Cape Girardeau, MO, USA
N590DM
BRUCE R PROUSE M24 ORION PLUS
The pilot was ferrying a gyroplane from Gulf Shores, Alabama, to his home in South Dakota. He made an overnight stopover in Cape Girardeau, Missouri, as part of his planned route of flight. The following morning he requested progressive taxi instructions from air traffic control to the assigned departure runway. After he taxied to the runway he departed to the northwest, consistent with what he told the controller. However, shortly into his climb, he reported to the controller that he wanted to return to the airport and the controller cleared him to land on his departure runway. The gyroplane flew the airport traffic pattern back to the runway to land; however, during the downwind leg the gyroplane rapidly descended to the ground following a loud crack that was heard by a witness at the airport. Postaccident examination of the gyroplane revealed no preimpact mechanical anomalies or malfunctions with the airframe or engine that could have precluded normal operation. Data retrieved from an onboard recording system suggests that the engine performance was unremarkable and consistent with the throttle movements throughout the final moments of the flight. Paint transfer marks on the rotor blades suggested that the main rotor contacted the horizontal stabilizer right winglet in the final moments of the accident flight, which was likely the source of the “crack” sound heard by the witness. The postaccident examination revealed evidence of severe blade flapping from a partial bend of the teetering stop of one of the main rotor blades and rotor contact with the horizontal stabilizer, which is typically due to a several-second low g or zero rotor load condition that slows the autorotation speed of the rotor. This condition was likely the result of the 270° hard left roll before the gyroplane rapidly descended and impacted the ground. Without the ability to maintain a load on the rotor in the full roll over, the rotor would have slowed and began severe flapping. The investigation was unable to determine the reason for such a severe control input (hard left roll) based on the available evidence. The evidence does indicate distress in the pilot’s voice and that he had opened his door at some point during the flight. There was no damage to the door latches and the door was found at the same distance from the main wreckage as the right horizontal stabilizer (about 170 ft). As a door annunciation would have informed the pilot if the door was not properly latched on takeoff, it is likely that this occurred in flight, and was possibly intentional if the pilot anticipated a hard landing. The accident was the result of the pilot’s failure to maintain controlled flight, which resulted in a hard left roll, excessive blade flapping, and a subsequent inflight separation of the right horizontal stabilizer.
HISTORY OF FLIGHTOn May 22, 2022, about 0803 central daylight time, an experimental amateur-built Magni M24 Orion Plus gyroplane, N590DM, was substantially damaged when it was involved in an accident near Cape Girardeau, Missouri. The private pilot was fatally injured. The gyroplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. A witness reported that the pilot was ferrying the gyroplane to his home in South Dakota on a cross-country flight and had planned a stopover at Cape Girardeau Regional Airport (CGI), Cape Girardeau, Missouri. According to air traffic control audio, the pilot informed the CGI control tower of his intent to taxi to runway 02. After the controller issued taxi instructions, the pilot requested progressive assistance to the departure runway. GPS data retrieved from an onboard device showed that the pilot started to taxi the gyroplane about 0750. The pilot subsequently departed runway 02 to the north about 0758. During the gyroplane’s climbout, the pilot informed the controller that he wanted to return to the airport and the controller cleared him to land on runway 02. The GPS flight track showed the gyroplane make a left turn to the west as the gyroplane continued its climb to an altitude of about 1,400 ft mean sea level (msl). The gyroplane then made a left turn to the southeast about 0800:09, at which time it began a 600-700 fpm descent. The GPS data ceased at 0800:35, when the gyroplane, at a recorded airspeed of about 75 KIAS and an altitude of 1,112 ft msl, was about 320 ft north of the accident site. According to a witness, at some point along the downwind leg to runway 02, she heard a “crack” coming from the direction of the gyroplane. The same witness immediately observed the gyroplane descend rapidly towards the ground. The controller reported that the gyroplane appeared to enter a spin during the descent. Witnesses estimated that the gyroplane was between 750 ft and 1,000 ft above ground level before it descended rapidly and impacted the ground. PERSONNEL INFORMATIONAn instructor of the accident pilot who listened to the pilot’s request to air traffic control to return to airport on the day of the accident reported that this was not his normal tone and that he sounded distressed. AIRCRAFT INFORMATIONThe pilot had purchased the gyroplane kit from the manufacturer in Italy in 2021 and had it shipped to a facility in Gulf Shores, Alabama, where he assembled it with assistance from a mechanic. Assembly was completed in March 2022 and the pilot returned to his home in South Dakota. The following month, the pilot returned to Gulf Shores to complete phase one testing. The gyroplane subsequently received a condition inspection before the pilot returned again to pick up the gyroplane the day before the accident. The instructor who helped the pilot transition into the accident gyroplane model reported that he flew the gyroplane for 2.5 hours on Thursday, May 19, 2022, the day before the pilot picked it up and did not observe any mechanical anomalies. The pilot departed Friday, May 20, 2022, bound for CGI, which was an intermediate stop in his planned route of flight. His planned waypoints and stops beyond CGI are unknown. According to the instructor, after he had landed at CGI, the pilot informed him that his first two stops on his way to CGI were “great”. The instructor recalled that the pilot seemed pleased with the operation and performance of the gyroplane at the time. AIRPORT INFORMATIONThe pilot had purchased the gyroplane kit from the manufacturer in Italy in 2021 and had it shipped to a facility in Gulf Shores, Alabama, where he assembled it with assistance from a mechanic. Assembly was completed in March 2022 and the pilot returned to his home in South Dakota. The following month, the pilot returned to Gulf Shores to complete phase one testing. The gyroplane subsequently received a condition inspection before the pilot returned again to pick up the gyroplane the day before the accident. The instructor who helped the pilot transition into the accident gyroplane model reported that he flew the gyroplane for 2.5 hours on Thursday, May 19, 2022, the day before the pilot picked it up and did not observe any mechanical anomalies. The pilot departed Friday, May 20, 2022, bound for CGI, which was an intermediate stop in his planned route of flight. His planned waypoints and stops beyond CGI are unknown. According to the instructor, after he had landed at CGI, the pilot informed him that his first two stops on his way to CGI were “great”. The instructor recalled that the pilot seemed pleased with the operation and performance of the gyroplane at the time. WRECKAGE AND IMPACT INFORMATIONThe gyroplane impacted a muddy field about 1,000 ft west of the departure end of runway 10 at a field elevation of about 330 ft msl. All major structures were accounted for at the accident site. The main wreckage, comprised of the fuselage, rotor, engine, and empennage, was oriented on a northwest heading. A section of the right horizontal stabilizer had separated from the main wreckage and was located 171 ft south of the main wreckage. The engine was partially submerged in the mud along with two of the gyroplane’s four propeller blades. The other two propeller blades were visible above the surface, and both had separated about midspan; one blade tip was found about 200 ft south of the main wreckage. Both rotor blades were attached at the rotor hub and exhibited similar impact signatures about 3 ft from their outboard ends. They also displayed black transfer marks about 3 ft from the hub of each blade. One blade displayed blue transfer markings on the bottom of the blade about 3 ft from the outboard end, which corresponded to the paint color of the gyroplane including the separated right horizontal stabilizer. Photograph 1: Accident site Figure 1: Main wreckage and debris field Wreckage Examination Postaccident examination of the gyroplane did not reveal any preimpact mechanical anomalies. The cyclic control system was traced from the multifunction grips at the cockpit to the rotor head through one separation at the upper right control rod about midspan. The damage to the control rod was consistent with overload separation. The rudder cables were continuous from the cockpit to the rudder. All of the hardware for both the cyclic and rudder control systems were secured at their positions. Both rotor blades remained attached to the rotor hub after the accident and were later removed by recovery personnel. The rotor head remained attached to the mast through the hub bar. The blade 1 teetering stop displayed a partial bend. The engine was unremarkable. Mechanical continuity was established throughout the rotating group, valvetrain, and accessory section as the crankshaft was manually rotated at the propeller by hand. Thumb compression was achieved at all four cylinders and the valves displayed normal lift when the crankshaft was rotated. Examination of the cylinders’ combustion chamber interior components using a lighted borescope revealed normal piston face and valve signatures, and no indications of catastrophic engine failure. The four-bladed, ground-adjustable propeller remained attached at the crankshaft flange. All four blades were separated about midspan and remained attached to the hub. Door Examination The pilot side door was found undamaged except for a torn hinge, about 170 ft south of the main wreckage near the right horizontal stabilizer. The door locking mechanism for both the pilot and passenger sides are comprised of a closing block, a locking pin, a door pin, and a latching mechanism. Two door pins were mounted to each of the doors and two corresponding closing blocks were mounted to the door frame openings of the fuselage. To lock the door, with the door closed (and the door pins inserted into the closing block), movement of a hand-operated lever actuates the push/pull rod linkages to insert the locking pins into the closing blocks. A door annunciation on the instrument panel will illuminate if the door is ajar. If the pilot attempts to take off with the door ajar, the rotor tachometer necessary for the gyroplane to attain pre-rotation rpm before takeoff will not illuminate in addition to the door annunciation light. An NTSB materials laboratory examination of the pilot side door pins, corresponding locking pins, and closing blocks did not reveal any preimpact or postimpact mechanical anomalies or deformities that would have prevented the locking pins from engaging with the door pins. The passenger door was found normally latched at the accident site with the door damaged. ADDITIONAL INFORMATIONDynon HDX1100 The gyroplane was equipped with a Dynon HDX1100 panel-mounted unit that could serve as either a primary flight display or a multifunction display. Data retrieved from the unit included altitude, airspeed, attitude, vertical speed, and heading. In addition, the unit contained alert logs that showed both caution, warning, and aural alerts that were generated during the flight. According to the data, at 0800:01 as the gyroplane turned to the south at an altitude of about 1,437 ft msl, an audio annunciation began with the aural warning “GEES.” According to Dynon, this alert would have been prompted when the G meter was outside the yellow caution range. The configuration file from the Dynon showed that the G meter yellow range was set between -1 and +3 Gs. During this time, the gyroplane rolled about 36° left and maintained about a 3° positive pitch attitude. The gyroplane continued to maintain a left turn and then rolled into a 19° right roll with a pitch attitude of about -9° (nose down) at 0800:29. Three seconds later true airspeed rapidly decreased from about 85 KIAS to 0 KIAS. One second later the gyroplane rolled inverted in a 20° nose down attitude at an altitude of 1,210 ft msl. Over the 3 seconds beginning at 08:00:32, the gyroplane transitioned into a steep left roll attitude (about 130°) and then transitioned into a steeper 176° left roll. In the same second (0800:33) the data showed the gyroplane in a 174° right roll followed by a 94° right roll and returned to a left roll at 164° when the data ceased at 0800:35. An “OVER_GEE” warning was generated at 0800:34. This annunciation would have occurred when the G meter was in the red warning range. The configuration file from the Dynon showed that the G meter red range was set to -3 and +4 Gs. Engine Control Unit (ECU) The engine was equipped with an ECU responsible for controlling certain engine functions. Additionally, the ECU captures fault codes at their time of occurrence and logs engine parametric data. The data files recovered from the ECU included engine speed (in rpm), linearized throttle position, manifold air pressure, fuel flow rate, and oil pressure/temperature. The data showed that any adjustments in fuel flow, engine speed, and manifold pressure, were consistent with changes in the throttle position for the duration of the flight. The engine data’s operating time, which consisted of a running session counter, was compared to the Dynon data for geographic position as the engine data did not include location information. A review of the data showed that the engine performance remained fairly consistent until the remaining 11 seconds of flight (about 0800:24). During this time, after the gyroplane had turned to a southeastern heading, the engine speed decreased from about 4,600 rpm to about 2,750 rpm, consistent with the reduction in throttle and then a 600-700 fpm descent on downwind. At approximately 0800:28, the engine speed increased to about 6,200 rpm and was subsequently reduced to about 5,500 rpm, consistent with the throttle movements at the time. This engine speed was maintained for the remainder of the flight. Excessive Blade Flapping According to a gyroplane technical expert and representative of the manufacturer: Excessive blade flapping is the result of lower or zero load on the rotor. Excessive gyroplane blade flapping is often described simply as ‘Flapping the Blades.’ But the blades are always necessarily flapping or teetering in forward flight. Lower Rotor load does slow the Autorotation of the gyroplane rotor. If severe and extended low or zero rotor load, for more than a few seconds, the rotor will then require teeter angles that exceed the mechanical teeter limits – ‘flapping the blades’. The typical historical way low g-load has been the cause of gyroplane ‘blade blapping” is with a ‘push-over.’ In a gyroplane, as well as in a helicopter, too quick and severe a nose “push-over”, g-load can drop so far and so long as to require excessive blade teeter or ‘flap.’ In a helicopter this typically is called ‘mast bumping.’ In a gyroplane it is called a ‘bunt-over’ because in a pitch unstable gyroplane airframe, that nose-down forward bunt continues and quickly reduces the rotor lift or g-load and slows the autorotation of the rotor as the relative air transitions to the top of the rotor disk as the gyroplane tumbles mostly forward. The rotor is unpowered, so rotor torque does not apply. This ‘buntover’ condition in gyroplanes is essentially prevented in modern gyroplanes with an adequate horizontal stabilizer that dampens and slows any forward pitch motion before it can progress into a full buntover – typically fatal. In a helicopter, the same sudden nose-down pitch change can result in extreme rotor flapping to cause ‘mast bumping’, often separating the mast, before it can progress into an actual full ‘buntover.’ [A]n excessive flapping situation [can also develop] due to a severe roll attitude without continued back stick pressure to maintain positive g-load and airflow on the autorotating rotor. Even if positive aft cyclic stick is maintained in a complete roll-over, the aft stick necessarily slows the airspeed reducing the rotor disk airflow and g-load quickly losing rotor RPM until teeter flapping mechanical limits are exceeded. The reason for the tumble as a result of excessive blade flapping is that once the mechanical teeter stop limit is exceeded, the cyclic stick range is then bumped – ‘bumping the stick’, the pilot’s cue they are exceeding teeter stop limits. This most often occurs on takeoff acceleration where ground airspeed exceeds the ability of the rotor RPM to increase without exceeding the teeter stops. In the air this is rare but can occur quickly in the extreme maneuvers mentioned above. In the air, if the ‘bumping’ of the stick is not quickly corrected, extreme flapping quickly tumbles the whole airframe erratically. According to a representative of the manufacturer, the high power and torque of this engine could contribute to a sudden additional roll of a gyroplane following a rapid change in throttle. He further remarked that a rapid decay in rotor rpm will be accompanied by a bump in the cyclic. According to the accident aircraft flight manual, “Load factors less than 1g cause a rapid decay in rotor rpm and could lead to blade flapping. Detection of low g-factor is pilot sensor cue of lightness in the seat.”
The pilot’s failure to maintain controlled flight, which resulted in a hard left roll, excessive blade flapping and a subsequent in-flight separation of the right horizontal stabilizer.
Source: NTSB Aviation Accident Database
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