Flight 232 and the Tragedy
Flight 232 from the United States was engaged in a terrible aviation catastrophe twenty-eight years ago. Thankfully, 185 of the 285 passengers miraculously escaped due to the successful emergency management aircrew's containment, but 111 passengers died in the tragedy. As a result, Flight 232 made an emergency landing northwest of Sioux City, Iowa, USA. Following the disaster, investigations took a 360-degree spin to leave no stone unturned (Aronstein, Hirschberg, & Piccirillo, 1998). Finally, the investigations contained riveting and integrative scientific detective and investigative features. For instance, the employment of super-secret labs to dive deepest into the hearts of every smaller detail that could lead to the establishment of factors that brought the plane down. This paper, therefore, is a comprehensive review of the Sioux City Flight 232 focusing on accident investigation of turbine engines, understanding of the causes, findings, as well as recommendations.
Investigation Regarding the Turbine Engines
According to (Aronstein, Hirschberg, & Piccirillo, 1998), investigations established the probable cause of the accident to be directly dependent of the human negligence. For instance, the investigations revealed that their inadequate considerations in regards to human factors limitations in aspects of inspection as well as quality control procedures that the United States Airline employed to inspect the engine overhaul. Such limitations led to the failure of the then assigned inspection and quality assurance personnel to detect fatigue crack relative to metallurgy defect. Worst still was the realization that such undetected defect existed in the critical region of the Stage 1 fan disk. The fan disk had been manufactured by the General Electric Aircraft Engines. Following the undetected metallurgy defect, the investigative and detective team noted that separation hence fragmentation occurred due to the possible forceful discharge of uncontained stage 1 rotor assembly parts originating from Number 2 engine. The inefficiency and ineffective functioning of the number 2 engine resulted in loss of three fundamental hydraulic systems responsible for powering the aircraft's flight controls.
Understanding the Causes
Examination of the reconstruction process of Number 2 Engine Stage 1 Fan Disk revealed that the disk had two fractures. The fractures were due to mechanical deformation in which approximately one-third of the rim was noted to have been separated from the disk. Thus, features observed on the circumferential fracture typically revealed scenarios of overstress separation resulting from multiple origins concluded to be possibly the radius between the disk arm and the web. Similarly, the near-radial also had fractures suggestive of overstress (In Karakoc et al., 2016). In addition, metallurgy evaluations showed that fatigue crack initiated near a small cavity as observed on the surface of the disk bore.
Other Number 2 Engine Hardware
Other Number 2 engine hardware as revealed by findings of the metallurgy investigations including the fan forward shaft, engine booster disk, and the No.1 ball bearings, as well as the bearing support, had fractures and deformations. Such deformations were consistent with the initial separations of the Stage 1 fan disk. Furthermore, there were revelations of damaged patterns on the aforementioned engine components as well as the containment ring indicative of smaller pieces of the disk departing the aircraft towards the left while the larger pieces went towards the right side of the aircraft. Hence, the failure of No.2 engine affected the functionality of the three hydraulic systems which are imperative to the aircraft's flight controls.
Understanding the Aircraft's Flight Controls
In understanding the aircraft's flight controls and the hydraulics, the report by (In Korovin, 2011) regarding the accident revealed that the flight controls of Flight 232 (McDonnell Douglas DC-10-10-N1819U) primarily consisted of inboard and outboard ailerons, two-section elevators, and rudders respectively. On the other hand, the secondary flight controls consisted of leading edge slats, the spoilers, both inboard and outboard flaps dual rate stabilizer that is movable. The flight control surfaces are thus segmented to achieve redundancy such that the primary and the secondary control surfaces function with two to three independent hydraulic systems. Indeed, the plane stands not chance to maintain flight if the hydraulic systems are damaged or interfered with through any mechanical breakdown.
Hydraulic System Damage
Correspondingly, the three hydraulic flight control systems function independently of each other such that the plane remains operational in the absence of one or two of the hydraulic systems. Unfortunately, in the case of flight 232, two or all the hydraulics experienced failure. Yet based on its hydraulic system design, the manufacturer demonstrated in the presence of the FAA in compliance with the 14 CFR 25.905 that no single power malfunctions or the combination of various sources of failures could interfere with the operations of the aircraft. According to (Galison & Roland, 2000), hydraulic system damage caused interference to the flight. For example, during the reconstruction investigative process, it was identified that part of the right horizontal stabilizer was not at the Sioux City Airport where the plane crashed. Nevertheless, photographs showed that the parts were missing prior to the plane landing. Therefore, the missing portion contained the No.1 hydraulic system tubing responsible for the supply of fluid to both inboard and outboard elevator actuators.
Findings on the Crash of Flight 232
General findings for the accrued factors that lead to the crash of Flight 232 include circumstances where the plane experienced an uncontained failure in the No.2 engine, affecting the stage 1 rotor disk assembly. Consequently, the No.2 engine severed to affect the No.1 and No.3 hydraulic system lines respectively. On the same note, forces discharged thereof by the engine damaged the No.2 hydraulic system, which made the three independent hydraulic systems malfunction. Thus, the pilots experienced difficulties in maintaining the plane at a balanced state owing to the typical design of the plane to acquire flight based on the power provided by the three hydraulic systems to necessitate flight control. Technically, the pilots managed to keep the plane flyable asymmetrically with the thrust provided by No.1 and No.3. Unfortunately, safer landing virtually became impossible since the plane had lost all its conventional flight control (In Korovin, 2011).
Recommendations
Based on the findings and understanding of the cause, it is recommended that airline companies, in compliance with the FAA safety board standards, should develop together with their respective manufacturers the alternative methods of conducting an inspection in regards to the bore areas of the engine. For instance, the engine fan stage 1 rotor disk in order to be able to detect any presence of surface cracks. There should be constant evaluation of every certified turbine engine in order to identify the engine parts or rather the components which in the event of any fracture hence separation could possibly be a threat to the entire airplane operations. Nonetheless, the inspection personnel should make sure to evaluate the components on the basis of performing damage tolerance.
The United States airline should reinforce their training programs to ensure that the human resource responsible for inspections is highly qualified to detect any form of cracks or defects in order to eliminate possibilities of human errors and limitations. It is a recommendation that it should be a requirement that turbine manufacturers be able to perform macroeth inspection concerning the final part shape for the critical alloy rotating components through the manufacturing process. This follows the realization that many deformations and stress stemmed from aspects of metallurgy. Finally, it is recommended the investigation outcomes be used in conducting system safety reviews for the recently certified airplanes. The safety review would ensure that possible considerations are given to aspects of redundancy to protect power sources essential for the flight control and engine operations. Moreover, the manufacturers should have longer record-keeping technologies to promote traceability critical of lost portions of aircraft.
Conclusion
The unforgettable extraordinary triumph over the plane tragedy and ingenuity of human over the technical mechanical breakdown of Flight 232 remains an imperative masterpiece that aviation colleges and airlines crew will live to remember. Gratifying investigation results, as reported by the safety board, were that the accident emanated from a catastrophic separation of the stage 1 disk from the No.2 engine. Consequently, there were separation, fragmentation, and forceful discharge of the uncontained stage 1 fan rotor parts which impaired the functionality of the three hydraulic systems, hence the flight crew faced difficulties in attempts to land the plane using differential power from the remaining two engines for partial control of the plane. Unfortunately, the plane crashed during attempts of the emergency landing at Sioux City Airport.
References
Aronstein, D. C., Hirschberg, M. J., & Piccirillo, A. C. (1998). Advanced tactical fighter to F-22 raptor: Origins of the 21st century air dominance fighter. Reston, Va: American Institute of Aeronautics and Astronautics.
Galison, P., & Roland, A. (2000). Atmospheric Flight in the Twentieth Century. Dordrecht: Springer Netherlands.
In Karakoc, T. H., In Ozerdem, M. B., In Sogut, M. Z., In Colpan, C. O., In Altuntas, O., & In Açıkkalp, E. (2016). Sustainable aviation: Energy and environmental issues.
In Korovin, I. (2011). Drama in Sioux City: The crash of United Airlines flight 232.
