Unknown or undetermined: Davis DA-3, N88DT, fatal accident occurred on April 4, 2024, Antlers, Oklahoma

• Location: Antlers, Oklahoma 
• Accident Number: CEN24FA148 
• Date & Time: April 4, 2024, 16:33 Local 
• Registration: N88DT 
• Aircraft: Davis DA-3 
• Aircraft Damage: Destroyed 
• Defining Event: Unknown or undetermined 
• Injuries: 3 Fatal 
• Flight Conducted Under: Part 91: General aviation - Personal

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/194033/pdf

https://data.ntsb.gov/Docket?ProjectID=194033

On April 4, 2024, about 1633 central daylight time, a Davis DA-3 airplane, N88DT, was destroyed when it was involved in an accident near Antlers, Oklahoma. The pilot and two passengers were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The private pilot and two passengers departed in the experimental airplane into day visual flight rules conditions for a local personal flight. A witness reported that the airplane departed to the south, and that the takeoff seemed routine and there were no obvious anomalies with the airplane.

About 15 to 20 minutes later, local authorities received a report of an explosion. Upon arriving at the site, first responders observed the airplane with an active fire. There were no known witnesses to the accident itself, and no ADS-B data related to the accident flight was located. The airplane came to rest adjacent to a large tree about 1.4 miles south southwest of the departure airport. A post-impact fire consumed portions of the fuselage and charred the large tree and low brush in the surrounding area.

The airplane exhibited impact and postimpact fire damage. Portions of the fuselage and both wings were consumed by fire. Flight control continuity was confirmed from each control surface to the cockpit area. The engine was separated from the airframe and rested inverted on the ground near the fuselage. An examination did not identify any anomalies attributable to a preimpact failure or malfunction. The propeller was consumed by the postimpact fire; however, the retaining plates and propeller attachment bolts were intact. No evidence of an inflight failure or separation of the propeller was observed.

Although the extent of the postimpact fire limited the scope of the wreckage examinations, no evidence of an in-flight structural failure, flight control system anomaly, or inability of the engine and propeller to provide rated thrust were observed.

The pilot’s coronary artery disease was associated with increased risk of an impairing or incapacitating cardiovascular  event; however, there was no autopsy evidence that such an event had occurred.

The pilot’s postmortem toxicology results indicated use of the sedating antihistamine medication diphenhydramine, but the level in his postmortem heart blood was low. Detected norchlorcyclizine indicated the pilot also likely used another antihistamine medication long enough before the accident that the medication itself was no longer detectable in his blood. Based on these results, there was no evidence that the pilot was experiencing any significant impairing effects at the time of the accident.

- Probable Cause: Impact with terrain for reasons that could not be determined.

Loss of engine power (total): Bell 206L-4 LongRanger IV, N988B, fatal accident occurred on April 26, 2024, near Anaconda, Motana

• Location: Anaconda, Montana 
• Accident Number: WPR24FA132 
• Date & Time: April 26, 2024, 06:59 Local 
• Registration: N988B 
• Aircraft: Bell 206-L4 
• Aircraft Damage: Destroyed 
• Defining Event: Loss of engine power (total) 
• Injuries: 1 Fatal 
• Flight Conducted Under: Part 133: Rotorcraft ext. load

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/194154/pdf

https://data.ntsb.gov/Docket?ProjectID=194154

On April 26, 2024, at 0659 mountain daylight time, a Bell 206-L4 helicopter, N988B, was destroyed when it was involved in an accident near Anaconda, Montana. The pilot was fatally injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight.

The pilot of the helicopter was performing aerial application operations. Security video showed the helicopter approach the loading truck for a third load of fertilizer and complete an onload of fertilizer before departing. The helicopter reached about 150 ft above ground level (agl) and 40 kts groundspeed when it rotated about 180° to the left and descended, consistent with an emergency autorotation. The helicopter impacted an area of flat terrain in a mostly level attitude. Examination of the wreckage revealed no anomalies with the airframe or flight controls that would have precluded normal operation.

Examination of the engine revealed that the gas producer turbine rotor did not turn when the N1 rotor was rotated. The N2 rotor was continuous from the 4th-stage power turbine rotor to the output driveshaft, but an audible rubbing or scraping sound was heard when it was rotated. The engine was disassembled and the turbine-to-compressor coupling shaft was found fractured into three pieces. Coking was observed in the forward and aft spline locations of the turbine to-compressor coupling shaft and between the turbine-to-compressor coupling shaft and the power turbine outer shaft. Extensive coking was noted upon removal of the powerturbine-to-pinion-gear coupling shaft. The two O-rings of the spur adapter gearshaft, which manage oil distribution in the turbine-to-compressor coupling shaft, were not present in their designated grooves.

Coked material was found that restricted oil flow in one orifice of the piccolo tube and blocked a second orifice of the oil jet to the No. 3 bearing. Analysis of the coked material revealed fluorocarbon rubber signatures consistent with O-ring material. The engine manufacturer stated they were not aware of any previous instances of O-rings disintegrating. The initiating event for the disintegration of the O-rings could not be determined.

Maintenance records indicated that the spur adapter gearshaft, where the O-rings would normally be located, was last accessible when the engine was overhauled about 5 years (1,414.1 flight hours) before the accident. According to the engine manufacturer, a damaged or wrong part number O-ring (or a missing O-ring) may allow cooling oil flow to leak back into the gearbox rather than flow between the concentric shafts. The reduced oil flow between the shafts is not sufficient to cool the shafting below oil carboning temperatures, as evidenced by the finding of coked carbon material in the area of the fractured compressor coupling shaft. Carbon deposits on the outside diameter of the turbine-to-compressor coupling and the inside diameter of the power turbine inner shaft and turbine-to-compressor coupling can build up until rub occurs, causing interference between the shafts, resulting in frictional heating and ultimate failure, which subsequently resulted in a total loss of engine power.

It is likely that the carbon buildup in the piccolo tube screen and nozzles reduced cooling oil flow to the turbine-to-compressor coupling and the turbine inner shaft that caused the shafts to operate at a higher temperature than the carboning limits of the oil, allowing coke to build up between the shafts. The reason for the carbon accumulation in the piccolo tube screen and nozzles was not determined.

The helicopter’s Height-Velocity performance chart indicated that, in general, pilots should avoid operations below 600 ft agl and below 65 kts, when above 4,150 lbs gross weight, and 500 ft agl and below 45 kts when below 4,150 lbs gross weight. Operations within these parameters reduce the likelihood of completing a successful autorotation. Practice 180° autorotations are not recommended below 700 ft agl. Given the helicopter’s altitude and speed at the time of the engine power loss, the pilot likely had insufficient altitude from which to establish an autorotation and perform a successful landing following the loss of power.

The pilot’s toxicology results indicate he had used the sedating antihistamine medication diphenhydramine. Although caution must be used interpreting the diphenhydramine level measured in postmortem subclavian blood, the level indicates a reasonable probability that the pilot was experiencing some associated sedation or psychomotor impairment at the time of the accident. However, given the lack of clear evidence for any deficiency of the pilot’s preflight or inflight performance, and the altitude at which the sudden total loss of engine power occurred, it is unlikely that the pilot’s use of sedating antihistamine medication contributed to the accident.

- Probable Case: A total loss of engine power due to a loss of cooling oil to the turbine-to-compressor coupling shaft and subsequent fracture of the shaft at an altitude too low for the pilot to complete a successful autorotation. Contributing to the accident was carbon buildup in the piccolo tube screen and nozzles and the disintegration of the spur adapter gearshaft O-rings for reasons that could not be determined.

Loss of control in flight: Mooney M20K 252 TSE, N4387W, fatal accident occurred on March 25, 2024, near Northeast Florida Regional Airport (SGJ/KSGJ), St. Agustine, Florida, and Mooney M20K 231, N262MK, accident occurred on May 6, 2023, at Central Jersey Regional Airport (47N), Manville, New Jersey

• Location: St. Augustine, Florida 
• Accident Number: ERA24FA154 
• Date & Time: March 25, 2024, 11:54 Local 
• Registration: N4387W 
• Aircraft: Mooney M20K 
• Aircraft Damage: Substantial 
• Defining Event: Loss of control in flight 
• Injuries: 2 Fatal 
• Flight Conducted Under: Part 91: General aviation - Personal 

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193984/pdf

https://data.ntsb.gov/Docket?ProjectID=193984

On March 25, 2024, about 1154 eastern daylight time, a Mooney M20K airplane, N4387W, was substantially damaged when it was involved in an accident in St. Augustine, Florida. The commercial pilot and passenger were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

Shortly after takeoff, the pilot reported to the air traffic controller that he had a door that had “popped open,” and the controller cleared the flight to return for landing. A review of ADS-B data and surveillance video revealed that, while the airplane was on the base leg for the approach back to the departure airport, it entered a steep, nose-down descent while rolling to the right, consistent with an aerodynamic stall/spin. Postaccident examination of the airplane revealed that both of the airplane’s doors (the rear baggage door and the main cabin door) remained attached to the airframe. Examination of the rear baggage door revealed damage consistent with it having been closed and latched at the time of impact; this included damage on the door latch pins (which were found extended) and striker plates indicating that the rear baggage door latch pins had been forced past the striker plates during the impact sequence.

Examination of the main cabin door upper and aft center latch components revealed no damage to the latch pins and striker plates, indicating that the door was likely not closed and latched at the time of impact. Because the examination of the door lock and latching mechanisms did not reveal any mechanical failure or malfunction that would have precluded normal operation, the door was likely not closed properly before takeoff. The examination of the remainder of the airframe and the engine did not reveal any mechanical malfunction or failure that would have precluded normal operation.

According to the airplane’s Pilot’s Operating Handbook (POH), if the main cabin door is not properly closed, it may come unlatched in flight but will not affect the airplane’s flight characteristics. The POH prescribed either returning to the field and landing normally or climbing the airplane to a safe altitude to perform the procedures for shutting and latching the door.

The airplane was equipped with an engine data monitor that recorded various engine data parameters for the entire accident flight. A review of the engine data revealed that, at the time that the monitor stopped recording, all readings were consistent with normal engine operation and a high power setting. Based on these data, it is likely that, during the aerodynamic stall/spin, the pilot added full power to the engine in an attempt to recover from the aerodynamic stall/spin. According to the POH, to recover from a spin, it is necessary to bring the engine back to idle; however, the POH also stated that stalls at low altitude are extremely critical and that up to 2,000 ft of altitude may be lost during a one-turn spin and recovery. Thus, due to the airplane being below traffic pattern altitude when it entered the aerodynamic stall/spin, it is unlikely that the pilot could have recovered even if he had properly conducted the spin recovery items.

- Probable Cause: The pilot’s failure to maintain adequate airspeed of the airplane while in the traffic pattern, which resulted in an aerodynamic stall/spin. Contributing was the pilot’s distraction due to the in-flight opening of the main cabin door, which resulted from the incorrect closure of the door before takeoff.

...

- Pilot Information:

According to the pilot’s logbook, the pilot’s last flight was the day before the accident and was for less than 1 hour and the pilot recorded only one landing. According to 14 CFR 61.57 a pilot could not act as pilot in command of an aircraft carrying passengers unless the pilot had performed 3 takeoffs and landings in the previous 90 days. 

The flight prior to that, was May 6, 2023, where the pilot recorded in his logbook “crash on takeoff Rwy 25.” An NTSB investigation was performed, according to the report, the pilot entered an aerodynamic stall after a partial loss of engine power. For additional information refer to NTSB Aviation Investigation Final Report for ERA23LA225.

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/130453/pdf

https://data.ntsb.gov/Docket?ProjectID=193984

Structural icing: Cessna 208B Grand Caravan, N1983X, incident occurred on January 19, 2024, near Washington-Dulles International Airport (IAD/KIAD), Dulles, Virginia

• Location: Dulles, Virginia 
• Incident Number: ERA24LA094 
• Date & Time: January 19, 2024, 12:47 Local 
• Registration: N1983X Aircraft: Cessna 208 
• Aircraft Damage: Minor Defining Event: Structural icing 
• Injuries: 7 None 
• Flight Conducted Under: Part 135: Air taxi & commuter - Scheduled

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193691/pdf

https://data.ntsb.gov/Docket?ProjectID=193691

On January 19, 2024, at 1247 eastern standard time, Southern Airways Express flight 246, a Cessna 208B airplane, N1983X, was involved in an incident near Dulles, Virginia. The two commercial pilots and five passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 scheduled domestic passenger flight from Washington Dulles International Airport (IAD), Dulles, Virginia, to Lancaster Airport (LNS), Lancaster, Pennsylvania.

During initial climb, the flight crew began to feel a vibration and loss of engine power. They declared an emergency and turned back toward the departure airport. Upon realizing they would not be able to return to the departure airport, they landed on a road, resulting in minor damage to the airplane.

Postincident examination of the airframe and engine found no preincident mechanical malfunctions or failures that would have precluded normal operations. Postincident photographs taken of the airplane by first responders shortly after the incident show contamination buildup on some of the airplane’s lift-generating surfaces (that is, the wings and horizontal and vertical stabilizers).

Weather before and around the time of the incident included light snow and below freezing temperatures. When the flight crew checked the airplane for contamination during their preflight inspection, they did not observe any ice or snow accumulation, but the airplane appeared wet. Neither crewmember performed a tactile check of the airplane’s lift generating surfaces, and the captain chose not to deice the airplane. He reported that the company had deicing services available and that it would normally be applied at the gate. Company procedures stated that the only acceptable deice fluid was Type 1.

The operator’s standard operating procedures dictated that a visual contamination check was required to be performed within five minutes before takeoff. The same guidance left the decision to perform a tactile check of the airplane’s lift-generating surfaces to the captain. This directly contradicted the airplane manufacturer’s guidance, which stated that a tactile check must be completed when the outside air temperature is below 10°C. The second-in-command (SIC) reported that before entering the runway, they looked out at the wing and did not observe any contamination, stating that it was “just wet.” Due to contradictory guidance on when a tactile versus visual check must be performed, it is likely the crew believed they had completed an appropriate contamination check before departing.

Based on the weather conditions at the time, reports that another airplane—which had been on the ground for a similar amount of time—was observed with ice accumulation, and the failure of the crew to perform a tactile contamination check within 5 minutes before takeoff; it is likely that ice had accumulated on the airframe before takeoff. Based on the taxi time of about 6 minutes and a holdover time of 11 minutes, it is also likely that had the crew chose to deice, any accumulated ice would have been removed, and the airplane subsequently would not have accumulated additional ice.

Review of ADS-B data showed that during initial climb the airplane’s groundspeed (after accounting for the prevailing 8 knot headwind component) decreased below the stall speeds listed in the airplane pilot’s operating handbook. The vibration the crew felt was likely the beginning stages of an aerodynamic stall that was likely exacerbated by the degraded performance associated with structural icing.

- Probable Cause: The pilot-in-command’s approach to the critical angle of attack during initial climb, which resulted in a vibration the flight crew improperly identified as an engine issue and resulted in the subsequent off-airport landing. Contributing to the accident was the operator’s inadequate and contradictory guidance for flight crews operating in winter conditions. Also contributing was the pilot-in-command’s decision not to perform a tactile check or deice, which resulted in taking off with ice contamination.

Loss of control on ground: Honda HA-420 HondaJet, N103JT, accident occurred on January 28, 2024, at Orlando International Airport (MCO/KMCO), Orlando, Florida

• Location: Orlando, Florida 
• Accident Number: ERA24LA100 
• Date & Time: January 28, 2024, 16:23 Local 
• Registration: N103JT 
• Aircraft: HONDA AIRCRAFT CO LLC HA-420 
• Aircraft Damage: Substantial 
• Defining Event: Loss of control on ground 
• Injuries: 4 None 
• Flight Conducted Under: Part 135: Air taxi & commuter - Non-scheduled

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193714/pdf

https://data.ntsb.gov/Docket?ProjectID=193714

On January 28, 2024, about 1623 eastern standard time, a Honda Aircraft Company LLC HA420 airplane, N103JT, was substantially damaged when it was involved in an accident at Orlando International Airport (MCO), Orlando, Florida. The airline transport pilot, commercial co-pilot, and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 on-demand passenger flight.

The on-demand air taxi flight proceeded to the destination airport and, about 1 hour and 22 minutes before landing, the flight crew reviewed the destination airport automated terminal information service (ATIS), which indicated the wind was from 270° at 14 kts, gusting to 24 kts. The cockpit voice recorder (CVR) recorded the crew discussing the crosswind component of the winds reported on the ATIS, the aircraft operating limitations, company procedures, and an alternate airport, but the pilot flying (PF) elected to continue to the planned destination airport.

About 16 minutes before the airplane touched down, when it was about 39 nautical miles (nm) from the destination airport, the PF advised the pilot monitoring (PM) that he checked the airport’s automated surface observing system (ASOS) and reported the wind velocity was currently at 270° at 13-14 kts. While on final approach, about 1.2 nm from the approach end of runway 36L, the tower controller advised that the wind was from 290° at 19 kts, gusting to 24 kts.

The PF continued the approach and just about when the airplane was at touchdown the controller broadcast on the frequency for another airplane that was on approach that the wind was from 290° at 20 knots, gusting to 24 kts. After the airplane touched down, it began drifting to the left side of the runway. The PF applied left aileron control input, deployed the speedbrake, and applied right rudder; however, the airplane departed the runway and impacted a frangible runway distance-remaining sign. The PF then corrected the airplane to the right, returned it to the runway, and taxied off onto a taxiway, where the pilot stopped the airplane and evacuated.

Postaccident inspection of the airplane revealed substantial damage to the left wing’s forward spar in the area that impacted the sign. The rudder and aileron trims were found in the neutral position. The operator reported there was no preimpact mechanical failure or malfunction with the airplane that would have caused the runway excursion.

Although the PF reported about 16 minutes before touchdown that he received the ASOS observations for the previous 20 minutes and stated to the PM that the crosswind was at 13 or 14 kts, with the wind from 270° at 13 kts, a review of the 14 previous 5-minute ASOS observations revealed that gusts were reported in all but 2 of the 14 observations. The PF’s reference specifically to the wind being from 270° at 13 kts corresponded to an observation that also reported gusts to 24 kts, which occurred about 23 minutes before the airplane touched down. That gust value exceeded the airplane’s published crosswind limitation of 20 kts.

The gust values at the destination airport consistently exceeded the airplane’s published crosswind limitation for the majority of the 5-minute ASOS observations in 1 hour 23 minutes preceding the accident. These conditions should have necessitated either an earlier diversion to an alternate airport that was more aligned with the wind or a go-around during short final approach after the flight crew was informed, when the airplane was about 1.2 nm from the runway threshold, that the wind was gusting above the published crosswind limitation.

The PF chose to continue with the landing and, due to a crosswind gust, failed to maintain directional control of the airplane after landing. The PF also did not incorporate the gust values into the crosswind calculations about 16 minutes before the accident, which likely influenced his decision to continue the approach.

- Probable Cause: The failure of the pilot flying to maintain directional control after touchdown with wind gusts that exceeded the airplane’s crosswind limitation. Contributing to the accident were the flightcrew’s continued approach to the runway despite the consistent wind gust crosswind component that exceeded the airplane’s published crosswind limitation, and their incorrect wind gust crosswind calculation in flight.

Sys/Comp malf/fail (non-power): Beechcraft 95-B55 Baron, N7371R, accident occurred on April 1, 2024, at Northeast Florida Regional Airport (SGJ/KSGJ), St. Augustine, Florida

• Location: St. Augustine, Florida 
• Accident Number: ERA24LA214 
• Date & Time: April 1, 2024, 12:00 Local 
• Registration: N7371R 
• Aircraft: Beech 95B55 
• Aircraft Damage: Substantial 
• Defining Event: Sys/Comp malf/fail (non-power) 
• Injuries: 2 None 
• Flight Conducted Under: Part 91: General aviation - Flight test

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/194230/pdf

https://data.ntsb.gov/Docket?ProjectID=194230

On April 1, 2024, about 1200 eastern daylight time, a Beech 95B55 airplane, N7371R, was substantially damaged when it was involved in an accident near St. Augustine, Florida. The pilot and pilot-rated passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 test flight.

The pilot and the pilot-rated passenger, who was also a mechanic, were conducting a postmaintenance flight test after an extensive annual inspection of the airplane. Shortly after takeoff, the airplane lost complete electrical power. The pilot turned back toward the airport, while the pilot-rated passenger contacted the control tower with his mobile phone and declared an emergency. The pilot said that he, with some help from the pilot-rated passenger, attempted to manually lower the landing gear with the emergency gear extension handle; however, he may not have been able to get the landing gear fully extended to the down and locked position. When the airplane touched down on the runway, the right main landing gear collapsed, and the airplane went off the right side of the runway and collided with a runway sign, resulting in substantial damage to the fuselage and right wing. A postaccident examination of the airplane’s electrical system revealed no mechanical issues and the reason for the loss of electrical power could not be determined from the available information. A functional test of the landing gear system could not be performed due to damage sustained during the accident.

- Probable Cause: The incomplete extension of the landing gear into the down-and-locked position for reasons that could not be determined.

Loss of engine power (total): Cozy Mark IV, N20MN, accident occurred on March 25, 2024, near Roger M Dreyer Memorial Airport (T20), Gonzales, Texas

• Location: Gonzales, Texas 
• Accident Number: CEN24LA141 
• Date & Time: March 25, 2024, 18:53 Local 
• Registration: N20MN 
• Aircraft: Cozy Mark IV 
• Aircraft Damage: Substantial 
• Defining Event: Loss of engine power (total) 
• Injuries: 1 None 
• Flight Conducted Under: Part 91: General aviation - Personal 

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193992/pdf

https://data.ntsb.gov/Docket?ProjectID=193992

On March 25, 2024, about 1853 central daylight time, a Cozy Mark IV airplane, N20MN, was substantially damaged when it was involved in an accident near Gonzales, Texas. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

While enroute, at 9,500 ft above mean sea level (msl), the engine lost all power. After multiple attempts to restart the engine, the pilot executed a forced landing to a nearby airport. The airplane landed short of the runway threshold and its nose landing gear separated as the airplane transitioned onto the asphalt runway. The left wing and left canard sustained substantial damage.

Postaccident examination of the engine revealed that the left crankshaft idler gear shaft separated from its attach points, which prevented the crankshaft idler gear from engaging its corresponding crankshaft and camshaft gears. The disengagement prevented camshaft rotation and valvetrain timing to the crankshaft. The left crankshaft idler gear’s attachment hardware were both separated into two sections from abrasion. The capscrew was lockwired to the idler shaft but no lockwire was observed through the stud and slotted shear nut.

It is likely that maintenance personnel did not follow the engine manufacturer’s service instructions and undertorqued the fasteners during installation, resulting in insufficient clamping force. Additionally, the absence of lockwire likely permitted the shear nut to back off during engine operation. Because the airplane’s maintenance records were not available for review, the investigation was not able to identify when the crankshaft idler gear was last serviced.

- Probable Cause: Maintenance personnel’s failure to properly torque the crankshaft idler gear hardware according to the engine manufacturer’s service instructions, which resulted in separation of the crankshaft idler gear’s fasteners and disengagement of the camshaft, crankshaft, and crankshaft idler gear and a subsequent total loss of engine power.

Fuel starvation: Rans S-7S Courier, N599YY, accident occurred on April 22, 2024, near Benson, Arizona

• Location: Benson, Arizona 
• Accident Number: WPR24LA130 
• Date & Time: April 22, 2024, 09:42 Local 
• Registration: N599YY 
• Aircraft: JAMES E DAVIDSON JR RANS S7S COURIER 
• Aircraft Damage: Substantial 
• Defining Event: Fuel starvation 
• Injuries: 1 None 
• Flight Conducted Under: Part 91: General aviation - Personal

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/194136/pdf

https://data.ntsb.gov/Docket?ProjectID=194136

On April 22, 2024, at 0942 mountain standard time, a Rans S-7S experimental amateur-built airplane, N599YY, was substantially damaged when it was involved in an accident near Benson, Arizona. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot was evaluating the airplane’s engine performance with a different fuel after changes were made to the fuel system. Shortly after a normal takeoff, the pilot noticed a low fuel pressure warning. The engine subsequently sustained a partial and then total loss of power. The pilot restarted the engine, and it momentarily produced power. As he advanced the throttle, the engine again stopped producing power. During an off-airport landing, the main landing gear collapsed.

On previous flights, the engine had produced less power than the pilot expected. In response, he performed an engine examination and observed lead deposits on the exhaust valves. He contacted the engine manufacturer, who recommended switching from 100LL avgas to unleaded auto fuel. The pilot then created a mixture of winter-blend auto fuel and a small, precise amount of 100LL avgas.

An examination of the engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. Examination of the fuel system revealed that the inside diameter of the fuel supply and return lines were smaller than recommended by the engine manufacturer. This undersized condition limited the volume of fuel available to the engine.

A small fuel leak was discovered at an exit fitting in one of the fuel pumps. Investigators could not determine if the leak existed before the accident or if it was a result of impact forces. Additionally, the vent tube in the left-wing fuel tank was obstructed and did not permit airflow until investigators inserted a small wire several inches into the tube, after which the vent permitted air passage.

Accident flight data recorded by the airplane’s engine monitoring device revealed that the fuel pressure and flow both declined slowly as the flight progressed and became increasingly erratic. Shortly thereafter, a sudden and complete loss of both fuel pressure and flow occurred. When the pilot attempted to restart the engine, the available fuel pressure and flow was insufficient to sustain engine operation. Recorded data from the flight was consistent with air bubbles present in the fuel system, followed by fuel starvation due to vapor lock.

After an operational test of the engine, several firewall-mounted fuel-system components (including the gascolator, fuel filters, electric fuel pumps, and associated metal fuel lines) that had been positioned near the engine exhaust system remained hot for more than 20 minutes after engine shutdown. Under these heat-soaked conditions, investigators noted that the fuel pumps required an extended period to achieve priming, and the fuel exiting the pumps initially appeared cloudy and aerated before gradually clearing as normal pressure and flow were restored. The pumps emitted abnormal noises consistent with cavitation during the period when cloudy, vapor-entrained fuel was present.

The locally procured auto fuel was a winter blend, which is formulated in a manner that makes it susceptible to vaporization at warmer fuel temperatures. Because the fuel was routed through metal fuel system components exposed to exhaust heat, the fuel in the system was likely heated to a temperature that resulted in vaporization. Although the investigation also found a small leak at a fuel line exit fitting and a blocked vent tube in the left-wing fuel tank, the engine data and postaccident engine testing was consistent with fuel vaporization. The vaporization of the fuel likely led to a vapor-lock condition and subsequent fuel starvation.

- Probable Cause: The pilot’s unintentional use of a winter-blend fuel that was susceptible to vaporization, which resulted in fuel starvation and a loss of engine power due to vapor lock. Contributing to the accident was the airplane’s undersized fuel lines, which limited the available fuel flow and volume.