AIRCRAFT ACCIDENT REPORT AND EXECUTIVE SUMMARY

Transcription

1 Section/division Accident and Incident Investigation Division Form Number: CA 12-12a AIRCRAFT ACCIDENT REPORT AND EXECUTIVE SUMMARY Reference: CA18/2/3/8694 Aircraft Registration ZS-RMN Date of Accident 25 September 2009 Time of Accident 2100Z Type of Aircraft ROBINSON R44 Raven II Type of Operation Commercial Pilot-in-command Licence Type Commercial (H) Age 36 Licence Valid Yes Pilot-in-command Flying Experience Total Flying Hours Hours on Type Last point of departure Next point of intended landing Rand Aerodrome (FAGM) Gauteng Grand Central Aerodrome (FAGC) Gauteng Location of the accident site with reference to easily defined geographical points (GPS readings if possible) Lawley, Ennerdale South of Soweto: (GPS position: S 26º E 027º ) Meteorological Information Surface wind: 015 /08KTS, Visibility: > 10 km, Clou d cover: CAVOK, Temperature: 17ºC Number of people on board 1+1 No. of people injured 0 No. of people killed 0 Synopsis On 25 September 2009 at approximately 2100Z, the pilot and a passenger, an air tracker, were doing vehicle tracking in the Lawley area when suddenly the throttle start hunting (opening and closing movement of the throttle). During a left turn he suddenly heard a highpitched sound. He then observed the engine and rotor rpm over-revving on the rpm gauge. The pilot then levelled the helicopter, closed the throttle and lowered the collective pitch lever slightly to terminate control of the rpm. This action did not resolve the overspeed condition, and the pilot put the helicopter in autorotation. A hard landing followed and the main rotor blades severed the tail boom. The helicopter sustained substantial damage during the hard landing. Neither the pilot nor his passenger were injured in the course of the accident. Probable Cause Unsuccessful emergency landing following a reported in-flight engine and rotor overspeed condition. IARC Date Release Date CA 12-12a 23 FEBRUARY 2006 Page 1 of 11

2 Section/division Accident and Incident Investigation Division Form Number: CA 12-12a Telephone number: AIRCRAFT ACCIDENT REPORT Name of Owner/Operator : National Airways Corporation (PTY) LTD Manufacturer : Robinson Helicopter Company Model : R44 Raven II Nationality : South African Registration Marks : ZS-RMN Place : Lawley Date : 25 September 2009 Time : 2100Z All times given in this report are Co-ordinated Universal Time (UTC) and will be denoted by (Z). South African Standard Time is UTC plus 2 hours. Purpose of the Investigation: In terms of Regulation of the Civil Aviation Regulations (1997) this report was compiled in the interest of the promotion of aviation safety and the reduction of the risk of aviation accidents or incidents and not to establish legal liability. Disclaimer: This report is produced without prejudice to the rights of the CAA, which are reserved. 1. FACTUAL INFORMATION 1.1 History of Flight On 25 September 2009 at approximately 2100Z the pilot and his passenger, a Netstar air tracker, were engaged in a commercial vehicle tracking operation The pilot overflew Lawley for approximately 19 minutes at 6400 feet AMSL (Above Mean Sea Level) when he noticed that the throttle had started hunting (opening and closing movement of the throttle). As he had had a governor failure in the past, he decided to monitor the situation The pilot had gone into a 15 degree turn to the left to get reference on a vehicle; both the tracker and pilot had been looking at the vehicle for approximately 10 seconds when the pilot and tracker suddenly heard a change of the engine pitch The pilot immediately looked at the engine and rotor rpm gauge and noticed that both needles had moved to the top of the gauge. The pilot then levelled the helicopter, closed the throttle and lowered the collective slightly to reduce the rpm. (See Figure 1.) CA 12-12a 23 FEBRUARY 2006 Page 2 of 11

3 Figure 1 The two arrows at the top of the gauge indicate the position of the needles during the overspeed condition As the pilot realised the rotor rpm had been at their maximum for a short period and were now uncontrollable, he entered autorotation. In the autorotation profile he nominated a landing zone and commenced an emergency landing. The pilot flared the helicopter in close proximity to the ground and a hard landing followed. He managed to keep the helicopter on its skids; however, the hard landing caused the main rotor blades to sever the tail boom The pilot and the passenger were not injured in the accident and evacuated the helicopter unassisted. 1.2 Injuries to Persons Injuries Pilot Crew Pass. Other Fatal Serious Minor None Damage to Aircraft The helicopter sustained substantial damage. 1.4 Other Damage No other damage was caused as a result of the accident. CA 12-12a 23 FEBRUARY 2006 Page 3 of 11

4 1.5 Personnel Information Nationality South African Gender Male Age 36 Licence number **************** Licence type Commercial (H) Licence valid Yes Type endorsed Yes Ratings Night rating Medical expiry date 31 May 2010 Restrictions None Previous accidents None According to available information, the last time the pilot underwent governor off training was during a proficiency check on 20 August Flying Experience: Total hours 426,2 Total past 90 days 114,1 Total on type past 90 days 109,3 Total on type 296,7 1.6 Aircraft Information Airframe: Type Robinson R44 Raven II Serial number 0910 Manufacturer Robinson Helicopter Company Year of manufacture 2000 Total airframe hours (at time of accident) 2130,3 Last MPI (date & hours) 17 July ,0 Hours since last MPI 31,3 C of A (issue date) 23 September 2000 C of R (issue date) (present owner) 25 July 2007 Operating categories Standard Weight and Balance According to the pilot, no weight and balance calculation was done for the accident flight. According to the pilot Netstar made use of a generic Weight and Balance sheet and will only do recalculations should they carry another passenger or additional equipment. The pilot informed the investigator the Weight and Balance was within limits for the accident flight, so a Weight and Balance sheet was not completed for the accident flight. Engine: Type Lycoming O-540-F1B5 Serial number L A Hours since new 2130,3 Hours since overhaul 129,6 CA 12-12a 23 FEBRUARY 2006 Page 4 of 11

5 1.7 Meteorological Information The weather information was obtained from the pilot questionnaire. Wind direction 015 ºM Wind speed 8 KTS Visibility > 10 km Temperature 17 ºC Cloud cover CAVOK Cloud base N/A Dew point N/A 1.8 Aids to Navigation The aircraft was equipped with the standard navigational equipment as per the approved minimum equipment list approved by the Regulator. There were no recorded defects to navigational equipment prior to the flight. 1.9 Communications The aircraft was equipped with one VHF (Very High Frequency) radio which was approved as within the minimum equipment list by the Regulator. There were no recorded defects in communication equipment prior to the flight. The pilot did communicate his intentions on the VHF radio frequency 125,8 MHz Aerodrome Information The accident did not occur at or near an aerodrome Flight Recorders The helicopter was not fitted with a cockpit voice recorder (CVR) or a flight data recorder (FDR), and neither was required by regulations to be fitted to this type of helicopter Wreckage and Impact Information The helicopter landed on its skids in an open grass-covered field located next to Lawley Township During the hard landing following the autorotation, the tail boom was severed from the fuselage by the main rotor blades as indicated by Figure 2. CA 12-12a 23 FEBRUARY 2006 Page 5 of 11

6 Figure 2 The tail boom severed from the helicopter 1.13 Medical and Pathological Information Neither the pilot nor his passenger were injured in the course of the accident Fire There was no evidence of a pre- or post-impact fire during the sequence of the accident Survival Aspects This accident was considered survivable due to minimum impact forces on the fuselage, and the pilot and passenger were wearing safety harnesses Tests and Research RPM Governor Components The components listed below were removed from the wreckage and sent to the helicopter manufacturer, Robinson Helicopter Company (RHC), for testing under the supervision of the National Transportation Safety Board (NTSB) of the United States of America: i. Governor controller box; part number D278-1, serial number 0962 ii. RH magneto; part number , serial number H120012E iii. Governor motor; part number B247-5, rev O, lot 128 On 7 January, 2010, in the presence of the NTSB, the components were inspected CA 12-12a 23 FEBRUARY 2006 Page 6 of 11

7 and functionally tested by RHC personnel with the following results: 1. The first component examined was a governor controller box, part number D278-1, serial number 0962, Rev D, Lot 50. A visual inspection of the box revealed no external damage and that the box had not been opened or overhauled since its production. The electrical connector was clean and undamaged. A functional test was performed using the production acceptance criteria used at the time the box was produced. The controller passed most of the test specifications with the exception of the dead band symmetry. The engineer performing the test (and designer of the controller) stated that "this would result in a slight increase in RPM (less than 0,25%) during turbulence and in straight and level flight; the pilot would probably not even notice the difference. A copy of the test results is attached. See Appendix A for test results. 2. The second component to be examined was an engine magneto, part number , serial number H120012E. A visual inspection of the magneto revealed that the data plate was yellow in colour, indicating that it had been overhauled in the field (not by the manufacturer). The mounting surface was painted black and had some residual sealer (orange silicone) on it. One of the tachometer point wires had a small bare spot in its insulation. No other external damage was noted. 3. The magneto was mounted to a test stand and all six ignition leads fired properly both at low and high RPM. The P-lead was grounded and all six leads ceased firing. The tachometer wires were connected to an oscilloscope, which resulted in a very uneven sine wave (13% duty cycle; 50% is normal). The point cover was removed to reveal that the tachometer points had no measurable gap between the contact points (manufacturer's specification is 0, ,003. The point base was secure and all the proper hardware was in place. The magneto points E-gap angle was measured at 14 degrees after neutral position (manufacturer s specifications recommend ). 4. The tachometer points were removed for inspection. The points appeared new and undamaged, but did have what appeared to be carbon dust on the contact pads. The tachometer points were reinstalled and gapped at 0,016 0,022. The coil wire terminal to the magneto points was loose, so the terminal was adjusted for a secure fit and the cover reinstalled. The tachometer wires were then reattached to the oscilloscope, which resulted in an even, steady sine wave (53% duty cycle). The governor controller (which gets its input from the tachometer points) requires an input with a 35% to 65% duty cycle and less than 0.25 m/sec point bounce to operate. The tachometer will operate with a much lower duty cycle. 5. The third component to be examined was a governor motor, part number B247-5, rev O, lot 128. Visual inspection revealed no external damage. A functional test was performed on the motor with satisfactory results when compared with production specifications. CA 12-12a 23 FEBRUARY 2006 Page 7 of 11

8 1.17 Organisational and Management Information The last mandatory periodic inspection (MPI) on this helicopter was certified on 17 July 2009 at hours by an approved aircraft maintenance organisation (AMO) This operation was conducted by an approved SACAA Air Operator which was in possession of a valid Air Operator s Certificate, number FO4605 which includes G3 (Aerial patrol, observation and survey) Additional Information RPM governor system: (Reference: Robinson R44 II Maintenance Manual, Chapter 8, Pages 8 to 32) The governor system senses engine RPM and apply corrective input forces to the throttle; when RPM is low, the governor increases throttle and vice versa. Throttle inputs are through a friction clutch, which can be easily overridden by the pilot. The governor is active from 79% to 111% engine RPM and can be switched on or off by the pilot using the toggle switch on the end of the right-seat collective control. The governor system consists of the following major components: 1. The D278 governor controller, a solid-state analogue-circuit control unit, is mounted behind the left aft seat backrest. The controller senses RPM via tachometer points in the engine right magneto and provides a corrective signal to the governor assembly. All governor controllers operate on 14V; 28V ships utilise a 28V to 14V converter to power the controller. 2. The governor assembly is attached to the collective stick assembly behind the left front seat. When activated by the governor controller, the governor gear-motor and attached worm gear drive a friction clutch connected to the throttle Signal and power wiring: (Reference: Pilot s Operating Handbook, Section 7, System Description, Page 7-6) The governor maintains engine RPM by sensing changes and applies corrective throttle inputs through a friction clutch that can easily be overridden by the pilot. The governor is only active above 80% engine RPM and can be switched on or off using the toggle switch at the end of the right-seat collective. The governor is designed to assist in controlling RPM under normal conditions. It may not prevent over- or under speed conditions generated by aggressive flight manoeuvres. CAUTION: When operating at high density altitudes, governor response rate may be too slow to prevent over speeding during gusts, pull-ups or when lowering collective. CA 12-12a 23 FEBRUARY 2006 Page 8 of 11

9 Governor Failure (POH, Section 3, Emergency Procedures page 3-7) If engine RPM governor malfunctions, grip throttle firmly to override the governor, then switch the governor off. Complete flight using manual throttle control Although work had been done to the helicopter as a result of a recorded overspeed condition, the helicopter had flown 20 hours since maintenance was done to rectify the overspeed condition. During this maintenance, the right hand magneto was removed, points were checked, the magneto was reinstalled and the timing was set The pilot stated he never switched the governor off to see if he could recover from the overspeed condition Useful or Effective Investigation Techniques None. 2. ANALYSIS 2.1 The pilot was conducting a visual flight rules (VFR) flight (by night) doing vehicle tracking at the time of the accident. 2.2 Available evidence indicated the flight preparation for this flight was done properly, as all documentation was in place for this flight. 2.3 According to CAA records, the pilot was the holder of a Commercial Pilot Licence (Helicopter) which was valid at the time of the accident. The pilot had the required rating for the flight and was in possession of a valid medical certificate without any medical restrictions imposed. 2.4 The aircraft s logbooks were verified and all records indicated that the airframe and engine had been properly maintained and all work carried out was properly certified. 2.5 The weather at the time of the accident, as obtained from the pilot, was fine. The sky was clear with a 15 knot wind from the north, temperature was 17 C and visibility greater than 10 km. 2.6 Communication during the accident flight was normal; the pilot was communicating his intentions on frequency 125,8 MHz. No mayday call was communicated during the autorotation before the accident. 2.7 An overspeed condition was reported previously, but after maintenance the helicopter flew 20 hours before the accident flight with no abnormalities reported. The investigator-in-charge was not convinced this overspeed condition could be related to the overspeed condition during the accident flight. 2.8 Function tests were done on all RPM governor controlling components under supervision of the National Transport and Safety Bureau (NTSB), which showed that all the tested components operated within prescribed specifications with no abnormalities noted. CA 12-12a 23 FEBRUARY 2006 Page 9 of 11

10 3. CONCLUSION 3.1 Findings The pilot was licensed and qualified for this flight in accordance with existing regulations The accident aircraft was properly certified, equipped and maintained in accordance with current regulations. Recovered components showed no evidence of structural, engine or system failure Weather conditions that prevailed at the time of the accident did not contribute to the cause of the accident except that the emergency landing was made in darkness Sufficient flight preparations were made for this flight No evidence of any mechanical failure which could lead to the overspeed condition during the accident flight was found during the investigation The helicopter was operated by a SACAA approved operator at the time of the accident which was in possession of an approved Air Operators Certificate with G3 Operations (Aerial Patrol, observation and survey) endorsed onto the certificate. 3.2 Probable Cause/s Unsuccessful emergency landing following a reported in-flight engine and rotor overspeed condition. 4. SAFETY RECOMMENDATIONS 4.1 None 5. APPENDICES 5.1 Appendix A Governor control box test results. Report reviewed and amended by the Advisory Safety Panel on18 May END- CA 12-12a 23 FEBRUARY 2006 Page 10 of 11

11 Appendix A Governor control box test results. CA 12-12a 23 FEBRUARY 2006 Page 11 of 11