Risk Assessment and Clinical Aeromedical Decision ...

Reprint & Copyright 9 by Aerospace Medical Association, Alexandria, VA

CLINICAL MEDICINE

Risk Assessment and Clinical Aeromedical Decision-Making JONATHAN B. CLARK, M.D., M.P.H.

CLARK JB. Risk assessment and clinical aeromedical decisionmaking. Aviat. Space Environ. Med. 1993; 64:741-7. This article presents a format of aeremedlcal decision-making used in n e u r o l o g y cases referred to a U.S. N a v y Special Board of Flight Surgeons (SBFS) f r o m 1988 to 1990. The format consists o f a series o f questions addressing aeremedical concerns, an ner omedical disposition flowchart, and a decision analysis tree. Decision Analysis is a t o o l used in clinical medicine to assist decision-making under conditions of uncertainty. The Decision Analysis approach may be applied to complex aeromedical disposition questions that face flight surgeons. The concept o f r i s k assessment as it applies to decision-making and aeromedical disposition is discussed. The outcome of 24 neurology cases ref e r r e d for aeromedical disposition are presented.

EDICAL D I S Q U A L I F I C A T I O N is one of the .most frequent reasons for the premature involunM tary termination of an aviator's career (8). Medical standards are designed to ensure that healthy aircrew are medically capable of performing flight duties. The traditional aeromedical disposition process is based on applying an accurate diagnosis to a medical policy standard which prescribes an aeromedical disposition. A specific condition would be considered disqualifying or not, based on such policy. Such standards, regulations, or guidelines do not always take all factors into consideration. Overly strict medical standards may paradoxically increase accident rates (3). Neurologic conditions represent one of the more significant areas of concern in aeromedical disposition, because of the concern of sudden incapacitation or subtle performance decline. Neurologic conditions are one of the most frequent medical causes for inflight incapacitation (7,11). In the 3 years 1988-1990, 34 Naval aviation personnel were referred to the U.S. Naval Aerospace and Operational From the Aeromedical Department, Marine Aviation Weapons and Tactics Squadron One, MCAS Yuma, AZ, and Neurology Department, Naval Aerospace and Operational Medical Institute, NAS Pensacola, FL. This manuscript was received for review in March 1991. It was revised in July 1992 and January 1993. The revised manuscript was accepted for publication in January 1993. Address reprint requests to: Marine Aviation Weapons and Tactics Squadron One, Attn: CDR Jonathan B. Clark, MC, USN, S-5/ Aeromedical Department, Box 99200, Yuma, AZ 85369-9200.

Medical Institute Special Board of Flight Surgeons (SBFS) for aeromedical disposition, and 24 of these cases had primary neurologic diagnoses. As these cases have involved progressively more complicated clinical syndromes, a more formal process has evolved to address these aeromedical issues. Each aviator and aircrew represents a valuable asset, and, therefore, a premium is placed on appropriate aeromedical disposition. Aeromedical Evaluation

Naval aviation personnel with complex medical conditions that are considered disqualifying may be referred to the Naval Aerospace and Operational Medical Institute (NAMI) Special Board of Flight Surgeons for consideration of a waiver for the condition. The aviator receives an evaluation by flight surgeon clinical specialists, including ophthalmology, ear, nose and throat (ENT), aerospace medicine, internal medicine, neurology, and psychiatry. In approaching the aviator with a complex medical problem, a series of questions has been formulated to aid in the waiver consideration process, and to include specific issues that might be addressed (Table I). Although guidelines and regulations address what is and is not disqualifying, the waiver process affords flexibility in aeromedical disposition. Flexibility of these options provides the maximum opportunity to return the flyer to the cockpit, perhaps in a restricted status. The initial approach involves dissecting the three components of aeromedical disposition, "the three M ' s " (Man, Machine/mission, Medical issues). Traditional SBFS aeromedical disposition primarily concerned the medical issue. In recent U.S. Navy Special Boards of Flight Surgeons, the aeromedical issues have addressed the man and machine. The complex interaction of the Man-Machine-Medical issues is best approached on an individual basis. The Man Issue

Specific issues concerning the man (or woman) issue include the aviator's flight career and experience level. A senior aviator may have an overall advantage. A junior pilot with a permanent "dual pilot, dual controlled Aviation, Space, and Environmental Medicine 9 August, 1993

741

AEROMEDICAL DECISION-MAKING---CLARK TABLE I. CONSIDERATIONS IN AEROMEDICAL DECISION-MAKING. What are the implications of this disease or condition on aviation safety? Inflight incapacitation? Flight performance degradation? What are the implications of the aviation environment on the course of this disease or condition? Have Operational and Aircrew factors been considered? What are the implications of this disease or condition in a survival situation or captivity? Will medical followup be required or available during deployment? If medication is required, what are the medication side effects? Dose-related toxicity Acute idiosyncratic toxicity Chronic toxicity/carcinogenicity Is the nature of this disease: Progressive? (over how long?) Unpredictable? Is enough information available to make an adequate decision? (literature review of medical, aeromedical, and aviation safety data) Has enough time transpired to establish the course or outcome in this flyer? Given a chance of recurrence, what is the likelihood the flyer will bring the symptoms to the attention of a flight surgeon? What is the worst-case scenario in flight? What is the probability of the worst-case scenario? Do we return this flyer to flight status? If so, when?

aircraft" waiver (U.S. Navy Service Group III waiver) has a restricted career potential, while a senior aviator may still fill a leadership role as a Service Group III aviator. A factor in support of the senior aviator is the time course over which a medical risk factor is projected. A medical problem with a 2% chance per year of recurrence is more likely to affect flight safety in a young aviator with 15 more flying years than it will a senior aviator who will be flying for only 2 to 5 more years. Another factor is the aviator's understanding and acceptance of the medical problem. The flyer who tends to deny or cover up a problem might not bring future symptoms to the attention of a flight surgeon. This could represent an added risk if the condition has an increased potential for recurrence. The Machine~Mission Issue

The disposition process should also consider the machine, mission, and flight crew duties. A U.S. Navy or Marine Corps aviator must hold a Class 1 medical qualification. A U.S. Navy Class 2 medical rating is required for Naval Flight Officers (NFO), such as a weapons system officer, Naval Flight Surgeons or Physiologists, or aircrew (flight engineer). Medical standards differ for Class 1 and 2. The U.S. Navy Class 1 medical rating is required for duty involving actual control of the aircraft (DIACA). There are more potential safety concerns for DIACA, although all aircrew functions may affect the aircraft mission. The U.S. Navy subdivides the Class 1 aviation medical qualification. A Class 1, Service Group I (SG I) aviator may be assigned to flight duties of an unlimited or unrestricted nature. This includes student naval aviators (SNA), and fixed wing aviators making arrested carrier landings (tailhook arrestment) or shipboard vertical and/or short takeoff and landings (V/STOL). An 742

Aviation, Space, and Environmental Medicine 9 August, 1993

aviator with a U.S. Navy Class 1, Service Group II (SG II) medical rating may fly in single piloted aircraft, but is restricted from arrested carder or shipboard V/STOL landings. A medical Service Group III (SG III) aviator is restricted to dual controlled aircraft with a qualified SG I or II aviator on the controls. An SG III aviator must have a separate waiver to fly as the pilot in command (PIC). Multipiloted aircraft afford some additional safety, although the copilot is not a spare pilot. The Medical Issue

The medical condition is the primary issue in the aeromedical disposition process. Every effort should be made to thoroughly review the available literature on a medical condition, including medical, aeromedical, and aviation safety sources. Although a group of experienced aeromedical personnel, such as a Special Board of Flight Surgeons, may maintain corporate memory on a wide variety of medical issues, they may lack experience concerning rare or new diseases or new medical technologies. The data available on military and civilian aviation personnel with medical conditions and the statistics compiled by aviation safety centers are invaluable resources. The medical literature may not provide all the necessary information to make a risk assessment, leaving aeromedical consultants to make a "best estimate" of the risk. Medical decision-making and aeromedical disposition will always include some degree of uncertainty. Sources of this uncertainty include errors in clinical data, ambiguity of data, and uncertainty in the relationship between clinical presentation and disease, between treatment and effect, and between disease progression and outcome. A medical condition, such as Mitral Valve Prolapse (MVP), which represents a potential problem, is different from a disease or syndrome, such as vertigo or headache, which in itself is symptomatic or disabling. Another factor that confuses the disposition process is whether the medical issue represents an active ongoing condition or a past history of a resolved condition. In the case of active disease, disposition is centered around symptoms, treatment, and disease progression. In the case of a past history of a condition, the concern involves risk of recurrence. A person with a previous history of a seizure may be disqualified from flight duty, even though currently asymptomatic with a normal examination and diagnostic tests.

Aeromedical Considerations The primary aeromedical concerns relate to the development of symptoms inflight that would adversely affect flight performance, which could ultimately affect mission accomplishment or safety of flight. Inflight incapacitation can be classified as total (obvious) or partial (subtle), and as transient or permanent. Although the outcome of total inflight incapacitation is obvious, subtle flight performance degradation may have consequences just as grave, depending on the phase of flight and the responsibilities of the crewmember during normal and emergency situations (4,6). Another concern in the aeromedical decision process is the effect of the aerospace environment on the medical problem. Spe-

AEROMEDICAL D E C I S I O N - M A K I N G - - C L A R K cific operational and aircrew factors involving the aeromedical environment might potentially aggravate a medical condition (Table II). Decision-Making Techniques One technique used in decision-making is dichotomous choice analysis, which assesses the composite effect of desirable and undesirable outcomes of each choice. This is a useful statistical tool for solving polar choices. Dichotomous choice analysis may have an economic base (cost/benefit or cost/effectiveness analysis) or a risk base (risk/benefit analysis). Cost/benefit analysis has been applied to screening tests used in aeromedical disposition (2). Aeromedical disposition standards weigh the potential o u t c o m e of a medical condition in the flight environment vs. the potential lost investment in training and experience the aviator has to offer. This relationship in part accounts for the difference in medical standards between a student pilot and an already qualified aviator, or between a pilot responsible for controlling the aircraft and other aircrew. Risk Assessment Risk/benefit analysis is commonly applied to health issues. Inherent in risk/benefit analysis as a decisionmaking process is the concept of risk assessment. Risk assessment techniques are used in environmental policy making, safety programs, and clinical medicine. Risk assessment is an integral part of clinical decision analysis, where the clinician assigns a value or utility score and probability estimate to each possible outcome state. Risk assessment is used in the Naval Aviation Safety Program, where a Risk Assessment Code (RAC), based on hazard severity and probability, is assigned to aviation safety problems. An aviation mishap that involves a fatality, damage over $I million, or loss of aircraft is considered a severe hazard, and is monitored for corrective action. Risk assessment occurs daily on the flight line and in the clinic. A military aircraft rarely lifts off without a gripe in the maintenance logbook, and the pilot must decide for that mission whether the problem is such that the aircraft is or is not acceptable. Risk TABLE II. OPERATIONAL AND AIRCREW FACTORS IN THE AEROSPACE ENVIRONMENT. Operational Factors Flight duration--sustained or continuous flight operations Hypoxia Barometric pressure changes--trapped and evolved gas disorders Time zone changes---circadian rhythm disruption Sustained G forces---G-induced loss of consciousness Altered visual/vestibular cues--spatial disorientation Vibration/noise Temperature/humidity Toxicologic hazards Electromagnetic radiation hazards Aircrew Factors

Crew fatigue/task saturation Nutrition Restricted posture and movement Waste excretion Normal crew functions Emergency crew functions (including egress)

assessment and decision analysis also have application in aeromedical disposition. Risk Estimation Risk estimation is the process of identifying, quantifying, and characterizing risk. The intent of risk estimation is not to make decisions, but to illuminate risk, so that uncertainty may be avoided, reduced, or managed. Risk estimation implies uncertainty, but improves with knowledge and time. The best estimates come from the population to which the estimates would be applied; thus, whenever possible, epidemiologic data should be derived from the same population to which the estimates will be applied. Epidemiologic studies used in risk estimation may be classified as sufficient, limited, or inadequate. Comparing and contrasting risk estimates may aid in appreciating relevant risk. Risk analysis provides quantification of the adverse outcomes and the probability or chance of the different outcomes (5). The subjective or intuitive component of risk assessment, called perception of risk, may be subject to significant bias. Risk is often perceived to be greater when the risk associated with an event occurs over a short length of time (dying in an aircraft accident), rather than when risk extends over a long period of time (dying from tobacco-related cancer), and an individual's perception of risk may vary depending on the way it is expressed (mortality rate vice survival rate) (13).

Acceptable Risk Once the risk has been estimated, the next step is to decide what is acceptable risk. Factors that influence acceptable risk include risk perception (voluntariness, dread, information, controllability), benefit of the hazard, and deaths from the hazard in an average year and in a disastrous year (12). The acceptability of risk from an activity has been estimated to be proportional to the third power of the benefit from that activity (12). Generally the public will accept 1000 times more risk from voluntary activity than from involuntary activity (12). Although a zero risk or a mishap-free accident rate is desirable, they are rarely possible. Accident rates are generally considered acceptable when they do not exceed comparable past rates. Human factor (judgment) errors, responsible for up to 75% of aircraft accidents, are a more significant problem than are medical causes of inflight incapacitation. In a recent analysis, the fatality rate for human factors-related aircraft accidents was determined to be 50 times greater than the fatal accident rate for inflight incapacitation from medical causes (11). Acceptable risks in civil aviation, in terms of past rates, are one incapacitation event in 20 million flight hours (MFH) and one fatal aircraft crash due to incapacitation per 8000 million flight hours (7). In a recent U S A F study, one incapacitation occurred every 5 M F H (7). In terms of civil aircraft airworthiness standards, the occurrence of a catastrophic mechanical failure which would prevent safe flight or landing should be "extremely improbable," or a likelihood of failure of 1 in 1000 MFH (I). A less than catastrophic failure, which would reduce the crews' ability to cope under adverse operating conditions, should be "improbable," or a Aviation, Space, and Environmental Medicine 9 August, 1993

743

AEROMEDICAL DECISION-MAKING

CLARK

likelihood of failure between 1 in I00,000 to 1 in 100 MFH.

The Worst-Case Scenario The worst-case scenario in the aeromedical disposition process would be to give a waiver to an individual with a medical condition who subsequently developed incapacitating symptoms inflight. Such an occurrence in a single-piloted aircraft would be the worst of the worst case scenarios, while occurrence in a non-pilot crewmember would be the least of the worst cases, affecting the mission but not necessarily safety of flight. There have been cases of pilot incapacitation inflight (loss of consciousness, seizure) in which aircraft control has been recovered by the copilot (11). Development of incapacitating symptoms during critical stages of flight (landing or takeoff), or in conjunction with other inflight emergencies, would also represent the worst of the worst situations (4). In a study conducted to assess the consequences of inflight incapacitation in an airline flight simulator during the critical phase of flight, 1.6% of the trials resulted in a "crash" if the incapacitation occurred in conjunction with other inflight emergencies, but only 0.25% of flights "crashed" when incapacitation occurred without other aircraft system failures (1). Airline pilots undergo training in management of inflight incapacitation including maintaining aircraft control, care of the incapacitated crewmember, and cockpit task reorganization (6,8). Decision Analysis Process Decision analysis is a mathematical process that provides a systematic approach to decision-making under conditions of uncertainty. The process involves developing a strategy based on a sequence of contingent decisions. The decision tree is the basic analytic tool to aid in identifying alternate strategies. Branches of the decision tree, called nodes, are either Choice nodes or Chance nodes. The end of each branch is the Outcome. Each outcome is assigned a value, or "utility," based on the decision-maker's estimate of good (positive) or bad (negative) outcomes. Worst-case outcomes would be assigned an appropriately ranked negative value. A probability is assigned for each chance node branch point, based on estimates of the decision maker. The expected value outcome is the summation, at each branch point, of the probability of outcome multiplied by the value (utility) assigned to that outcome. The summated value outcomes for each Choice node are compared, and the higher value of the two nodes would be the analytically supported favorable choice. Personal computer-based decision analysis programs are available to aid the clinician in analyzing various diagnostic and therapeutic options, to assist in clinical decisions (10). Another feature available is sensitivity analysis, which assesses the effect of changing the utility value or probability, and at what point the process would favor one choice node over the other (9). Probability Assignment The assignment of a likelihood or probability at each chance node is applied from available information or 744

Aviation, Space, and Environmental Medicine ~ August, 1993

best estimate. The probabilities of concern in the aeromedical decision analysis process would include the likelihood of disease or symptom recurrence, the likelihood of incapacitating or disabling symptoms, and the probability the symptoms would occur inflight. Medical, aeromedical, and safety sources can be used to provide information to make these probability estimates. For example, closed head trauma, with various injury parameters, such as length of unconsciousness or amnesia, intracranial hemorrhage, and time since injury, can be used in predictive models to estimate the probability of posttraumatic epilepsy (PTE). This probability is then used in the appropriate recurrence (or occurrence) chance node. The occurrence of symptoms in flight is probabilistic, and based on an individual's flight hours per unit time, if symptoms are independent of the flight environment. An aircrew member who logs 48 hours per year has a 0.0055 annual probability of a symptom occurring in flight, or 48 hours/8760 hours (24 hours/day times 365 days/year). An aviator who logs 30 hours/month would have a 0.041 probability of a symptom occurring in flight per year, or 30 hours/month times 12 months/year divided by 8760 hours/year. If symptom occurrence were not independent of the flight environment then this value could be adjusted accordingly (multiplying the estimated relative increase by the basic probability). The probability of symptoms not occurring in flight would be 1 minus the estimated probability of symptoms occurring inflight. The probability of symptoms being disabling or not is empiric for the specific condition. In the author's estimation, conditions such as seizure and loss of consciousness represent situations which have a very high probability (>90%) of disabling symptoms, while stroke or vertigo have a high probability (>75%) of disability, and migraine a low to moderate probability (20-50%).

Outcome States and Assigning Value (Utility) The decision analysis process involves identifying options (choice nodes and chance nodes) and outcomes, assigning probabilities to each chance node and values DECISION ANALYSIS PROCESS CHOICE NODES C

CHANCE NODES P

OUTCOME STATES U

~

C ]

~

PI

P

RECURRENC~

u1

U2

~ NOT IN FLIGHT I U 3 NO RECURRENCE ]

U4

CONDITION

p/RECURRENCE C 2

I

U5

INO WAIVER ]

~a ~ N O

RECURRENCE J U 6

Fig. 1. Decision Analysis tree applied to aeromedical disposition, using Choice Nodes (C), Chance Nodes with estimated probabilities (P), and Outcome States (U).

AEROMEDICAL DECISION-MAKING--CLARK TABLE III. NAMI NEUROLOGY SPECIAL BOARD OF FLIGHT SURGEONS, 1988-90. Year 1988

1989

1990

Rank

Age

Status

0-2/USN

26

NA

0-4/USN

36

NA

0-3/USN

27

NA

0-5/USMC 0-3/USN

44 26

NA NA

0-4/USN 0-4/USN 0-4/USMC

35 38 37

NA NFO NA

0-6/USMC 0-5/USN 0-4/USN

47 38 34

NA NFS NA

0-3/USMC

33

NA

0-6/USN 0-3/USN 0-4/USNR

42 29 35

NA NA NA

0-4/USNR

35

NA

0-4/USN

30

NA

0-3/USN

29

NA

0-4/USN

37

NA

0-4/USMC 0-4/USMC

42 38

NA NA

0-6/USN

47

NA

0-4/USNR 0-5/USMC

34 38

NA NA

Diagnosis Recurrent TVL, FMD, MVP Encephalitis, ABNL EEG Recurrent G-Induced HA Recurrent Vertigo Meniere's (Vertigo/HL) Moderate CHUWPW Recurrent Vertigo Acephalgic sensory migraine LOC, Mildly ABNL EEG Recurrent HA Disequilibrium in Flight CHI, Skull FX, EpiduraFICH Recurrent LOC Recurrent LOC Cervical Torsion Dystonia CVA, Resolved Dysphasia Hypothalamic Tumor/ Infertility Frontal Sinus FX, Dural Tear Cerebellar Hemangioblastoma Recurrent LOC Acute Agitated Delirium Cluster HA, Disequilibrium TTP, Seizure, ABNL EEG Optic Nerve Tumor, VF Loss

Disposition

Period (months)

No

12

Yes (SG III)

24

Yes (SG III) Yes (SG III)

3 36

No No Yes (CLASS 2)

6 14 36

Yes (SG II)

34

Yes (SG I) Yes (CLASS 2)

17 6

Yes (SG II)

11

Yes (SG III) Yes (SG I) Yes (SG III)

12 9 21

Yes (SG II)

10

Yes (SG III)

24

Yes (SG I)

13

Yes (SG III)

24

Yes (SG III) Yes (SG III)

22 24

Yes (SG I)

24

Yes (SG I) No

22 9

Yes (SG III)

4

Disposition Abbreviations: RANK--Officer Pay Grades 0-1 Through 0-6 USN--United States Navy USNR--United States Navy Reserve USMC--United States Marine Corps Class 1 Aviation Personnel NA--Naval Aviator (Pilot) SG--Service Group (Duty Involving Actual Control of Aircraft) Service Group I--Single Pilot Aircraft, Carrier Landing Service Group II--Single Pilot Aircraft, Non Carrier Landing Service Group III--Dual Pilot/Dual Control Aircraft Class 2 Aviation Personnel Class 2 (Flight Duty hot Involving Actual Control of Aircraft) NFO---Naval Flight Officer (Bombardier, Navigator, Weapon System Operator) NFS---Naval Flight Surgeon Disposition--Returned to Flight Status (Yes or No) Period---Grounding Period in Months, Prior to Special Board Consideration Medical Abbreviations: TVL.--Transient Visual Loss; FMD--Fibromuscular Dysplasia; MVP--Mitral Valve Prolapse; HA--Headache; HL--Hearing Loss; ABNL EEG--Abnormal Electroencephalogram; CHI--CIosed Head Injury; ICH--Intracerebral Hematoma; LOC--Loss of Consciousness; CVA--Cerebrovascular Accident; FX--Fracture; WPW--Wolf-Parkinson-White; Tl'P--Thrombotic Thrombocytopenic Purpura.

(utility) to each outcome state, then selecting the " b e s t " choice. The design of the basic decision analysis tree (Fig. 1) applied to aeromedical disposition starts with building the branches of the two choice nodes: WAIVER (return to flight status) or NO WAIVER (remove from flight status). The first branches are the two

chance nodes, labelled RECURRENCE or NO RECURRENCE, and are based on symptom occurrence or disease recurrence. In the NO WAIVER branches, the two chance nodes, RECURRENCE or NO RECURRENCE, are final outcome states, and one branch of the WAIVER choice node, the NO RECURRENCE Aviation, Space, and Environmental Medicine 9 August, 1993

745

AEROMEDICAL DECISION-MAKING--CLARK branch, is also a final outcome state. Branches off the WAIVER choice node/RECURRENCE chance node, are divided into further chance nodes and outcome states. These are the INFLIGHT or NOT INFLIGHT chance nodes. The INFLIGHT chance node is further subdivided into D I S A B L E D or NOT D I S A B L E D chance node/outcome states. The last chance node in each decision tree branch is an outcome state. The assignment of a value score or utility to each outcome state is based on parameters established by the decision-maker. In this paradigm " g o o d " outcomes are assigned positive values, and " b a d " outcomes negative values. The value (utility) scores are based on arbitrary units of relative "goodness" or "badness" chosen by the decision-maker. Appendix A describes the steps in the aeromedical decision analysis process, and shows two examples of its use.

AEROMEDICAL DISPOSITION TREE I MEDICAL C O N D I T I O N OR HISTORY I

/%

I PHYSICALLY QUALIFIED(

CONSIDER REEVALUATION

I E~ECTION SEn WAIVER I

I AIRCRAFT WAIVER I

Summary of Neurology Special Board of Flight Surgeons 1988-90 There were 24 neurology cases referred to a Naval Special Board of Flight Surgeons for aeromedical disposition from 1988 to 1990. The majority (22 of 24) were Naval Aviators (Medical Class 1), and 2 were Medical Class 2 personnel (one Naval Flight Officer and one Naval Flight Surgeon). Both the Class 2 personnel were returned to flight status. Of the 22 Naval Aviators referred with neurologic diagnoses, 18 (82%) were returned to flight status. Three were disqualified for neurologic conditions; the other one was disqualified for an incidental cardiac arrhythmia discovered during the evaluation. The period of grounding prior to evaluation by a SBFS was 10.25 months for those conditions not waivered, and 18.8 months for those conditions that were waivered. The average age of the non-waivered group was 30.25 years, and 36.8 years for the waivered group. Diagnosis, grounding period, and disposition are presented in Table III. Conclusions

The decision to return an aviator with a medical condition back to the cockpit is the challenge of aeromedical disposition. The outcome of any aeromedical disposition ultimately is based on the issues of safety and risk, although other factors, such as the economic cost of the lost aviator, might also be considered. In aeromedical disposition, determining acceptable risk in dealing with medical conditions with a chance of incapacitation or flight performance degradation is difficult to estimate. The decision analysis process, using information on disease recurrence or symptom occurrence, probability of occurrence in flight, and likelihood of disabling symptoms, can aid the aeromedical decisionmaker. The constantly changing epidemiologic and clinical data concerning medical conditions that affect aviators warrant continual reevaluation of the aeromedical disposition process. Decision analysis principles can aid the flight surgeon in aeromedical disposition by providing an estimate of risk (probability and severity). This technique is applicable to medical conditions where the risk of recurrence remains stable or decreases 746


~ NOT PHYSICALLY QUALIFIED I

GEOGRAPHIC RESTRICTION ]

REEVALUATION OF CONDITION I

A REQUIRED (HOW OFTEN?)

[ NOT REQUIRED

l

1

I CONSIDERATION OF HIGHER WAIVER

/-,,,

I YES (WHEN?) I I NO (PERMANENT) I Fig. 2. Aeromedical Disposition Tree. Flexible approach used in Neurology Special Board cases (see Table III for abbrevia-

tions).

over time (symptom free interval). Waiver consideration may be delayed until a level of acceptable risk has been reached. Using decision analysis principles and a flexible disposition posture, 20 of 24 (83.2%) neurology cases referred for aeromedical deliberation by a Special Board of Flight Surgeons from 1988 to 1990 were returned to flight status after an appropriate grounding interval. Factors that tended to preclude return to flight status included duty involving actual control of aircraft, low flight experience level, frequency of disease recurrence, severity of clinical syndrome, and disease prognosis or progression. The common feature relating to disqualification from flight status was the potential for incapacitation or significant performance degradation occurring in flight while at the controls of an aircraft. A systematic approach to decision-making under conditions of uncertainty using risk assessment and decision analysis techniques has potential application in aeromedical disposition as an adjunct to clinical decisionmaking. Aeromedical disposition may be aided by the decision analysis process (Fig. 1) and a flexible approach to returning an aviator to flight status with some prudent restrictions (Fig. 2). ACKNOWLEDGMENTS Opinions and assertions expressed herein are those of the author and do not necessarily reflect the views of the Navy Medical Department, Department of the Navy, or the Department of Defense.

AEROMEDICAL

DECISION-MAKING---CLARK

APPENDIX A. STEPS IN AEROMEDICAL DECISION ANALYSIS PROCESS 1) Estimate probability of symptom occurrence or disease recurrence: PI 2) Calculate symptom non occurrence/disease non recurrence: Pa = 1.0 - P1 3) Estimate probability being inflight (flight hours/yr divided by 8760): P2 4 ) Calculate probability of not being inflight: Pb = 1 . 0 - P2 5) Estimate probability of disabling or incapacitating symptoms: P3 6) Calculate probability of nondisabling or nonincapacitating symptoms: Pc = 1.0 - P3 7) Assign utility score to outcome states: WAIVERED WITH DISABLING RECURRENCE INFLIGHT U1 WAIVERED, WITH NON DISABLING RECURRENCE INFLIGHT U2 WAIVERED, WITH RECURRENCE NOT INFLIGHT U3 WAIVERED, NO RECURRENCE U4 NOT WAIVERED, RECURRENCE U5 NOT WAIVERED, NO RECURRENCE U6 8) Calculate value for Choice Node WAIVER: C1 CI = (Pa)(U4) + PI[(Pb)(U3) + P2[(Pc)(U2) + (P3)(UI)]] 9) Calculate value for Choice Node NO WAIVER: C2 C2 = (Pa)(U6) + (PI)(U5) 10) Select the " b e s t " Choice Node: If CI > C2, then CI is the best choice node; If C2 > C1, then C2 is the best choice node; If C1 = C2, then either may be the best choice node. EXAMPLE 1. USE OF AEROMEDICAL DECISION ANALYSIS PROCESS A helicopter pilot with a history of infrequent migraine headaches is estimated to have a risk of recurrence of less than l%/year. He flies 150 hours a year, and if an event were to occur, estimates are that it would be disabling 30% of the time. Step 1) PI = 0.01 2) Pa = 0.99 3) P2 = 150/8760 = 0.017 4) Pb = 0.983 5) P3 = 0.3 6) Pc = 0.7 7) Assign utility scores (based on relative value): in this example, a good decision is positive 100, a bad decision is negative 100, a terrible decision is negative 100,000 and a disastrous decision is negative 1 million. V V OR UTILITY(U) SCORE WAIVERED WITH DISABLING RECUR- U 1 - 1,000,000 RENCE INFLIGHT WAIVERED, WITH NON DISABLING U2 -100,000 RECURRENCE INFLIGHT WAIVERED, WITH RECURRENCE NOT U3 - 100 INFLIGHT WAIVERED, NO RECURRENCE U4 + 100 NOT WAIVERED, RECURRENCE U5 + 100 NOT WAIVERED, NO RECURRENCE U6 - 100 8) C1 = (Pa)(g4) + PI[(Pb)(U3) + P2[(Pc)(U2) + (P3)(UI)]] = (0.99)(+100) + 0.01[(0.983)(-100) + 0.017[(0.7)(- 100,000) + (0.3)(- 1,000,000)]] = 99 + (-63.9) = +35.1 9) C2 = (Pa)(U6) + (P1)(U5) = (0.99)(-100) + (0.01)(+ 100) = - 9 8 . 0 10) C1 ( + 35.1) > C2 ( - 98.0), therefore node C1 (WAIVER) is best choice. EXAMPLE 2. USE OF AEROMEDICAL DECISION ANALYSIS PROCESS A jet pilot had a history of recurrent vertigo and hearing loss con-

sistent with Meniere's disease with an estimated recurrence of 10%/ year. He flies 360 hours a year, and if an event were to occur, estimates are that it would be disabling 70% of the time. Step 1) P1 = 0.10 2) Pa = 0.90 3) P2 = 360/8760 = 0.041 4) Pb = 0.959 5) P3 = 0.7 6) Pc = 0.3 7) Assign utility scores (based on relative value): in this example, a good decision is positive 100, a bad decision is negative 100, a terrible decision is negative 100,000 and a disastrous decision is negative 1 million. V V OR UTILITY (U) SCORE WAIVERED WITH DISABLING RECUR- U1 - 1,000,000 RENCE INFLIGHT WAIVERED, WITH NON DISABLING U2 -100,000 RECURRENCE INFLIGHT WAIVERED, WITH RECURRENCE NOT U3 - 100 INFLIGHT WAIVERED, NO RECURRENCE U4 + 100 NOT WAIVERED, RECURRENCE U5 + 100 NOT WAIVERED, NO RECURRENCE U6 - 100 8) CI = (Pa)(U4) + PI[(Pb)(U3) + P2[(Pc)(U2) + (P3)(UI)]] = (0.9)(+ 100) + 0.1[(0.959)(- 100) + 0.041[(0.3)(- 100,000) + (0.7)(- 1,000,000)]] = 90 + (-3002.6) = -2912.6 9) C2 = (Pa)(U6) + (P1)(U5) = (0.9)(-100) + (0.1)(+ 100) = - 8 0 . 0 10) C2 (-80.0) > CI (-2912.6), therefore node C2 (NO WAIVER) is best choice.

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