Introduction
On 21 August 2023, a C-17A Globemaster III (tail number 10-000215) from the 437th Airlift Wing, Joint Base Charleston, South Carolina, departed Joint Base Elmendorf-Richardson (JBER), Alaska, for a planned seven-hour high-altitude simulated airdrop mission. The aircraft carried a mishap member (MM), a General Schedule civilian assigned to the Missile Defense Agency (MDA), Redstone Arsenal, Alabama, who was participating as mission essential personnel.
Sequence of Events
The C-17 took off from JBER at 1008 local time. After an uneventful takeoff, departure, and cruise, at approximately 1400 local time the aircraft was fully depressurized to 24,900 feet mean sea level (MSL). All personnel were on oxygen. The crew opened the cargo doors and executed a test pass of a medium range ballistic missile payload. Shortly after the cargo doors were closed, the MM signaled distress to nearby personnel, sweating profusely and complaining of shortness of breath and pain in his right arm. High Altitude Airdrop Mission Support (HAAMS) physiological technicians attended to him.
The aircraft landed at JBER at 1700 local time. JBER Emergency Medical Services (EMS) transported the MM by ambulance to the JBER emergency room (ER) at 1749 local time.
Medical Response and Outcome
Upon arrival at the ER, physicians immediately treated the MM for decompression sickness (DCS) and coordinated follow-on treatment in a hyperbaric chamber. The following day, 22 August 2023, at 0806 local time, while being transported to a higher level of care at a local hospital, the MM entered cardiac arrest. ER personnel were unable to resuscitate him, and he was pronounced deceased at 0832 local time.
The Medical Examiner determined the cause of death as decompression sickness with contributing factors of obesity, hypertension, and atherosclerotic cardiovascular disease, with an unknown role for SARS-CoV-2 infection. The manner of death was declared accidental.
Investigation Findings
The Accident Investigation Board (AIB) President found, by a preponderance of the evidence, that the mishap resulted from decompression sickness induced by the high-altitude, unpressurized portion of the military test mission. The AIB President further found that the pre-existing and underlying medical conditions of the MM substantially contributed to the mishap.
The investigation reviewed the aircraft's systems, maintenance, environmental conditions, and personnel qualifications. No issues with the C-17's environmental control or oxygen systems were identified. The mishap crew was properly qualified and trained.