Technical failure

A loss of engine power due to internal failure.

Conclusions
Findings as to Causes and Contributing Factors:
1. The right engine lost power when the intermediate spur gear on the torque sensor shaft failed. This resulted in loss of drive to the high-pressure engine-driven pump, fuel starvation, and immediate engine stoppage.
2. The ability of the left-hand No. 2 ejector pump to deliver fuel to the collector tank was compromised by foreign object debris (FOD) in the ejector pump nozzle.
3. When the fuel level in the left collector tank decreased, the left fuel level warning light likely illuminated but was not noticed by the crew.
4. The pilots did not execute the fuel level warning checklist because they did not perceive the illumination of the fuel level left tank warning light. Consequently, the fuel crossfeed valve remained closed and fuel from only the left wing was being supplied to the left engine.
5. The left engine flamed out as a result of depletion of the collector tank and fuel starvation, and the crew had to make a forced landing resulting in an impact with a concrete noise abatement wall.
Findings as to Risk:
1. Depending on the combination of fuel level and bank angle in single-engine uncoordinated flight, the ejector pump system may not have the delivery capacity, when the No. 1 ejector inlet is exposed, to prevent eventual depletion of the collector tank when the engine is operated at full power. Depletion of the collector tank will result in engine power loss.
2. The master caution annunciator does not flash; this leads to a risk that the the crew may not notice the illumination of an annunciator panel segment, in turn increasing the risk of them not taking action to correct the condition which activated the master caution.
3. When cockpit voice and flight data recordings are not available to an investigation, this may preclude the identification and communication of safety deficiencies to advance transportation safety.
4. Because the inlets of the ejector pumps are unscreened, there is a risk that FOD in the fuel tank may become lodged in an ejector nozzle and result in a decrease in the fuel delivery rate to the collector tank.
Other Findings:
1. The crew’s decision not to recover or jettison the birds immediately resulted in operation for an extended period with minimal climb performance.
2. The composition and origin of the FOD, as well as how or when it had been introduced into the fuel tank, could not be determined.
3. The SkyTrac system provided timely position information that would have assisted search and rescue personnel if position data had been required.
4. Saskatoon police, firefighters, and paramedics responded rapidly to the accident and provided effective assistance to the survivors.

Emergency landing after the engine caught fire in flight for unknown reasons.

It is believed that the loss of control on final approach was the consequence of the failure of both right engines n°3 and 4.

Comprehensive technical examination of the nose wheel steering on OY-NPB uncovered no single causal factor, but some indications of unsatisfactory maintenance. Irregularities that alone or in combination could have caused a temporary fault with the steering were present. The Accident Investigation Board believes that a temporary fault caused the nose wheel to unintentionally lock itself in a position towards the right. No other defects or irregularities that could explain why the aircraft veered off the runway were found. The AIBN reported that the same fault had occurred 6 days earlier as well, during that encounter the captain managed to disconnect nose wheel steering quickly enough to regain control. Maintenance could not replace the fault and the aircraft was released to service.

The following findings were identified:
- The LEFT MAIN LANDING GEAR ASSEMBLY (PN D23189000-19 and SN MN1700) collapsed, failing with 5,130 cycles after the last overhaul.
- A specific component (pin) of the assembly connecting the landing gear to the airframe, the AFT PIVOT PIN (P / N D61000, S / N 25), broke on account of fatigue, whose onset was facilitated by a machining process carried out in the pin section transition region.
- The ANAC-approved ATR72 Series Aircraft Maintenance Program of the TRIP Linhas Aéreas company read that the LEFT MAIN LANDING GEAR ASSEMBLY had to undergo overhaul every eight years or 18,000 cycles.
- On 27 February 2009, the PR-TTI landing gear was removed and, on 09 March 2009, was sent to be overhauled by the AV Indústria Aeronáutica Ltda. It had 31,684 cycles since new and 18,095 cycles since the last overhaul.
- AV Indústria Aeronáutica Ltda. was homologated for conducting such inspection, as specified in the List attached to the Addendum, Revision no. 11, dated 05 January 2009, and accepted by means of the Official Document no. 0173/2009-GGAC/SAR, issued by the Civil Aviation Authority.
- The AV Indústria Aeronáutica Ltda. company disassembled the legs of the landing gear, and outsourced some of the tasks for not possessing technical knowledge and/or appropriate machinery (necessary for the process of reconditioning the AFT PIVOT PIN (D61000 SN 25).
- Two of the three companies outsourced by AV Indústria Aeronáutica Ltda. were not homologated by the Civil Aviation Authority.
- The AV Indústria Aeronáutica Ltda. company conducted external audits of the three companies involved in the overhaul.
- The audits carried out by AV Indústria Aeronáutica Ltda. were not sufficient to identify that the contractors lacked qualified personnel, manuals and the machinery necessary to work with aeronautical products.
- The AV Indústria Aeronáutica Ltda. Technical Manager did not supervise the overhaul inspections and services performed by the contracted companies.
- The AFT PIVOT PIN (D61000 SN 25) is part of the assembly that connects the landing gear to the airframe.
- All revision tasks were described in the manuals of the manufacturer.
- The AFT PIVOT PIN (D61000 SN 25) failure-analysis report stated that the PRTTI aircraft left main landing gear collapsed on account of fatigue, whose onset was facilitated by a machining process carried out in the section transition region of the pin.
- The manufacturer's maintenance manual did not refer to any machining work in that region of the pin.
- In only one stage of the pin reconditioning process was it possible to observe that a machining task was required, namely, the Grinding of chromium.
- The lack of capacitation and training of the subcontractors’ professionals for handling aircraft material hindered the execution of an efficient maintenance work as prescribed by the manufacturer's manual, culminating in inadequate machining during the maintenance process.
- The lack of an effective process of supervision, both on the part of TRIP Linhas Aéreas and on the part of the other contractors and subcontractors allowed the existing maintenance services’ latent failures not to be checked and corrected, in a way capable of subsidizing, in an adequate and safe manner, the execution of the landing gear maintenance service.
- The process of supervision of the TRIP Linhas Aéreas and the AV Indústria Aeronáutica Ltda. companies by the Civil Aviation Authority, prescribed by specific legislation in force, was not enough to mitigate the latent conditions present in the accident in question.
- According to the technical opinion issued by the DCTA, the AFT PIVOT PIN (D61000 and SN 25) presented fracture surfaces with ± 45º inclination, as well as a flat area with multiple initiations, indicative of a fracture mechanism related to fatigue. In examinations of the external surface of the pin, in a region close to the fatigue fracture, cracks were observed that had initiated from scratches created by an inadequate maintenance machining process. In the region where the overload-related fracture occurred, it was also possible to identify that the machining process had modified the profile of the part in the section transition region, by producing a depression. Thus, it can be said that the AFT PIVOT PIN (D61000 and SN 25) of the PR-TTI left main gear broke on account of fatigue, whose onset was facilitated by an inadequate machining process that had been performed in the section transition region of the pin.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The captain’s decision to continue the flight with the left engine backfiring, resulting in an engine fire shortly after takeoff. Contributing to the accident were the captain’s decision to continue the flight following a report of black smoke trailing the airplane and in-flight fire damage to the left wheel brake system, resulting in a loss of directional control during an emergency landing.