Question

include the image of an aircraft accident that was caused by failure of a fastener or any image(s) related to the accident. Discuss the following:

• Discuss the details of the accident.
• How did the failure of the fasteners contribute to the accident?
• What could have been done to prevent the accident?

Answer 1

Hi, thanks for the question.

For the purpose of this question, we will consider the case of Aloha Airlines Flight 243. In this case, a simple fastener fault caused the fatality of 1 crew member and injuries to about 65 passengers on board.

Here is the image of the catastrophic damage caused due to the failure.

And here is the close-up image of the damage.

It is often considered a miracle on how the pilots managed to avert a major incident mid-skies and managed to land the flight. So, here is the problem that caused this failure.

The rivets in the upper row near the cabin door had developed cracks. During the pre-flight, hangar, and climb out, no anomalies were reported by the inspection crew. Since no visible problems were reported, the flight was taken to the runway strip for departure. It was when a passenger getting on board the flight gazed upon the row of rivets that she noticed the crack.

During take-off and general climbing, there were no problems. And as soon as the flight hit 24,000 feet altitude, the pilots heard a clapping sound from the cabin which was further followed by wind noise. As soon as the pilots understood the events unfolding, they declared an emergency and immediately took action to land the flight.

The flight in question was a Boeing jet that was being used by Aloha Airlines. After the flight landed, the inspection revealed that one of the four butt jointed panels of the fuselage had not bonded properly. After three rows of rivets and hot bonding, the joint still did not get secure. During production, the Boeing engineers had reported that there were problems in the bonding process which further gave way to the idea that some parts would not bond altogether.

The outside pressures at high altitudes are low, and at low altitudes, they are high. And since 24,000 feet is counted as a low altitude range, the primary reason for the damage was decompression. Upon further inspection of the damage, it was reported that the disbonding caused the hoop load to be transferred to the three rows of rivets. These rivets were countersunk and hence extended through the entire thickness of the fuselage panel. This caused knife edges to form and concentration of stresses at the holes of the rivets. This ultimately led to the failure of the panel due to improper fastening of the rivets, and inadequate bonding.

Learnings from this accident provided the Boeing engineers to come up with a failsafe design. This failsafe design laid the foundation for inclusions of tear straps with 10-inch spacing. These would come in handy in redirecting the running cracks to external damage. Also, the fuselage could now withstand up to 40-inch cracks without ever suffering major failures in the fuselage panel.

Also, new bonding techniques that included hot bonding followed with adhesive curing were used to make sure the panels of the fuselage remained integral with the overall frame of the plane and disbonding does not become concentrated, hence preventing the formations of knife edges.