HISTORY OF FLIGHTOn November 30, 2020, at 1213 central standard time, a Piper PA-38-112 airplane, N9879T, was destroyed when it was involved in an accident near Franklin, Arkansas. The flight instructor and the private pilot receiving instruction were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. Automatic dependent surveillance-broadcast (ADS-B) data were obtained for the accident flight, which is overlaid on Google Earth in Figure 1. The airplane departed Country Air Estates Airport (1AR9), Lonoke, Arkansas, at 0931, made a short flight to Carlisle Municipal Airport (4M3), Carlisle, Arkansas, and arrived at 0946. The airplane remained at 4M3 for about 16 minutes before it departed at 1002. The airplane then traveled about 100 nautical miles (nm) north-northwest, turned to a northeast heading and overflew Marion County Regional Airport (FLP), Flippin, Arkansas, and Baxter County Airport (BPK), Mountain Home, Arkansas, before it turned eastbound. The airplane did not land at FLP, and due to a gap in the ADS-B data it could not be determined if the airplane landed at BPK. After it passed BPK, the airplane turned to the east, contacted the Memphis Air Route Traffic Control Center (ARTCC) and obtained an instrument flight rules (IFR) clearance to Walnut Ridge Regional Airport (ARG), Walnut Ridge, Arkansas, which was about 76 nm east of BPK. During the portion of the flight from BPK to ARG, air traffic control initially established radar contact and voice communication with the flight. When the airplane was about 60 nm west of ARG, radar contact was lost, and voice communication became intermittent and was eventually lost. The final transmissions received from the airplane were unclear. The controller attempted to maintain communication with the accident airplane using messages relayed through other aircraft and reverted to receiving acknowledgements to transmissions using microphone key clicks from the accident pilot. Figure 1. Map showing the airplane’s ADS-B track (red), the relative positions of airports, the straight-line course from BPK to ARG (white), and the accident location. The airplane did not follow a straight-line course between BPK and ARG, as it first deviated up to 2.8 nm north of the straight-line course then turned toward south. The airplane then deviated south of the straight-line course by as much as 4.5 nm. During the final 5-1/2 minutes of the flight, the airplane made 3-3/4 left turns of varying radius, followed by 1-1/4 right turns before the end of the recorded ADS-B data. The final ADS-B position was at 1213:36 and the accident site was located about 0.2 nm south southeast of the last ADS-B position, 4.7 nm south of the straight-line course, and about 35 nm from BPK (figure 2). Figure 2. Map showing the final 7.5 minutes of the accident flight path (red), with the last recorded ADS-B position, the accident location, and the straight-line course from BPK to ARG (white). PERSONNEL INFORMATIONThe flight instructor’s flight logbook was not available for review. He reported flight experience that included 3,200 total flight hours and 45 hours in last 6 months as of his last medical exam dated October 26, 2020. The flight logbook for the pilot receiving instruction showed that he had 154.8 hours total flight experience, including about 98 hours in Piper PA-38 airplanes, as of the last entry dated November 28, 2020. The final three logged flights were in the accident airplane with one flight recorded on November 27, 2020, that lasted 2.2 hours, and two flights on November 28, 2020, that lasted 2.2, and 3.0 hours respectively. The final three flight entries noted simulated instrument flight instruction. AIRCRAFT INFORMATIONMaintenance records for the accident airplane showed that the airframe and engine had received a 100-hour inspection that was approved on November 20, 2020, by the accident flight instructor who also held an airframe and powerplant mechanic certificate. A separate endorsement for an annual inspection was approved by a different mechanic holding an inspection authorization on that same day. The endorsement for the 100-hour inspection noted that it was completed in accordance with the Piper PA38 Service Manual. METEOROLOGICAL INFORMATIONSurface temperatures were consistent with the use of cabin heating for the accident flight. Airmen's Meteorological Information notices (AIRMET) for turbulence and icing were in effect at the time of the accident. In addition, pilot reports of turbulence ranging from light turbulence to occasional severe turbulence were reported in the area where the accident occurred. AIRPORT INFORMATIONMaintenance records for the accident airplane showed that the airframe and engine had received a 100-hour inspection that was approved on November 20, 2020, by the accident flight instructor who also held an airframe and powerplant mechanic certificate. A separate endorsement for an annual inspection was approved by a different mechanic holding an inspection authorization on that same day. The endorsement for the 100-hour inspection noted that it was completed in accordance with the Piper PA38 Service Manual. WRECKAGE AND IMPACT INFORMATIONThe airplane impacted trees and terrain as seen in Figure 3. The debris path was about 230 ft long and oriented on a magnetic heading of 320°. The airplane was severely fragmented, and the main portion of the wreckage came to rest about 160 ft from the initial tree impact point. The engine was located about 230 ft from the initial impact point. There was no fire. FIGURE 3. Photograph showing the main wreckage at the accident site. The cabin heating system used a heat shroud over the exhaust system mufflers to draw heat from the exterior of the muffler for cabin heating. A postaccident metallurgical examination of the muffler and cabin heat shroud system revealed multiple branched cracks in the outer shell of one of the two mufflers (figure 4). The fracture faces of the cracks were covered with oxidation product, consistent with its presence before the accident crash sequence. Metallurgical cross sections revealed oxidative degradation that progressed through the thickness of the muffler shell from the inside surface outwards. Other than the cracked muffler, examination of the wreckage by Federal Aviation Administration inspectors and an investigator from Piper Aircraft revealed no preimpact mechanical malfunctions or anomalies with the airframe, or engine that would have precluded normal operation. Figure 4. Photograph showing the two mufflers from the airplane. ADDITIONAL INFORMATIONThe PA38 Service manual stated: WARNING: A VERY THOROUGH INSPECTION OF THE ENTIRE EXHAUST SYSTEM, INCLUDING EXHAUST SHROUD ASSEMBLY, MUFFLER AND MUFFLER BAFFLES, STACKS, AND ALL EXHAUST CONNECTIONS AND WELDS MUST BE ACCOMPLISHED AT EACH 100 HOUR INSPECTION. The entire exhaust system, including upper and lower shroud assemblies, muffler assembly, stack assemblies, and all exhaust clamps and connections must be rigidly inspected each 100 hours. The possibility of exhaust system failure increases with use. Check the system even more carefully as the number of hours increase; for example, an inspection at the 700-hour period would be more critical than one in the 100 hour period. The system should also be checked carefully before winter operation when cabin heat will be used. MEDICAL AND PATHOLOGICAL INFORMATIONToxicology testing performed by the FAA’s Forensic Services Laboratory on specimens from the flight instructor detected carboxyhemoglobin at 29%. Toxicology was positive for ethanol at 0.032 gm/hg in the muscle tissue but no ethanol was detected in the liver tissue; n-butanol was also detected in muscle tissue but not in liver tissue. Methamphetamine was detected in the urine at 307 ng/mL and amphetamine was detected in urine at 31 ng/mL. Toxicology testing performed by the FAA’s Forensic Services Laboratory on specimens from the private pilot did not detect carboxyhemoglobin in the cavity blood; FAA laboratory’s reporting limit for carboxyhemoglobin is 10%. Toxicology was positive for sedating antihistamine diphenhydramine at 848 ng/mL in the private pilot’s cavity blood and in his urine; the sedating antihistamine cetirizine was detected in his muscle and liver tissues. The non-impairing high blood pressure medications losartan and amlodipine were detected in the private pilot’s cavity blood and urine. TESTS AND RESEARCHIn December 2021, the NTSB made recommendations regarding the use and installation of carbon monoxide detectors in enclosed cabin airplanes equipped with reciprocating engines. Recommendation A-22-1 to the Federal Aviation Administration stated: Require that all enclosed-cabin aircraft with reciprocating engines be equipped with a carbon monoxide detector that complies with an aviation-specific minimum performance standard with active aural or visual alerting. Recommendation A-22-2 to the Aircraft Owners and Pilots Association and Experimental Aircraft Association: Inform your members about the dangers of carbon monoxide (CO) poisoning in flight and encourage them to 1) install CO detectors with active aural or visual alerting and 2) proactively ensure thorough exhaust inspection during regular maintenance.