Greyout, Blackout, and G-Loss of
Consciousness in the Brazilian Air Force:
A 1991 -92 Survey
KATIA M . ALVIM, M . D .
ALVlM K. Greyout, blackout, and G-loss of consciousness in the
Brazilian A i r Force: a 1991-92 study. Aviat Space Environ Med 1995;
66:675-7.
A national survey has been performed with high and medium
performance aircraft pilots on the incidence of symptoms due to
+Gz acceleration, in order to make up a human centrifuge physiological training profile directed to the needs of the Brazilian
Air Force pilots. Anonymous questionnaires were sent to Flight
Squadrons of F-S, AMX, Mirage F-103, Xavante AT-26, and Tucano T-27. They consisted of inquiries about the occurrence of
visual symptoms and/or loss of consciousness during +Gz (G-LOC)
maneuvers, and post-G-LOC symptoms. Some 193 pilots answered the questionnaire: 23 (11.92%) reported greyout and/or
loss of peripheral vision; 40 (20.72%) reported blackout; 20
(10.36%) reported G-LOC. Those who reported LOC also reported
post-G-LOC symptoms (100%), 16 (80%) being gradual and 4
(20%) instantaneous. Incidence of G-LOC did not depend upon
the type of aircraft flown (p > 0.05). Considering the pilots who
reported G-LOC, 80% were preceded by blackout, which could
allow them to relieve +Gz load before they would reach their
endpoint for the occurrence of G-LOC. For these reasons we recommend intensive human centrifuge training periodically, similar to the hypexia-recognition test in the hypobaric chamber,
not only for high performance aircraft pilots but for any pilot
who can perform aerobatics (thus exposing himself to the adverse effects of "pulling G"). This will allow each pilot to recognize his consciousness endpoint when undergoing +Gz maneuvers, in a controlled and safe environment.
AS
NANSEN, THE FAMOUS ARCTIC explorer
said, The history of the human race is a continuous struggle from darkness towards light. It is therefore
purposeless to discuss the use of knowledge. Man wants
to know, and when he ceases to do so, he is no longer
a Man."
The more we know about G-induced loss of consciousness (G-LOC), the more we want to study it. For
several years we have been reading articles from and
listening to qualified people who described it, set its
physiological basis, suggested means of protection
against it, made surveys, and proposed human centrifuge training profiles. And still the problem has not been
solved. Instead, it challenges aerospace medicine, since
the aircraft itself is of almost unlimited performance,
Aviation, Space, and Environmental Medicine 9 Vol. 66, No. 7 9 July 1995
but "What limits the performance of the machine is the
man," as Bleriot stated in 1922.
We should not be different. Brazilian Air Force
fighter/attack pilots fly aircraft ranging from turbopropeller engine airplanes to supersonic platforms. This variety of planes and missions led us to begin a survey on
the incidence of symptoms due to + Gz acceleration in a
variety of flight squadrons, in order to make up a human
centrifuge training profile based upon data collected
from their experience, needs, and types of aircraft/
mission flown.
METHODS
Five types of aircraft flown by pilots can expose them
to significant + Gz effects (Table I). We sent questionnaires to these squadrons, to be anonymously answered, during the years 1991 and 1992. The questionnaires asked about the occurrence of visual symptoms
and G-LOC during +Gz maneuvers, requesting each
pilot to report if they were wearing an anti-G suit and
performing AGSM (Anti-G Straining Maneuvers), in addition to obtaining data about the type of flight profile
(Air Combat Maneuvers, Aerobatics, for instance), approximate duration, and magnitude of G.
Those who reported G-LOC were also asked if the
episodes were gradual or instantaneous, and if they felt
anything upon recovery. The distribution of the questionnaires was always preceded by a briefing made by
the squadron's flight surgeon, to make it as clear as
possible.
From the Brazilian Air Force Institute of Aerospace Physiology,
Air Force University, Rio de Janeiro, Brazil.
This manuscript was received for review in March 1994. It was
revised and accepted for publication in August 1994.
Address reprint requests to K. Alvim, who is a Flight Surgeon,
Instructor of Aerospace Medicine, Physiological Training and a Research Physician, R. Comendador Siqueira # 445, Jacarepagua--CEP
22740-000, Rio de Janeiro, RJ, Brazil.
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BLACKOUT & G-LOC IN B A F m A L V I M
TABLE I. TYPES OF AIRCRAFT, MANUFACTURER, POWER
SOURCE AND KIND OF MISSION FLOWN BY
EACH SQUADRON.
Aircraft Types
T-27 TUCANO
(Embraer)
AT-26 XAVANTE
(Embraer, under
license of Aermacchi)
AMX (Embraer/
Aermacchi/Aeritalia)
F-103 MIRAGE
(Dassault-Breguet)
F-5 (Northrop)
Power
Source
1 Turboprop
1 Turbo
2 Turbo
1 Turbo
2 Turbo
Mission
Primary Trainer
Ground Attack
Advanced Jet Trainer
Subsonic Fighter
Ground Attack
Subsonic-Tactical
Fighter/Bomber
Supersonic
Fighter/Interceptor
Supersonic Tactical
Fighter
RESULTS
We had 193 questionnaires returned. The majority of
the pilots answered the questions correctly, but some
did not mention certain variables, such as performance
of AGSM, G-duration, and G-magnitude. For this reason, we compiled only data concerning the incidence of
greyout/loss of peripheral vision, blackout and G-LOC
(Fig. 1), as well as post-G-LOC symptoms.
From the group of 193 pilots, 83 (43%) reported some
sort of symptom related to +Gz: 23 (11.92%) greyout,
and/or loss of peripheral vision; 40 (20.72%) blackout;
20 (10.36%) LOC. Concerning those who reported
G-LOC episodes, 16 (80%) were preceded by blackout
and 4 (20%) were instantaneous, or without warning
(Tables II and III). All of the pilots (100%) who underwent G-LOC reported post-G-LOC symptoms (Table
IV).
Pearson's Chi-square test demonstrated that the incidence of G-LOC was not found to depend upon the type
of aircraft flown (p > 0.05); the observed frequency
versus the expected frequency was not significant.
TABLE II. GRADUAL INSTALLATION G-LOC (#).
T-27
AT-26
AMX
F-103
F-5
TOTAL
G-LOC Preceded
by Blackout
Total G-LOC
6
3
2
2
3
16
7
4
3
2
4
20
TABLE III. INSTANTANEOUS G-LOC (#).
T-27
AT-26
AMX
F-103
F-5
TOTAL
Without Previous
Visual Symptoms
Total G-LOC
1
1
1
-1
4
7
4
3
2
4
20
TABLE IV. POST-G-LOC SYMPTOMS.
Symptoms
Dream-like State
Dream-like State + Psychomotor Incoordination
Dream-like State + Numbness
Psychomotor Incoordination
Scotoma
Scotoma + Tunnel Vision + Impaired Hearing
N
%
5
10
I
1
2
1
25%
50%
5%
5%
10%
5%
Fig. 1. Distribution of visual symptoms due to +Gz acceleration and G-LOC by aircraft type. (N = aircraft per squadron)
of airplane which can perform aerobatics (2). Considering that in Brazil every pilot candidate starts his instruction in propeller aircraft, the phenomenon turns out to
be of major concern to flying safety, and should be
given the correct emphasis, side-by-side with research
in high performance military aviation. Many LOC episodes were reported by high performance pilots when
they flew the T-25 in the beginning of their flying training course at the Air Force Academy (data not included
in this survey). The T-25 Universal is a side-by-side
single propeller trainer, with no anti-G system. This fact
led us to make up a survey protocol for the First Air
Instruction Squadron of the Air Force Academy alone.
The high incidence of symptoms related to the T-27
may be explained by the following aspects: a) unlike the
other aircraft mentioned in this paper, the T-27 lacks an
anti-G system; and b) pilots like to perform advanced
aerobatics with the T-27, a highly maneuverable aircraft. It is used by the Brazilian "Smoke Squadron"
Demonstration Team because of its performance. It is a
two-seater trainer, in the tandem configuration, and the
second pilot is often surprised by the unexpected G-maneuver performed by the pilot in command.
Interesting results were achieved concerning the use
of the anti-G suit. Many aviators reported that they weren't using their anti-G garment for many reasons. One
reason was that by not using it they wouldn't overpass
the +Gz limit imposed by the squadron's doctrine (in
the case of the AT-26, +7.5G). Another explanation
was that some of them wouldn't find it vital if they were
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Aviation, Space, and Environmental Medicine. Vol. 66, No. 7 9 July 1995
DISCUSSION
A review of the literature about G-induced loss of
consciousness reveals a great deal of interest in high
performance aviation, regardless of the occurrence of
the phenomenon in the medium performance field, as
well as with propeller aircraft.
It is a fact that G-LOC can and does occur in any sort
BLACKOUT & G-LOC IN B A F - - A L V I M
not on alert. Some pilots reported that they flew with
their anti-G suit loose in the abdomen, because it was
"more comfortable." Similarly to the survey in the
U.S. Navy (1), it would also appear that, "as a group,
our aviators do not consider the anti-G suit to be of
much value for G protection" (1).
The high incidence of prodromal visual symptoms,
such as greyoutfloss of peripheral vision and blackout,
shown in the survey reflects a positive point. We know
that the visual system is a protective mechanism of the
central nervous system concerning ischemia; it is a
means of warning the organism that LOC is about to
occur (3,4). If the pilot experiences any of these visual
symptoms, he can recognize the possible subsequent
G-LOC shortly thereafter, if he insists on sustaining
high + Gz. This is the basis for the human centrifuge
training concerning the recognition of each pilot's endpoint, the line that separates consciousness from unconsciousness, the frontier between the organism's maximum resistance to + Gz and the failure of the whole
system involved.
Just as pilots undergo periodical physiological training in the hypobaric chamber to recognize their hypoxia
symptoms, the continuous training in the centrifuge
would enhance their capacity for the recognition of each
one's G-tolerance. Additionally, recognition of individual symptoms resulting from G-LOC should decrease
the relative incapacitation period following LOC, thus
increasing the pilot's chance of survival should it occur
(5).
Our data on physiologic symptoms resulting from
G-LOC are relevant. All (100%) of the individuals who
reported LOC said they had some sort of incapacitation
after the episode, due to sequelae classically described
in the literature (5): dream-like state, psychomotor incoordination (including convulsive movements), numbness (perioral/extremities), scotoma, tunnel vision, and
impaired hearing, in combination or alone, all of which
indicate Type II G-LOC. One pilot wrote that he was
flying in the backseat of an AT-26 (subsonic jet trainer),
with the other pilot performing acrobatic maneuvers,
when unexpected LOC occurred. About the recovery,
he wrote:
"All of a sudden, everything around me looked like a cartoon;
it was like I were Roger Rabbit inside the movie ! I tried to touch
Aviation, Space, and Environmental Medicine 9 Vol. 66, No. 7 ~ July 1995
the instrument panel but my arm didn't obey . . . It was very
confusing. Then it seemed that I was gradually getting out of the
cartoon back into reality. I only realized what was going on
when I checked my altimeter and saw we had dropped from
22,000 ft to 10,000 ft, and the nose was still downwards. I finally
got the plane back to control at 6000 ft. I knew when we landed
that my partner, too, had lost consciousness, and the only reason I am writing this now is because we were flying in high
altitude when we both lost consciousness."
What can be said about the pilots who undergo G-LOC
and do not realize it? If we consider that about 50% of
the individuals who experience G-LOC don't remember
it (6), the percentage in this research doubles from
10.36% to 20.72%. This is enough to justify a continuous
program of physiological training in the human centrifuge, not only for high performance aircraft pilots, but
for every pilot who flies an airplane that can pull enough
" G " to lead to LOC. Obviously, the profile for each
type of aircraft would be adjusted for specific missions.
ACKNOWLEDGMENTS
This survey would not have been possible without the cooperation
of the pilots involved and their flight surgeons. We are indebted to
them. We are also grateful for the help of Captain Flavio Xavier from
the Institute of Aerospace Physiology for his guidance during the
statistical analysis of this data. And last, but not least, we would like
to thank the General Air Command (COMGAR) for their comprehension of the importance of such research by "opening all doors" that
might be shut throughout our study.
The views expressed here are those of the author and do not necessarily reflect the official position of the Brazilian Air Force.
REFERENCES
1. Johanson DC, Pheeny HT. A new look at the loss o f consciousness experience within the U.S. Naval Forces. Aviat. Space
Environ. Med. 1988; 59:6--8.
2. Ross JA. A case of G-LOC in a propeller aircraft. Aviat. Space
Environ. Med. 1990; 61:567-8.
3. Whinnery JE. Medical considerations for human exposure to acceleration-induced loss of consciousness. Aviat. Space Environ. Med. 1991; 62:618-23.
4. Whinnery JE, Shender BS. The opticogravic nerve: eye-level anatomic relationship within the central nervous system. Aviat.
Space Environ. Med. 1993; 64:952--4.
5. Whinnery JE. Converging research on + Gz-induced loss of consciousness. Aviat. Space Environ. Med. 1988; 59:9-11.
6. Whinnery JE, Burton RR, Boll PA, Eddy DR. Characterization of
the resulting incapacitation following unexpected + Gz-induced
loss of consciousness. Aviat. Space Environ. Med. 1987; 58:
631-6.
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