HISTORY OF FLIGHTOn January 14, 2024, about 0747 mountain standard time, a Kubicek BB85Z balloon, N4961D, was involved in an accident near Eloy, Arizona. The pilot and three passengers were fatally injured, and one passenger sustained serious injuries. The balloon was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 sightseeing passenger and skydiving (commercial) flight. The flight originated about 0630, an hour before sunrise. The departure area was about 18 miles west-northwest from the accident site. The flight was scheduled with 13 people onboard, including 8 skydivers that planned to jump from the balloon at a planned altitude. Interviews with skydivers revealed that after about 35 minutes, the balloon had ascended to about 10,000 ft msl and all 8 skydivers departed the balloon in small groups, as planned. The 4 passengers and pilot remained in the basket. A few minutes later witnesses and a few of the skydivers saw the balloon descending towards the ground. A review of multiple mobile phone videos revealed that the balloon was descending with a deflated envelope trailing from above. Additionally, at times the engaged burner flame under the deflated envelope was observed. The balloon was equipped with a 360° field-of-view camera. Video from the accident flight begins during preflight, with the envelope being inflated during pre-dawn twilight lighting conditions. Movement of the envelope indicated surface winds were not calm. As passengers boarded the balloon, several of them were noted walking underneath the tie-off rope. A few minutes later ground crew personnel replaced an onboard padded fuel cylinder with a non-padded fuel cylinder. The pilot placed the new fuel cylinder in the pilot compartment of the basket and returned to operating the burner without securing the cylinder to the basket. The pilot released the quick release and the balloon began climbing. About a minute later, about 100 ft above ground level, the pilot pulled the Red line about 5 arm-lengths, then pulled the Red-White line about 7 arm-lengths. The rapid deflation system was observed opening and closing. About 2 minutes later, the pilot deployed the anticollision lights below the basket. The pilot retrieved a pair of pliers and manipulated fuel line fittings, then secured the pliers. About 8 minutes into the flight the pilot and passengers discussed the planned jump sequence. The pilot then moved a bag and secured the previously unsecured fuel tank and placed the bag on top of the fuel tank. About 16 minutes into the flight the pilot mentioned the sunrise and stowed the night lights. About 21 minutes into the flight the first video segment ended and after an undetermined amount of time, the second video segment began. A jumper began climbing out on the rim of the basket, followed by two more jumpers. As the balloon was reaching its planned altitude, the pilot performed several long duration burns, causing the jumpers on the side of the basket to duck to avoid the heat. As the pilot was preparing the jumpers he moved the pole-mounted camera from one side of the basket to the opposite side and in doing so, the deflation system was visible at the top of the envelope and was fully closed. A few minutes later the pilot commented, “We’re a tad bit lower but otherwise we’re gonna miss it.” Four groups of jumpers departed the basket; each time a swing rope was used, the swing line was noted impacting the fabric of the upper portion of the envelope. Jumpers departed in groups of three, two, one and two. Immediately after the last group of jumpers departed the basket, the pilot began pulling the Red line a total of 12 arm-lengths, looking up at the end of the sequence. Shortly after pulling the Red line, the pilot pulled the Red-White line about 2 arm-lengths, while looking up. The envelope began to deflate noticeably. The pilot moved the pole-mounted camera from one side of the basket to the opposite side of the basket and in doing so, the rapid deflation system was visible at the top of the envelope. The rapid deflation system was opened, revealing an opening around the vent aperture (see Figure 1). While the pilot was securing the camera to the burner support rods and conversing with passengers, the envelope was rapidly changing shape and the scoop and mouth, which were loose, moved in toward the basket and burner. The deflation system control lines were then observed dropping slowly into the basket and the Red-White line also looping between the envelope flying cables at the carabiner and basket attach point. Figure 1. Rapid deflation mode open. About 46 seconds after opening the rapid deflation vent panel, the pilot grabbed the Red line momentarily, looked up, and began operating the burner and pulling on the Red-White line. At this point, the skirt was distorted and closing in to only a few feet from side to side. He continued pulling unsuccessfully on the now pinched Red-White line, then climbed out onto the rim of the basket to free the line from the flying cables. The pilot pulled all the slack from the Red-White line, while operating the burner. Eventually the mouth of the envelope would not take in any air and most of the air from the envelope escaped from the rapid deflation vent opening. Over the next 2 minutes, the pilot relit the burner pilot light several times, and he continued to operate the burner. Despite his efforts, the balloon envelope never reinflated and remained in streamer form until the basket impacted the ground. Throughout the video, the pilot was noted coughing persistently. PERSONNEL INFORMATIONThe pilot, age 37, held a commercial pilot certificate with a rating for lighter-than-air balloon operation. Additionally, he held a senior parachute rigger certificate. Review of FAA records revealed that the pilot’s most recent first-class medical certificate was issued on April 22, 2022. At that time, he reported a total flight experience of 500 hours. The pilot’s logbook revealed that the last entry was on November 24, 2019. The accident balloon was not recorded in the logbook. The pilot stored the accident balloon at the Eloy Municipal Airport (E60), Eloy, Arizona. Internet research revealed onboard videos showing the accident pilot holding the red cord during two high-altitude flights. AIRCRAFT INFORMATIONThe balloon envelope was installed with a Smart Vent system, which consists of two types of venting: parachute valve mode and rapid deflation mode (see Figure 2). In-flight venting uses the parachute valve mode, which is controlled by the Red-White line. In this mode, the valve is pulled vertically downward to open the vent, and the line is then released and the vent closes automatically from the envelope’s air pressure. The parachute valve is used for controlled descents and must not be held open for more than 3 seconds at a time. The parachute valve is also used during preflight to release the Velcro tabs that hold the vent panel in place during initial inflation. The rapid deflation mode is controlled by both the Red and Red-White lines. By pulling the Red line, the vent panel is gathered in to the center of the vent aperture, creating a large area for hot air to escape. The rapid deflation system is used for fast and efficient deflation of the envelope when landing below 6.5 ft above ground level to prevent the basket from being dragged in windy conditions. A swing rope is not a standard part of the accident balloon. The flight manual advises against modifying the balloon and warns that modifying the balloon may cause severe personal injury or death. Maintenance documentation revealed that on November 3, 2022, an annual inspection was completed on the balloon and basket. No other maintenance documentation was available during the investigation. Figure 2- Kubicek-Hot Air Balloon Flight Manual, Smart Vent. METEOROLOGICAL INFORMATIONAt 0800, near the accident site, the winds aloft ranged from 7 knots near ground level to 43 knots, from 279°, at 10,585 ft msl (the highest altitude in the flight was about 10,000 ft msl). On the morning of the accident flight astronomical twilight was between 0603 and 0708, and sunrise began at 0731. It is unknown if the pilot had received a weather brief or reviewed the winds aloft for the flight. AIRPORT INFORMATIONThe balloon envelope was installed with a Smart Vent system, which consists of two types of venting: parachute valve mode and rapid deflation mode (see Figure 2). In-flight venting uses the parachute valve mode, which is controlled by the Red-White line. In this mode, the valve is pulled vertically downward to open the vent, and the line is then released and the vent closes automatically from the envelope’s air pressure. The parachute valve is used for controlled descents and must not be held open for more than 3 seconds at a time. The parachute valve is also used during preflight to release the Velcro tabs that hold the vent panel in place during initial inflation. The rapid deflation mode is controlled by both the Red and Red-White lines. By pulling the Red line, the vent panel is gathered in to the center of the vent aperture, creating a large area for hot air to escape. The rapid deflation system is used for fast and efficient deflation of the envelope when landing below 6.5 ft above ground level to prevent the basket from being dragged in windy conditions. A swing rope is not a standard part of the accident balloon. The flight manual advises against modifying the balloon and warns that modifying the balloon may cause severe personal injury or death. Maintenance documentation revealed that on November 3, 2022, an annual inspection was completed on the balloon and basket. No other maintenance documentation was available during the investigation. Figure 2- Kubicek-Hot Air Balloon Flight Manual, Smart Vent. WRECKAGE AND IMPACT INFORMATIONThe accident site was located on flat desert terrain, sparsely populated with sage brush, and was about 2 1/2 miles northeast of E60. The basket landed upright and had impact damage to the burner frame and to the basket base. The envelope remained attached to the basket and showed thermal damage near the mouth of the envelope. The sewn rim load tape material near the top of the envelope had minor fraying, and several of the panels were damaged. The postaccident examination of the balloon revealed no preimpact anomalies with the basket, burner assembly, or envelope that would have precluded normal operation. ADDITIONAL INFORMATIONAccording to 14 CFR Part 91.205, an anticollision light system must be used during night visual flight rules flights, which end at sunrise. The balloon flight manual indicated that during the pre-takeoff check, the release of the Velcro tabs is conducted by pulling the Red-White line. The manual also specified that a functional check of the deflation system be conducted. The balloon flight manual reports that during skydiving operations, the maximum number of skydivers [parachutists] to be released at one time is one and that the pilot must react to the sudden loss of weight when the skydivers exit. FLIGHT RECORDERSThe operator’s laptop, altimeter, and onboard camera were sent to the NTSB recorders lab for download. Neither the laptop nor the altimeter had any flight data pertaining to the accident flight. MEDICAL AND PATHOLOGICAL INFORMATIONAn autopsy of the pilot was performed by the Pinal County Medical Examiner’s Office in Florance, Arizona, which listed the cause of death as “multiple blunt force trauma.” Toxicology tests detected ketamine, which was confirmed to have been administered to the pilot by emergency medical services as part of his resuscitation efforts. Other results detected Chlorpheniramine at 7 ng/g in liver tissue. Hydroxybupropion was detected in heart blood but not in liver tissue. Dextromethorphan, dextrorphan and chlorothiazide were not detected in heart blood, but were detected in the liver tissue.