AIRCRAFT ACCIDENT REPORT AND EXECUTIVE SUMMARY

Transcription

1 Section/division Occurrence Investigation Form Number: CA 12-12a AIRCRAFT ACCIDENT REPORT AND EXECUTIVE SUMMARY Aircraft Registration Reference: ZS- ELK Date of Accident 23 December 2013 CA18/2/3/9258 Time of Accident Type of Aircraft Piper (Aeroplane) Type of Operation Private 0643Z Pilot-in-command Licence Type PPL Age 48 Licence Valid Yes Pilot-in-command Flying Experience Last point of departure Total Flying Hours Private airstrip, Secunda, Mpumalanga 144,75 Hours on Type 67,55 Next point of intended Private airstrip, Secunda, Mpumalanga landing Location of the accident site with reference to easily defined geographical points (GPS readings if possible) On a farm 500 m from the end of a grass runway at GPS readings: (S26º 35'43.7", E029º 14' 41.0") ft field elevation. Meteorological Information Wind: calm; Temperature: 15 ºC; Visibility: Clear; Dew point: 6,2 ºC Number of people on board 1+0 No. of people injured 0 No. of people killed 0 Synopsis The pilot, being the sole occupant of the aircraft, took off from a private airstrip on his farm for a cross-country flight with the intention of landing at the airstrip again. During take-off the aircraft experienced a loss of engine power that led to a forced landing. During the forced landing, the aircraft sustained substantial damage to the undercarriage, propeller, left cockpit window and right wing. The pilot was not injured during the accident sequence. During the recovery of the wreckage by the approved aircraft maintenance organisation (AMO), a fuel leak was noticed on the fuel selector valve mounted on the left cockpit wall. The investigation found that interruptions of fuel supply to the engine contributed to the engine power loss. Probable Cause Unsuccessful forced landing following engine power loss due to fuel starvation6.13 Contributory factors 2.Improper maintenance ASP Date 12 August 2014 Release Date CA 12-12a 11 JULY 2013 Page 1 of 14

2 Section/division Occurrence Investigation Form Number: CA 12-12a Telephone number: address of originator: AIRCRAFT ACCIDENT REPORT Name of Owner/Operator : Botha P M Manufacturer : Piper Model : PA Nationality : South African Registration Marks : ZS- ELK Place Date : 23 December 2013 Time : 0643Z : Secunda, 1640, 4 ft from end of airstrip runway 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 accidents 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, the sole occupant on board the aircraft, departed from a private airstrip on his farm for a cross-country flight with the intention of landing at the farm again. The pilot reported that the aircraft experienced a loss of engine power during take-off. The pilot then executed a forced landing on an open field at the end of the runway The aircraft landed hard, the right main landing gear broke off and the nose gear collapsed, and finally the propeller struck the ground. The aircraft sustained substantial damage to the undercarriage, propeller, right wing and left side window during the accident sequence The accident occurred in daylight conditions at Secunda. The aircraft came to rest approximately 500 m from the end of the runway, at the location with GPS coordinates S26 35'43.7", E029 14' 41.0" and elevation of ft The aircraft wreckage was recovered by the approved AMO at Wonderboom Airport in Northern Gauteng The recovery crew informed the investigating team about their findings on the leaking fuel selector valve which was observed during recovery. CA 12-12a 11 JULY 2013 Page 2 of 14

3 1.2 Injuries to Persons Injuries Pilot Crew Pass. Other Fatal Serious Minor None Damage to Aircraft The aircraft was substantially damaged. Figure 1: Aircraft as it came to rest 1.4 Other Damage None 1.5 Personnel Information Nationality South African Gender Male Age 48 Licence Number Licence Type Private Pilot Licence valid Yes Type Endorsed No Ratings Single Engine Piston Medical Expiry Date 31 May 2014 Restrictions Corrective lenses Previous Accidents None CA 12-12a 11 JULY 2013 Page 3 of 14

4 Flying Experience: Total Hours 144,75 Total Past 90 Days 29,15 Total on Type Past 90 Days 29,15 Total on Type 67, Aircraft Information Airframe: Type PA Serial Number Manufacturer Piper Aircraft Corporation Date of Manufacture 1978 Total Airframe Hours (At time of Accident) 4 380,75 Last MPI (Date & Hours) 3 July ,26 Hours since Last MPI 23,49 C of A (Issue Date) 17 October 2013 C of R (Issue Date) (Present owner) 8 July 2013 Operating Categories Part The Piper PA28 Cherokee is a family of light aircraft designed for flight training, air taxi work and personal use. All members of the PA28 family are all-metal, unpressurised, single-engine, piston-powered airplanes with low-mounted wings and tricycle landing gear. They all have a single door on the co-pilot side, which is entered by stepping on the wing. Engine: Type Lycoming A4A Serial Number L A Hours since New 6 118,25 Hours since Overhaul 33,49 Propeller: Type Sensenich 76EM Serial Number 31160K Hours since New 604,25 Hours since Overhaul 33,49 Weight and balance The weight and balance was within limits. On the previous flight of 23 November 2013, 92 litres (24,3 US gal) of fuel was uplifted. There was enough fuel for the flight on the day of the accident. The aircraft had a sole occupant with no baggage; hence its weight was within limits. CA 12-12a 11 JULY 2013 Page 4 of 14

5 Fuel System The PA and airplane is equipped with aluminium fuel tanks, one placed in the inboard leading edge section of each wing. Each tank has a capacity of 25 gallons. A strainer is installed in the fuel outlet of each tank. From the tank outlet a fuel line is routed through the wings to the fuel selector valve located on the left side of the cabin in front of the pilot's seat; from the fuel selector valve a line leads to the fuel strainer bowl mounted on the left forward face of the fire wall. Figure 2: Typical PA-28 fuel system The fuel line is routed from the strainer bowl to the electric fuel pump, engine-driven fuel pump and then the carburettor injector inlet port. Two electrical fuel quantity gauges are mounted within the instrument cluster. Each gauge is connected to a transmitter unit installed in the fuel tanks. See Figure 2 above FUEL SELECTOR VALVE OPERATION Information extracted from: Piper Cherokee service manual. Chapter 9, page: 3C23, (P/N ) 1A1 When the fuel selector handle is not in a positive selector detent position, more than one fuel port will be open at the same time. It should be ascertained that the fuel selector is positioned in a detent, which can be easily felt when moving the handle through its various positions. CA 12-12a 11 JULY 2013 Page 5 of 14

6 1.6.4 Aircraft documentation such as maintenance records, certificates and service bulletin letters were studied and reviewed. Not all service bulletins published by the engine and aircraft manufacturers were complied with during aircraft servicing. The last mandatory inspection carried on the aircraft specifically stated that the inspection of the selector valve operation. The following service bulletin (SB) was released by the aircraft manufacturer to improve the flight safety use of the aircraft. According to the recorded information, the SBs were never complied with by the maintenance organisations that carried out the aircraft services. Service Bulletin Piper: PA28-180; Worn Fuel-select Valve; ATA 2823 of March 2012, AC 43-16A A general aviation mechanic writes, "When the fuel tank selector valve (P/N ) was rotated it was stiff to move, and the detents could not be felt at each position. A teardown showed the valve was very dirty inside, and the detent ring was worn. A review of Airworthiness Directives (ADs) and SBs revealed two bulletins that directly refer to problems with this valve. This defect (worn and dirty) led to improper fuel selection (position), greatly reducing fuel flow and causing stoppage of the engine. a.sb 0355: Fuel Selector Valve Lubrication. I was unable to locate a sign-off in the maintenance records of (compliance) with this bulletin. b.sb 0840: Fuel Selector Valve Cover Replacement. I was unable to locate a signoff in the maintenance records of compliance with this bulletin. This bulletin deals directly with preventing the pilot from inadvertently moving the valve to the 'off' position. Piper considers this SB to be mandatory. No AD was issued relating to the fuel selector valve" The mandatory periodic inspection (MPI) work pack of the last service indicates that the service carried out on the fuel selector valve did not include disassembling and cleaning (refer to MPI 3H18 of 01/31/08). 1.7 Meteorological Information The weather information was obtained from the pilot questionnaire. Wind direction No wind Wind speed Calm Visibility Good Temperature 15 ºC Cloud cover None Cloud base None Dew point 6,2 ºC 1.8 Aids to Navigation The aircraft was equipped with the standard factory-fitted navigational equipment approved by the Regulator. There were no recorded defects to navigational equipment prior to flight. CA 12-12a 11 JULY 2013 Page 6 of 14

7 1.9 Communications The aircraft was equipped with one VHF (very high frequency) radio approved by the Regulator. There were no recorded defects regarding the communications equipment prior to flight Aerodrome Information The accident occurred approximately 500 m from the end of the private grass runway at GPS co-ordinates S26º 35'43.7" E029º 14' 41.0" and elevation of ft Flight Recorders The aircraft was not equipped with a flight data recorder or a cockpit voice recorder. Neither recorder was required by the relevant aviation regulations Wreckage and Impact Information Figure 3: View of accident site The accident occurred in an open field 1 640,4 ft from the end of a private airstrip at the owner s farm The observation was that the aircraft impact with the ground was at a low angle and high speed. The aircraft crashed hard and the undercarriage was damaged. The right main landing gear was ripped off from the main airframe attachments. The landing gear was found 164 ft behind the main wreckage at the point of initial impact. CA 12-12a 11 JULY 2013 Page 7 of 14

8 The aircraft skidded on its belly, with the right wing and the propeller striking the ground until it came to rest 1640,4 ft from the end of the runway. The right tank ruptured due to damage by the right main wheel during impact. The aircraft sustained damage to the undercarriage, propeller, right wing and the left window. Figure 4: Damage to the right wing Figure 5: Damage to the propeller The damage to the propeller indicates that the engine was turning at low power (windmilling or idling) or at a complete stop before impact. Only one blade of the propeller was bent backward during the accident sequence Medical and Pathological Information There was no evidence that incapacitation or physiological factors affected the flight crew s performance Fire There was no evidence of post- or pre-impact fire Survival Aspects The accident was considered survivable. The aircraft was equipped with a shoulder harness. The pilot used it during the flight and the harness did not fail during the accident. The pilot evacuated the aircraft unassisted Tests and Research During the recovery of the aircraft wreckage, it was reported that the fuel selector valve was found leaking. The fuel was leaking onto the sidewall insulation blanket installed on the aircraft, causing further damage. According to the Piper PA 28 maintenance manual, selector valves are subjected to 50-hour leak checks. CA 12-12a 11 JULY 2013 Page 8 of 14

9 DISASSEMBLY OF FUEL SHUTOFF VALVE On aircraft equipped with fuel selector valve P/N , the valve must be disassembled according to the latest revision of Piper SB No Disassembly of other fuel selector valves is not recommended. CLEANING, INSPECTION AND REPAIR OF FUEL SHUTOFF VALVE Fuel selector valve P/N must be cleaned, inspected, and repaired according to the latest revision of Piper SB No No cleaning, inspection, or repair is recommended for other fuel selector valves. leaking elbow connection showing two full turns of threads that were not fully screwed in. Green discolouration as result of fuel leak absorbed by the insulation blanket Figure 6: View damage caused by fuel leak The selector valve was removed and inspected. During investigation it was found that the elbow was not fully screwed in during connection. Only three threads were connecting the elbow, with evidence of a compound sealant that looked like dirt. The sealant compound used in the fuel system applies to the fuel tanks only. Figure 7: View of fuel pipes connected to the selector valve CA 12-12a 11 JULY 2013 Page 9 of 14

10 When connecting elbows 18, 19 and 20 to the fuel selector valve (85) assembly, no synthetic sealant compound or O-rings are used to prevent fuel leaks. The pipes connections are taper-type threads (self-tight sealant). When connecting the elbow (18) to the selector valve, the seal must be watertight and the elbow aligned with the fuel feed line. The elbow is a tapered-thread (self-lock tight type). The elbow in use was of the correct type and size. Elbow (18) shows threads Consist of six full turn threads Two full turn threads were not fully screwed in Only three full turn threads were connected Dirt resulting from a sealant compound Figure 8: View of valve conditions The condition of the fuel selector valve assembly were consistent with that of a component that was not maintained in accordance with the manufacturer s recommendations Organisational and Management Information The aircraft was operated in a private capacity by the owner Additional Information The information below was extracted from: Fuel selector valve The fuel selector valve allows selection of fuel from various tanks. A common type of selector valve contains four positions: LEFT, RIGHT, BOTH, and OFF. Selecting the LEFT or RIGHT position allows fuel to feed only from that tank, while selecting the BOTH position feeds fuel from both tanks. The LEFT or RIGHT position may be used to balance the amount of fuel remaining in each wing tank. CA 12-12a 11 JULY 2013 Page 10 of 14

11 Fuel placards will show any limitations on fuel tank usage, such as level flight only and/or both for landings and take-offs. Regardless of the type of fuel selector in use, fuel consumption should be monitored closely to ensure that a tank does not run completely out of fuel. Running a fuel tank dry will not only cause the engine to stop, but running for prolonged periods on one tank causes an unbalanced fuel load between tanks. Running a tank completely dry may allow air to enter the fuel system, which may cause vapour lock. When this situation develops, it may be difficult to restart the engine. On fuel-injected engines, the fuel may become so hot it vaporises in the fuel line, not allowing fuel to reach the cylinders During investigation it was discovered that the fuel was leaking from an elbow connecting the engine feed pipe to the selector valve. The observation of a leak indicates that it has been on for more than a month. The leak could not be detected during a pre-flight inspection (Figure 9), because the leaking fuel was being absorbed by the insulation blankets and damaging them. Left tank Shut-off position Right tank Fuel Leaking Figure 9: View of selector valve position as it was found after the accident The selector valve is mounted slightly below the fuel tanks and engine feed pipe, which allowed gravity to force fuel through the leaking elbow fitting. Fuel remaining in the engine fuel feed pipe leaked when the aircraft engine was not operating. In some cases, the fuel tank supply piping to the engine leaks and fuel is lost. This can cause engines to starve. Fuel starvation is slightly different from fuel exhaustion, in that fuel is in the tank but there is a supply problem which either fully or partially prevents the fuel from reaching the engine. Causes may include a blocked fuel filter, problems with fuel tank selection if multiple tanks are installed, CA 12-12a 11 JULY 2013 Page 11 of 14

12 system leak (air in the system) or more commonly, water-contaminated fuel Useful or Effective Investigation Techniques None 2. ANALYSIS Man 1.1 The pilot did not have the aircraft type endorsed on his licence. There are records showing evidence of course conversion for the aircraft type but he was not properly licenced for the aircraft in accordance with existing regulations. Machine 1.2 Weight and balance were within limits at the time of the accident and were not considered a contributing factor to the accident. There was sufficient fuel of the correct grade in the aircraft tanks. The selected fuel tank had sufficient fuel. 2.3 During the pre-flight inspection, the pilot is required to inspect the fuel selector valve for functionality of the valve. The inspection method is limited; one is only required to check the valve s smooth rotational operation. 2.4 The aircraft had been operated 23,49 hours since the latest mandatory periodic inspection service carried out at 4 357,26 hours. If the fuel selector smoothly rotates and supplies fuel to engine fuel feed piping when in open position, one would not suspect any fuel leak. The 50-hour selector valve inspection as noted on the MPI work procedure was never carried out on the aircraft. The condition of the fuel selector valve assembly was consistent with a component that was not maintained in accordance with the manufacturer s maintenance recommendations. 2.5 During investigation it was observed that the fuel selector valve was leaking. However, the fuel leak through the elbow was from the engine fuel feed pipeline. Fuel leaks may cause fuel supply interruption during engine operation. The elbow was connected with only three threads, and a compound sealant was used as an extra measure to seal the connection. It is not specified anywhere in the maintenance manual that a compound sealant be used during connection of elbow to selector valves. 2.6 The pilot reported that the aircraft engine lost power during take-off. During take-off, the aircraft engine is set to high power settings, which requires an increased fuel supply to the engine to maintain the desired power. This is in response of the fuel supply from either selected tank. When fuel is drawn through the engine feed line from the fuel tanks through the selector valve, the two fuel pumps exert a suction force. If the connection is not properly sealed (leaking), air is sucked into the system, which will in turn cause fuel supply interruption (air in the fuel system). Air drawn through the leaking elbow connection caused fuel supply interruption (reduction of fuel supply) throughout the engine fuel feed line to the carburettor. This affected the air/fuel mixture ratio and resulted in engine fuel starvation. When CA 12-12a 11 JULY 2013 Page 12 of 14

13 fuel starvation occurs the engine will develop power failure which results in a complete power loss (engine stops). Environment 2.7 Good weather conditions prevailed and were not considered a factor during the accident sequence. 3 CONCLUSION 3.1 Findings The pilot did not have the aircraft endorsed on his licence. The pilot was not qualified and licenced properly in accordance with existing regulations The aircraft fuel selector valve was found leaking The condition of the fuel selector valve assembly was consistent with a component that was not maintained in accordance with the manufacturer s maintenance recommendations The aircraft certificates and documents were valid and up to date The aircraft was operated under private capacity with regulatory Standard Part Weight and balance were not considered a factor contributing to the accident Good weather conditions prevailed on the day of the accident There was sufficient fuel in the aircraft tanks during recovery All damage to the aircraft airframe, landing gears and power plant are attributed to the severe impact Manufacturer s SBs were not complied with Dirt was found on the front part of an elbow that goes into the valve. 3.2 Probable Cause(s) Unsuccessful forced landing following engine power loss due to fuel starvation. 3.3 Contributory factors Air drawn through leaking elbow connecting engine feed to fuel sector valve Improper maintenance CA 12-12a 11 JULY 2013 Page 13 of 14

14 4. SAFETY RECOMMENDATIONS 4.1 The Regulator should implement a system to monitor private aircraft owners/operators, enforcing compliance to manufacturer s safety related service bulletins and service letter recommendations for each aircraft type. In most cases where the private owned aircraft is involved in an accident, the findings are lack of compliance to the service bulletins and letters and SB which results in poor maintenance. 5. APPENDICES 5.1 None CA 12-12a 11 JULY 2013 Page 14 of 14