Aviation Accident Preliminary Report - National Transportation Safety Board
The National Transportation Safety Board travelled to the scene of this accident.
Investigator In Charge (IIC): Fox, Andrew
Additional Participating Entities:
William G. Muller; Federal Aviation Administration - Minneapolis FSDO; Minneapolis, MN
Daniel L. Sindt; Federal Aviation Administration - Minneapolis FSDO; Minneapolis, MN
https://registry.faa.gov/AircraftInquiry/Search/NNumberResult?nNumberTxt=N339L
L39 Aircraft LLC
- Location: Granite Falls, MN
- Accident Number: CEN25FA269
- Date & Time: July 21, 2025, 17:28 Local
- Registration: N339L
- Aircraft: Aero Vodochody L-39C
- Injuries: 1 Fatal, 1 Serious
- Flight Conducted Under: Part 91: General aviation - Instructional
https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/200598/pdf
On July 21, 2025, about 1728 central daylight time, an Aero Vodochody L-39C airplane, N339L, was substantially damaged during an accident near Granite Falls, Minnesota. The flight instructor, seated in the front seat, sustained serious injuries after ejecting from the airplane. The pilot-receiving-instruction, seated in the rear seat, did not eject from the airplane and was fatally injured when the airplane impacted terrain. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 instructional flight.
The flight instructor stated that the pilot-receiving-instruction was interested in purchasing an Aero Vodochody L-39 airplane and was receiving initial “familiarization” flight training. The airplane operator, L39 Aircraft LLC, held a Federal Aviation Administration (FAA) Letter of Deviation Authority (LODA) that authorized initial flight training, unusual attitude and upset training, formation flight training, instrument competency, and biennial flight reviews in the experimental category Aero Vodochody L-39C high-performance jet trainer airplane.
The flight instructor held an airline transport pilot certificate with type ratings for Boeing 777, Airbus 320, McDonnell Douglas DC-9, Bombardier Canadair Regional Jet CL-65, Saab 340, Embraer 500, Embraer 505, SIAI-Marchetti S.211, and Aero Vodochody L-39 airplanes. The flight instructor reported having flown about 50 hours in an Aero Vodochody L-39 airplane.
The pilot-receiving-instruction held a private pilot certificate with airplane single-engine land and instrument airplane ratings. Additionally, the pilot-receiving-instruction held a type rating for a Cirrus SF-50 airplane. The pilot-receiving-instruction had no previous flight experience in an Aero Vodochody L-39C airplane before the day of the accident.
On July 20, 2025, the flight instructor provided about 1 hour of ground instruction to the pilot-receiving-instruction during which they discussed the operation limitations of the Aero Vodochody L-39C airplane and the use of the VS-1 BRI ejection seat system. The ground instruction was conducted at the pilot-receiving-instruction’s residence (not in the airplane).
On July 21, 2025, the flight instructor provided 2-3 hours of additional ground instruction to the pilot-receiving-instruction during which they discussed the positive and negative aspects of owning/operating an experimental category warbird jet. Additionally, they discussed flight planning, normal flight operations, use of helmet oxygen, weather considerations, and the fuel planning for the Aero Vodochody L-39C airplane. The flight instructor then demonstrated a preflight of the airplane before he assisted the pilot-receiving-instruction into the airplane’s rear seat and its associated parachute harness.
The flight instructor stated that he intended to provide flight instruction during three flight legs to reposition the airplane from its normal base-of-operations at Alpine Airport (46U), Alpine, Wyoming, to Wittman Regional Airport (OSH), Oshkosh, Wisconsin, where they would attend the 2025 Experimental Aircraft Association (EAA) AirVenture event.
The flight instructor was the pilot-in-command and was seated in the front seat of the airplane. The flight instructor noted that the pilot-receiving-instruction was seated in the rear seat because he was unfamiliar with the airplane. All takeoff and landings were flown by the flight instructor.
The flight instructor stated that the first two flight legs, 46U to Northeast Wyoming Regional Airport (GCC), Gillette, Wyoming, and GCC to Watertown Regional Airport (ATY), Watertown, South Dakota, were uneventful. The accident occurred during the third flight leg from ATY to OSH. The flight instructor noted that he filed an instrument flight rules (IFR) flight plan from ATY to Fond Du Lac County Airport (FLD), Fond Du Lac, Wisconsin, but intended to cancel the instrument flight plan while enroute and proceed under visual flight rules (VFR) to OSH via the published warbird arrival procedure associated with the EAA AirVenture event.
According to ADS-B flight data, at 1707:16, the airplane was on initial climb from runway 12 at ATY. The airplane then continued eastbound as it climbed toward flight level 270 (FL270). The flight instructor reported that the airplane’s engine power was set at 103% during the continuous climb yielding 280 knots true airspeed. As the airplane climbed through flight level 200 (FL200) the flight instructor and the pilot-receiving-instruction simultaneously smelled an odor emitted from inside their helmet oxygen masks followed by smoke intrusion into the cockpit. About 4-5 seconds later the aircraft shook briefly in conjunction with an audible metal-to-metal grinding noise. The flight instructor depressurized the airplane which resolved the odor issue and the smoke dissipated from the cockpit. He then began decelerating the airplane toward best glide airspeed (140 knots) and located the nearest airport using the airplane’s Garmin navigational/communication device. The flight instructor attempted to restart the engine using the auxiliary power unit (SAFIR air-turbine system) which is normally used to start the engine. After three unsuccessful attempts to restart the engine using the SAFIR system the flight instructor shifted his focus to flying the airplane towards an airport where a forced landing could be completed.
According to ADS-B flight data, at 1718:05, the airplane entered a descent from about 21,800 ft mean sea level (msl), as depicted in figures 1 and 2. At 1718:09, the flight instructor told the air traffic controller that the airplane had an “engine failure.” The controller acknowledged the loss of engine power and cleared the flight to descend to maintain 10,000 ft msl. At 1718:36, the controller told the flight instructor that Granite Falls Municipal Airport (GDB), Granite Falls, Minnesota, was at the 1 o’clock position and 20 nautical miles (nm) and that Montevideo-Chippewa County Airport (MVE) was at the 10 o’clock position and 15 nm. The flight instructor was subsequently told to change ATC frequencies.
At 1719:53, the flight instructor established contact with a different controller, reiterated that the airplane had an engine failure, and that they were heading direct to GDB for an “emergency landing.” After a brief discussion, the flight instructor told the controller that he intended to fly a visual approach to GDB. At 1720:34, the controller told the flight instructor that GDB was at the 12 o’clock position and 10 nm and asked the flight instructor to report when the airport was in sight. At 1721:00, the controller cleared the flight direct to GDB and descend to maintain 3,000 ft msl.
According to ADS-B flight data, at 1722:35, the airplane descended below 12,500 ft msl as it continued east-southeast toward GDB, as depicted in figure 3. At 1724:09, the flight instructor told the controller that they were attempting to land at Southwest Minnesota Regional Airport (MML), Marshall, Minnesota. The flight instructor cleared the flight direct to MML and descend to maintain 3,000 ft msl. However, at 1725:24, the flight instructor told the controller that they could not reach MML and that they would land at GDB. The controller then cleared the flight direct to GDB. When interviewed after the accident, the flight instructor stated that the airplane’s ground speed decreased significantly while flying toward MML and that was why he decided to resume a flight path toward GDB instead of MML.
Based on ADS-B flight track data, the airplane continued a right descending turn over GDB, as depicted in figure 3. At 1727:48, the airplane crossed over GDB as it descended through 3,000 ft msl. According to available weather data for GDB, there was a 1,200 ft above ground level (agl) broken ceiling at the time of the accident. At 1728:14, the airplane descended below 1,200 ft agl and the airplane’s right roll angle increased in a turn toward runway 15 at GDB. When interviewed after the accident, the flight instructor stated that he saw the yellow chevrons depicting the overrun for runway 15 at GDB and turned the airplane to head directly to the end-of-pavement.
The flight instructor extended the landing gear during the right descending turn toward runway 15. However, during the turn, the flight instructor determined that the airplane would not reach the runway and told the pilot-receiving-instruction to “prepare to eject.” The pilot-receiving-instruction reportedly replied “okay.” The flight instructor stated he brought the airplane into a wings level attitude and reduced the descent rate before he told the pilot-receiving-instruction to “eject.” When he did not hear the rear seat eject from the airplane, the flight instructor again told the pilot-receiving-instruction, using his first name this time, to “eject.” The flight instructor again did not hear the rear seat eject from the airplane. According to the flight instructor, the airplane was nearing the bottom of the ejection envelope and heading toward a power line when he said “eject” for a third time before he activated his own ejection seat. The front seat was ejected from the airplane and the flight instructor subsequently descended under an open parachute canopy to the surface. The flight instructor sustained non-life-threatening serious injuries during the seat ejection and parachute landing.
Figure 1. Plots of airplane altitude, ground speed, true airspeed, calibrated airspeed, and
vertical speed.
Figure 2. Plots of airplane heading, roll angle, and flight path angle
Based on the wreckage debris path, the upper portion of the airplane’s vertical stabilizer clipped a power line about 821 ft short of the runway 15 overrun (end-of-pavement). Based on the wreckage distribution, the airplane descended beneath the power line before it impacted a berm adjacent to railroad tracks that run parallel to Minnesota State Highway 23. The impact with the berm was about 590 ft short of the end-of-pavement and about 105 ft right of the runway 15 extended centerline. The airplane’s ground track was about 150° true between the power line and berm. The entire fuselage separated from the wing when the airplane impacted the berm. The fuselage came to rest upright about 45 ft past the berm and was rotated about 70° counterclockwise relative to the airplane’s flight path before it impacted the berm.
There was a strong smell of Jet-A fuel around the accident site and fuel was observed pouring from impact penetrations on the wing tip fuel tanks, and fractured fuselage fuel lines during recovery. The drop pod fuel tanks were separated during the impact with the berm. Both drop pod fuel tanks had impact penetrations. A small amount of residual fuel remained in one of the pods.
The airplane nose and cockpit sustained heavy impact crushing deformation. The front canopy was found intact along the railroad tracks and between the power lines and the berm that the airplane impacted. Portions of the fragmented rear canopy were found throughout the debris field past the berm that the airplane impacted. The pilot-receiving-instruction was found restrained in the rear ejection seat that separated from the airframe during the ground impact sequence. Based on the damage to the ejection seat and its unused firing mechanism components (first stage telescopic ejection mechanism and second stage accelerating rocket motor) the Yellow Medicine County Sheriff requested bomb-squad assistance from the Bloomington Police Department, Bloomington, Minnesota, and the 148th Fighter Wing of the Minnesota Air National Guard, based in Duluth, Minnesota, to safely separate the pilot-receiving-instruction from the damaged rear ejection seat. After the pilot-receiving-instruction was separated from the seat, the bomb-squad personnel rendered the seat safe by a controlled detonation of Composition 4 (C4) plastic explosive.
The engine bay, located in the aft section of the fuselage, remained mostly intact. The Ivchenko model AI-25TL turbofan engine, serial number 9052524100057, remained mounted in the engine bay. The engine cases/bypass ducts were intact and there were no indications of radial uncontainment or undercowl fire, as shown in figures 4 and 5. The inlet guide vanes (IGV) and visible compressor blades were all complete and in good condition. There was organic debris, including small pieces of leaves and dirt collected at the 6 o’clock position of the inlet. There was a stick wedged between the IGVs and the 1st stage compressor blades at the 11 o’clock position, as shown in figures 6 and 7. The compressor/low pressure spool was seized and could not be rotated by hand, or when pressure was applied with a pry bar. During the attempt to rotate the compressor rotor blades, there was a small amount of low pressure turbine (LPT) rotor movement observed through the engine exhaust. The engine oil tank mounted on the compressor case at the 3 o’clock position had impact damage on the forward face. Oil was visible in the tank sight glass and no case penetrations or oil leakage was noted. An external engine air duct on the compressor case had crushing damage at the 12 o’clock position near the inlet. The turbine case bypass duct had impact deformations between the 9 and 10 o’clock positions at the aft flange.
The LPT 1st and 2nd stage rotor blades and nozzle vanes exhibited thermal damage and were partially consumed. The LPT 2nd stage blades visible were consumed to 1/3 span and the LPT 2nd stage nozzle vanes were consumed from the inner diameter platform to 1/2 span, as shown in figure 8. Metal debris was collected at the 6 o’clock position in the exhaust case aft of the LPT, axially in line with the case struts. The exhaust gas temperature (EGT) thermocouples were intact and appeared undamaged.
The airplane wreckage was recovered from the accident site to a secure location where additional examinations will be completed.
Figure 7. Inlet Guide Vanes, Axial Compressor
