Because the aircraft was American-made, the United States
National Transportation Safety Board (NTSB) had observer status for the investigation. Asked for confirmation on the claims, NAMA decided to deny the reports, stating that "it is not our responsibility to do so".
Engine failure The crew of Flight 0992 had reported dual-engine failure just minutes before it crashed onto the packed residential area of Iju-Ishaga. Crash site inspection confirmed that both engines had not generated much power as the observed damage was consistent with low-to-no RPM at the time of impact. Further examination was therefore needed to confirm the source of the failure. As the engines were overhauled by the Miami-based Millenium Engine Associates Inc, both engines were sent to the United States for a teardown. During the teardown of both engines, investigators discovered several fractures in the fuel lines of the left engine. The fuel feeder lines had fractured flush, exhibiting shear lips. The primary fuel manifold had bent downwards. The secondary fuel manifold had twisted. Its fuel transfer tube had nearly blocked the flow of the fuel, reducing the diameter of the fuel nozzle. On the right engine, the secondary fuel manifold had collapsed and there were fractures on the primary fuel manifold. The fuel lines of both engines had also fractured and bent on its fittings, the No.5 and No.6 fittings. The AIB wanted a closer examination on the engines. Subsequently, the engines were shipped back to Lagos but Millenium only sent the left engine, while the right engine was not shipped back, for reasons unknown. As the AIB conducted tests on the left engine, metallurgical analysis on the manifolds revealed that both of the manifolds had been overstressed. Despite the findings, there was no evidence that the fracture had occurred prior to the crash. Combined with the absence of the right engine, the team hit a dead end. They eventually began to shift their attention towards the fuel pumps. Investigators eventually discovered that there was a possibility of a microbial growth in the fuel supply. This was caused by the storage of the fuel, which was exposed to effects of the sun. This exposure might have caused the temperature of the fuel to rise to as high as . Added with the typically high humidity in the tropical climate setting, this eventually promoted fungal growth, which would have led to fuel tank corrosion, fuel filter and fuel pipe obstruction, and erratic indication of the fuel tank. The preliminary fuel sample analysis, however, didn't find any positive contamination of the fuel. Despite this, and due to the earlier findings of possible microbial contamination, investigators issued a recommendation for Dana Air to conduct a visual inspection for possible fuel contamination and to use biocidal treatment for the matter. Apart from the fuel samples, there was also suspicion of a certain flying culture in Dana Air, which was called by the investigators as "peculiar fuel management". According to the investigation, the team discovered that there was a certain flying culture for every Dana Air MD-83 flight in which, during an aircraft's approach to its intended destination, the fuel in the centre fuel tank was almost entirely depleted, while the fuel tanks in the wings remained full. The fuel tanks in the wings were, somehow, not used at all by the pilots. Due to this finding, investigators issued another recommendation to Dana Air, which stated that a minimum of of fuel must be maintained in the centre fuel tank of the aircraft on landing at any destination. Though there was no evidence that fuel exhaustion was the cause of the crash [the recordings revealed that the crew had reported a total of of fuel on board], the investigation concerning this issue remained ongoing, eventually resulting in a major breakthrough.
Breakthrough On 6 October 2013, Dana Air Flight 0348, an MD-83 flying from
Port Harcourt to Lagos, registration 5N-SAI, reported troubles with the aircraft's engine during its climbing phase. The crew reported the exact same problem that the crew Flight 0992 had faced - an engine that was unresponsive with the commanded thrust. The pilot had noticed the abnormality during the previous leg, and thus, he asked the flight engineer to observe with him in the cockpit. During the climb, he noticed that the engine had suffered slow acceleration with it taking around 30 seconds to accelerate from idle power to about 60% rather than the usual 6 seconds. Contrary to the action of Flight 0992, the crew of Flight 0348 reported the problem to the ATC and declared an emergency. The aircraft landed safely, and the engine was sent for a teardown. The engine of Flight 0348 had just been overhauled by the contractor on 11 April 2013. As the engines of 5N-RAM and 5N-SAI had been overhauled by the same company, the Millenium Engine Associates Inc (now renamed as Global Engine Maintenance LCC), the engine was shipped to Miami for further examination. The results from the teardown revealed that the engine of 5N-SAI (Flight 0348) had suffered the exact same damage as the engines of 5N-RAM (Flight 0992). The malfunctioning engine of the aircraft, the right engine, had suffered fractures on its fuel manifold. The said manifold had fractured on the secondary inlet tube, causing the tube to be separated from its fuel nozzle. The resulting fuel leak could be seen from the engine's fan, and the engine was also not responsive to the commanded thrust. The AIB discovered that the fuel manifold had been improperly installed by Millenium. The protective fairings of the tube had been installed in a way that was not in conformity with the correct standard that had been issued by Pratt & Whitney Canada, causing the fuel lines to be severed.
Faulty maintenance Pratt & Whitney Canada was fully aware of the possibility of the secondary fuel manifold fractures. The fractures would have resulted in fuel leaks, causing significant problems for flights. In one instance, in 2001, there was a reported engine fire due to the issue. As such, Pratt & Whitney issued a service bulletin to fix the problem. In October 2003, Pratt & Whitney addressed all operators to replace or modify the secondary fuel manifold with new tube material. The new tube would have reduced the occurrence of fractures due to the significantly greater fatigue life. According to the history of the aircraft's engine, the right engine had been overhauled in accordance with the bulletin by Volvo Flygmotor in 2005. At the time, the engine was still in operation with
Alaska Airlines. The left engine, however, was not overhauled. It was sold to Dana Air in its original condition. The left engine was eventually overhauled by Millenium Engine Associates Inc in August 2011. The right engine was eventually overhauled by Millenium as well in September 2011. Both of the overhauls, however, were not carried out in accordance with the bulletin. The company also installed the manifold incorrectly, putting more
bending stress on the secondary manifold inlet tubes. The installation of the fairing, a part of the manifold, was also not in accordance with the correct procedure. Due to the procedure, the fairing was not sealed tightly. The loose fairing remained open to the side. Following the combustion of fuel, the engine created hot air. The loose fairing then caught the bypassing air and acted like a sail, creating significant drag. The fuel inlet tube was then pulled by the loose fairing. Combined with the bending stress that had been put upon by the improper installation of the fuel manifold, the unchanged tube material of the fuel manifold, and its exposure to hot air, the fuel inlet tube eventually cracked. The fuel lines inside the tube then collapsed, causing a significant drop in fuel flow and the subsequent slow acceleration of the aircraft's engines. Investigators however could not explain why the right engine had also suffered the exact same failure as the left engine, even though the engine overhaul had been carried out with the supposed procedure. During the investigation, the pilot of Flight 0348 stated that there were other Dana Air aircraft that had suffered slow acceleration, all of which had been overhauled by Millenium. The finding prompted the Nigerian Civil Aviation Authority (NCAA) to immediately order every aircraft with engines installed by Millenium to be sent to an NCAA-approved engine shop. Until the issue was resolved, the aircraft involved would not be allowed to continue operation. Flight simulations were conducted in the
Pan Am International Flight Academy (PAIFA) to investigate whether the accident was preventable or not. After simulating every possible scenario in Flight 0992, all of the results indicated that the crash was not inevitable. It was evident that had the crew taken the appropriate decisions and measures during the emergency, the crash could have been avoided. Even in the worst-case scenario of a possible crash, the number of casualties on board could have been minimized. Despite the dual-engine failure emergency, the condition was actually still within limits for permitting safe operation of the aircraft.
Poor decision-making It was evident that the actions of the crew had a significant impact on the crash of Flight 0992. Throughout the entire flight, the crew didn't adhere to the correct procedure for an engine failure. The checklist for an engine failure emergency was not used by the crew. Had they read the checklist, then the crew would have diverted the aircraft to the nearest airport in the area. There were at least three airports near Flight 0992;
Ilorin,
Ibadan and
Abuja.
Ibadan was actually listed in the checklist as an official alternative airport. Since the crew didn't read the checklist, all said airports were ignored. The first engine failure occurred as early as 17 minutes into the flight. The flight from Abuja to Lagos typically takes a little over an hour. Thus, the crew had plenty of time to declare an emergency over the issue, but they delayed their emergency declaration until the failure of the second engine. They did not mention the occurrence of an engine failure to the ATC. The decision to not declare an emergency over the engine failure was possibly influenced by Captain Waxton's fear of being investigated by Nigerian authorities. In the CVR recording, he could be heard saying that if they declared an emergency, then the Nigerian authorities would investigate them. At one point, Captain Waxton asserted that the aircraft could not quit on them. Recording analysis also revealed a steep cockpit-authority gradient between the flight crew. Captain Waxton was far more experienced on the MD-83 than First Officer Rathore. As such, First Officer Rathore became less assertive. During the descent to Lagos, First Officer Rathore stated that they should delay the descent. Captain Waxton overruled him and asked to descend. According to the AIB, had the pilots maintained a high altitude as suggested by First Officer Rathore, then the flight would have had a better chance of reaching Lagos. As a result of the decision not to delay the descent, the aircraft was ultimately nearer to the ground than it would otherwise have been. The crew was consequently left in a difficult situation, as the final approach required additional thrust. The airspeed, however, kept decaying. Captain Waxton could be heard panicking, repeatedly stating that he "didn't want to stall the plane". Since they did not read the appropriate checklist for engine failure emergency, which would have outlined the correct procedures so that any kind of difficulties would have been minimized, the crew incorrectly configured the aircraft. They decided to extend the gear and flaps, further increasing drag, and reducing the aircraft's ability to maintain its airspeed. They eventually realized that their speed had dropped further, but by this point the aircraft was already too low.
Captain Waxton and Dana Air Both flight crew members of Flight 0992 were of foreign origin. A comprehensive review on the recruitment process of both pilots was then conducted. The review eventually revealed several findings. While there was no peculiar notes or documents on First Officer Rathore, documents retrieved by the Nigerian AIB revealed that Captain Waxton's flying license had been suspended by the United States
Federal Aviation Administration (FAA) in 2009 for misdemeanours related to a heavy landing and an unreported panel fix. The revalidated license issued to him by
Nigerian Civil Aviation Authority (NCAA) was stamped but was not signed by any NCAA official. The investigation also revealed that Waxton had been given comments by his pilot instructor to improve his performance. However, the AIB could not find any documents to show that Waxton had indeed improved his flying performance. There was also no documented evidence that Captain Waxton had followed the mandatory requirements for recruitment, including selection interview and background check. All of the findings indicated that Waxton had been hurriedly hired by Dana Air. The performance assessment also indicated that he had been hurriedly trained to immediately fly the MD-83, even though there were plenty of notes about Waxton's unsatisfactory performance. Findings related to Captain Waxton's recruitment eventually led to more discovery on the corporate culture within Dana Air. The Quality Department of Nigeria's Dana Air had never been involved in the recruitment process of foreign pilots. Interviews by former pilots further revealed issues regarding the maintenance culture within Dana Air. According to the interviews, there was a habit for Dana Air crew to not enter flight defects into the technical logbook. Several of these malpractices had been conducted by senior Dana Air pilots. Most of the interviewees were pilots who had either been kicked out of the company or had decided to quit due to the issues. The Nigerian Civil Aviation Authority, the regulatory body for Nigerian aviation safety, was supposed to oversee the operation of every airliner in Nigeria. The fact that there were malpractices inside the aviation industry proved that there was ineffective oversight on airliners in the country. The AIB eventually asked the NCAA to intensify the safety oversight of the country's aviation sector.
Final report On 13 March 2017, a 210-page final report by Nigeria's AIB into the crash was released and made public. The investigation identified the following Probable Causal Factors: 1. Engine number one lost power 17 minutes into the flight, and thereafter on final approach, engine number two lost power and failed to respond to throttle movement on demand for increased power to sustain the aircraft in its flight configuration. 2. The inappropriate omission of the use of the checklist, and the crew's inability to appreciate the severity of the power-related problem, and their subsequent failure to land at the nearest suitable airfield 3. Lack of situational awareness, inappropriate decision making, and poor airmanship The AIB issued several recommendations to the involved parties, mainly to Dana Air. Nigeria's NCAA was ordered to intensify its oversight, particularly on Maintenance, Repair and Overhaul (MRO). The FAA was asked to ensure that Pratt & Whitney re-categorize the issuance of the service bulletin to mandatory and to re-design the shimming and installation of the manifold assembly so as to prevent incorrect installation. == Aftermath ==