Kennet Ayala AMNT 260 Module 5 Inicdent Analysis PL1
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G73-T Aircraft Structural Failure Analysis
Kennet Ayala Guadalupe
Embry-Riddle Aeronautical University
AMNT 270: Airframe Structures and Applications
David McClelland
August 28, 2023
1
G73-T Aircraft Structural Failure Analysis
Incidents within the aviation industry caused by an electrical failure, engine failure, or other circumstances that are outside the pilot’s control represent severe issues for a series of aircraft. When an airplane undergoes a system failure, this event can serve alert technicians and manufacturers since the same issue could affect another aircraft or a significant number of airplane manufactured by the same company and of the same model. On or about August 17, 2012, around 2320 hours, an incident was reported around the vicinity of London Heathrow Airport
(AAIB Field Investigation, 2014)
. An engine failure resulted in the final cause of the incident, caused by a series of electrical failures
(Lockerby, 2014)
. On August 17, 2012, an airplane, Boeing 747-4H6, operated by Malaysian Airlines,
left London Heathrow Airport to Kuala Lumpur International Airport. The total of personnel aboard the aircraft was 340 passengers and a total of 22 crew members among flight and cabin crew
(AAIB Field Investigation, 2014)
. S
hortly after the departure, a significant vibration was noted on one of the engines; the Boeing 747 was equipped with four Pratt & Whitney engines
(Lockerby, 2014)
. As the airplane climbed up, all indications were up to standard, but the engine number 2 vibration indicator was over the regular readings; it read 2.3, while all other engines’ vibration indicators read 0.9. As an attempt to troubleshoot and fix the issue, the commander disconnected the autopilot and verified all flying controls and indicators before reengaging the autopilot. As the airplane continued to climb up, the vibration increased, and then an abnormal reading on the fuel flow for engine number 2 was noted. Pilots proceeded to place the engine in idle mode, resulting in a decrease in vibration
(AAIB Field Investigation, 2014)
.
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After placing engine number 2 on idle mode, pilots noticed an increase in the oil pressure
gauge for engine number 2; shortly after that, a loud noise was heard, and an engine fail message
was displayed. At the moment of the failure message, the pilot requested to level at the current altitude FL190 failed and was shut down by the crew
(AAIB Field Investigation, 2014)
. Once the crew noticed the failure
and requested to level the aircraft, the pilots stated that the flight was returning to Heathrow Airport. The pilots decided to discard fuel, which took around 45 minutes,
and the airplane began to approach the airport
(AAIB Field Investigation, 2014)
. Given the conditions, the limited visibility, the failure of engine number 2, and the current weight of the plane, the pilots informed ATC that an auto-landing was going to be conducted. Once the airplane reached an altitude of 3,200 AMSL, the crew engaged the other two autopilot controls. Upon reaching 3,000 AMSL, all three autopilot control disengaged, all lights and control in the cockpit started to flicker, and a large number of failure messages were displayed
(AAIB Field Investigation, 2014)
. Subsequently, the flight commander began to manually pilot the aircraft while approaching the runway; approximately 30 seconds later, the auto thrust disengaged. Pilots decided that the best way to react to the situation was to approach the runway instead of continue
experimenting and managing the failures
(AAIB Field Investigation, 2014)
.
Since the engine failure message was displayed, there was evidence of electrical failures. The commander was concerned
about a major failure on all displays and that the aircraft landing could have become more difficult. When the auto thrust disengaged, the pilot decided that the best course of action was to land the aircraft as soon as possible. The commander attempted to engage the auto thrust one more time, but the attempt was unsuccessful. After all the technical issues and failures
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experienced by the flight crew since the airplane departed London Heathrow Airport, the pilots were able to land the airplane safely with no passengers or crew members injured
(AAIB Field Investigation, 2014)
. The Boeing 747-4H6 presented mechanical issues since the first moments after departure;
the display continued to flicker continuously until touchdown. Although the flight control display presented several failure messages and its operation was in abnormal conditions, the standby instrument did not present failure or issues during the landing. On the morning after the events, experts examined the airplane. Although there was minimum physical evidence once the electrical system was evaluated, utilizing the Centralized Maintenance Computer (CMC), the report included several faults related to engine number 2 and its shutdown; additionally, the Present Legs Faults presented other faults related to the aircraft electrical system and faults related to the loss of power of AC Bus two
(AAIB Field Investigation, 2014)
. The CMC history report showed two fault messages associated with the electrical bus tie breaker, both faults indicating a difference in current, resulting in a tripped breaker; both faults were within two minutes of each other. In addition, two months before the incident, the CMC showed the same fault, bus tie breaker four tripped due to a difference in current. The electrical network system on the B747 consists of four networks. Each network provides 115 V Alternating Current (AC) and 28 V Direct Current (DC). In addition, a separate network acts as an emergency power source, a standby power source, to power up the most critical and essential flight controls and system when the primary power source is lost
(AAIB Field Investigation, 2014)
.
Results of the examination proved that while the aircraft was approaching the runway, the
Integrated Drive Generator (IDG) for engine number two was offline, and Bus Control Unit 1 commanded Bus Tie Breaker one and three to open, enabling IDG four to provide power to AC
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bus 2. Tests were conducted repetitively after the incident to simulate and re-create the same conditions that caused the electrical failure, resulting in the loss of power on engine number two. Technicians utilized the Autoland Unique Test of the CMC to verify that the correct signals were
going through the electrical system. Technicians noticed that BTB three operation was outside the usual parameters and conditions. A series of electrical components were removed for further investigation and testing, and no anomalies were found except on BTB three
(AAIB Field Investigation, 2014)
.
Throughout the course of the flight, the flight controls and instruments inside the cockpit were operating in an unusual way. As stated previously, the BTBs interconnect the different AC buses, and the continuous operation of the standby instrument display served as an indication that one of the BTBs was not working correctly. While examining BTB three, only some of the primary and auxiliary contacts were transiting from a closed to an opened, tripped position. Examination of the main contacts revealed that they exhibited very little wear for a unit of its age (14 years), although there were indications that the contacts had been filed or buffed at some point after manufacture. BTB 3 had been installed on the aircraft since delivery and the component history records indicated that it had never been removed or overhauled.
(AAIB Field Investigation, 2014)
After an electrical examination and physical examination were conducted, the findings concluded that the reason for the contacts not completing the transition from a closed phase to a closed phase was due to a nut on one of the guide posts of the armature not being adequately secured. Technicians concluded that this could have been a result of airframe vibration or possible dissembling of the BTB after initial installation by the manufacturer
(AAIB Field Investigation, 2014)
.
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The Boeing 747-4H6, departing from London Heathrow Airport, passed through a series of failures; pilots received several message failures, loss of autopilot control, failure on flight control displays, and a loss of power of one of the four engines. Technical testing and investigation results concluded that all faults and failures were caused by one of the Bus Tie Breakers (BTB). Furthermore, it was concluded that the reason which caused the BTB three to cease its operation was a loose nut within the armature of the mentioned BTB.
References
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AAIB Field Investigation. (2014, April). AAIB Bulletin: 4/2014.
Retrieved from https://assets.publishing.service.gov.uk/media/5422f72e40f0b613420005d9/Boeing_747-
4H6__9M-MPL_04-14.pdf
Lockerby, P. (2014, April 14). Boeing 747 AAIB Accident Report Reveals Electrical Failures. Retrieved from https://www.science20.com/the_chatter_box/blog/boeing_747_aaib_accident_report_reve
als_electrical_failures-134042#.