Allison on Ailiners-A Fly in the Ointment
By Steve Allison
Aircraft technicians often complain that, whilst they are the ones responsible for keeping aircraft in the air, pilots earn more money. Yes, they are responsible for keeping the aircraft in the air but it's the pilots who are responsible for getting them back to the ground safely. One Saturday evening in the mid 80s, Captain Karl Jensen experienced the challenge of getting his 174 passengers safely back to the ground when an emergency developed.
The first item on the checklist is to silence the alarm; rational thinking is easier without the distraction of noise. The next item on the checklist is to ensure that the fire detection system is operating correctly. The alarm could just be the result of a faulty system - which is why there are two systems operating together. After identifying the cargo hold in which the problem had occurred, the crew configured the bleed valves so that there was as little oxygen as possible in the hold. There are two fire extinguisher bottles in each hold; the checklist calls for the first one to be discharged.
Having completed the checklist, the fire warning light was still glowing brightly. The procedure in this situation is to descend to an altitude least able to sustain a fire, which is around 25000 feet. Yes, there is less oxygen the higher you are flying but if the fire pierced the skin, the aircraft would depressurise. At 25000 feet, the air is still relatively thin but if the skin were pierced, it is easier to get the aircraft down to an altitude where the air is dense enough to breath. Of course, the next priority is to find the nearest suitable airfield and get the aircraft on the ground.
The nearest suitable airfield is of course open to interpretation and the captain has to make that decision. The aircraft was, at the time when the alarm started sounding, in the vicinity of Grootfontein. Karl decided that Grootfontein, then a military airfield, wasn't suitable, preferring to go to an airfield that had a more comprehensive fire service and technical support. Karl made the decision that Windhoek was the best choice and advised Johannesburg air traffic control of his intentions.
Now, an airliner's maximum landing weight is significantly lower than the maximum take off weight. Landing a very heavy aircraft would put too much stress on the landing gear. During a flight the aircraft, under normal circumstances, will have burned off enough fuel to arrive at its destination at or below maximum landing weight. In the case of an emergency, fuel must be jettisoned to get the aircraft down to its maximum landing weight. In this case, the crew had to dump 54 tonnes of fuel, which would be enough to run the average family car for about 80 years.
Karl really had to think fast, the fuel had been dumped, the fire alarm warning light was still on; they needed to land. The next best airfield was Keetmanshoop and they were in the process of setting course when, fortunately, there was a voice on the radio saying that the runway would be cleared. It would take about 20 minutes but it was still a better option than Keetmanshoop.
Eventually, once the runway was clear, in the failing light of dusk, the crew landed the aircraft, destroying 200 meters of freshly laid bitumen. The bitumen had been laid as a waterproof membrane, part of the resurfacing operation.
The checklist says that the second fire extinguisher bottle should be discharged on touchdown, and that's exactly what the crew did but - you guessed it, the fire warning light stayed on. They taxied the aircraft to the apron followed by a fire tender. The overzealous fireman wanted to open the cargo hold but Karl persuaded him that that was the last thing that should happen until all the passengers were off the aircraft.
The problem with getting the passengers off is that you need steps and since the runway was being resurfaced no one had expected to use them that night. You might have expected to see dramatic scenes of escape chutes bursting out of the side of the aircraft and people bouncing down them. Since there was no smoke and no heat coming through the floor of the aircraft, Karl decided not to deploy the chutes. There is always a risk of minor injuries when passengers have to slide down the chutes.
While all this was going on, a South African Airways ground crewman had arrived. Karl told him to go and get the steps, which he was reluctant to do because the key was locked away. For those of you who don't remember, the steps were attached to the back of a truck that was driven to the aircraft. Karl ordered the lock to be broken so that the steps could be brought to the aircraft. Ground technicians are not used to driving steps and he didn't know how to operate the rig. All that happened was the jacks kept going up and down. It took another ten minutes to get the steps to the aircraft, which, in an emergency, feels like a lifetime.
Eventually, the passengers and crew got off the aircraft and the firemen opened the cargo hold. There was no fire or any indication that there had been a fire. The technician climbed into the hold, went to the fire detector tube and removed an insect. How did he know? Well, apparently it wasn't the first time it had happened.
The flight had been delayed four hours and 54 000 kilograms of fuel had been lost. New fire extinguisher bottles had to be flown up from Johannesburg before the flight could continue and all because of an insect. Why didn't they have a piece of Gauze over the tube? Because that apparently also prevents the smoke form entering. Whilst not fail safe, fire detection systems in modern aircraft have improved significantly compared the old SP. Today they use a chemical detection smoke detector rather than a light sensitive system.
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