Accident Overview
On June 18, 2022, about 1710 central daylight time, a Eurocopter Deutschland GmbH EC-135 P2+ helicopter, registration N226SA, sustained substantial damage when it was involved in an accident near Waukesha, Wisconsin. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 air medical flight. The pilot and three passengers were not injured.
Sequence of Events
According to the operator, the pilot received a flight request for an inter-facility transfer. The intended route was from the primary base at Waukesha County Airport (UES) to pick up a patient at Aurora Lakeland Medical Center, Elkhorn, Wisconsin, and then transport them to Children's Hospital of Wisconsin, Milwaukee. After departing from UES, when the helicopter was about 150 ft agl, the pilot heard a thump, and the helicopter pitched up. The pilot immediately executed an emergency landing, and all occupants exited the helicopter uninjured. The pilot had full control of the helicopter during the emergency landing. The helicopter sustained substantial damage to the fenestron blades.
Investigation Findings
The accident site was situated over a large area adjacent to a concrete ramp and taxiway. The fairing cover was missing from the fenestron assembly. Debris was found about 600 ft in all directions, consisting of fenestron fairing (hub cover) fragments, composite fragments from the fenestron body, attachment bolts, and brackets. Some debris was found on top of a one-story hangar rooftop. Small fragments of the fairing cover were scattered on the ramp and the top of the one-story hangar. Larger fragments were wedged between the fenestron housing and the fenestron blades. The fairing fragments showed damage consistent with ingestion into the rotating blades of the fenestron. There was no evidence of a bird strike. After an extensive search, investigators were unable to identify any foreign debris that might have contacted the cover before its separation. Other than the fenestron fairing cover and fenestron housing, the entire helicopter (airframe and engine) had no other damage or missing hardware.
The fenestron blades within the housing were found attached with no evidence of malfunction. The blades and inside of the housing were impact damaged, consistent with ingestion of fragments from the fairing cover. No evidence of preaccident malfunctions of the fenestron housing, blades, gearbox, or drive was found. No improper maintenance anomalies were found with the fenestron assembly.
Five of the fenestron fairing cover attachment bolts were found attached to their respective brackets, and all were torqued. A sixth bolt was not found; however, a portion of its bracket was found embedded in a fairing cover fragment, consistent with the bolt being attached before the accident. All fairing cover attachment hardware was accounted for and showed no evidence of preaccident material failure.
On an exemplar fenestron assembly, a security test of the fairing cover was conducted with various combinations of retaining bolts and clips. The cover was attached with six attachment bolts, brackets, and anchors. The hub cover was secure. Two bolts were removed, and the cover remained secure. Two more bolts were removed, and with only two bolts remaining, the cover remained secure.
The helicopter flew about 5.8 hours without incident after the most recent maintenance of the fenestron. Since that maintenance, numerous daily maintenance checks and pilot prefights were conducted with no unresolved items or anomalies. No uncorrected maintenance anomalies were found in the maintenance logbooks.
Historical Events
There were six historical events involving the fenestron fairing cover separating from the same model helicopter. All six events were related to foreign object debris (FOD) ingestions that caused the fenestron fairing cover to separate.