HISTORY OF FLIGHT On March 30, 2024, at 1320 eastern daylight time, a twin-engine Piper PA-44-180 airplane, N595ND, sustained substantial damage when it was involved in an accident at the Treasure Coast International Airport (FPR), Fort Pierce, Florida. The flight instructor was fatally injured, and the pilot receiving instruction was seriously injured. The airplane was operated as a 14 CFR Part 91 instructional flight. Flight and engine performance data recovered from the airplane’s PFD and MFD showed that the airplane departed from FPR at 1239:30. According to the pilot receiving instruction, he and the flight instructor climbed the airplane to 5,000 ft mean sea level (msl), where they practiced single-engine emergency procedures. These procedures included shutting down and feathering the right engine. Recovered PFD and MFD data showed that, between 1247 and 1251, the recorded parameters for the right engine were consistent with it having been shut down. The pilot receiving instruction stated that they subsequently returned to FPR to practice a single-engine instrument approach, and ATC cleared them for the ILS or LOC RWY 10 approach. He said that, to simulate the engine failure, thrust on the right engine was reduced, and the left engine was operated normally. Recovered PFD and MFD data showed that the airplane began descending at 1256:47. At 1308:39, the airplane was at 2,824 ft pressure altitude, both engines were operating at 2,380 rpm, and the fuel flow for the left and right engines was 9 and 10.7 gallons per hour (gph), respectively. (Maximum speed for the engine model is normally about 2,700 rpm, and target idle speed is about 700 rpm.) The data showed that, as the airplane continued to descend on a long approach toward runway 10R, the right engine’s rpm continued to decrease, and the left engine’s speed was increased to and maintained about 2,700 rpm for the remainder of the flight. The pilot receiving instruction said that, when the airplane was at 1,000 ft msl, he extended the landing gear and brought the mixture and propeller levers for both engines full forward. When the airplane reached the decision height for the approach (250 ft above ground level), he initiated a missed approach. He brought both throttles full forward to go-around, but there was “no thrust on either engine.” He then turned right to the missed approach heading provided by ATC. He said that the instructor “realized there was no engine power” and took control of the airplane, declared an emergency, and continued to turn the airplane to the right to try to land on runway 14. Recovered PFD and MFD data showed that, at 1318:09, the right engine was operating at 1,220 rpm with a fuel flow 3.1 gph, and the left engine was at 2,670 rpm and 15.8 gph. About 12 seconds later (when the airplane was on short final approach to runway 10R), the right engine speed and fuel flow increased briefly to 1,280 rpm and 11 gph, respectively, and the left engine was operating at 2,670 rpm and 16.5 gph, before the data ended at 1319:33 (MFD), and 1319:52 (PFD), about 500 ft from where the airplane impacted the ground and came to rest. A review of ATC communications revealed that at 1319, the flight instructor contacted the FPR ATC tower and stated that they wanted to return to the traffic pattern. She said they were “single engine” with two souls on board. A controller asked the instructor if she was declaring an emergency, and she said yes. The controller then cleared the airplane to land on runway 10R followed by a clearance to land on any runway. There were no further communications with the airplane. According to the pilot receiving instruction, neither he nor the flight instructor had time to use the emergency checklist or feather the engine. He said that he was focused on the emergency and that the flight instructor was hoping to get engine power restored. He did not look at the engine gauges and could not recall the flap setting. ATC tower personnel reported they saw the airplane make a low-level “tight right downwind” back to runway 14. As the airplane approached the modified midfield right downwind for runway 14, the airplane attempted to turn toward the runway but continued to lose altitude and went nose-down into the ramp west of runway 14. ADS-B data for the last minute of the flight showed a flight track consistent with the ATC tower personnel’s description (see figure 1). Figure 1. ADS-B flight track data for the last minute of the flight. (Inset shows time, altitude, and ground speed for each numbered data point.) A witness sitting in a parked airplane near taxiway echo observed the accident airplane in a “moderate” right bank turn at a “slow speed heading in our direction.” The airplane appeared to stall, then rolled right inverted and impacted the ground. The witness said the engine power “sounded normal for this aircraft type at the time of [the] stall.” Another witness said the airplane was in a steep right bank and losing altitude before it impacted the ground. PILOT INFORMATION The flight instructor held a commercial pilot certificate with ratings for single-engine land, multi-engine land, and instrument airplanes. She also held a flight instructor certificate with ratings for single- and multi-engine land airplanes. The flight instructor held a current first-class FAA medical certificate with no limitations. A review of her pilot logbook revealed she had about 1,395 total flight hours, of which about 180 hours were in the same make/model as the accident airplane. The pilot receiving instruction held a private pilot certificate with ratings for airplane single-engine land and instrument airplanes. He held a current first-class FAA medical certificate with no limitations. A review of his pilot logbook revealed he had about 224 total flight hours, of which about 2.8 hours were in the same make/model as the accident airplane. AIRPLANE INFORMATION The Piper PA-44-180 is a four-seat, multi-engine airplane widely used for pilot training. The airplane was powered by two 180-horsepower Lycoming engines that were adapted to rotate in opposite directions. The left engine (O-360-A1H6) had a right rotation and the right engine (LO-360-A1H6) had a left rotation. This adaptation, which results in counter-rotating propellers, is designed to improve single-engine handling performance in the event of an engine failure. The airplane’s pilot operating handbook (POH) contained a warning that a one-engine inoperative GO-AROUND “should be avoided if at all possible.” The emergency checklist for a one-engine inoperative go-around and a summary of factors that would reduce climb performance stated, “WARNING – The propeller on the inoperative engine must be feathered, the landing gear retracted, and the wing flaps retracted for continued flight.” A review of the airplane’s maintenance records revealed that the last annual inspection was completed the day before the accident on March 29, 2024. At that time, the total airframe time in service was 6,980 hours. Total time since overhaul for both engines was 196 hours. The annual inspection was performed by two mechanics employed by the flight school, and the inspection was endorsed by the flight school’s director of maintenance (DOM). According to the DOM, he was the only person authorized to endorse annual inspections at the flight school. WRECKAGE AND IMPACT INFORMATION The airplane came to rest inverted on the airport’s tarmac. There was no postimpact fire. All major components of the airplane were located at the accident scene. The flaps were retracted, and the landing gear were fully extended. Flight control continuity was established for all major flight controls to the cockpit area. Both wing fuel tanks were breached from impact. Continuity of the fuel system was confirmed to both engines. Left Engine and Accessories The left engine remained attached to the airframe, but the propeller separated at the crankshaft. Both blades were found twisted in the hub and exhibited rotational scoring at the tips. Rotating the engine’s crankshaft via the vacuum pump spline established compression and valvetrain continuity on all four cylinders. Both magnetos produced spark at each ignition tower when rotated via a drill. The air filter was absent of debris. The spark plugs appeared gray in color consistent with normal wear per the Champion Check-A-Plug chart. The carburetor was removed from the left engine. The throttle lever was found in the full power position, and the mixture control lever was found in the full rich position. Fuel found in the carburetor bowl was tested for the presence of water, and none was observed. The fuel screen was absent of debris. No mechanical deficiency or malfunction was observed with the left engine that would have precluded normal operation. Right Engine and Accessories The right engine separated from the airframe and came to rest next to the right wing. The propeller remained attached to the engine and was not feathered. Both propeller blades appeared straight with some damage observed near the tip of one of the blades. Rotating the right engine’s crankshaft manually via the propeller established compression and valvetrain continuity to each cylinder except the No. 1 cylinder due to impact damage. Both magnetos were removed and rotated via a drill. Spark was produced at each ignition tower. The air filter was absent of debris. The colors of the spark plugs were inconsistent with each other. The No. 2 top and No. 4 bottom spark plugs were gray in color and consistent with normal wear per the Champion Check-A-Plug chart. The other spark plugs displayed varying degrees of discoloration inconsistent with normal wear. The No. 1 bottom spark plug electrodes had no gap on one side, and the No. 3 bottom plug had two excessively tight gaps to the electrode. The carburetor was removed from the right engine. Fuel found in the carburetor bowl was tested for the presence of water, and none was observed. The fuel screen was absent of debris. The carburetor’s mixture control arm was found secured to the mixture control lever via a castle nut and cotter pin. As first viewed, the mixture was halfway between full rich and idle cut-off. The throttle plate was found in the fully closed position, the throttle control assembly was impact-damaged, and the throttle arm was found fractured at one of the two screw holes (where the throttle arm attaches to the throttle valve). The throttle arm was found secured to the throttle control lever via castle nut and cotter pin. The interlocking teeth of the serrated mating surfaces between the throttle arm and throttle control lever were found not securely mated, such that the throttle control lever was loose and could be fully rotated without moving the throttle arm. The teeth on the throttle control lever side of the mating surfaces appeared to be rounded and worn down (see figure 2). Figure 2. Right engine’s carburetor showing gaps between the serrated mating surfaces of the throttle arm (bottom) and throttle control lever (top). The right engine’s carburetor was sent to the NTSB’s Material’s Laboratory for further examination. The examination revealed that the throttle arm fracture (at the screw hole) resulted from torsional and bending overstress. Two bosses of the carburetor housing were fractured from overstress due to bending of the throttle arm and fuel cutoff valve lever. Microscopic examination of the crests of the serrated teeth of the throttle control lever side of the mating surface showed that they exhibited circumferentially-oriented wear, scars, and gouges, as well as local absence of the cadmium coating, consistent with a loss of the outer coating material in many areas of the teeth crests. This damage and wear patterns were consistent with the throttle control lever having been loose from the throttle arm over a period of time. Per the right engine’s maintenance logbook, the carburetor was last overhauled in October 2021 and installed in March 2023 when the engine was overhauled. From the time the engine was installed to the time of the accident, the engine had undergone two 100-hour inspections and an annual inspection. No maintenance log entries mentioned any specific maintenance to the carburetor or the throttle control arm. As stated previously, the airplane’s most recent annual inspection was performed the day before the accident and endorsed by the flight school’s DOM. During an interview, the DOM was asked if he checked the security of the throttle arm to the carburetor as part of his inspection, and he said, “I must have.” He said he had experienced an in-flight loss of engine power due to a loose throttle connection, and, as such, he was a stickler for checking for loose connections during his inspections. The DOM was shown postaccident examination pictures of the right engine’s throttle arm linkage. He acknowledged that the damage to the serrated interface could result in the gears skipping, and he said that he was unsure how he missed it during the inspection. The DOM said the flight school’s maintenance department had been short-staffed and there was pressure on him to get required FAA maintenance inspections completed in a timely manner. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was conducted on the flight instructor by the Medical Examiner - District 19, Fort Pierce, Florida. The cause of death was determined to be multiple blunt force injuries, and the manner of death was an accident. Toxicology testing performed at the FAA Forensics Sciences Laboratory was negative for all substances tested. Toxicological testing was conducted on the pilot receiving instruction when he was admitted to the hospital. The NTSB made several attempts to obtain his postaccident medical records, but the records were not produced before the release of this report. ADDITIONAL INFORMATION Title 14 CFR 91.409 specifies the annual and 100-hour inspection requirements for aircraft used in flight instruction for hire, which must be performed in accordance with 14 CFR Part 43 and the aircraft approved for return to service by an authorized certificated mechanic. Specifically, Part 43, Appendix D, paragraph (d)(6) mandates the inspection of the engine controls for “defects, improper travel, and improper safetying.” As a result of the accident, the flight school implemented a required inspection item (RII) maintenance program. The program would “…cover specific inspection of any maintenance action that, if improperly done, could result in immediate danger to an aircraft or person. RII will cover but not limited to rigging flight controls, installing a propeller, or performing another maintenance action that affects flight critical systems and components.”