National Transportation Safety Board
Office of Public Affairs
(Washington, DC) -- Calling for permanent special pilot training and tougher operating standards for helicopters with sensitive flight controls, the National Transportation Safety Board reported that the cause of a series of Robinson Helicopter R22 accidents "most likely stems" from big and sudden pilot movements of the aircraft's highly-responsive flight controls. The NTSB said it found no mechanical failure or other defect behind the crashes.
In a special investigation report, the Safety Board focused mainly on accidents resulting from the loss of main rotor control and covered 31 crashes of the two-seat R22 and three accidents involving the R44, a larger version. Common to these accidents was the loss of control from rotor blades striking the fuselage or tailboom, resulting in in-flight breakups that killed a total of 58 persons since 1981.
The Safety Board previously had issued numerous recommendations to address the problem, prompting the Federal Aviation Administration (FAA) to implement several operational changes. These primarily were designed to ensure better training and proficiency for pilots and flight instructors and restricted R22 flights in certain adverse conditions.
There have been no loss of main rotor control R22 accidents in the U.S. since the changes were implemented more than a year ago, according to NTSB. The aircraft has had a history of such mishaps much greater than other helicopters.
The Safety Board said that because the R22 is more responsive to cyclic control inputs than other helicopters used by students or low-time pilots special training requirements are needed. The cyclic controls the tilt of the main rotor system and directs the course of flight.
"Flight instructors probably do not have sufficient time to react to R22 students' large, abrupt flight control inputs," said the Board. "Therefore, they must guard the cyclic closely to prevent such inputs."
Computer modeling has been done at the Georgia Institute of Technology to better understand the R22. The Safety Board said the work "suggests that large, abrupt cyclic control inputs may result in mast bumping or blade angles-of-attacks greater than the stall angle; however, the mathematical model was not developed sufficiently to demonstrate that flight control inputs would lead to loss of control of the main rotor. "The Board said it hoped more work would be done in this effort.
During its special investigation, the NTSB said it found that FAA staff made several internal recommendations related to the R22 accidents and the special certification reviews conducted by that agency.
"Based on documents provided by the FAA, under (NTSB) subpoena, the Safety Board could not conclusively determine what action, if any in some cases, the FAA initiated as a result of these internal recommendations, but it concluded that little action resulted from the(m)...," said the Board's report.
The Safety Board recommended that FAA make permanent the special training and operational requirements that were put in place for the R22, and in certifying future lightweight highly-responsive helicopters, that similar measures be considered.
The NTSB also called for more research into lightweight helicopter behavior. Such a step should be undertaken by FAA and NASA to "create a national resource tool that would aid in the certification of future helicopter models, especially those that are lightweight and highly responsive," said the Board.
The Safety Board's complete printed report, PB96-917003, will be available from the national Technical Information Service, 5285 Port Royal Road, Springfield, VA. 22161. The telephone number is (703) 487-4650.
Media contact: NTSB Office of Public Affairs
The National Transportation Safety Board (NTSB) is an independent federal agency charged with determining the probable cause
of transportation accidents, promoting transportation safety, and assisting victims of transportation accidents and their families.