AIRCRAFT ACCIDENT REPORT AND EXECUTIVE SUMMARY

Transcription

1 Section/division Accident & Incident Investigations Form Number: CA 12-12a AIRCRAFT ACCIDENT REPORT AND EXECUTIVE SUMMARY Ref No. CA18/2/3/8082 Aircraft Registration ZS-RAT Date of Accident 10 March 2006 Time of Accident 1500Z Type of Aircraft ROBINSON R44 RAVEN II Type of Operation Private Pilot-in-command Licence Type Private Age 41 Licence Valid Yes Pilot-in-command Flying Experience Total Flying Hours Hours on Type Last point of departure Kloof Hospital, Pretoria Next point of intended landing Marken, Limpopo Province Location of the accident site with reference to easily defined geographical points (GPS readings if possible) 100m from the Kloof Hospital, Pretoria (GPS position: South 25 48,627 and East ,757 ) Meteorological Information Surface wind; Light variable, Temperature, 26 C, CAVOK Number of people on board No. of people injured No. of people killed 0 Synopsis The pilot, accompanied by a passenger, took off from Rand Aerodrome (FAGM) on a private flight and landed on the helipad at Kloof Hospital, located in the East of Pretoria, to pick up a second passenger en route to Marken in the Limpopo Province. The helicopter was fuelled to capacity with 100 LL Avgas prior to their departure from Rand Aerodrome. An uneventful landing was achieved at the hospital helipad, which is located on top of the roof of the hospital. After uplifting a second passenger, and completing all standard take-off procedures, the pilot indicated that he had managed to establish an in ground effect (IGE) hover. According to the pilot, he then proceeded into forward flight. However, as the ground effect (roof structure) dissipated, the helicopter could not maintain altitude. The low main rotor RPM light and audio warning came on and the helicopter descended and crashed in a nose-down attitude between trees approximately 100m from the helipad, in close proximity to the hospital perimeter fence. All three occupants sustained injuries and were admitted to the Kloof Hospital. Probable Cause The pilot over-pitched the helicopter on take-off. It was not possible to sustain flight following a decay in main rotor rpm, and it crashed. IARC Date Release Date CA 12-12a 23 FEBRUARY 2006 Page 1 of 20

2 Section/division Accident & Incident Investigations Form Number: CA 12-12a AIRCRAFT ACCIDENT REPORT Name of Owner/Operator : Delmon Mining and Civils Pty (Ltd) Manufacturer : Robinson Helicopter Company Model : R44 Raven II Nationality : South African Registration Marks : ZS-RAT Place : Kloof Hospital, Pretoria Date : 10 March 2006 Time : 1500Z 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 interests 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 given without prejudice to the rights of the CAA, which are reserved. 1. FACTUAL INFORMATION 1.1 History of Flight: The pilot, accompanied by a passenger, took off from Rand Aerodrome (FAGM) and landed on the helipad at Kloof Hospital, located in the East of Pretoria, to pick up another passenger en route to Marken in the Limpopo Province. The helicopter was fuelled to capacity with 100 LL Avgas prior to their departure from Rand Aerodrome An uneventful landing was achieved at the hospital helipad, which is located on top of the roof of the hospital. CA 12-12a 23 FEBRUARY 2006 Page 2 of 19

3 1.1.3 After uplifting the second passenger, and completing all standard take-off procedures, the pilot indicated that he had managed to establish an in-ground effect (IGE) hover. According to the pilot, he then proceeded into forward flight. However, as the ground effect (roof structure) dissipated the helicopter could not maintain altitude, the low main rotor RPM light and audio warning came on, whereupon the helicopter descended. According to the pilot, he then lowered the collective and overrode the governor to gain more power. This didn t have the desired effect and the helicopter crashed in a nose-down attitude between trees approximately 100m from the helipad, in close proximity to the hospital perimeter fence. 1.2 Injuries to Persons: Injuries Pilot Crew Pass. Other Fatal Serious Minor None The passenger that was seated in the left front seat sustained serious injuries, while the pilot and the rear-seated passenger sustained minor injuries. All three occupants were admitted to the Kloof Hospital for medical attention. 1.3 Damage to Aircraft: The helicopter was substantially damaged The cabin and the instrumentation panel were destroyed. The vertical and horizontal stabilizers and the tail rotor assembly separated from the tail boom. The main rotor blades were extensively damaged during the impact sequence. 1.4 Other Damage: Apart from minor damage to vegetation, no other damage was caused. CA 12-12a 23 FEBRUARY 2006 Page 3 of 19

4 1.5 Personnel Information: Pilot-in-command Nationality South African Gender Male Age 41 Licence Number **************** Licence Type Private Licence valid Yes Type Endorsed Yes Ratings Night Rating Medical Expiry Date 31 May 2006 Restrictions Must wear corrective lenses Previous Accidents None Flying Experience: Total Hours Total Past 90 Days 41.1 Total on Type Past 90 Days 41.1 Total on Type Aircraft Information Airframe: Type Robinson R-44 Raven II Serial Number Manufacturer Robinson Helicopter Company Year of Manufacture 2005 Total Airframe Hours (At time of Accident) Last MPI (Hours & Date) March 2006 Hours since Last MPI 5.2 C of A (Issue Date) 28 October 2005 C of R (Issue Date) (Present owner) 27 October 2005 Operating Categories Standard CA 12-12a 23 FEBRUARY 2006 Page 4 of 19

5 1.6.2 Engine: Type Lycoming IO-540-AE1A5 Serial Number L A Hours since New Hours since Overhaul T.B.O not yet reached Weight and balance calculation: Weight (lbs) Arm (inches) Moment (in.lb) A/C empty weight Pilot (120kg) Fwd passenger (85kg) Aft passenger (85kg) Baggage (10kg) Fuel main tank (24 US gal) Fuel aux tank (18 US gal) Total T/O Weight The Maximum Certificated take-off Mass for the helicopter as stipulated in Section 2, page 2-3 of the POH (Pilot s Operating Handbook) is given as pounds (1134 kg). Centre of Gravity (CG) = Total Moment Weight = = inches (i) The fuel conversion factor used to compile this report was: 1 US Gallon = 6 pounds. (ii) A total of 7 US Gallons of fuel was subtracted from the total fuel load for the flight from Rand Aerodrome to the Kloof Hospital. (iii) The helicopter was operated within its allowable Centre of Gravity envelope (CG) as indicated by the graph on the next page. CA 12-12a 23 FEBRUARY 2006 Page 5 of 19

6 (iv) The in ground effect (IGE) hover graph, as documented in the POH, Section 5, page 5-3 was consulted. The graph indicated that an in ground effect hover at 4975 feet pressure altitude at 26 C and a gross weight of lbs would have been possible. The pilot was able to attain an in ground effect hover over the helipad. CA 12-12a 23 FEBRUARY 2006 Page 6 of 19

7 (v) Relating to the out of ground effect (OGE) hover graph, the performance graph indicates that the maximum out of ground hover gross weight at 4975 feet pressure altitude and 26 C should not exceed lbs. The maximum gross weight for the helicopter on take-off was lbs, which exceeded the OGE calculated limit by 57 lbs lbs CA 12-12a 23 FEBRUARY 2006 Page 7 of 19

8 1.7 Meteorological Information Weather information was obtained from the pilot s questionnaire. Wind direction N/W Wind speed 3 knots Visibility Good Temperature 26 C Cloud cover None Cloud base None Dew point N/A According to the Density Altitude chart tabled in Section 5 of the POH, at feet pressure altitude and a temperature of 26 C, the Density Altitude would have been about 7500 feet ft 26 C CA 12-12a 23 FEBRUARY 2006 Page 8 of 19

9 1.8 Aids to Navigation No difficulties were reported with the navigational equipment. 1.9 Communications The Kloof Hospital was located within the Control Zone (CTR) of Waterkloof Air Force Base The pilot broadcasted his intentions on the VHF frequency MHz, which was the frequency for the Waterkloof Air Force Base control tower Aerodrome Information The helicopter took off from the Kloof Hospital helipad, which is located at a GPS position determined to be South East at an elevation of feet AMSL (above mean sea level) The Kloof Hospital Helipad was a licensed helipad with the CAA in terms of Part (c) of the Civil Aviation Regulations of It was approved for VFR (visual flight rules) day and night operations. Following the accident, the CAA personnel wanted to inspect the helipad (roof area) but was unable to do so, as only certain hospital employees have the required key combinations to the path way going up to the roof, and neither was available Prior to the landing at the hospital, an indemnity form was made available to the pilot by hospital management, which he completed, signed and returned to the hospital prior to the intended landing. The indemnity form, however, did not allow the pilot permission to land on the helipad 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. CA 12-12a 23 FEBRUARY 2006 Page 9 of 19

10 1.12 Wreckage and Impact Information The helicopter crashed in a nose-down attitude in close proximity to the hospital perimeter fence, about 100m (in a horizontal line) from where it took off The vertical and horizontal stabilizers and the tail rotor assembly separated from the tail boom during the impact sequence and were found a few metres from the main wreckage Medical and Pathological Information Not applicable Fire There was no pre- or post-impact fire Survival Aspects The accident was regarded as survivable. The rear-seated passenger and the pilot sustained minor injuries, and the front-seated passenger (seated on the left) sustained serious injuries. All three occupants were admitted to the Kloof Hospital The occupants were properly restrained prior to take-off by making use of the helicopter-equipped three-point safety harness (similar to that of an automobile) Tests and Research None considered necessary Organisational and Management Information CA 12-12a 23 FEBRUARY 2006 Page 10 of 19

11 This was a private flight The last MPI (Mandatory Periodic Inspection), prior to the accident was certified by AMO (Aircraft Maintenance Organisation) No. 27. The AMO was in possession of a valid AMO Approval Additional Information Civil Aviation Regulations (CARs) of 1997 Part Helicopter landings and take-offs (1) No pilot-in-command of a helicopter shall land at or take off from any place unless the place is so situated to permit the helicopter, in the event of an emergency arising during such landing or take-off, to land without undue hazard to persons or property on the surface. (2) No pilot-in-command of a helicopter shall land on, or take off from, any building, structure or place situated within 100m of any other building or structure, in the area of jurisdiction of local government, unless such building, structure or place has been approved for the purpose by the Commissioner: Provided that this restriction shall not apply - (a) to a helicopter landing on, or taking off from, a building, structure or place within an industrial area, a commercial warehouse area or an open farm land which is suitable for such purposes and in respect of which helicopter the pilot-in-command is the holder of a valid commercial or airline transport pilot s licence (helicopter) or, in the case of the holder of a private pilot s licence (helicopter), with the written permission of the Commissioner, unless specifically prohibited by the local government; (b) to a helicopter engaged in an emergency medical service operation referred to in Part 138, or undertaking of a flight necessary for the exercising of any power in terms of the law. CA 12-12a 23 FEBRUARY 2006 Page 11 of 19

12 Application for Non-Scheduled Helicopter Flying Operation: For the purpose as referred to in Part (2) the CAA has an approved form, reference No. CA This form should be completed and returned to the Flight Operations Department prior to any intended non-scheduled landing for approval of such landing Air Density and Flight: Reference: Meteorology for Pilots, Pg , by K.M. Wickson Low air density can considerably reduce the performance of engines and airframes; in the former case because of the reduction in the mass of air entering the engine. For airframes, the amount of lift from a wing is directly proportional to the density. For these reasons, for both take-off and landing, when density is very low, the pilot must either use a longer take-off and landing run or, alternatively, reduce the aircraft weight (either fuel or payload). Cruising at height in a jet aircraft, the lower density gives reduced thrust. However, the aircraft s drag is also reduced because of the lower density and the lower thrust produced by the engine means it will have a lower fuel consumption. As a consequence, fuel consumption can be expected to reduce as height increase. For helicopters the engine effects are as for fixed wing aircraft. The equivalent to lift from a wing is lift from the rotor blades. In low-density conditions the rotor blades have to be set at a higher angle of attack, and this makes the retreating blade more liable to stall. A lower density can also significantly reduce the hovering ceiling. Lastly, in extreme cases of low density, vertical take-off or landing may not be possible, necessitating a running take-off and landing. Low-density conditions are most likely to occur where: Airfield elevation is High (hence low pressure) Temperature is High, and Humidity is High. Each of these will produce low density. An airfield with a high elevation near the equator in the rainy season will therefore suffer from all the low-density effects. A CA 12-12a 23 FEBRUARY 2006 Page 12 of 19

13 good example of the above is Nairobi airport at latitude S, which has an elevation of some ft (1.7 km). It is a frequent occurrence that aircraft have to operate with a reduced payload when taking off in the early afternoon. Another, somewhat less of a low-density regime, concerns Bahrain in the Arabian Gulf. In summer, in the afternoon temperatures are high and humidity is high. Despite the fact that the airfield is virtually at sea level, when a Concorde service operated from Bahrain its passenger load had to be reduced for take-offs during summer. It is for this reason that the Concorde service to Bahrain was terminated. Singapore at latitude N is widely used as a refuelling stop for aircraft flying to Japan and Australasia. These stops are usually scheduled for night-time or the early morning hours when temperatures are cooler and thus density is greater. Density Altitude: Performance of an aircraft, and particularly for helicopters, is often argued against the term Density Altitude. This is the height in the ISA (International Standard Atmosphere), which has a density corresponding to the actual ambient density at a specific location. Alternatively, it can be considered as the pressure altitude corrected for temperature. Hence if reference is made to a high Density Altitude it means that the air density as such, must be low The Effect of Gross Weight on Helicopter Performance: Reference: (Basic Helicopter Handbook, US Department of Transportation) We learned earlier that the total weight of a helicopter is the first force that must be overcome before flight is possible. Lift is the force that is needed to overcome or balance this total weight. It is easily seen that the greater the gross weight of the helicopter, the more lift is required to hover. The amount of lift available is dependent upon the angle of attack at which the rotor blades can operate and still maintain required rotor RPM. The angle of attack at which the blades can operate at required rotor RPM is dependent upon the amount of power available. Therefore, the heavier the gross weight, the greater the power required to hover and for flight in general, and the poorer the performance of the helicopter since less reserve power is available, or to state it another way, the heavier the gross weight, the lower the hover ceiling. A study of the hovering ceiling chart reveals the following interesting information for CA 12-12a 23 FEBRUARY 2006 Page 13 of 19

14 one helicopter, and this is fairly typical for all helicopters (with unsupercharged engines). At 60 F in dry air, the hovering ceiling for gross weights of 1 300, 1 400, and pounds are feet, feet, 5900 feet, and feet, respectively. An increase of 300 pounds in gross weight decreases the hovering ceiling by more than half. At gross weight of 1300, 1 400, 1 500, and pounds at a temperature of 100 F (37.8 C) in air with a relative humidity of 80% the hovering ceiling are feet, feet, 2900 feet, and feet, respectively. In the latter case, an increase of 300 pounds in gross weight reduces the hovering ceiling by almost 80%. A comparison of the two examples illustrates vividly the reduction in performance brought about by a combination of heavy gross weight and high-density altitudes. Of the three major factors affecting the performance of a helicopter at high elevations (density altitude, wind, and gross weight), the pilot can control only the gross weight. It should be obvious that the gross weight carried on any flight must be considered not only for take-off under the existing density altitude, wind conditions, and power available at point of departure, but also under the expected density altitude, wind conditions, and power available at the landing destination. Smaller amounts of fuel may be carried to improve performance or to increase useful load. It must be remembered, however, that this necessitates a sacrifice in range Maximum Performance Take-off Reference: (Flying the Helicopter, by John J. McDonald, Pg ) When such a take-off is required, the pilot must be thoroughly familiar with the capabilities and limitations of his ship. The pilot s best friend is his flight manual for that particular ship and is an invaluable tool here, as it is under so many conditions. Besides the capabilities and limitations of your ship, the pilot will have to know about, and take into consideration: wind velocity, air density, temperature, CG, and gross weight. These, and other factors affecting technique and performance, are absolutely essential before attempting a maximum performance take-off. The procedures for this type of take-off are critical and must be followed explicitly, along with certain required observations, if the manoeuvre is to be safely and successfully accomplished. Increase collective pitch and throttle while watching the tachometer. Continue increasing both until the maximum redline engine rpm is indicated on the tachometer and the ship becomes light on its landing gear. As the ship becomes airborne, increase the pitch and apply full throttle. When the helicopter becomes CA 12-12a 23 FEBRUARY 2006 Page 14 of 19

15 airborne it should be climbing and going forward at the same time in a very steep ascent angle. When climbing airspeed is achieved, come back on the cyclic stick slightly to prevent too much forward speed from decreasing the required angle of ascent. Continue with full power until the ship is safely clear of all obstacles, then power may be reduced and a normal or standard rate of climb established. The goal of this type of take-off is to obtain a maximum altitude in a minimum amount of forward distance. The result will depend not only on the pilot s skill, but also to a great extent on the performance and conditions outlined earlier. The less favourable these conditions, the shallower the angle of ascent will be. Extreme caution must be employed when climbing very steeply, for if airspeed is permitted to get too low, there is the ever-present danger that the helicopter may settle back to the ground. What could be even more dangerous is the possibility of a power failure at low altitude and airspeed, which would place the craft into a very dangerous situation one that would require a very high degree of skill to make a safe autorotation landing. Considerable caution and anticipatory judgement of any changing conditions and circumstances cannot be over-emphasised Over-Pitching Reference: (Principles of Helicopter Flight, by W.J. Wagtendonk, Pg 81-82) Over-pitching is different from recirculation, even though the symptoms have similarity. While over-pitching can occur at any altitude and at various stages of flight, it is more likely to occur when approaching a hover or during hover. If the rotor rpm decreases during those phases (for whatever reason), total rotor thrust reduces and an unwary pilot might attempt to restore the rotor thrust by pulling up the collective. This action invariable tilts the total reaction away from the axis of rotation, worsening the total rotor thrust/rotor drag ratio. Thus up collective will only result in further decay in rotor rpm. Decaying rotor rpm also causes the helicopter blades coning angles to increase. The consequence of this is that, firstly, the disc becomes smaller so that rotor thrust falls off. Secondly, large coning angles cause rotor thrust to point inward so that smaller vertical components become available to overcome the helicopter s weight. There comes a stage where the rotor rpm is so low that even full power can no longer restore it. This is the beginning of over-pitching. Any further raising of collective creates more rotor drag and rotor rpm decays even further. The only CA 12-12a 23 FEBRUARY 2006 Page 15 of 19

16 recovery action from over-pitching is to lower the collective lever to increase rotor rpm. This will cause the helicopter to lose some height. Over-pitching may occur when approaching a high altitude landing site if the power required to hover is not available. As airspeed decreases and the need for power increases, the helicopter descend rate builds when the engine cannot supply the power required. Pilots who then instinctively pull up the collective to arrest the sink rate are in trouble. The high inflow angles and associated rotor drag quickly decay the rotor rpm and the stage is set for over-pitching. The best scenario ends in hard landing, while the worst-case scenario ends in full rotor stall, at which point the helicopter virtually falls out of the sky Useful or Effective Investigation Techniques None considered necessary. 2. ANALYSIS 2.1 This was a private flight. The helicopter was taking off from the Kloof Hospital helipad, which was located on top of the roof of the hospital after the pilot uplifted a second passenger. The pilot was able to establish the helicopter within an in ground effect over (IGE) hover. 2.2 At no given time prior to take-off had the pilot performed a weight and balance calculation, nor had he consulted the POH (Pilot s Operating Handbook) Section 5 to ensure that the helicopter configuration at the time of take-off was within the performance capabilities for the given environmental conditions. The density altitude at the time was calculated to be feet AMSL (above mean sea level), which had a direct effect on the performance capabilities of the helicopter. 2.3 All parameters were found to be within limits, while the helicopter was within ground effect. As soon as they started moving forward and the ground effect dissipated as they moved over the edge of the helipad (hospital roof surface), which now became an out of ground effect scenario, the main rotor rpm light and audio warning came on. The pilot then aggravated the condition by overriding the governor, which is an electrically sensing device located on the throttle, which assists the pilot in CA 12-12a 23 FEBRUARY 2006 Page 16 of 19

17 maintaining a constant engine RPM, which also results in a constant manifold pressure. He was unable to restore the low rotor RPM condition as the power required exceeded the power available and with limited height available to unload the rotor system and regain rpm, the pilot over-pitched the rotor system, rendering ground impact inevitable. 3. CONCLUSION 3.1 Findings The pilot was the holder of a valid private pilot s licence (helicopter) and had the helicopter type endorsed in his logbook The last MPI prior to the accident was certified on 8 March 2006 by AMO No.27 at airframe hours The helicopter had flown a further 5.2 hours since the last MPI was certified Weather conditions were fine at the time, with a reported temperature at the helipad area of 26 C. The wind was north-westerly at approximately 3 knots The calculated density altitude at the time was feet AMSL (above mean sea level) The take-off weight of the helicopter was within its maximum certified take-off limit of pounds The helicopter was capable of performing an in ground effect (IGE) hover according to the IGE performance graph The pilot did not follow the requirements to perform a Non-Scheduled landing at the Hospital as stipulated in Part of the Civil Aviation Regulations (CARs) of The out of ground effect (OGE) performance graph indicates that the helicopter weight should not have exceeded pounds, which was 57 pounds below the take-off weight. CA 12-12a 23 FEBRUARY 2006 Page 17 of 19

18 No weight and balance calculation was performed by the pilot following the uplift of a second passenger prior to take-off The helipad was licensed with the CAA as called for in Part of the Civil Aviation Regulations of This was a private flight. 3.2 Probable Cause/s The pilot over-pitched the helicopter on take-off. It was not possible to sustain flight following a decay in main rotor rpm and it impacted with terrain. 3.3 Contributory factor/s The density altitude of feet had a profound effect on the helicopter performance during the take-off phase of the flight Failure by the pilot to perform a proper weight and balance calculation prior to takeoff, following the upliftment of a second passenger after landing at the hospital helipad Failure by the pilot to consult the IGE and OGE hover charts in POH prior to take-off should be regarded as a significant contributory factor to this accident. 4. SAFETY RECOMMENDATIONS 4.1 It is recommended that the CAA, Flight Operations Department along with the Aerodrome Safety Department, inspect the helipad at Kloof Hospital in order to establish if the helipad does have the required fire-fighting equipment available as well as the necessary quick access plan to the helipad via the hospital in the case of an emergency. It came to the attention of the writer that the CAA had attempted to inspect the helipad shortly after the accident occurred, but was unable to visit the helipad as they were unable to gain access via the hospital to the helipad (internal CA 12-12a 23 FEBRUARY 2006 Page 18 of 19

19 hospital logistical shortcoming). 4.2 It is further recommended that the CAA draft an official letter to the hospital management, clearly outlining the primary purpose of the helipad. It should be emphasised that it should only be used by approved EMS (Emergency Medical Service) helicopter operators and at no time should it be used for any nonscheduled / private operations. The circumstances where an unforeseen medical event justifies a landing by a non-ems approved helicopter(s) should, however, be considered and catered for. NOTE: The location of the helipad (being on top of the roof of the hospital) is somehow problematic to the writer as it does impose a certain degree of risk. Should a helicopter crash on top of the helipad (roof) and a fire erupt, it could be highly problematic to the safety of the hospital and its occupants. 5. APPENDICES 5.1 None -END- Report reviewed and amended by Advisory Safety Panel 27 January 2009 CA 12-12a 23 FEBRUARY 2006 Page 19 of 19