CEN16LA223

A hard landing on rough terrain due to a faulty deployment of the airplane’s airframe parachute system following a partial loss of engine power for reasons that could not be determined, because postaccident examination revealed no malfunctions or anomalies that would have precluded normal operation. Contributing to the accident was the low altitude deployment of the parachute system.

The commercial pilot was conducting a local flight when he noted a lower-than-normal oil pressure indication and engine roughness. The engine subsequently experienced a partial loss of power and the airplane could not maintain altitude. The pilot deployed the Cirrus Airframe Parachute System (CAPS) at an estimated 472 ft above ground level, and the airplane impacted rough terrain under canopy in a nose-low, upright attitude. A test run of the engine and review of recorded data did not reveal the reason for the partial loss of engine power. Examination of the airframe parachute system revealed that, during deployment of the CAPS, the rocket separated from its lanyard in overstress. Fracture testing of the lanyard revealed that it did not exceed the minimum value in several tests, and the examined lanyard sections did not fully conform to specification; however, it is unlikely that these anomalies resulted in the overstress fracture. Features observed on the CAPS retaining harness suggested that some resistance was encountered when pulling the incremental bridle from the sleeve during the deployment. The cover flap from the retaining harness had discoloration and heat damage consistent with abnormal exposure to the rocket exhaust, and pulled stitches were noted in the vicinity of the sleeve where the incremental bridle was stowed. It is likely that the incremental bridle was not released immediately from the sleeve, which kept the rocket closer to the retaining harness and placed abnormal loads on the lanyards. At some point, the incremental bridle was released from the sleeve and loaded to separate the stitches in the incremental bridle as designed. During a nominal CAPS deployment, the airplane enters a nose-low attitude before leveling off, a stage of deployment referred to as "tail drop." For tail drop to occur, the deployment must be initiated to allow adequate time and/or altitude. During the accident, the parachute inflated fully; however, the abnormal CAPS deployment, as well as low deployment altitude resulted in the airplane touching down in a nose-low attitude before tail drop occurred. Based on static pull tests in the lab, the orientation of the incremental bridle within the sleeve can significantly affect the force required to release the incremental bridle from its stowed position. A review of parachute packing procedures revealed that the orientation of the incremental bridle as it was inserted in its sleeve was not specified. In the absence of any specific procedure for orienting the incremental bridle in the sleeve, it would be possible for the incremental bridle to be inserted in either orientation. The investigation could not determine whether the incremental bridle had been inserted in an unfavorable orientation or if such an orientation would have resulted in the lanyard fracture. Based on review of the parachute deployment and subsequent testing, an exact cause for the abnormal CAPS deployment could not be determined.

The engine was shipped to and examined at Continental Motors in Mobile, Alabama. Both front engine mounts were damaged and replaced with exemplar mounts. The engine was mounted on a test stand and placed in a test cell. During the initial engine test run, the engine reached an indicated manifold pressure of 35 inches of mercury at 2,700 RPM. The altitude control valve was connected and the indicated engine performance was within the supplemental type certificate holder's specifications and no anomalies were noted. The CF memory chip from the MFD was shipped to the National Transportation Safety Board (NTSB) Recorder Laboratory. The MFD card was received in good condition and a senior recorder specialist downloaded and examined the card's data. The recorder specialist subsequently produced a report that showed the MFD card contained 138 data files, representing data from 69 electrical power cycles. The last 2 files recorded were identified as the accident flight. The data from the accident flight and the previous 11 engine cycles before the accident were plotted. According to the pilot, some preceding flights were to retrieve the airplane after the installation of the supercharger and then to return back to Centennial Airport (APA), near Denver, from COS for a 2-hour inspection. The engine was reported to have operated nominally on the flights to/from APA, as well as on the first flight on the day of the accident. Some of the recorded engine cycles occurred with the airplane on the ground and were only a few minutes in duration. Although review of the engine operation data showed fluctuations in their values, the recorded data did not reveal any anomalies that could explain the engine power loss. The occupants of the other airplane in the formation flight collected GPS and photographic data during the accident airplane's power loss and descent. A review of the images revealed the parachute traveled aftward and below the airplane. The parachute subsequently inflated, the airplane descended downward in a nose low attitude, and impacted terrain in a nose low attitude. The CAPS components were shipped to the NTSB Materials Laboratory. A senior materials engineer examined the components and produced Materials Laboratory Factual Report No. 17-009. In the accident airplane, the cable for the rocket lanyard (included in the pickup collar assembly) had separated. As designed, the rocket lanyard from the pickup collar assembly attach to the incremental bridle. The other end of the incremental bridle is attached to lanyard on the parachute deployment bag. The folded parachute is contained within the deployment bag. When stowed, the retaining harness covers the top of the deployment bag and retains the deployment bag in the airplane parachute bay. During a deployment, the rocket is launched, carrying the pickup collar assembly, incremental bridle, and parachute deployment bag with it. The incremental bridle is positioned between the rocket lanyard and the deployment bag and is designed to absorb the impact associated with the acceleration difference between the rocket and the deployment bag during deployment. As assembled, the middle portion of the incremental bridle is folded to a shorter length, and the folded segment is stitched together. The stitches in the folded segment separate until the velocity of the deployment bag matches the velocity of the rocket. During a typical deployment, some stitches in the incremental bridle remain intact, and a portion of the incremental bridle remains folded. Ten rows of stitches remained intact in the incremental bridle from the accident airplane. The pickup collar assembly includes a zinc-coated steel pickup collar, aluminum pickup collar support, and rocket lanyard. The rocket lanyard consists of two lengths of a single stainless steel cable that connect the pickup collar to the incremental bridle. The cable for the lanyard loops through and around the pickup collar and pickup collar support, and cable eyes at each end are connected to a loop at one end of the incremental bridle. The cable bends 90° at two locations on either side of the pickup collar support, and the center of the cable is routed around the center tube of the support. Cable stop sleeves made of copper are attached to the cable adjacent to the pickup collar. During manufacturing, each pickup collar assembly is proof tested to a tensile load of 1,000 pounds. The submitted cable from the accident airplane for the rocket lanyard was separated into two segments that were arbitrarily labeled segments A and B. Teflon tubes, which cover each leg of the lanyard between the pickup collar and the cable eyes, were also included. The Teflon tube that had covered the segment A lanyard was displaced along the length of the cable segment and was covering the separation. The Teflon tube from segment B was completely separated from the cable. Based on engineering drawings, the calculated total length of the rocket lanyard cable in the pickup collar assembly is 105.1 inches ± 1.0 inch. The rocket lanyard cable was constructed of 7 strands (6 strands wrapped around a core strand) with 7 wires per strand consistent with manufacturer specifications. The lengths of segment A and segment B were measured from the separation to the end of the cable eye. Segment A was 55.38 inches long, and segment B was 50.50 inches long, for a measured total cable length of 105.88 inches, consistent with the cable length calculated from the engineering drawings. The cable segments were closely examined visually and using an optical stereomicroscope for contact damage, deformation, and metal transfer. Individual wires showed necking deformation and chisel-type separation features consistent with overstress separation. A material consistent with red grease was present on the surfaces of the cable, and no evidence of corrosion was observed. Orange metal deposits consistent with copper were observed along the surface of cable segment A between approximately 0.5 inches and 5.3 inches from the separation. The deposits were consistent with material transfer from a copper cable stop sleeve. On segment B, isolated areas of orange metal deposits consistent with copper were observed on two of the wires approximately 0.28 to 0.34 inch from the separation. Further from the separation on segment B, the outer surfaces of wires on two strands were flattened consistent with sliding contact damage at a location between 0.07 to 0.09 inch from the separation. On most of the wires with the contact damage, gray metal was observed at the edge of the flattened surface on the side furthest from the separation. The separation end of segment B was examined using a scanning electron microscope (SEM). The SEM examination revealed portions of the area with sliding contact appeared relatively lighter gray than the surrounding material, consistent with the presence of an element with a higher atomic weight. Analysis of the area using energy dispersive x-ray spectroscopy (EDS) showed the bright areas showed a peak indicating the presence of zinc. The gray metal adjacent to the sliding contact areas was also examined using SEM and EDS. The EDS analysis of the gray metal at the edges of the sliding contact damage resulted in spectra consistent with stainless steel, matching the spectra obtained from intact areas of the lanyard cable wires. Two lengths of cables were cut from each rocket lanyard segment to facilitate tension tests to fracture. Four tension specimens were fabricated. The test specimens fractured at peak loads of 905 pounds, 916 pounds, 893 pounds, and 930 pounds. All specimens broke within the crimp for the cable eyes. The specified minimum cable strength as listed in the current Military Standard MIL-DTL-83420N is 920 pounds. The cover flap of the retaining harness has a pocket on its flap exterior. The clear plastic face of the pocket is intended to observe par