# NTSB LAX93LA208: Robinson R-22, N4071G, Corona, CA, May 8, 1993 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: May 7, 1993, 17:15 local (May 8, 1993, 00:15 UTC) - Place: Corona, CA - Location: 33.8753° N, 117.5664° W: Placed by OpenAirDocs: center of Corona, CA, within about 6 miles (OpenAirDocs) - Nearby events: https://openairdocs.org/map.md?lat=33.8753&lon=-117.5664&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 1 minor, 1 uninjured - Status: Completed, report June 30, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 28377 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX93LA208 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/28377/pdf - Page: https://openairdocs.org/ntsb/LAX93LA208 ## Probable cause THE FAILURE OF THE PILOT TO ACCOMPLISH THE PUBLISHED EMERGENCY PROCEDURE BY NOT IMMEDIATELY LOWERING THE COLLECTIVE TO REGAIN MAIN ROTOR RPM. A FACTOR IN THE ACCIDENT WAS THE PILOT'S SELECTION OF A CRUISE ALTITUDE INSUFFICIENT TO ALLOW FOR CONTINGENCY SITUATIONS. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - In flight collision with terrain/water, cruise - altitude - inadequate, pilot in command (contributing factor) - adequate rotor rpm - not maintained, pilot in command (contributing factor) - emergency procedure - not performed, pilot in command (cause) - collective - improper use of, pilot in command (cause) - terrain condition - mountainous/hilly - object - tree(s) ## Analysis A ROBINSON R-22 COLLIDED WITH TREES IN MOUNTAINOUS TERRAIN AFTER SUSTAINING LOSS OF ENGINE AND MAIN ROTOR RPM WHILE IN FORWARD FLIGHT AT 20 TO 30 KNOTS 100 TO 150 FEET ABOVE THE GROUND. THE MAIN ROTOR RPM DROOPED ABOUT 3 TO 4 PERCENT TO 101 PERCENT. THE PILOT FAILED TO IMMEDIATELY LOWER THE COLLECTIVE TO REGAIN LOST ROTOR RPM AS SPECIFIED IN THE FLIGHT MANUAL. THE WRECKAGE EXAMINATION DISCLOSED NO EVIDENCE OF PREEXISTING MECHANICAL FAILURES OR MALFUNCTIONS. ## Factual narrative On May 7, 1993, at 1715 hours Pacific daylight time, a Robinson R-22, N4071G, collided with trees in mountainous terrain about 5 miles southwest of Corona, California. The pilot was conducting a local visual flight rules personal flight. The helicopter, operated by Parflite, Inc., Riverside, California, was substantially damaged. The certificated commercial pilot was not injured; the passenger received minor injuries. Visual meteorological conditions prevailed. The flight originated at the Riverside Airport at 1700 hours. The pilot reported the helicopter sustained a loss of engine and main rotor RPM while in forward flight at about 20 to 30 knots between 100 to 150 feet above trees in rugged mountainous terrain. The pilot indicated that the main rotor RPM dropped about 3 to 4 percent to 101 percent. The pilot increased the throttle in an attempt to regain the rotor rpm, but without success, and the helicopter began to descend. The pilot noted that the engine manifold pressure was indicating 27 inches during the loss of rotor RPM. The pilot turned the helicopter away from uprising terrain, and reduced the collective and increased the throttle in order to regain the main rotor RPM. The engine and rotor RPM did not increase and the low rotor RPM warning horn and caution light activated. The pilot selected a forced landing area in the forested rugged mountainous terrain. The helicopter descended into the trees, struck the ground and slid down slope on its left side. The Robinson R-22 is equipped with a low rotor RPM warning horn and caution light. The low rotor RPM warning horn and caution light indicate rotor RPM at 95 percent or below. The horn stops and amber caution light extinguishes when the RPM is increased to safe limits or when the collective control is full down. Robinson Helicopter Company publishes information on the R-22 helicopter that states that at airspeeds below 53 knots the helicopter is considered on the "back side of the power curve" and that more power is required to be provided to the rotor system. The helicopter emergency procedure for activation of the low rotor RPM warning horn and caution light states "Immediately lower collective." The helicopter was examined at National Aircraft Transportation, Inc. facilities in Long Beach, California, after the accident. There was no evidence of any mechanical failure or malfunction found. ## Aircraft - Registration: [N4071G](https://openairdocs.org/deregistered/N4071G-2013-09-24), registration cancelled 2013-09-24, S/N 1833, built 1991 (OpenAirDocs) - Reported make and model: ROBINSON R-22 - Registry model: [Robinson Helicopter R22 BETA](https://openairdocs.org/model/robinson-helicopter-r22-beta) (registry code 7640110) (OpenAirDocs) - Registry engine: [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series) (registry code 41508, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 1833 - Airframe hours: 1183 - Engines: LYCOMING O-320-B2C 160 horsepower reciprocating - Damage: Destroyed - Flight: Personal, Part 91 - Operator: Parflite Incorporated, doing business as Los Angeles Flight Academy - Registered owner: Mendoza, Akira - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, February 16, 1993, 83 hours before - Departed: RAL, RIVERSIDE, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 28; commercial, flight instructor; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 2,404 total, 2,225 in this make and model, 2,338 as pilot in command, 155 in the last 90 days, 33 in the last 30 days, 3 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 230° at 15 knots - Visibility: 5 statute miles - Lowest ceiling: none - Altimeter: 29.00 inHg - Observed at: CNO, 9 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19930507012729A](https://openairdocs.org/incident/19930507012729A), May 7, 1993: Robsin R22BETA, Corona, CA, Destroyed. Low and slow over mountains. Lost rotor RPM. Below power curve unable to regain RPM. Crashed into trees. From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.