Robinson Helicopter Company R22 Loss of Main Rotor Control Accidents

The National Transportation Safety Board's special investigation of accidents involving loss of main rotor control by the Robinson Helicopter Company (RHC) R22 was prompted, in part, by an accident that occurred during an instructional flight near Richmond, California, on June 29, 1992. The flight instructor had 2,000 hours in the R22, and the student had 4 hours. The findings in that accident—that the helicopter was being operated at normal main rotor revolutions per minute (rpm) within the approved flight envelope and with no indication of weather being a factor—coupled with the Safety Board's difficulty in determining the causes of many similar loss of main rotor control accidents in the past, led the Safety Board to investigate these accidents as a group in an attempt to find common factors and to develop appropriate recommendations to prevent occurrence of similar accidents in the future.

For this special investigation, the Safety Board reviewed fatal accidents involving certificated helicopters; reexamined the available wreckage of the R22 from the Richmond accident and other accidents; reviewed the Federal Aviation Administration's (FAA) original certification process, certification requirements, and subsequent reviews of the R22 certification; and reviewed the Safety Board's recommendation history for the R22. In addition, the Safety Board analyzed various potential scenarios that could lead to loss of main rotor control. During the Board's special investigation, the FAA implemented several operational changes, primarily to ensure that pilots of the R22 and flight instructors were better trained and more proficient and that flights in R22s in certain adverse weather conditions were restricted. There have been no loss of main rotor control R22 accidents in the United States since the changes were implemented more than a year ago.

The following issues are addressed in this special investigation report:

• The implementation of appropriate measures to reduce the probability of loss of main rotor control accidents.
• The need for continued research to study flight control systems and main rotor blade dynamics in lightweight, low-rotor inertia helicopters.
• The establishment of operational requirements to be addressed during future certification of lightweight, low rotor inertia helicopters.
• The need for the FAA to review and revise, as necessary, its procedures to ensure that internal recommendations, particularly those addressed in special certification reviews, are appropriately v resolved and brought to closure.

As a result of this special investigation, recommendations concerning these issues were made to the FAA and the National Aeronautics and Space Administration (NASA).