Cervical injuries during high G maneuvers: a review of Naval Safety Center data, 1980-1990.

As aircraft capable of sustaining high "G" maneuvers enter the U.S. Navy Fleet, the reported incidence of cervical injury to aircrew seems to have increased. To determine the extent of the problem, personal injury reports submitted to the Naval Safety Center were reviewed for the 10-year period from 1980 to 1990. In addition, confidential questionnaires were sent to flight surgeons supporting fighter/or fighter-attack units. The data collected were statistically analyzed. The incidence of cervical injuries, defined as at least one day's absence from the flight schedule, was computed. Other subjective factors, such as the type helmet worn, the cockpit position flown and the type of mission profile completed, were examined. As might be expected, the most common offender was air combat maneuvering. The most common aircraft was the F/A18, but the radar intercept officer position in the F14B was also a significant contributor. The most common injury pattern reported was a simple muscle strain. Cervical pain after high "G" missions poses a potential threat to combat readiness. However, the use of the newer lightweight helmet seems to have reduced the severity. Muscle strengthening exercises appear to help in prevention. Treatment is successful in most cases with minimal or no residuals noted. As yet, there exist little official data to support the notion of a major problem.

Loss of cabin pressurization in U.S. Naval aircraft: 1969-90.

During the 22-year period from 1 January 1969 to 31 December 1990, there were 205 reported cases of loss of cabin pressure in US Naval aircraft; 21 were crew-initiated and 184 were deemed accidental. The ambient altitudes varied from 10,000 ft (3048 m) to 40,000 ft. (12192 m). The most common reason for crew-initiated decompression was to clear smoke and fumes from the cockpit/cabin (95%). The most common cause for accidental loss of cabin pressure was mechanical (73.37%), with aircraft structural damage accounting for the remaining 26.63%. Serious physiological problems included 1 pneumothorax, 11 cases of Type I decompression sickness, 23 cases of mild to moderate hypoxia with no loss of consciousness, 18 cases of hypoxia with loss of consciousness, and 3 lost aircraft with 4 fatalities due to incapacitation by hypoxia. In addition, 12 ejections were attributed to loss of cockpit pressure. Nine of the ejections were deliberate and three were accidental, caused by wind blast activation of the face curtain. Three aviators lost their lives following ejection and seven aircraft were lost. While the incidence of loss of cabin pressure in Naval aircraft appears low, it none-the-less presents a definite risk to the aircrew. Lectures on the loss of cabin/cockpit pressurization should continue during indoctrination and refresher physiology training.

Through the canopy glass: a comparison of injuries in Naval Aviation ejections through the canopy and after canopy jettison, 1977 to 1990.

Two methods of ejection from tactical aircraft are commonly used: jettisoning the canopy prior to seat travel, and ejecting through a closed canopy. This report compares the ejection injury experience of Naval Aviation in each mode during January 1977-August 1990. During that period, 336 through-canopy and 580 canopy-jettison ejections were accomplished. The former group sustained 10.7% fatal injuries, and only 17.0% egressed injury-free. By comparison, the latter cohort incurred only 4.7% fatalities and fully 31.9% egressed without injury. Analysis of patterns of injuries confirms higher G-forces in through-canopy ejections, resulting in not only more injuries, but more severe injuries. In spite of these findings, we discuss the compelling tactical and financial reasons to consider through-canopy systems.

Spatial disorientation in naval aviation mishaps: a review of class A incidents from 1980 through 1989.

Spatial Disorientation (SD) has long been a major aeromedical factor contributing to naval aviation mishaps. In the past, it has been viewed as a generalized phenomenon, described by its vertigo-related symptoms. More recently, however, three distinct types of SD have been identified, each based on whether the aviator recognizes and responds to its onset. In the current retrospective study, Flight Surgeon and Mishap Investigation Report narratives from 33 Class A mishaps occurring from 1980 through 1989 were reviewed. SD was determined to have been a causal factor in all cases. The mishaps were examined to categorize SD into the three descriptive types and to describe the relationship (if any) between SD and various mission-related factors. Aircraft type, phase of flight, time of day, pilot experience, and flight topography were all considered. The results indicate that Types I and II SD could be identified as causal factors in all 33 Class A mishaps. Further, most Type I SD was experienced primarily by helicopter pilots at night while most Type II SD incidents affected jet pilots during day missions.

Flight experience and the likelihood of U.S. Navy aircraft mishaps.

Although the flight experience level of U.S. Navy pilots has not declined in recent years, current budget constraints will eventually lead to reductions in flight hours per pilot. This implies an eventual shifting of the distribution of flight hours. Analyses show that the rate of aircrew factor and pilot error mishaps tends to decrease as pilots' flight experience in model increases. Aviation loss rates are higher during a pilot's first 500 hours in model. This seems to be true no matter if the pilot is simply inexperienced overall or a highly experienced aviator transitioning to a different aircraft. These data suggest, therefore, that if the in-model experience levels of naval aviators decline sufficiently, the mishap rate will increase.

Decompression sickness: U.S. Navy altitude chamber experience 1 October 1981 to 30 September 1988.

This study reports the incidence of decompression sickness (DCS) occurring in U.S. Navy altitude chambers in association with physiological training of aircrews for the 7-year period from 1 October 1981 to 30 September 1988. There were 140 total cases of DCS in 136,696 chamber exposure, an incidence of 0.10%. Among trainees, there were 78 cases in 111,674 exposures, and incidence of 0.07%. Among inside observers, there were 62 cases in 25,022 exposures and incidence of 0.25%. The incidence of DCS among inside observers was reduced almost two-fold over the last Navy report and is the lowest reported since 1973. Reasons for the reduction are discussed. In addition, analysis of the data includes types of DCS, symptoms, frequency of joint involvement, predisposing factors, altitude and time of onset of DCS, and treatment tables employed.

Decompression sickness: USN operational experience 1969-1989.

This report presents data on the U.S. Navy's experience in decompression sickness occurring in operational flight from 1 January 1969 to 30 December 1989. During these 21 years, decompression sickness was reported in 12 USN aircraft and involved 15 aircrew. The primary cause of decompression, as might be expected, was a loss of cabin or cockpit pressurization. The most common manifestation of decompression sickness was limb or joint pain although some crewmembers experienced various manifestations of neurological dysfunction. One crewmember experienced chokes. Of the 15 afflicted aircrew, 13 (87%) had complete remission of symptoms by the time they landed. Two crewmembers required compression therapy for resolution of symptoms. None of the reported symptoms were incapacitating and none of the aircraft involved crashed or received even minor damage.

Trapped gas dysbarism requiring recompression therapy.

The clinical manifestation, pathophysiology, and treatment of dysbarism continues to pose a dilemma for physiologists and flight surgeons. This paper presents a case of trapped gas dysbarism resulting from exposure to 40,000 ft, which was severe, disabling, and required recompression therapy to resolve.

Incidence of decompression sickness in Navy low-pressure chambers.

This study reports the incidence of decompression sickness occurring in U. S. Navy altitude chambers in association with physiological training of aircrews for the period 1 Jan. 1972 to 31 Dec. 1975. There were 79 cases of decompression sickness in 88,520 altitude chamber exposures, an incidence of 0.089%. Among trainees, there were 22 cases in 73,561 exposures, an incidence of 0.029%. Among chamber inside observers, there were 57 cases in 14,959 exposures, an incidence of 0.38%. This 12-fold greater incidence among inside observers over trainees was statistically significant (p less than 0.01). Reasons for the increased incidence of decompression sickness among inside observers are discussed.

Frequency and duration of interval training programs and changes in aerobic power.

This study was designed to ascertain whether 7- and 13-wk interval training programs with training frequencies of 2 days/wk would produce improvement in maximal aerobic power (VO2max) comparable to that obtained from 7- and 13-wk programs of the same intensity consisting of 4 training days/wk. Sixty-nine young healthy college males were used as subjects. After training, there was a significant increase in VO2max (bicycle ergometer, open-circuit spirometry) that was independent of both training frequency and duration. However, there was a trend for greater gains after 13 wk. Maximal heart rate (direct lead ECG) was significantly decreased following training, being independent of both training frequency and duration. Submaximal VO2 did not change with training but submaximal heart rate decreased significantly with greater decreases the more frequent and longer the training. Within the limitations of this study, these results indicate that: 1) maximal stroke volume and/or maximal avO2 difference, principle determinants of VO2max, are not dependent on training frequency nor training duration, and 2) one benefit of more frequent and longer duration interval training is less circulatory stress as evidenced by decreased heart rate, during submaximal exercise.