean number of private pilot licence holders (aircraft) was 15,885 PPLa and the mean hours flown was 357,931 hr.  See Table 1.

 

Year Aircraft PPLa Hrs flown Hrs/Aircraft Hrs/PPLa
2001 8,762 N/A 364,152 41.6
2002 8,792 16,519 378,673 43.1 22.9
2003 8,934 16,330 347,035 38.8 21.3
2004 9,071 15,079 351,146 38.7 23.3
2005 9,218 15,612 348,647 37.8 25.5
Mean 8,955 15,885 357,931 40.0 22.4

 

Table 1.  Fixed-Wing activity 2001-2005 (from ATSB Rep. 20070099)

 

The near-constancy of the number of aircraft, number of pilots and hours flown over the five years makes it easy to convert the number of any events per hours flown to rates per aircraft-year or PPLa-year.   Twenty six (26) fatal accidents over that period from all causes give rise to the following rates, where 100,000 PPLa-years is a composite unit meaning 1000 PPLa licences for each of 100 years or10,000 PPla multiplied by 10 years – similarly for Aircraft-years:

 

33 per 100,000 PPLa-years

58 per 100,000 (Reg.) Aircraft-years

18 per million hours flown.

 

There were just two fatal accidents due to medical incapacitation, so the rates above can be divided by 26/2 = 13 to obtain the equivalent rates for fatal accidents due to medical incapacitation over the five years, i.e. 1.4 fatal accidents  per million hours flown.  The record shows a rate of 0.3 per year due to incapacitation for aeroplane GA 1991-2000 and 0.4 per year for 2001-2005, which figures are surprisingly close, considering the few accidents.

 

1.4       “Aviation Occurrence Statistics 2005-2014”, ATSB AR-2015-082 Dec 2015

 

The report5 for the decade 2005-2014 lists, for the General Aviation Private+Business+Sports (GA-PBS) category, 103 aircraft associated with a fatality and 168 fatalities , giving rise to a rate of 1.63 fatalities per fatal accident (incl. rotary wing).  Flying hours were not available for year 2014 and accident rates are given for the preceding nine years.  We assume that flying hours were reasonably uniform for each year, as they were in the preceding period 2001 -2005, in order to average the rates of accidents over the nine years.  This gives a figure of 18 fatal accidents per million flying hours, the same as the rate for fixed wing aircraft for 2001-2005.

 

In GA Sports (Report Table 20), there were 24 fatalities from 20 fatal accidents, which is a rate of 1.2 fatalities per fatal accident.  This is lower than figures seen for previous broader categories and reflects the smaller seating capacity (presumably 2-seat or single seat.) The number of hours flown is not given.

 

This report is the first to include aircraft registered with Recreational Aviation Administration Organisations (RAAOs).  Report Table 22 lists 98 fatalities from 82 fatal accidents over the decade, again giving a figure of 1.2 fatalities per fatal accident.  These aircraft are all limited to two seats.  The mean fatal accident rate over the years through 2013 (9 years) was 27 fatal accidents per million flying hours, which figure is 50% higher than that for GA-PBS.    During the years 2011-2014 (to use in Table 3 with RA-Aus data) there were 48 fatalities from 38 fatal accidents which is a rate of 1.3 fatalities per fatal accident.

 

The proportion of the total of 82 fatal accidents that could be attributed to medical incapacitation is not listed.

 

1.5       Recreational Aviation Australia Ltd Response (Dec 2016) to the Avmed Discussion paper

 

In their response6 to the CASA Avmed discussion paper, RA-Aus published the following table:

 

Year Fatal Accidents Medically related
2011 6 0
2012 3 1
2013 11 2
2014 6 1
2015 9 2
2016 6 2
Mean 6.8 1.3

 

Table 2.  RA-Aus Fatal Accidents 2011-2016

 

RA-Aus have listed 26 fatal accidents during the four year period 2011-2014 as their component of 38  listed for all RAAOs for the same period by ATSB in their report ATSB AR-2015-082.  The RA-Aus medically-related component is listed to be about 20% of the total of fatal accidents, which is markedly higher than the corresponding figures for GA, which have been in the range 4% for GA from the first report3 for 1991-2000 to 8% (from just two such accidents) for fixed-wing aeroplanes for the period 2001-20054.

 

 

2          Summary of statistics

 

What do we call the person in the front right-hand seat of an aeroplane?  If we call them crew we presume them well informed as to the risks.  More often than not in sports and recreational aircraft that person is a passenger (PAX) rather than a crew member, although he or she suffers just the same risk as the pilot-in-command (PIC) in any accident.  At this point, we will just call them non-PIC.

 

Table 3 summarizes some of the statistics contained in and derived from the ATSB reports and RA-Aus figures.  I have used the following labels: aero = fixed-wing, PBS = Private+Business+Sports, Med.Inc = Medical Incapacitation, non-PIC = not the Pilot in Command, Acc = Accident.

 

 

Period Category All Fatal Acc./Yr

 

All Fatal Acc./106 Hrs Med.IncFatal Acc./Yr All Fatal-ities/Yr All Fatal-ities/ Fatal  Acc. All non-

PIC  Fatal-

Ities/Yr

 1975-2005 GA-PBS 0.3 1.8
1991-2000 GA-aero 16 11 0.6 33 2.0 18
2001-2005 GA-P aero   5 18 0.4 11 2.2   6
2005-2014 GA-PBS 10 18 17 1.6   7
2005-2013 RAAO   8 27 10 1.2   2
2011-2014 RA-Aus   7 42 1.4   9 1.3   2

 

Table 3.  Summary of fatality statistics 1975 – 2014.   (The hours-flown data for RA-Aus were taken from the annual report for 2016 and corrected 30/07/2107).

 

One can note that fatal accidents/year show no distinctive trend, but fatal accidents/106 hours are higher for RAAOs and RA-Aus in particular.   RA-Aus only flew about 28% of the hours that GA-PBS flew over the years 2011-2014 for which we have corresponding data.  Unfortunately the ATSB data for 2005-2014 do not give the number of fatal accidents attributed to medical incapacitation.

 

The data (Tables 2 and 3) do seem to indicate that the present regime of medical self-certification for RAAOs have increased the proportion of fatal accidents due to pilot incapacitation.  This might be expected, but is it something that CASA should be concerned about to the extent of regulation?  Here the author seeks guidance from CASA’s charter and its proclaimed policies.  Its charter is to “enhance and promote the safety of civil aviation, with particular emphasis on preventing aviation accidents and incidents7.  Again, we must point to the aim of reducing all serious accidents from whatever cause and not focus unduly on the small number due to medical incapacitation.  This conclusion is amplified by the finding of Newman2 and others (e.g. aviation medical specialist P. Froome8) that inflight incapacitation was and is in many cases unforeseeable by medical testing.  In 2007 CASA promulgated Policy CEO-PN001-2004, which included (in Section 2.1)9 that it would base its priorities on the estimated degree of public risk.  The lowest priority was given to “Aviation Activities involving Crew and/or Participants”.  CASA’s role would be that of “General oversight and compliance assurance for flights in which participants “…. have explicitly accepted those risks (non-acceptance includes choosing not to fly).

 

It would seem from that published statement that CASA intended either to put the issue of recreational PIC and crew fatalities due to medical incapacitation outside its regulatory jurisdiction or at a low priority.   There is still an argument for maintaining some concern over participant fatalities, given that sometimes participants might include minors in particular and/or partners who have an unwarranted trust in the PIC.  The ATSB figure (1991-2000) that all POB died in about 69% of fatal accidents for which POB was more than one sounds a cautionary note.

 

The degree of risk undertaken by non-PICs can be estimated from the overall fatality rate.    In Newman’s study of fatal accidents 1975-2005 he recorded that in the ten fatal accidents due to pilot incapacitation, all PICs died.  In the nine fatal accidents due to medical incapacitation considered here from his study (see earlier for details) sixteen people died and the accident/fatality rate was 1.8.  That is the rate listed in Table 3 because I do not know the figure from all accidents.  In the 1991-2000 data3 the proportion of solo fatal flights was about 40%.  For a solo accident to be listed as a ‘fatal’, the PIC fatality rate will be 100% (except for rare ground accidents).  In a fatal accident with at least two POB, the PIC fatality rate can be expected to be close to 90%.   Hence we can expect an overall PIC fatality rate for fatal accidents of around 0.94.  That is the figure used for all the data in Table 3.   The non-PIC fatality rate on that basis is given in the last column of Table 3 and that is the figure I deem most important and relevant to regulatory review.    While GA-aero for 1991-2000 may seem to have been a bad period for non-PICs, it should be noted this category includes GA business and passenger flights and the rate of fatal accidents per million flying hours is the lowest in the list.  The overriding messages from these statistics are that any accident of fatal severity most often kills all on board and, accordingly, the ratio of fatalities per fatal accident is very largely set by the number of POB.  An increase in POB without reducing the accident rate from all causes will result in more non-PIC fatalities.  Self-certified RAAOs have more fatal accidents than GA, but with fewer POB they don’t cause as many fatalities to others.  RAAOs have never killed any third-party on the ground.

 

  1. References

 

1  CASA Discussion Paper “Medical Certification Standards” Dec 2016, p.14

2  D.Newman, “Analysis of Medical Conditions Affecting Pilots Involved in Accidents and Incidents 1 January 1975 to 31 March 2006”, ATSB Transport Safety Report B2006/0170 Jan 2007

3  “General Aviation Fatal Accidents – how do they happen?” 1991-2000, ATSB B2004/0010.

4  “An analysis of fixed-wing and rotary wing aircraft accidents involving private operations, 2001 to 2005”, 99ATSB Report 20070099, Final, 2007, pp.1-23

5  “Aviation Occurrence Statistics 2005-2014”, ATSB AR-2015-082 Dec 2015

6  “Response to the CASA Medical Certification Standards Discussion Paper”, Recreational Aviation Australia Ltd, 22 pp., 30 March 2017

7  Civil Aviation Act 1988 Sect. 3A

8  P.Froome, private communication, April 2017

9 CASA Regulatory Policy – CEO 001/2004 Issue 2 CASA’s Industry Sector Priorities  and Classification of Civil Aviation Activities, April 2007, 9 pp.

 

 

 

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Mark Smith

Editor, Australian Pilot.

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