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The value of safety procedures

25 years ago today, the Aviation industry suffered an unmitigated reminder of how a chain of disregard shown towards safety procedures could have catastrophic consequences. Sometimes, company or industry wide standards and measures can be perceived as monotonous. As a species, humans are prone to complacency, and we often seek to find the quickest or easiest solution to a problem.

We can lose sight of why certain arduous safety checks are in place, yet this bears the risk that a one-off shortcut can turn into a regular flouting of the rules. On the 11th May 1996, some seemingly innocent sidesteps of company safety procedures led to the demise of Valujet flight 592 and 110 lives being perished. The industry must learn from the mistakes of the past to prosper in the future.

What happened?

Flight 592 was a routine leg from Miami to Atlanta before the triumphant Summer Olympic games. After an ordinary take-off, the smell of smoke was noticed in the cabin followed by rising temperatures from beneath the cabin floor. The pilots heard a loud ‘bang’ over their headset and the battery charger activated, indicating a loss of electrical power in their aircraft, a DC-9. The crew reported smoke onboard to Air Traffic Control, as it began to seep into the cockpit. The situation quickly turned from bad, to worse. After battling with the aircraft, the pilots realised the flight control surfaces were not responding to their inputs, and they were quickly losing control. Smoke in the cabin had become so impenetrable that a cabin crew member entered the cockpit, requesting for oxygen masks to be deployed. With distorted situational awareness, the pilots refused, concluding that oxygen will fuel whatever fire they were up against. Despite their best efforts to recover the stricken aircraft, only 9 minutes after leaving the runway, flight 592 slammed into the Florida everglades at 800 km/h.

Why did it happen?

The investigation into the accident considered multiple scenarios given that a fire onboard was known. Engine fire, maintenance issues, and explosives were all ruled out. Once the Cockpit Voice Recorder was discovered, the Cabin Crew member’s request for oxygen masks in the cabin indicated that the fire engulfed the passengers before the pilots. This suggested that the fire was in the cargo hold and hence correlated to the cabin floor having melted away in the wreckage. It was estimated that the cabin saw temperatures as high as 815°C, hot enough to melt aluminium.

A cargo hold fire was suggested; however, the compartment was airtight and had a fireproof layer, hence any fires should have burnt out due to lack of oxygen. This drew attention to the cargo manifest. This list detailed: 3 mail bags containing 28kg of mail, 3 aircraft tyres, and company material boxes being transported by Sabretech; a maintenance contracting firm. The boxes were labelled as containing empty oxygen canisters, yet upon investigation, it was discovered that this was false. They were instead, chemical oxygen generators that can reach 260°C when activated. A Sabretech inspector signed off these boxes as being correctly packaged.

These generators were out of date and were being transported for disposal. The correct procedure for disposal involves activating the generator to empty them and placing a safety cap over the firing mechanism. Out of 144 onboard, 28 were found in the wreckage, and only 8 showed signs of activation. They also sported no safety cap, only duct tape covering the firing mechanism.

Safety procedures warrant secure packaging to avoid movement in-flight with adequate shielding between the generators. The items were packed loosely in boxes under only a single layer of bubble wrap. Therefore, not only was the cargo incorrectly labelled, but they were not empty as procedures called for, did not have sufficient protection over the trigger and were packaged insecurely. Hazardous cargo regulations were breached when the boxes were placed freely round the tyres within the aircraft and the crew were not made aware of their potentially dangerous load. It can be argued however that due to the mislabelling of the boxes, empty oxygen canisters were not considered a concern.

In the investigation, conditions replicating taxi, take-off, and in-flight were simulated paired with an arrangement of boxes of generators surrounded by tyres and paper. The jolting and vibrations of taxiing triggered a number of the generators. The exothermic reaction of the generators led to rising temperatures and plentiful oxygen, eventually alighting the surrounding materials, and causing a further immense chain reaction of other generators. The burning simulation reached over 3000°C. The tyres then burst, correlating with the loud noise over the pilot’s headsets, and eventually the control cables would have been destroyed in such a fire, diminishing any control the pilots once had.

What can we learn?

Holly Dimmick - Business Insights Analyst - ANSL
Holly Dimmick studied a number of aircraft accidents in detail as part of her degree and provided this blog post to highlight the importance of safety regulations and a strong and credible safety culture in aviaiton. Holly is a Business Insights analyst in ANSL, she supports the insights and business intelligence capability, amongst other things providing great value to our Safety and Security Department.

Leading up to this tragic event, company and industry safety regulations regarding the safe disposal, storage, and transportation of high-risk goods were not complied with. It was suggested that the mishandling of the hazardous material and lack of contractor oversight was due to poor training, low paid staff, or simply from cutting corners amid tight company budgets. Safety culture can be likened to ‘doing the right thing even when no one is watching’, even with sparse resources or unideal circumstances. This is the value and importance placed on safety at all levels of the organisation. The accountability to abide by such an approach must therefore also fall to each individual or group, regardless of the processes completed before or after. The Swiss-Cheese model of failure regarding errors and violation can relate to Valujet 592. The safety procedures represented layers of defence that were, whether deliberately or not, no longer in place. Each individual or group transferred their responsibility to follow safety procedures to the next party at every layer of the model, resulting in the failures aligning and the accident occurring. Cargo smoke detectors were mandated following flight 592, however learning must continually extend right down to each individual. This anniversary is poignant reminder that no one is exempt from following safety procedures and evidences the criticality of why they are in place.

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