AIRCRAFT INCIDENT REPORT AND EXECUTIVE SUMMARY

Transcription

1 Section/division Occurrence Investigation Form Number: CA 12-12a AIRCRAFT INCIDENT REPORT AND EXECUTIVE SUMMARY Aircraft Registration Type of Aircraft Reference: CA18/3/2/1055 ZU-CUF Date of Incident 23 May 2014 Time of Incident 1505Z UFM-10 Samba (Aeroplane) Type of Operation Private flight Pilot-in-command Licence Type Private pilot (PPL) Age 56 Licence Valid Yes Pilot-in-command Flying Experience Last point of departure Next point of intended landing Total Flying Hours Hours on Type 42.3 Plettenberg Bay aerodrome (FAPG): Western Cape. Plettenberg Bay aerodrome (FAPG): Western Cape. Location of the incident site with reference to easily defined geographical points (GPS readings if possible) During taxiing on the grass apron at GPS co-ordinates determined to be S E at an elevation of 465 feet above mean sea level (AMSL). Meteorological Information CAVOK. Number of people on board No. of people injured 0 No. of people killed 0 Synopsis On Friday 23 May 2014, a certified private pilot being the sole occupant on board the aircraft was conducting a private flight from Plettenberg Bay (FAPG) aerodrome when the incident occurred. Visual meteorological conditions (VMC) prevailed in the area and according to the pilot, the flight took 0.7 hours after which a successful landing on asphalt runway 12. During taxiing on the grass apron towards the hangar, the aircraft nose pitched down resulting in the propeller smashing the ground. The pilot instantly switched the master switch off and vacated the aircraft unassisted and unharmed. Post inspection of the aircraft by the pilot after the incident revealed a broken nose gear strut and damage was limited to the aircraft nose gear assembly and the propeller. The AP took pictures of the gear portions after which they were discarded without metallurgical analysis being conducted. The investigation concluded that the mishap was as a result of a fractured nose gear strut. Probable Cause Metal fatigue/fracture. IARC Date Release Date CA 12-12b 25 MAY 2010 Page 1 of 14

2 Section/division Occurrence Investigation Form Number: CA 12-12a Telephone number: address of originator: AIRCRAFT INCIDENT REPORT Name of Owner/Operator : Ferreira M M Manufacturer : Ferreira M M Model : UFM-10 Samba Nationality : South African Registration Marks : ZU-CUF Place : Plettenberg Bay (FAPG) aerodrome Date : 23 May 2014 Time : 1505Z 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 given without prejudice to the rights of the CAA, which are reserved. 1. FACTUAL INFORMATION: 1.1 History of Flight: On Friday 23 May 2014, the pilot being the sole occupant on-board the aircraft was conducting a private flight under visual flight rules (VFR) from Plettenberg Bay (FAPG) aerodrome, Western Cape Province when the incident occurred. According to the pilot, a thorough pre-flight inspection was performed prior to the flight and nothing abnormal was detected. The pilot boarded the aircraft and completed the before- start check list where after he started the engine without difficulty. The aircraft taxied to runway 12 and took off. According to the pilot the flight took 0.7 hours, after which a successful landing on asphalt runway 12 was carried out The pilot reported that during taxiing on the grass apron leading to the hangar, the nose gear wheel went through a concealed hole, about four inches in diameter where after the nose gear strut broke. The aircraft nose pitched down due to forward momentum and the propeller blades struck the ground. The pilot immediately switched off the master switch and disembarked the aircraft unassisted and unharmed. Post inspection of the aircraft by the pilot after the incident revealed a broken nose gear strut and damage was limited to the aircraft nose gear assembly and the propeller. By CA 12-12b 25 MAY 2010 Page 2 of 14

3 means of a forklift the aircraft was lifted and later recovered to the hangar upon which the approved person (AP) replaced the unserviceable nose gear strut and the propeller. The aircraft was then released to service and flown to Brits aerodrome, the aircraft owner s home town The incident happened during day time at GPS co-ordinates determined to be S E at an elevation of 465 feet above mean sea level (AMSL). 1.2 Injuries to Persons: Injuries Pilot Crew Pass. Other Fatal Serious Minor None Damage to Aircraft: The aircraft nose gear wheel fairing, the nose gear strut and the propeller. Figure 1: View of the aircraft and the damage sustained to the propeller and the nose gear CA 12-12b 25 MAY 2010 Page 3 of 14

4 1.2 Other Damage: None. 1.5 Personnel Information: Nationality South African Gender Male Age 56 Licence Number Licence Type Private pilot licence Licence valid Ratings Yes Night Rating Medical Expiry Date 31 May 2014 Type Endorsed Yes Restrictions Previous Incidents To wear suitable corrective glasses Nil Flying Experience: Total Hours Total Past 90 Days 3.9 Total on Type Past 90 Days 3.9 Total on Type 42.3 TYPE 1.6 Aircraft Information: Aircraft description: The UFM-10 Samba is a two seat, single engine, low wing aircraft with side by side seating. It is all composite in construction. The fuselage is made mainly of carbon laminate with local sandwich construction. The wing is equipped with slotted flaps. The flap positions are 20 and 45. The tail section is of conventional layout. The undercarriage is fixed tricycle with steerable front wheel and the main wheels are equipped with hydraulically operated foot brakes. The main undercarriage is a continuous laminated sprung composite lay-up. The nose gear is made of high quality steel tubes welded together and has a rubber shock absorber to spring the gear. The CA 12-12b 25 MAY 2010 Page 4 of 14

5 aircraft is equipped with integral fuel tanks with a capacity of 13 US gallons (50L) each. Below is ZU-CUF aircraft picture shot sometime before the incident. Figure 2: ZU-CUF aircraft photo Airframe: Type UFM-10 Samba Serial Number 28/10/2002 Manufacturer Service ceiling Maximum take-off weight Empty weight Urban Air S.R.O ft 990 lb 584 lb Date of Manufacture 2002 Total Airframe Hours (At time of Accident) 162 Last Annual (Hours & Date) September 2013 Total Hours Flown 11.8 Authority to fly (Issue Date) 06 September 2013 Authority to fly (Expiry Date) 01 September 2014 CA 12-12b 25 MAY 2010 Page 5 of 14

6 C of R (Issue Date) (Present owner) 03 August 2006 Fuel used Avgas LL 100 Operating Categories Standard Part 24 NTC *NOTE: The AMO that performed the last annual inspection on the aircraft prior to the event was in possession of a valid AMO approval certificate, No 969. All relevant aircraft documentation such as the certificate of registration, the authority to fly and the mass and balance certificates were inspected during the investigation and were valid. Engine: Type Rotax 912 ULS Serial Number Hours since New 162 Hours since Overhaul TBO not reached Propeller: Type Serial Number PA 150 Hours since New 162 Wood comp Varia two blades manufactured from carbon fibre Hours since Overhaul TBO not reached Weight and balance calculation: The aircraft s empty weight, at the day of the incident was determined to be 260kg. The pilot, who was the sole occupant on board at the time of the incident, weighed 92kg. Approximately 80 litres of fuel, equating to 72kg, remained in the aircraft. Together, these brought the total landing weight to 424kg. The aircraft s maximum certified take-off weight (MTOW) limitation was 450kg. 1.7 Meteorological Information: The pilot reported CAVOK weather conditions. CA 12-12b 25 MAY 2010 Page 6 of 14

7 1.8 Aids to Navigation: The aircraft was fitted with standard navigation equipment for the aircraft type as approved at the time of certification. 1.9 Communications: No difficulties with communications were known or reported prior to the incident. In addition, no malfunction on any of the equipment was reported at the time of the incident Aerodrome Information: Aerodrome Location Aerodrome Co-ordinates Aerodrome Elevation Aerodrome Status Plettenberg Bay (FAPG) S E feet (AMSL) Licensed Runway Designations 12/ X 20 Runway Dimensions N/a N/a Runway Used 12 Runway Surface Approach Facilities Asphalt Runway Lighting CA 12-12b 25 MAY 2010 Page 7 of 14

8 Figure 3: Aerodrome layout as on the aeronautical information publication (AIP) 1.11 Flight Recorders: The aircraft was not fitted with a flight data recorder (FDR) or a cockpit voice recorder (CVR), neither was it required in terms of the South African Civil Regulations to be fitted to this aircraft type Wreckage and Impact Information: The aircraft nose gear strut broke and the nose pitched down due to forward momentum, resulting in a propeller impacting the ground and the aircraft coming to a halt. Damage was limited to the nose gear fairing, the nose gear strut and the propeller. CA 12-12b 25 MAY 2010 Page 8 of 14

9 Figure 4: The site where the mishap occurred Figure 5: Closer view of the nose gear strut after the event 1.13 Medical and Pathological Information: There was no evidence of physiological factors or incapacitation that affected the performance of the pilot Fire: There was no evidence of pre or post impact fire Survival Aspects: The incident was considered survivable. CA 12-12b 25 MAY 2010 Page 9 of 14

10 1.16 Tests and Research: Scrutiny onto the aircraft technical documentation revealed no reported hard landings and about 110 landings were registered. Follow up with the FAPG responsible person revealed that the grass apron was well prepared to allow uninterrupted movement of the aircrafts. Meaning that the apron does not have holes or ditches as per the pilot version. The grass was cut or mowed a week before the incident and there was no rain in the area in the past two weeks. This aircraft type nose gear wheel assembly comprises of a 4.00 x 4, 8 ply tyre with a rim width of 2.25 inches. Practically, this nose gear strut shall under no circumstances break as a result of it being steered through a 4 inch diameter hole. The AP provided photos to the investigators since the failed gear strut portions were discarded without metallurgical analysis being conducted. For the analysis of the failed strut, the investigation had to rely solely on the photographs provided by the AP. Attached below are the pictures. Evidence of fracture initiated from the front section of the gear and 45 shear lip Figure 6/7: Closer view of the upper and lower sections of the nose gear strut An analysis of the photos on the upper/lower section of the failed gear strut showed evidence of fatigue failure initiating from the front flat surface extending to the rear and eventually failing in a single cycle ductile overstress mode as witnessed by a 45 shear lip. The main fatigue crack showed a distinctive area that grew over a period of time. The crack had initiated in an external nose gear strut welded joint and developed over an extended period of time without being detected. No aircraft landing gear nondestructive testing (NDT) interval requirement is available Research on fatigue. Fatigue is a phenomenon which results in the sudden fracture of a component after a period of cyclic loading. Failure is the end result of a process involving the initiation and growth of a crack, usually at the site of a stress concentration on the surface. Occasionally, a crack may initiate at a fault just below the surface. CA 12-12b 25 MAY 2010 Page 10 of 14

11 Eventually the cross sectional area is so reduced that the component ruptures under a normal service load, but one at a level which has been satisfactorily withstood on many previous occasions before the crack propagated. The final fracture may occur in a ductile or brittle mode depending on the characteristics of the material. Fatigue fractures have a characteristic appearance which reflects the initiation site and the progressive development of the crack front, culminating in an area of final overload fracture. The initiation site and the shell like markings, often referred to as beach markings because of their resemblance to the ridges left in the sand by retreating waves, are caused by arrests in the crack front as it propagates through the section. The hatched region on the opposite side to the initiation site is the final region of ductile fracture. Sometimes there may be more than one initiation point and two or more cracks propagate. This produces features with the final area of ductile fracture being a band across the middle. This type of fracture is typical of double bending where a component is cyclically strained in one plane or where a second fatigue crack initiates at the opposite side to a developing crack in a component subject to reverse bending. Some stress induced fatigue failures may show multiple initiation sites from which separate cracks spread towards a common meeting point within the section. Attached below on figure 8 is an illustration of fatigue failure. Figure 8: An illustation of a fatigue failure Fatigue strength is determined by applying different levels of cyclic stress to individual test specimens and measuring the number of cycles to failure. Standard laboratory test use various methods for applying the cyclic load, e.g. rotating bend, cantilever bend, axial push pull and torsion. The data are plotted in the form of a stress number of cycles to failure curve, as on figure 9 below. Owing to the statistical nature of the failure, several specimens have to be tested at each stress level. CA 12-12b 25 MAY 2010 Page 11 of 14

12 Some materials, notably low carbon steels, exhibit a flattening off at a particular stress level in which is referred to as the fatigue limit. As a rough guide, the fatigue limit is usually about 40% of the tensile strength. In principle, components designed so that the applied stresses do not exceed this level should not fail in service. The difficulty is a localized stress concentration may be present or introduced during service which leads to initiation, despite the design stress being normally below the safe limit. Most materials, however, exhibit a continually falling curve and the usual indicator of fatigue strength is to quote the stress below which failure will not be expected in less than a given number of cycles which is referred to as the endurance limit. See figure 9 below. Figure 9: An illustratuon of components stress level monitoring 1.17 Organisational and Management Information: This was a private flight The Aircraft Maintenance Organisation (AMO) that performed the annual inspection on the aircraft was in possession of a valid AMO Approval certificate No Additional Information: None Useful or Effective Investigation Techniques: None. CA 12-12b 25 MAY 2010 Page 12 of 14

13 2 ANALYSIS: 2.1 Available information indicated that fine weather conditions prevailed in the area at the time of the occurrence. The pilot was in possession of a valid private pilot s licence as well as a valid aviation medical certificate issued by the SA CAA accredited medical examiner, and was fit to undertake the flight. The flight was conducted in fine weather conditions that had no bearing on the incident. The pilot was familiar with the area and had flown the incident aircraft several times prior to the flight in question. The technical documentation showed that the aircraft was properly maintained in accordance with the manufacture s approved procedures. An analysis of the photos of the failed strut revealed evidence of fatigue failure. 3. CONCLUSION: 3.1 Findings: The pilot was a holder of a valid private pilot s licence and had the aircraft type endorsed in his logbook The pilot s medical was valid, with restrictions to wear suitable corrective lenses The flight was operated as a general aviation private flight under VFR rules Fine weather prevailed at the time and was not considered to have any bearing on the occurrence The aircraft was in possession of a valid authority to fly at the time of the incident The Aircraft Maintenance Organisation (AMO) that performed the annual maintenance inspection on the aircraft prior to the occurrence was in possession of a valid AMO Approval certificate No The failed nose strut pieces were discarded without metallurgical analysis being conducted Analysis of the photos failed gear strut portions revealed a fatigue failure The incident was considered survivable. 3.1 Probable Cause/s: Metal fatigue/fracture. CA 12-12b 25 MAY 2010 Page 13 of 14

14 4. SAFETY RECOMMENDATIONS: 4.1 None. 5. Appendices 5.1 None. CA 12-12b 25 MAY 2010 Page 14 of 14