ANNEX D: PHYSIOLOGICAL EPISODES
1. The Navy’s definition of a physiological episode (PE) is when a pilot experiences loss in
performance related to insufficient oxygen, depressurization, or other factors during flight. For the
purposes of this review, the Comprehensive Review Medical Sub-Specialty Team considered five
general categories of PEs, with appropriate sub-categories.
a. Hypoxia
(1) Hypoxic hypoxia: reduced oxygen available, usually caused by reduced partial
pressure. In the aviation community, this would likely be due to altitude or a faulty oxygen supply
system.
(2) Anemic hypoxia: reduced oxygen carrying capacity caused by reduced quantities of
hemoglobin (i.e., reduced blood-carrying cells available to deliver oxygen.)
(3) Stagnant hypoxia: reduced oxygen carrying capacity caused by stagnation, or
‘pooling’, of blood. This could be experienced in a sustained G-load or from restrictive flight gear.
(4) Histotoxic hypoxia: reduced oxygen carrying capacity caused by a foreign substance,
or toxin, preventing normal oxygen transport. An example of this would be carbon monoxide
exposure.
b. Decompression Illness (DCI)
(1) Decompression Sickness, Type I (DCS-I): mild form of DCS, often called “the
bends”, typically limited to musculoskeletal or cutaneous (skin and subdermal tissue)
manifestations and joint pain.
(2) Decompression Sickness, Type II (DCS-II): serious, potentially life-threatening form
of DCS, potentially involving neurologic issues.
(3) Pulmonary barotrauma: physical rupturing of the tissue of the pulmonary system.
(4) Arterial gas embolism (AGE): gas bubble forming in or entering the blood vessels
often resulting from pulmonary barotrauma.
c. Acapnia: abnormal levels of carbon dioxide (CO2) in the blood resulting in abnormal
control of respiration rate in the body. (Blood CO2 levels sensed in the brain control the body’s rate
of breathing.)
(1) Hypocapnia (hypocarbia): low blood CO2, often due to hyperventilation (increased
breathing rate), thus ‘breathing off’ excess CO2. This could lead to physiological symptoms similar
to hypoxia.
(2) Hypercapnia (hypercarbia): high blood CO2, often due to hypoventilation (decreased
breathing rate), thus retaining excess CO2. In the absence of supplemental oxygen and if excessive,
this will have similar physiologic symptoms as hypoxia.
d. Vestibular

 ANNEX D: PHYSIOLOGICAL EPISODES
(1) Spatial disorientation
(2) Motion sickness
e. Psychological and/or psychosocial
(1) Anxiety disorders
(2) Panic disorders
(3) Psychogenic hyperventilation (psychological state causing hyperventilation.)
(4) Aerophobia (fear of flying.)
(5) Somatoform disorders (psychological state manifesting in physical symptoms.)
2. The issue of ‘mass-spectrum’ or ‘catch-all’ characterizations have come into question. Many
PEs are combined into a conceptual single, larger PE category. This potentially suggests a single,
common cause. Finding a common, or root, cause is not likely.
3. General Navy guidance for when a PE is considered to have occurred, outside a naval aviation
mishap, can be found in OPNAVINST 3750.6S NAVAL AVIATION SAFETY MANAGEMENT
SYSTEM (Section 503.h). The Navy considers a PE to have occurred whenever any of the
following specified conditions are present:
a. Hypoxia, proven or suspected;
b. Carbon monoxide poisoning or other toxic exposure;
c. Decompression sickness (DCS) because of evolved gas (bends, chokes, neurocirculatory
[blood supply to the brain] collapse or severe reaction to trapped gas resulting in incapacitation;
d. Hyperventilation;
e. Spatial disorientation (SD) or distraction resulting in unusual attitude;
f. Loss of consciousness (LOC) for any cause;
g. An unintentional rapid decompression exposing personnel to cabin altitudes above flight
level (FL) 250 [or 25,000 ft pressure altitude], regardless of whether dysbarism [physiologic effects
of excessive or decreased pressure] or hypoxia occurs;
h. Other psychological, pathological, or physical problems that manifest during or after actual
flight.
4. The 3 April 2017, Naval Safety Center (NAVSAFECEN) AMENDED AVIATION
PHYSIOLOGIC EPISODE REPORTING REQUIREMENTS (copied at the end of this annex)

 ANNEX D: PHYSIOLOGICAL EPISODES
modified the Navy instruction on PEs, specifically expanding the definition for PEs and adding
requirements for reporting . The modified guidance read, in part:
a. PEs are reportable safety incidents in accordance with Navy policy and must be reported via
Web Enabled Safety System (WESS). Squadrons shall generate a PE initial notification in WESS
within 24 hours of any PE diagnosis and provide a brief description of the event and any medical
treatment provided to aircrew. A completed Hazard Report (HAZREP) or Safety Investigation
Report (SIR) is due on Risk Assessment Code (RAC) timeline. PEs are defined as:
(1) Hypoxia, proven or suspected
(2) Carbon monoxide poisoning or other toxic exposure
(3) Decompression illness (DCI)
(4) Hyperventilation
(5) Spatial disorientation (SD)
(6) Loss of consciousness (LOC) for any cause
(7) Other psychological, pathological, or physical problems that manifest during or after
actual flight
(8) All aircraft pressurization events (in-flight or ground-based) resulting in aircrew or
maintainer symptoms
b. With the inclusion of “all aircraft pressurization events” (the eighth condition listed above),
unintentional rapid decompression with cabin altitude above FL250 was removed from the original
list of conditions considered a PE and, unless symptomatic, is no longer a reportable PE event. This
is appropriate because a cabin decompression event by itself does not necessarily result in a PE.
c. Historically, physiologic incidents were FA-18 focused. However, reported events
illustrate the scope of the problem as it applies to all aval aircraft. The reduction, elimination
and/or mitigation of PEs remain the top safety priority for Commander, Naval Air Forces (CNAF).
CNAF, Commander, Naval Air Force Atlantic (CNAL), Chief, Naval Aviation Training
(CNATRA), Bureau of Medicine and Surgery (BUMED) and Naval Air Systems Command
(NAVAIR) staffs are in full alignment with PE mitigation strategies.
d. As the naval safety reporting system of record, WESS must contain all reported hazard and
mishap events for documentation as well as for current and future safety analysis purposes.
e. Submission to NAVAIR of the NAVAIR Part A, B & C forms alone does not provide
enduring documentation within the official naval safety reporting system, nor do they inform key
Naval Aviation Enterprise (NAE) safety leadership in a timely manner when a PE occurs.

 ANNEX D: PHYSIOLOGICAL EPISODES
f. In addition to expanding the definition for what is considered a PE, NAVSAFECEN’s 3
April 2017 safety message set forth the following additional reporting requirements when PErelated hazards and mishaps occur:
(1) Classification of Severity:
(a) Post flight treatment protocols consisting of 100 percent oxygen, IV fluids,
emergency room admission, or hyperbaric chamber therapy are greater than first aid treatment and
are therefore classified, at a minimum, as a Class D mishap when treating PEs.
(b) One lost workday constitutes a Class C mishap.
(c) Permanent partial disability or three or more personnel hospitalized constitutes a
Class B mishap.
(d) Fatality or permanent total disability is a Class A mishap.
(2) Physiologic Episode Team (PET) Reporting Guidance:
(a) Squadrons must continue to complete and submit NAVAIR Part A, B & C forms
for PEs that resulted in/from hypoxia, carbon monoxide or other toxic exposure, decompression
illness, hyperventilation, and any pressurization event resulting in physiological symptoms.
(b) Timeline for submission of the Part A: immediately upon event diagnosis but no
later than 24 hours; Part B must be submitted within 10 working days of event diagnosis; Part C
must be submitted within 48 hours post-medical treatment.
(c) Submission will be in parallel to safety investigations required per OPNAVINST
3750.6S. Over time, data requirements result in changes to the Parts A-C. These forms will
continue to be updated and notification sent via CNAF message.
(d) Current versions of Parts A and B (for those communities that have created
them) and Part C (for all aircraft) can be found at:
http://www.public.navy.mil/navsafecen/pages/aviation/aeromedical/aeromedical.aspx
(3) Slam Stick/mu Data:
(a) For all PE events, squadrons must submit a copy of the aircraft mu data file with
the Part A.
(b) Squadrons flying with Slam Stick pressure recording devices must also include
the recorded Slam Stick data file from the PE event when submitting the Part A form.
(c) Medical professional use of Slam Stick data supports proper diagnosis and
treatment.
Note: Slam Sticks are small devices used in flight to measure and record pressure fluctuations in
the cockpit; the data produced from the Slam Stick is referred to as “mu” data.

 ANNEX D: PHYSIOLOGICAL EPISODES
(4) Medical Guidance:
(a) Blood samples are not required in support of Part C form protocol and shall not
be sent to NAMRU-D for toxicological testing.
(b) At the discretion of the attending flight surgeon, focused laboratory testing may
be deemed appropriate when considered relevant to PE investigation.
(c) Flight surgeons are encouraged to submit amplifying data in word document
form or as attachments (e.g., 72-hour medical history, Armed Forces Health Longitudinal
Technology Application (AHLTA) notes, etc.) when submitting the Part C form.
(d) Ensure flight surgeon name, phone number, and email address are included on
the Part C form.
Note: To date, there is no standardized medical evaluation protocol. The flight surgeon evaluates
suspected cases on scene and makes diagnosis based on patient presentation and available
information.
(5) Endorsement:
(a) PE HAZREPs and mishap reports must be endorsed per OPNAVINST 3750.6S.
(b) To ensure all pertinent findings are included in the final report of record in
WESS, NAVSAFCEN will conduct a close out of all PE HAZREPs and mishap reports pending
NAVAIR summary of PET analysis and findings, to include a final closing endorsement statement.
(6) Pre-Mishap Guidance:
(a) Squadrons must incorporate DCI details into their mishap response plan and
duty binders.
(b) At a minimum, include location of the two closest hyperbaric chambers with
contact information for 24/7 assistance and a transportation plan for getting aircrew to a chamber,
whether the aircrew are on or off base, at home, or deployed.
(c) In cases of suspected DCI, expert consultation is available 24/7 at NAMI's DCS
hotline: 850-449-4629. Additional references are available directly on the Part C form.