Underwater Escape Research Articles

A pre-exercise screening of helicopter underwater escape training using a modified human reliability analysis with rule-based mechanism

This study conducts a human reliability analysis to develop a pre-exercise screening tool for helicopter underwater escape training (HUET) to proactively improve training facilities and to contribute attendees' performance. In this context, a modified human error assessment and reduction technique (HEART) was adapted. The technique investigates error producing conditions (EPC) and general task type (GTT) variables considering attendees profile, training infrastructure conditions, and 16 sub-steps of HUET exercises. Since the identification of EPC and GTT is still a key limitation of traditional HEART, this study extends a basic rule-based mechanism based on if-then-else comparison matrix structure to enhance accuracy in practice. The case study underscores the feasibility of individual, provider, and procedural interventions, enhancing training success and practical application of skills in real incidents. The application of a rule-based selection algorithm for GTT determination enhances objectivity, contributing to a more controlled identification and minimisation of errors. The case study, tailored specifically for practical training, delineates the feasibility of individual-based, training provider-based, and procedural-based interventions. Additionally, mitigating factors like ‘emotional stress’ and ‘unfamiliarity’ through advanced safety measures can boost attendees' self-confidence, leading to improved training success and practical skill application in real-world scenarios.

Canadian Ultralight Accidents in Water (1990 to 2020).

INTRODUCTION: Recently, an analysis of Canadian seaplane accidents terminating in water (1995-2019) was conducted, but ultralight water accidents were excluded due to differences from general aviation operations. This is the first literature that reports a series of ultralight accidents that occurred in water. The purpose of this paper is to identify the circumstances surrounding ultralight water accidents in Canada and to identify actions with the potential to improve survival.METHODS: Ultralight water accidents that were reported to the Transportation Safety Board of Canada between 1990 and 2020 were reviewed.RESULTS: Of the 1021 accidents that involved ultralights, 114 terminated in water, involving 155 occupants and 8 fatalities, yielding an occupant mortality rate of 5%. Of the accidents, 52% occurred during landing. There was less than 15 s warning in 78% of cases, which included five (63%) fatalities. The aircraft inverted in 40% of the accidents and, in 21%, it sank immediately. Loss of control was the terminal cause of the accident in 43% of cases, while adverse environmental conditions were reported in 38% of accidents. Little or no details were included on lifejacket or restraint harness use, status of emergency exits, water temperature, or occupant diving experience or underwater escape training.CONCLUSIONS: The mortality rate in ultralight aircraft water accidents was less than half that of helicopter and seaplane ditchings, but the lack of warning time was similar. All pilots and passengers need to have a well-practiced survival schema before strapping in and can benefit from underwater escape training.MacDonald C, Brooks C, McGowan R, Rosberg A. Canadian ultralight accidents in water (1990 to 2020). Aerosp Med Hum Perform. 2023; 94(6):437-443.

An Autopsy Report of Hypoplastic Coronary Artery Disease Incidentally Identified in a Young Man

Hypoplastic coronary artery disease (HCAD) is a rare congenital abnormality characterized by underdevelopment of one or more major branches of the coronary arteries, which may lead to myocardial infarction and sudden death. We report a case of HCAD that was incidentally detected during autopsy in a 25-year-old male soldier who died during underwater escape training. On macroscopic examination, the right coronary artery measured 1 mm in diameter, which was significantly smaller than that of other coronary arteries. We observed no anomalies in addition to HCAD. Death was attributed to drowning, which was consistent with autopsy findings and the circumstances of death. Although extremely rare, if sudden cardiac death is suspected in children and young adults, it must be confirmed through careful evaluation.

Evaluation of the Helicopter Emergency Breathing Apparatus on Egress Performance.

BACKGROUND: Emergency helicopter landing at sea is dangerous. Specialized training, known as helicopter underwater escape training (HUET), prepares occupants to quickly exit the helicopter, which often inverts and sinks. In most jurisdictions, helicopter occupants are equipped with a helicopter underwater egress breathing apparatus (HUEBA) to provide sufficient air for escape. HUET trainees report that the HUEBA is easy to use, but it is well known that learners are often overconfident in their judgement of learning. To better understand how the HUEBA affects HUET sequence performance, we investigated whether using the HUEBA influences the sequence movement time and number of errors.METHODS: Twelve participants (7 men and 5 women, mean age 25.33 9.57 SD) with no prior experience with HUET performed consecutive trials of the HUET sequence, 5 with the HUEBA and 5 without the HUEBA. Video of each trial recorded the total movement time and enabled movement time analyses of each component of the sequence: crossing arms, tucking the head, pushing the window, inserting the regulator, and releasing the seatbelt. These recordings were also used to score performance errors according to a checklist.RESULTS: Analyses revealed that using a HUEBA increased the total movement time and time to release the seatbelt by 0.36 and 0.39 s, respectively, in comparison to without the HUEBA.DISCUSSION: Our study illustrates that using the HUEBA during the HUET sequence increases total movement time and time to release the seatbelt. However, this difference is marginal and unlikely to have practical significance during underwater escape.King M, Sanli E, Mugford K, Martina S, Brown R, Carnahan H. Evaluation of the helicopter emergency breathing apparatus on egress performance. Aerosp Med Hum Perform. 2020; 91(12):962965.

Psychological considerations in submarine escape training: brief overview and future directions.

The inability of a submarine to surface must rate as one of greatest risks to sailors in peacetime. To prepare for such emergencies, many navies provide training to master the procedures required to escape successfully from disabled submarines. This paper provides a brief overview of some of the psychological principles in simulated submarine escape training. It further discusses applicable psychological constructs such as positive outcome expectancies, the role of anxiety, and other personal factors mediating outcomes of such training. It concludes with recommendations for future research aimed at enhancing the safety and impact of submarine escape training. These include enhanced detection of psychological risk factors such as anxiety, as well as investigating the relative contribution of personality variables to in-training safety and positive outcome expectancies. These recommendations do not only apply to submarine escape training, but may also be applicable to high fidelity safety training in other off-shore survival contexts, such as helicopter underwater escape training, freefall lifeboat training and smoke diving.

Donald Campbell McNutt

After completing house jobs Donald Campbell McNutt joined the Royal Navy for his national service and obtained a permanent commission in 1954. He enjoyed flying and completed observer training and...

Injury Rate in a Helicopter Underwater Escape Trainer (HUET) from 2005–2012

Helicopter underwater escape training (HUET) carries a potential for injury and this paper identifies the injury rate. A marine survival training school registry of all students trained between 2005-2012 in HUET and the coinciding accident records were examined. There were 8902 students trained in a helicopter underwater escape simulator for a total of 59,245 underwater escapes. There were 40 cases where only first-aid was required and 3 serious injuries (a laceration requiring 5 sutures, 1 dislocated shoulder, and 1 water aspiration requiring hospitalization). There were no deaths and no problems reported with using the Emergency Breathing System (EBS) or Air Pocket. Of the injuries, 11 were due to the student using a poor escape technique. The overall probability of injury was 0.74 per 1000 ascents. In HUET training, there is a very low injury rate with almost no significant severity. Although not scientifically proven, this would suggest that the low incident rate is due to good medical screening and the attention given by instructors to anxious students. Compared to other training such as diving, parachute jumping, and submarine escape training, the rate of injury was considerably lower.

Crash attenuating seats: Effects on helicopter underwater escape performance

Surviving a helicopter ditching at sea involves a number of factors; however, none have as great an influence as impact forces. To minimize this influence, crash attenuating seat systems have recently been integrated into offshore transport helicopters. Unfortunately, no research has investigated the system’s effect on underwater egress. This study outlines the first known examination of the crash attenuating seats from the perspective of passenger egress. Results indicate that egressing from an inverted and flooded helicopter requires significantly more time, and is rated as being more difficult when the seat is fully attenuated (stroked). Results also indicate that egress is significantly influenced by environmental conditions and the position of a helicopter simulator. Based on these findings, it is recommended that all offshore personnel be trained to overcome the influence of attenuating seats, environmental conditions, and position of the helicopter during their occupationally required egress training course.

The effect of transportation suit induced heat stress on helicopter underwater escape preparation and task performance

Although essential in an emergency such as a helicopter ditching, mandatory survival suits worn by civilian personnel may lead to heat strain during a normal flight. To explore the possibility that wearing a helicopter transportation suit impairs emergency performance, 11 individuals completed underwater escape procedures immediately following a pre-recorded emergency announcement (randomly played between 50 and 90 min) in two ambient temperature conditions (Thermoneutral = 21 °C and Hot = 34 °C). Mean skin and rectal temperatures were recorded throughout the trials, while situation awareness and thermal sensation/comfort were recorded on completion of trials. Results indicate that although mean skin and rectal temperatures were significantly higher at the end of both trials, escape procedures were not impaired. It can therefore be concluded that although conditions inside an offshore transport helicopter are perceived as being hot and uncomfortable, no deficits in escape performance should be expected in the first 90 min of flight.

Performance of Emergency Underwater Breathing Systems in Cool (25°C) and Cold (12°C) Water

The shortfall between breath-hold time on cold-water immersion and the time required to make an underwater escape from a helicopter provides the rationale for emergency underwater breathing systems (EUBS) for passengers flying over cold water. This study compared three types of EUBS: a compressed gas system (CG); a rebreather system (RB); and a hybrid system (H). Each EUBS was examined during water deployment (W(dep)) and over 90 s in cool (25 degrees C) and cold water (12 degrees C) immersion to the neck (Imm) and submersion (Subm). Subjects wore standardized clothing, including dry suit. Measures included: W(dep) time, stay time (Imm and Subm), dyspnea rating, O2 and CO2 remaining in rebreather bags [H and RB (partial pressure mmHg)], and gas volume used (CG). Mean data show W(dep) was slowest in the H (17.7 s) compared to the RB (10.0 s) and CG (8.1 s). Stay time was greatest in the H (90.0 s) compared to the RB (68.3 s) and CG (87.0 s); stay time in CG was also greater than RB. Dyspnea ratings were greater in RB trials (6.5 cm) compared to the CG (2.4 cm) and H (1.9 cm). Across devices, stay time in cold water was shorter during submersion than immersion (85.9 s vs. 70.1 s). During submersion stay time was shorter in cold compared to cool water (12 degrees C: 62.8 s; 25 degrees C: 77.5 s). The data suggest that the CG and H devices outperformed the RB device, but the H device required longer to deploy.

Introduction of a Compressed Air Breathing Apparatus for the Offshore Oil and Gas Industry

When a helicopter ditches the majority of crew and passengers have to make an underwater escape. Some may not be able to hold their breath and will drown. For at least 15 yr, military aircrew have been trained to use a scuba system. In the offshore oil and gas industry, there has been more caution about introducing a compressed air system and a rebreather system has been introduced as an alternative. Recently, Canadian industry and authorities approved the introduction of Helicopter Underwater Emergency Breathing Apparatus (HUEBA) training using compressed air. This communication reports the training of the first 1000 personnel. Training was introduced in both Nova Scotia and Newfoundland concurrently by the same group of instructors. Trainees filled out a questionnaire concerning their perceived ratings of the ease or difficulty of classroom training and the practical use of the HUEBA. Ninety-eight percent of trainees found the classroom and in-water training to be "good/very good". Trainees found it to be "easy/very easy" to clear the HUEBA and breathe underwater in 84% and 64% of cases, respectively. Divers reported a greater ease in learning all the practical uses of the HUEBA except application of the nose clip. There were problems with the nose clip fitting incorrectly, and interference of the survival suit hood with the regulator, which subsequently have been resolved. When carefully applied, the introduction of the HUEBA into training for offshore oil and gas industry helicopter crew and passengers can be safely conducted.

ECG During Helicopter Underwater Escape Training

Coincidental stimulation of the sympathetic and parasympathetic nervous system can cause "autonomic conflict" and consequent cardiac arrhythmias. The present study tested the hypotheses that: 1) cardiac arrhythmias would be seen in those undertaking helicopter underwater escape training (HUET); 2) the occurrence of arrhythmias in individuals could be predicted; and 3) the heart rate response to HUET would habituate with repeated runs. There were 26 male volunteers who each undertook 5 HUET submersions into water at 29.5 degrees C, with each run separated by 10 min. Each submersion included a 3-min, 40-s pre-submersion period, a 10-s submersion, and 40-s post-submersion period. Participants wore a three-lead telemetric ECG system beneath an immersion suit and underclothing. Skin temperature was measured in one participant. Each participant undertook tests to establish their autonomic function, including heart rate variability, face immersion, cold pressor test, and aerobic capacity assessment. The heart rate response to HUET was reduced by the fourth run when compared to the first run. Across all runs, 32 cardiac arrhythmias were identified (25%) in 22 different participants; all but 6 of the arrhythmias occurred just after submersion. Only aerobic fitness appeared inversely associated with the occurrence of arrhythmias. The heart rate response to HUET habituates. HUET produces cardiac arrhythmias; these are asymptomatic and probably of little clinical significance in young, fit individuals. It remains to be seen if this is the case with either an older, less fit cohort of people or in those undertaking longer breath holds in colder water.

Physiological and Psychological Effects of Escape from a Sunken Submarine on Shore and at Sea

The stress effects induced by diverse military scenarios are usually studied under tightly controlled conditions, while only limited research has addressed realistic scenarios. This study was designed to compare the effects of two levels of realism in stressful training for escape from a sunken submarine. Thirteen qualified submariners served as subjects. All had previously participated in underwater escape training using a simulated submarine in a land-based tank submerged at a depth of 6 m; for this study, they repeated the simulator escape, following which six of them executed escape from an actual submarine lying at a depth of 30 m on the sea floor. The men were studied before the exercises, immediately after surfacing, and 2 h later. Measured variables included sympathovagal balance, salivary cortisol, perceived mood, and sleep, as well as short-term and declarative memory. Compared to the simulator exercise in the tank, the escape at sea showed the following significant differences: 1) higher salivary cortisol values (6.33 +/- 3.9 nmol x L(-1) on shore and 13.38 +/- 7.5 nmol x L(-1) at sea); 2) greater adverse changes in mood, including vigor, tension, and ability to fall asleep; and 3) impairment in declarative memory. Responses were found to differ further for the five submariners who had prior experience of accident or injury while at sea. The psychophysiological and cognitive effects of military exercises may be influenced by the realism of conditions and by prior exposure to life-threatening situations.

The effect of emergency breathing systems during helicopter underwater escape training for land force troops

A functional task analysis was carried out for 12 troops during helicopter underwater escape training (HUET) to identify performance difficulties while egressing from a submerged and capsized helicopter simulator. Troops and qualified HUET instructors rated performance during 22 trials of specific skill sets known to aid personnel in the event of a helicopter ditching into water. Results indicate that troops took considerably longer to egress through a forward exit and experienced fewer difficulties when using an emergency breathing system (EBS). Results further indicated that without an EBS, only 58% of the troops successfully escaped whereas 100% escaped unaided when using an EBS. To maximize survival rates in the event of a ditching, it can be concluded that all troops should be issued and trained to use an EBS.

Ethylene-promoted elongation: an adaptation to submergence stress.

A sizeable minority of taxa is successful in areas prone to submergence. Many such plants elongate with increased vigour when underwater. This helps to restore contact with the aerial environment by shortening the duration of inundation. Poorly adapted species are usually incapable of this underwater escape. Evidence implicating ethylene as the principal factor initiating fast underwater elongation by leaves or stems is evaluated comprehensively along with its interactions with other hormones and gases. These interactions make up a sequence of events that link the perception of submergence to a prompt acceleration of extension. The review encompasses whole plant physiology, cell biology and molecular genetics. It includes assessments of how submergence threatens plant life and of the extent to which the submergence escape demonstrably improves the likelihood of survival. Experimental testing over many years establishes ethylene-promoted underwater extension as one of the most convincing examples of hormone-mediated stress adaptation by plants. The research has utilized a wide range of species that includes numerous angiosperms, a fern and a liverwort. It has also benefited from detailed physiological and molecular studies of underwater elongation by rice (Oryza sativa) and the marsh dock (Rumex palustris). Despite complexities and interactions, the work reveals that the signal transduction pathway is initiated by the simple expediency of physical entrapment of ethylene within growing cells by a covering of water.

Ethylene regulates fast apoplastic acidification and expansin A transcription during submergence‐induced petiole elongation in Rumex palustris

The semi-aquatic dicot Rumex palustris responds to complete submergence by enhanced elongation of young petioles. This elongation of petiole cells brings leaf blades above the water surface, thus reinstating gas exchange with the atmosphere and increasing survival in flood-prone environments. We already know that an enhanced internal level of the gaseous hormone ethylene is the primary signal for underwater escape in R. palustris. Further downstream, concentration changes in abscisic acid (ABA), gibberellin (GA) and auxin are required to gain fast cell elongation under water. A prerequisite for cell elongation in general is cell wall loosening mediated by proteins such as expansins. Expansin genes might, therefore, be important target genes in submergence-induced and plant hormone-mediated petiole elongation. To test this hypothesis we have studied the identity, kinetics and regulation of expansin A mRNA abundance and protein activity, as well as examined pH changes in cell walls associated with this adaptive growth. We found a novel role of ethylene in triggering two processes affecting cell wall loosening during submergence-induced petiole elongation. First, ethylene was shown to promote fast net H(+) extrusion, leading to apoplastic acidification. Secondly, ethylene upregulates one expansin A gene (RpEXPA1), as measured with real-time RT-PCR, out of a group of 13 R. palustris expansin A genes tested. Furthermore, a significant accumulation of expansin proteins belonging to the same size class as RpEXPA1, as well as a strong increase in expansin activity, were apparent within 4-6 h of submergence. Regulation of RpEXPA1 transcript levels depends on ethylene action and not on GA and ABA, demonstrating that ethylene evokes at least three, parallel operating pathways that, when integrated at the whole petiole level, lead to coordinated underwater elongation. The first pathway involves ethylene-modulated changes in ABA and GA, these acting on as yet unknown downstream components, whereas the second and third routes encompass ethylene-induced apoplastic acidification and ethylene-induced RpEXPA1 upregulation.

Technical Training Conference

AN International Rotary Wing safety and life support symposium and exhibition was held recently in London which dealt with topics of vital interest to civil and military operators. These included the psychology of stress, flight deck automation, the physical limitations of the human body, underwater escape, HUMS, all weather operations, and night flying.

Detectability of emergency lights for underwater escape : Allan, J.R., Brennan, D.H., and Richardson, G.Aviation, Space and Environ Med, 1989, 60.3, 199–204, 11 refs

The time to detect each of three underwater lights by six subjects was measured in clear and turbid (attenuation coefficient = 4.2.m-1) water, at distances of 1.54 m and 3.1 m, from two viewing angles, straight ahead (0 degrees) or 65 degrees to one side, and under three levels of ambient illumination. The lights were viewed either through a window, to simulate the use of a face mask, or with the subjects immersed. All lights were detected rapidly (less than 1 s) when viewed through the window in clear water. In turbid conditions, none of the lights was seen at 3.1 m by any subject. At a 1.54 m viewing distance, reliable detection by immersed subjects was found only in the clear water under the two darker ambient illuminations. In turbid water, detection was unreliable. We conclude that the design of underwater escape lighting should not rely on visibility over distances greater than 1.5 m, and that an illuminated guide-bar might provide valuable assistance in directing escape from aircraft.

Maximum acceptable inherent buoyancy limit for aircrew/passenger helicopter immersion suit systems

Helicopter crew and passengers flying over cold water wear immersion suits to provide hypothermic protection in case of ditching in cold water. The suits and linings have trapped air in the material to provide the necessary insulation and are thus very buoyant. By paradox, this buoyancy may be too much for a survivor to overcome in escaping from the cabin of a rapidly sinking inverted helicopter. The Canadian General Standard Board requested that research be conducted to investigate what should be the maximum inherent buoyancy in an immersion suit that would not inhibit escape, yet would provide adequate thermal insulation. This experiment reports on 12 subjects who safely escaped with 146N (33 lbf) of added buoyancy from a helicopter underwater escape trainer. It discusses the logic for and recommendation that the inherent buoyancy in a helicopter crew/passenger immersion suit system should not exceed this figure.