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: CA18/2/3/8452 Aircraft Registration ZS-RJL Date of Accident 8 March 2008 Time of Accident 0900Z Type of Aircraft Robinson R44 II (helicopter) Type of Operation Private Pilot-in-command Licence Type Private Pilot (H) Age 56 Licence Valid Yes Pilot-in-command Flying Experience Total Flying Hours 153,1 Hours on Type 113,0 Last point of departure Next point of intended landing Rand Aerodrome (FAGM), Gauteng Province Sun City Heliport, North West Province Location of the accident site with reference to easily defined geographical points (GPS readings if possible) Sun City heliport, (GPS position: S E ) Meteorological Information Surface wind: Easterly / 10 kt; Temperature: 26 C; Visibility: Clear; Clouds: Nil Number of people on board No. of people injured 0 No. of people killed 0 Synopsis The pilot, accompanied by three passengers, flew from Rand Aerodrome (FAGM) on a private flight to Sun City heliport. As he applied power to cushion the landing at Sun City, the helicopter settled with power on. A hard landing followed onto the incline to the heliport causing damage to the helicopter s skids. The aircraft sustained substantial damage to the tail rotor gearbox, tail rotor blades, tail boom and main rotor blades when the pilot attempt to reposition the helicopter after the hard landing onto the incline. Neither pilot nor passengers suffered any injuries as a result of the accident. A shrub and the perimeter fence were damaged during the landing. Probable Cause Tail strike during a repositioning flight following a hard landing as a result of the helicopter entering a vortex ring state. IARC Date Release Date CA 12-12a 23 FEBRUARY 2006 Page 1 of 16

2 Section/division Accident and Incident Investigation Division Form Number: CA 12-12a AIRCRAFT ACCIDENT REPORT Name of Owner/Operator : CAPA AVIATION CC Manufacturer : Robinson Helicopter Company Model : R44 II Nationality : South African Registration Marks : ZS-RJL Place : Sun City, North West Province Date : 8 March 2008 Time : 0900Z 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 8 March 2008 at approximately 0800Z, the pilot of ZS-RJL, accompanied by three passengers, took off from Rand Aerodrome (FAGM) on a pleasure flight to Sun City. The flight itself was uneventful On arrival at Sun City, the pilot flew over the heliport, made a turn around the high ground, flew over the golf course and headed directly to the helipad. The initial approach speed was 40 kt with a 400 feet-per-minute rate of descent On the final stages of the approach, the pilot reduced the indicated airspeed (IAS) to 10 kt. During the application of collective pitch control to cushion the landing, the aircraft settled with power on, and then landed hard on the incline to the heliport causing damage to the skids of the helicopter The pilot did not climb out to verify the damage but re-applied power to reposition the helicopter on the level ground of the heliport. During this attempt, the tail rotor made contact with the perimeter fence, resulting in damage to the blades and gearbox There were no technical defects entered into the aircraft flight folio prior to the flight and the pilot did not experience any technical abnormalities during the flight. CA 12-12a 23 FEBRUARY 2006 Page 2 of 16

3 1.1.6 The pilot estimated the wind conditions as easterly at 10 kt during landing. Wind indication was observed from the windsock at the heliport. 1.2 Injuries to Persons Injuries Pilot Crew Pass. Other Fatal Serious Minor None Damage to Aircraft The helicopter sustained substantial damage to the landing gear skid and lower fuselage on initial impact with the ground. Figure 1 Damage to the helicopter skid During the repositioning of the aircraft, damage was caused to the tail rotor blades and gearbox when the rotor made contact with the perimeter fence. 1.4 Other Damage A shrub next to the heliport was struck by the main rotor blades during the initial impact. CA 12-12a 23 FEBRUARY 2006 Page 3 of 16

4 Figure 2. Helicopter alongside the damaged shrub Damage was also caused to the perimeter fence by the tail rotor blades when the pilot attempted to reposition the helicopter. Figure 3. Damage to the tail rotor and wire fence. CA 12-12a 23 FEBRUARY 2006 Page 4 of 16

5 1.5 Personnel Information Nationality South African Gender Male Age 56 Licence Type Private Pilot Licence Number **************** Licence valid Yes Type Endorsed Yes Ratings Night Rating Medical Expiry Date 31 May 2008 Restrictions Corrective lenses Previous Accidents None Flying Experience Total Hours 153,1 Total Past 90 Days 2,2 Total on Type Past 90 Days 2,2 Total on Type 113,0 1.6 Aircraft Information Airframe Type Robinson R44II Serial Number Manufacturer Robinson Helicopter Company Date of Manufacture 2005 Total Airframe Hours (at time of accident) 1 325,7 Last MPI (Date & Hours) 25 February ,1 Hours since last MPI 29,6 C of A (Issue Date) 10 February 2005 C of R (Issue Date) (Present Owner) 15 August 2005 Operating Categories Standard no restrictions Engine Type Lycoming IO-540-AE1A5 Serial Number L A Hours since New 1 325,7 Hours since Overhaul TBO not yet reached Mass and Balance The mass and balance sheet was obtained from the pilot after the accident (see Appendix A). According to the calculations, the helicopter was operating at lb at the time of the accident. This was 125 lbs within the maximum gross weight limit as set out in the pilot s operating handbook of lbs. CA 12-12a 23 FEBRUARY 2006 Page 5 of 16

6 1.7 Meteorological Information The following meteorological Information was obtained from the pilot s questionnaire: Wind direction Easterly Wind speed 10 kt Visibility Clear Temperature 26 C Cloud cover None Cloud base None Dew point Unknown 1.8 Aids to Navigation The aircraft was equipped with standard navigational equipment as per the minimum equipment list approved by the Regulator. There were no recorded defects prior to or during the flight. 1.9 Communications The aircraft was equipped with one VHF radio as per the minimum equipment list approved by the Regulator. There were no recorded defects to this radio prior to or during the flight According to the pilot, he transmitted on and monitored frequency MHz during his approach to the heliport Helipad Information Heliport Location Sun City Heliport Co-ordinates S E Heliport Elevation ft Heliport Surface Paved The heliport was approved by the SACAA on 8 November 2007 for VFR day and night use 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 During the landing sequence, a hard landing was made 27 m short of the helipad on an incline The main rotor blades made contact with a shrub about a metre from the helipad. Under normal circumstances, this shrub is not a hazard during approach and landing. CA 12-12a 23 FEBRUARY 2006 Page 6 of 16

7 The pilot did not alight from the aircraft to inspect the damage after the hard landing. Instead, he made an attempt to reposition the helicopter on the level ground of the helipad. During this attempt, the tail rotor blades made contact with the perimeter fence, causing substantial damage to the blades and gearbox Impact impressions were visible on the right-hand side of the aircraft where it initially made contact with the grass surface of the incline Medical and Pathological Information Neither pilot nor passengers sustained any injuries as a result of the accident Fire There was no evidence of a pre- or post-impact fire Survival Aspects The accident was considered survivable as impact forces were low, no damage was caused to the cabin area and all occupants were properly restrained Tests and Research The fuel strainer bowl and gasculator were inspected and found to be clear of contamination The engine was taken to an approved maintenance facility, ground-tested and found to be operating satisfactory. The following parameters were measured: Start to RPM Oil pressure Magnetos DC voltage Manifold pressure No difficulties during the start RPM Oil pressure Magnetos DC voltage Manifold pressure RPM Oil Pressure Magnetos DC voltage Manifold pressure 85 psi Normal 24 V 26,5 psi 85 psi Normal 24 V 26,5 psi 85 psi Normal 24,6 V 26,5 psi CA 12-12a 23 FEBRUARY 2006 Page 7 of 16

8 As there were no approach procedures for the heliport, the pilot complied with unmanned procedures for the landing Organisational and Management Information The aircraft was maintained by a SACAA-approved aircraft maintenance organisation (AMO) - which was in possession of a valid AMO approval certificate At the time of the accident, the aircraft was privately operated by the owner Additional Information During his interview, the pilot was not able to compute a mass and balance sheet manually; he was able to do the mass and balance sheet only on a computer According to the pilot s training records, 0,8 hours was spent on familiarising and training him on the vortex ring state During the inspection of the engine at the maintenance organisation that had recovered the helicopter, it was found that there was no data plate attached to the engine. The maintenance organisation reported this to the AMO responsible for the helicopter, and a new data plate was duly fitted (see Appendix B) Vortex ring state: The Federal Aviation Administration (FAA) Rotorcraft Flying Handbook explains vortex ring state as follows: 1.19 Useful or Effective Investigation Techniques None. 2. ANALYSIS 2.1 The pilot was conducting a private pleasure flight at the time of the accident. 2.2 Available evidence indicated that flight preparation had been performed properly, as all documentation was in order for the flight. 2.3 According to SACAA records, the pilot was the holder of a valid private pilot s licence (helicopter), had the required rating for the flight and was in possession of a valid medical certificate. He also had a night rating endorsed on his licence. 2.4 The aircraft had a valid certificate of registration and a valid certificate of airworthiness at the time of the accident. The aircraft s logbooks were verified and all records indicated that the airframe and engine had been properly maintained and all work carried out had been properly certified. CA 12-12a 23 FEBRUARY 2006 Page 8 of 16

9 2.5 The weather at the time of the accident, as obtained from the pilot, was fine. The sky was clear with a visibility of 10 km, there was a 10 kt easterly, and the temperature was 26 C 2.6 Communication during the approach and landing was conducted on frequency MHz. 2.7 The approach was started at 40 kt IAS. During the final stages, IAS was reduced to 10 kt with a descent rate of 400 feet per minute. This condition was likely to cause the aircraft to enter a vortex ring state. 2.8 When the pilot applied power and collective pitch control to cushion the landing, it was to no avail as the helicopter kept on settling with power, resulting in a hard landing causing damage to the helicopter skid 2.9 During the subsequence repositioning of the helicopter, damage was caused to the tail rotor gearbox, tail rotor blades and main rotor blades when contact was made with a perimeter fence and a shrub. 3. CONCLUSION 3.1 Findings Sufficient flight preparations were made for this flight 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 at the time did not contribute to the accident An incorrect landing/approach technique resulted in the aircraft entering a vortex ring state. The pilot did not climb out to verify the damage but re-applied power to reposition the helicopter on the level ground of the heliport. During this attempt, the tail rotor made contact with the perimeter fence, resulting in damage to the blades and gearbox. 3.2 Probable Cause/s Tail strike during a repositioning flight following a hard landing as a result of the helicopter entering a vortex ring state. 3.3 Contributing Factors None CA 12-12a 23 FEBRUARY 2006 Page 9 of 16

10 4. SAFETY RECOMMENDATIONS None 5. APPENDICES Appendix A(1-3) Mass and balance calculation Appendix B Certificate relating to maintenance of aircraft Appendix C Vortex ring state Report reviewed and amended by the Advisory Safety Panel 16 November END- CA 12-12a 23 FEBRUARY 2006 Page 10 of 16

11 Appendix A(1) Mass and balance table CA 12-12a 23 FEBRUARY 2006 Page 11 of 16

12 Appendix A (2) Centre of gravity chart CA 12-12a 23 FEBRUARY 2006 Page 12 of 16

13 Appendix A (3) Centre of gravity chart (lateral) CA 12-12a 23 FEBRUARY 2006 Page 13 of 16

14 Appendix B Data plate certificate relating to maintenance of aircraft. CA 12-12a 23 FEBRUARY 2006 Page 14 of 16

15 Appendix C VORTEX RING STATE (SETTLING WITH POWER) Vortex ring state describes an aerodynamic condition where a helicopter may be in a vertical descent with up to maximum power applied, and little or no cyclic authority. The term settling with power comes from the fact that helicopter keeps settling even though full engine power is applied. In a normal out-of-ground-effect hover, the helicopter is able to remain stationary by propelling a large mass of air down through the main rotor. Some of the air is recirculated near the tips of the blades, curling up from the bottom of the rotor system and rejoining the air entering the rotor from the top. This phenomenon is common to all airfoils and is known as tip vortices. Tip vortices consume engine power but produce no useful lift. As long as the tip vortices are small, their only effect is a small loss in rotor efficiency. However, when the helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the tip vortices. In this vortex ring state, most of the power developed by the engine is wasted in accelerating the air in a doughnut pattern around the rotor. In addition, the helicopter may descend at a rate that exceeds the normal downward induced-flow rate of the inner blade sections. As a result, the airflow of the inner blade sections is upward relative to the disc. This produces a secondary vortex ring in addition to the normal tip-vortices. The secondary vortex ring is generated about the point on the blade where the airflow changes from up to down. The result is an unsteady turbulent flow over a large area of the disc. Rotor efficiency is lost even though power is still being supplied from the engine (see below). Figure 3. Vortex ring state. A fully developed vortex ring state is characterised by an unstable condition where the helicopter experiences uncommanded pitch and roll oscillations, has little or no cyclic authority, and achieves a descent rate, which, if allowed to develop, may approach feet per minute. It is accompanied by increased levels of vibration. CA 12-12a 23 FEBRUARY 2006 Page 15 of 16

16 A vortex ring state may be entered during any manoeuvre that places the main rotor in a condition of high upflow and low forward airspeed. This condition is sometimes seen during quick-stop type manoeuvres or during recoveries from autorotations. The following combination of conditions is likely to cause settling in a vortex ring state: 1. A vertical or nearly vertical descent of at least 300 feet per minute. (Actual critical rate depends on the gross weight, rpm, density altitude, and other pertinent factors.) 2. The rotor system must be using some of the available engine power (from 20% to 100%). 3. The horizontal velocity must be slower than effective translational lift. Some of the situations that are conducive to a settling with power condition are: attempting to hover out of ground effect at altitudes above the hovering ceiling of the helicopter; attempting to hover out of ground effect without maintaining precise altitude control; or downwind and steep power approaches in which airspeed is permitted to drop to nearly zero. When recovering from a settling with power condition, the tendency on the part of the pilot is to first try to stop the descent by increasing collective pitch. However, this only results in increasing the stalled area of the rotor, thus increasing the rate of descent. Since inboard portions of the blades are stalled, cyclic control is limited. Recovery is accomplished by increasing forward speed, and/or partially lowering collective pitch. In a fully developed vortex ring state, the only recovery may be to enter autorotation to break the vortex ring state. When cyclic authority is regained, you can then increase forward airspeed. For settling with power demonstrations and training in recognition of vortex ring state conditions, all manoeuvres should be performed at an elevation of at least feet AGL. To enter the manoeuvre, reduce power below hover power. Hold altitude with aft cyclic until the airspeed approaches 20 kt. Then allow the sink rate to increase to 300 feet per minute or more as the attitude is adjusted to obtain airspeed of less than 10 kt. When the aircraft begins to shudder, the application of additional up collective increases the vibration and sink rate. Recovery should be initiated at the first sign of vortex ring state by applying forward cyclic to increase airspeed and simultaneously reducing collective. The recovery is complete when the aircraft passes through effective translational lift and a normal climb is established. CA 12-12a 23 FEBRUARY 2006 Page 16 of 16