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EL AL Flight 1862 is a Boeing 747 cargo plane of the Israeli airline El Al. The failure of flight EL AL 1862 was mainly due to the defective fuse pins. It was discovered after the crash that the only reason why the fuse pins failed, was due to metal fatigue. When engine #3 separated from the wing, it shot forward and in a split moment, collided with engine #4. This action resulted in 10m of the RH(Right hand) wing's leading edge to be damaged. In addition, hydraulic system #3 and #4 became malfunctioned and caused the pilot to have more difficulties in controlling the plane. After several damages to the plane, the pilot finally lost all his control to prevent the plane from rolling to the right, causing the plane to crash into the apartments after it reached a 90 degree angle. Actions such as improvement of the pylon to wing connections, improving the training of the flight crew and upgrading the warning system were then taken after the crash as it created an awareness of the danger of compromising on the small details of an aircraft.
The purpose of this report is to present the details of the tragedy of EL AL flight 1862, which happened in October 1992. This report will also identify the structural failure of the 747 which led to the crash and provide the various measures that will prevent such tragedy from happening again.
On October 4, 1992 at 6.20pm, EL AL flight 1862, a 747-200 cargo aircraft, took off smoothly from Schiphol airport near Amsterdam and climbed to an altitude of 6500 feet. However at 6.27pm, engine number three and the pylon became separated from the right wing due to the faulty fuse pins at the mid spar section. The fuse pins were found to have failed as a result of metal fatigue. (More information of the failure of fuse pins can be found at section 2.0.)
In addition, engine number four was struck by engine number three, causing the aircraft to lose both engines. During the separation of the two engines, the right wing leading edge became severely damaged. This damage and the loss of the two engines then caused the main pilot to struggle in the controlling of the aircraft as the aircraft rolls to the right. An emergency landing was hence required. The pilot started the landing by first circling around Amsterdam to reduce his altitude which was required for landing. However, as the aircraft became too hard for the pilot to manage, it spiraled out of control and crashed into an apartment in Amsterdam. This disaster resulted in a total of 43 casualties with 39 of the victims found on the ground. This misfortune has since been the worse aviation disaster in Netherlands.
The information obtained is from websites of international organizations. These websites include the Nederland Aviation Safety Board, National Aerospace Laboratory (NLR), Federal Aviation Administration (FAA) and a video from National Geographic Channel.
The areas of focus of this report, includes the structural failure which caused the crash, the sequence of events which led to the crash, the preventive measures and recommendations and lastly, the summary of the report.
Analysis of Fuse Pins in Engine #3
One of the main reasons of the crash was the fuse pins. This section will cover the details of how the fuse pins work and the cause of the fuse pins failure.
2.1 Function of Fuse Pins
The fuse pin is made from a high strength low alloy steel. It is a 14cm long hollow cylindrical steel bolt which is situated between the lugs of the pylons which holds the engines together.
If intense load occurs on the engine and pylon, the fuse pins, theoretically will start to shear off. The thin walled locations (Figure 1) within the fuse pin are designed to build up stresses at these locations. Hence, allowing a clean separation of the engine from the wing without doing any damage to the wing structure. Details of the function of fuse pins were taken from Wanhill & Oldersma (1997).
Figure 1. Thin walled locations on fuse pin (Wanhill & Oldersma 1997).
2.2 Cause of Fuse Pin Failure
The main reason for the crash of the plane was the defective fuse pins. The inboard midspar fuse pin failed by shear overload, while the outboard midspar fuse pin showed signs of metal-fatigue on the fracture surface.
Metallurgic investigations of the outboard midspar fuse concluded that a large fatigue crack up to 4mm in depth and encompassed about 50% of the inside circumference was present at the outboard location of the "bottle bore" configuration. The reason for the fatigue crack was due to multiple initiation sites along poor quality machining grooves.
Lastly, there was no evidence of corrosion pitting contributing to fatigue initiation as the material of the fuse pin were the accepted chemistry specification for 4330 M steel. Nevertheless, hardness measurements indicated that the tensile strength was roughly estimated to be 117 ksi, which is lesser than the specified range of 126-139 ksi. The details of the cause of fuse pin failure were taken from Luchtvaart (1993).
Separation of Engine #4
The inner engine of the plane was at full thrust as the plane climbs. As Engine #3 shears off, it does not fall away harmlessly from the wing but instead shoots forward. This action within seconds caused engine #3 to fall back and by shear chance, stroked the outer engine #4, in an outward and rearward direction. The location of engine #3 and #4 is illustrated in figure 2 below.
Figure 2. Location of engine #3 and #4
Parts Damaged due to Separation of Engines
The damages of some parts of the plane led to the crash of Flight 1862. The details of this section will be about the parts that are damaged due to the separation of engines.
Right Wing Leading Edge
The collision of engine #3 and #4 caused severe damages on the wing's leading edge. The damage was up to the front spar of the wing, over an area approximately 1 meter to the left of pylon #3 to approximately 1 meter to the right of pylon #4.
It is assumed that some parts of the aircraft were blown off from the leading edge of the right wing up to the front spar due to the speed of the aircraft, the aerodynamic distortion and turbulence. The whole impact ripped away a total of 10m stretch of the wing's leading edge and Figure 3 shows the estimated damage to the right hand wing. The information from this paragraph was taken from Luchtvaart (1993).
In addition, the right hand inboard aileron became less efficient due to the disturbed airflow produced by the damage of the wing leading edge and loss of pylon #3. This differential configuration caused the left wing to produce considerably more lift than the damaged right wing. Particularly when the pitch altitude increased as the airspeed decreased, and for this reason, the plane rolled further to the right (Luchtvaart 1993).
Figure 3. Estimated damage to the right hand wing leading edge (Luchtvaart 1993).
Due to the separation of engine #3 and #4, both engines' hydraulic systems became harshly damaged and consequently, ceased operation. As a result, system 3 and 4 hydraulic pressures were not accessible to the applicable flight controls and other user systems. Figure 4 gives a summary of the remaining and lost hydraulic systems after the separation of the engines.
Engines #1 and #2 were left unharmed in the flight. The pneumatic pressure required for the air driven pumps in the left wing bleed air duct was inferior than the normal system pressure and the reason behind this was due to the damage to the right hand wing pneumatic ducting. Details of the hydraulic systems were taken from Luchtvaart (1993).
Figure 4. Remaining and lost hydraulic systems (Luchtvaart 1993).
Final Loss of Control
Control of Aircraft
The right wing lost its capability of generating lift due to the loss of part of the wing's leading edge flaps and the damaged right wing. At small angles of the attack, the lift on both wings is fundamentally equal. On the other hand, at a higher angle of attack, the lift generated on the undamaged left wing will be higher than the damaged right wing. An increase in the angle of attack will consequently generate a roll moment; therefore causing bank steepening during the right turns in the direction of the damaged wing as the angle of attack of the plane increases. Details of the controllability of aircraft were taken from Luchtvaart (1993).
5.2 Increased Roll Moment to the Right
The airspeed of 270 knots was vital for the plane to generate enough lift to have a marginal level flight capability with its flight controls maxed out. As the plane was nearing the airport for landing, the pilot lifts the nose of the aircraft to slow the aircraft. However, the pilot did not know that by increasing the angle of attack of the plane, the aerodynamic effectiveness of the right hand inboard aileron and an asymmetric lift generation would be lost, hence causing the plane to roll to the right. The pilot then tries to jam the rudder further to the left but the plane barely responded.
As a result, the consequential roll moment exceeded the existing roll control and the pilot lost all ability to prevent the plane from rolling to the right. The roll continued until it reached a 90 degrees angle, just before impacting with the building. Details in regards to increased roll moment to the right were taken from Luchtvaart (1993).
After studying the various structures, it can be concluded that the metal fatigue of the fuse pins was the main factor of this fatal plane crash. At that time, the reliability of the fuse pins was questionable and insufficient to provide the required level of safety. In addition, the system to ensure the airworthiness of the fuse pins was unsuccessful and hence, the plane with the compromised fuse pins was eventually bound for an accident as its cracks enlarges after each flight cycle.
Due to the separation of engine #3 and #4, almost 10m of the entire wing leading edge was torn. This catastrophic incident posed a new and complex situation that raised the awareness of such a situation for both the researchers and pilots. The outcome of this incident might have been prevented had the pilot have a better understanding and knowledge of the situation.
After the tragedy of EL AL 1862, flight crews were given extra trainings in difficult conditions to ensure that the flight crews are better able to handle such situations in the event that such a tragedy does strike again.
Lastly, it is important for the structure of the plane to be in perfect condition with no faulty parts, because by compromising on even the tiniest of detail, it compromises the entire safety of the aircraft, as is evident in the crash of flight EL AL 1862.
7.1 Improvement for pylon-to-wing connections
A new design of a stainless steel fuse pin (Figure 5) was designed. This new fuse pin is corrosion resistant and without thin-walled locations, therefore giving it a better resistance to fatigue.
In addition, two extra connections between the mid-spar pylon fittings were added (Figure 6) which would greatly improve the reliability of the pylon-to-wing connections. Finally, larger mid-spar pylon fittings and tougher diagonal brace and upper link were fitted.
These corrective actions were implemented to avert an engine and pylon separating from the wing under tremendous loads in flight. Lastly, if there is a ground impact, the engines and pylons would break away with no damage done to the wing fuel tank. This section's information was taken from Wanhill & Oldersma (1997).
Figure 5. New design fuse pin (Wanhill & Oldersma 1997).
Figure 6. New mid-spar pylon connections (Wanhill & Oldersma 1997).
Redesign Warning Systems
Redesigning of the warning systems will allow the pilot to have a better knowledge of the situation and thus, being able to obtain more specific details of the problem. This would consequently allow the pilot to correctly evaluate the situation and take the appropriate steps to resolve the hitch. An example is a camera installed outside the plane to monitor the various vital parts of the plane.
Improve Training of Flight Crew
Assess the proficiency of flight crews and where necessary improve on their training and extend their knowledge in factors that will affect the aircraft control when flying in irregular conditions. For example, in a state whereby one or more engines is/are inoperative and when flight faces abnormal circumstances. The use of thrust in order to uphold controllability should also be highlighted in the training of flight crews.
In an event where there are multiple system failures or other beyond abnormal conditions, the flight crew should be prepared for such situations and not panic. They should remain calm work in an orderly manner to recover the situation.
Last but not least, Pilots and Air Traffic Control personnel should be advised on handling emergency situation to minimize any harm done to 3rd parties such as residential areas.