On July 18, 1993, a Hiller UH-12E (registration N4028M) operated by Bonanza Valley Aviation was involved in an aviation accident near Milbank, SD. Investigators recorded the probable cause as: The helicopter began spinning after the pilot heard a bang during hover, leading to an impact with obstacles and a post-crash fire; no pre-impact mechanical malfunction could be determined due to severe damage. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 3 related events involving the same aircraft type or operator are linked below.
A helicopter began spinning after the pilot heard a bang during a landing hover. The aircraft struck obstacles, rolled, and burned upon impact.
What happened
The pilot reported hearing an audible bang while the helicopter was in a hover phase during a landing maneuver. Immediately following this event, the aircraft began to spin uncontrollably. As it settled toward the ground, the rotorcraft struck various obstacles located near the intended landing area. The impact caused the helicopter to roll over and subsequently catch fire.
The investigation
An FAA inspector examined the wreckage to determine the cause of the incident. The inspector noted that the damage resulting from the impact was extensive. Additionally, a post-crash fire further compromised the airframe. Due to the severity of these damages, the inspector was unable to identify any pre-impact mechanical malfunctions.
Probable cause
The helicopter began spinning after the pilot heard a bang during hover, leading to an impact with obstacles and a post-crash fire; no pre-impact mechanical malfunction could be determined due to severe damage.