HISTORY OF FLIGHTOn January 23, 2024, about 1844 eastern standard time, a Cessna 172N airplane, N737VC, was substantially damaged when it was involved in an accident near Weston, Florida. Both commercial pilots were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The owner of the flight school from which the left-seat pilot rented the airplane reported that the purpose of the flight was to build flight time. He stated that the left-seat pilot had been a student at the school about two years before the accident and had completed a flight review with one of the school’s flight instructors on the morning of the accident flight. The owner also reported that the left- and right-seat pilots met for the first time on the day of the accident, and that the right-seat pilot was on board to act as a safety pilot at the request of the left-seat pilot. ADS-B data revealed that the airplane departed to the east from North Perry Airport (HWO), Hollywood, Florida, at 1830 before turning 180° right onto a westerly track. The airplane climbed to a maximum altitude of 1,950 ft mean sea level (msl) about 1834 before beginning to descend. The airplane’s altitude then varied between 1,000 and 1,600 ft msl, and its calibrated airspeed (based on a performance study of the ADS-B data) varied between 90 and 120 kts. Beginning about 1837:45, the airplane made a gradual right turn to a northerly track toward the Everglades Wildlife Management Area, an undeveloped wetland area with little to no ground lighting. At 1840, the right-seat pilot sent a text message that stated, “so dark night,” followed by another text message that stated, “U can’t see anything tonight.” During the final five minutes of the flight, the airplane continued to gradually turn onto a more northerly track. About 1841, the airplane gained airspeed while descending 100 to 200 ft. At 1843:43, the airplane began to descend at an initial rate of 1,700 ft per minute. At 1843:50, the descent rate increased to 3,400 ft per minute until the end of the ADS-B data at 1844:01, when the airplane’s altitude was 525 ft. The airplane wreckage was located about 1,000 ft farther along the final track from the last ADS-B point at an elevation 10 ft above sea level in a swampy area. The flight school owner reported the airplane missing to the local FAA flight standards district office and airport traffic control tower between 0800 and 0900 on the morning after the accident. PERSONNEL INFORMATIONThe left seat pilot held a commercial pilot certificate with airplane single and multi-engine land ratings as well as an instrument airplane rating. The flight school owner reported that the left-seat pilot had about 600 hours of flight time, and the flight instructor who performed the pilot's flight review reported that the pilot had about 700 hours of flight time. Neither the flight instructor nor the flight school had obtained a copy of the pilot’s logbook, and the investigation was unable to locate any logbooks for the left-seat pilot. The left seat pilot’s night and instrument experience could not be determined. The flight instructor reported that the left-seat pilot appeared fit and in good health during their time together on the morning of the accident. He also reported that the left-seat pilot was not from the area and had come from Texas because he had liked the school when he was a student there. He further stated that the left-seat pilot had come back to rent and build flight time. The right seat pilot held a commercial pilot certificate with airplane single and multi-engine land, airplane single engine sea, and instrument airplane ratings. The flight school owner reported that the right-seat pilot had about 1,200 hours of flight time. A third-party logbook vendor reported that the right-seat pilot had an account with their services and provided a copy of his electronic logbook. Examination of this logbook revealed the first entry was on May 19, 2022, and the last entry was on January 16, 2023; at that time, the pilot had logged a total of 214.3 hours of flight time. An examination of FAA records showed that the pilot obtained all of his certificates and ratings before the start of the electronic logbook. The third-party logbook vendor also reported that the pilot had 57 “draft entries” (that is, automatically created entries that had not yet been reviewed by the pilot and approved), which dated from January 19, 2023, to January 20, 2024. All of the non-draft entries in the electronic log represented a total 62.4 hours of flight experience at night, 99.3 hours of flight experience under actual instrument conditions, and 4.8 hours of flight experience in simulated instrument conditions. METEOROLOGICAL INFORMATIONThe US Naval Observatory reported sunset was at 1758 and the end of civil twilight was at 1823. Moon rise was at 1607, and the upper transit was reached at 2322. The phase of the moon was waxing gibbous with 96% of the moon’s visible disk illuminated. WRECKAGE AND IMPACT INFORMATIONThe debris path was about 300 ft in length and was oriented on about a 10° magnetic heading. The first piece in the debris path was the nosewheel, which had been impact separated from the nose landing gear strut and was about 300 ft from the main wreckage. The nose landing gear was near the nosewheel and had been impact separated from the firewall at all attachment points. The left wing was impact separated from the fuselage and was located about 150 ft from the main wreckage. The main wreckage came to rest on a heading of about 130° magnetic, in an area of water that was about 4 ft deep. There was a postimpact fire, which consumed portions of the fuselage and right wing. The instrument panel, firewall, and engine remained attached to each other and were impact separated from the main wreckage. They were found about 25 ft from the main wreckage. Control continuity was established from all primary flight control surfaces to the flight controls in the cockpit through multiple impact fractures consistent with tensile overload and cuts made to facilitate recovery of the wreckage. The flap actuator measurement was consistent with a flaps up position. Postaccident examination of the airplane revealed no evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation. ADDITIONAL INFORMATIONHuman spatial orientation is complex and relies on the brain's integration of visual, vestibular, and kinesthetic sensory inputs. Vision is the dominant source of sensory inputs used for spatial orientation, but when external visual cues are limited, vestibular inputs become more important. The vestibular system provides reasonably accurate information to the brain when walking on the ground, but it can provide misleading information when subjected to the forces of flight. One of the vestibular system's limitations is a difficulty distinguishing the acceleration of translational motion from the acceleration of gravity. Sustained forward acceleration can lead to a form of spatial disorientation known as somatogravic illusion. In coordinated flight, this illusion is most often experienced as a misperception of pitch. The angle that is apparent to the vestibular system is the angle between the person’s upright orientation and the gravito-intertial force. This angle is referred to as the GIF angle and may not be equal to the actual pitch of the seat. An aircraft performance study was conducted by the NTSB Office of Research and Engineering using ADS-B information. The study found the GIF angle remained nearly nose-level during the initial 20-second portion of the final descent. MEDICAL AND PATHOLOGICAL INFORMATIONAn autopsy of the left-seat pilot was performed by the Broward County Medical Examiner. According to the autopsy report, the cause of death was multiple blunt force injuries with a contributory cause of drowning, and the manner of death was accident. The FAA Forensic Sciences Laboratory and the Broward County Office of Medical Examiner and Trauma Services Toxicology Laboratory performed toxicological testing of postmortem specimens from the left-seat pilot. Broward County detected methamphetamine at 50 ng/mL in peripheral blood and also detected methamphetamine in urine. The FAA did not detect any tested-for drugs in urine. An FAA forensic toxicologist reported that urine screening included a method capable of detecting methamphetamine levels as low as 1 ng/mL. The toxicologist further reported that, upon learning of the Broward County results, the FAA additionally performed confirmation testing of blood, urine, and liver tissue for methamphetamine and its metabolite amphetamine, using a method capable of quantitating levels of those analytes as low as 6.25 ng/mL; this testing was done for both pilots with negative results. Both the Broward County and FAA laboratories hold forensic toxicology accreditation and incorporate quality assurance measures into their procedures. According to an FAA forensic toxicologist, the two laboratories communicated about the discrepant methamphetamine results and were unable to identify an explanation. Methamphetamine is a central nervous system (CNS) stimulant drug. Methamphetamine is available as a Federal Schedule II controlled substance prescription medication used to treat attention-deficit/hyperactivity disorder (ADHD), narcolepsy, and occasionally obesity. As a medicine, the drug typically carries a warning that it may impair the ability to engage in potentially hazardous activities. Some conditions that might be treated with methamphetamine also are potentially impairing, but the reviewed FAA medical certification and death investigation information for the left-seat pilot did not document any such condition. The FAA considers methamphetamine to be a “Do Not Issue/Do Not Fly” medication. In addition to being used medicinally, methamphetamine may be produced illicitly and abused recreationally. At low doses used as part of appropriate medical treatment, methamphetamine may improve reaction time, cognitive function, and fatigue, but may result in people making higher-risk choices. At higher doses, the drug may have a variety of impairing effects on psychomotor function, cognition, and perception. Impairment related to methamphetamine use can result from drug or withdrawal effects, with features of CNS stimulation or CNS depression. A measured drug level does not indicate whether a person is experiencing early- or late-phase effects. In living people, blood methamphetamine levels of 20 ng/mL to 50 ng/mL are typical with medicinal use, while levels of 10 ng/mL to 2,500 ng/mL are typical with recreational use. Methamphetamine may exhibit postmortem redistribution. An autopsy of the right-seat pilot was performed by the Broward County Medical Examiner. According to the autopsy report, the cause of death was multiple blunt force injuries, and the manner of death was accident. The FAA Forensic Sciences Laboratory and the Broward County Office of Medical Examiner and Trauma Services Toxicology Laboratory performed toxicological testing of postmortem specimens from the right-seat pilot. FAA testing detected ethanol at 0.011 g/dL in blood. FAA testing did not detect ethanol in vitreous fluid or urine, and Broward County testing did not detect ethanol in blood or vitreous fluid. Ethanol is the intoxicating alcohol in beer, wine, and liquor, and, if consumed, can impair judgment, psychomotor performance, cognition, and vigilance, with detrimental effects on piloting tasks that worsen as ethanol levels increase. FAA regulation imposes strict limits on flying after consuming ethanol, including a prohibition on piloting a civil aircraft while having a blood ethanol level of 0.04 g/dL or greater. Alcohol consumption is not the only possible source of ethanol in postmortem specimens. Ethanol sometimes may be produced by microbes in a person’s body tissues and fluids after death. Typically, vitreous fluid, and to a lesser extent urine, are the specimen types best protected against microbial contamination, and therefore are less susceptible to postmortem ethanol production than are other specimen types. FAA testing also detected minoxidil in urine but not in blood for the right-seat pilot. Minoxidil can be used as a prescription oral medication for treatment-resistant high blood pressure, or (at low doses) for hair loss. There are some potential safety concerns with oral minoxidil use, and the drug carries a warning that its use for high blood pressure should be reserved for certain cases where multiple other medications have been ineffective. However, minoxidil also is commonly used in topical products available over the counter to promote hair growth. When used as directed topically, minoxidil is absorbed into circulation to a low extent only and is not typically impairing. According to the FAA, minoxidil is acceptable for pilots if the underlying condition is acceptable. FAA toxicology testing for the right-seat pilot also identified sildenafil in urine but not in blood, as well as desmethylsildenafil and salicylic acid in blood and urine. Sildenafil is a prescription medication commonly used to treat erectile dysfunction, as a sexual enhancement aid, or in the treatment of certain other conditions, including pulmonary hypertension. Sildenafil is not typically impairing, although the FAA states that pilots should wait 8 hours after using it before flying, to monitor for side effects. Desmethylsildenafil is an active metabolite of sildenafil. Salicylic acid is the primary active metabolite of aspirin, a widely available over-the-counter medication that can be used to control pain and fever and to reduce cardiovascular risk. Salicylic acid also is a metabolite of some other drugs and is used as a topical skin exfoliant in a variety of retail products. Salicylic acid is not generally considered impairing.