NUTS, BOLTS AND ALL THINGS AERONAUTICAL

Even the smallest component of an aircraft needs at some stage to be designed, manufactured, tested and then submitted for certification…… Tom Chalmers reports. Rian Bester took the pictures unless otherwise indicated.

THE FACTORY is tucked away in the corner of an industrial complex in the back street of Boksburg North, on Gauteng’s East Rand. Like other facilities in the complex, it is heavily burglar-guarded which, perhaps, gives a faint clue as to what goes on inside the Aero Services’ plant. For it is in these premises that some of the thousands of armour-plated, terrorist-proof cockpit doors required around the world, are manufactured.

Aero Services’ managing director, Chris Scott, explains some of the intricacies of one of the six cargo pods which are used in the freighter conversion of Airlink’s Jetstream 41 aircraft.

Several months of meticulous design, most of it done with the aid of computers, had to be undertaken before the first door was built. Jigs and tools were made or prepared. The first door was a prototype and was designed specifically for a particular type of aircraft. Those for the Boeing 737, for example, require as many different designs as there are marques of the aircraft – the 737-300, - 400, - 500 etc right up to the latest -900 if required. Each marque has a different requirement. Aero Services has manufactured cockpit doors for many different aircraft – from the smallest airliner to the B747, and for many airlines at home and overseas. And like everything else that is part of an aircraft, it has to be tested usually to destruction and then certified.

 

Aero Services’ managing director, Chris Scott, explained: “One of the tests involved is that the door’s armour-plating must be able to withstand the impact of a bullet fired from a Magnum 44 weapon at a muzzle velocity of 436 metres/second. The problem was that the standard Magnum 44’s muzzle velocity is below this figure, so we had to find one that met the requirement. Fortunately, we found a gunsmith in Germiston who had a modified
Magnum with a long barrel – Clint Eastwood style – which was suitable. The plating withstood the impact and another part of the whole reached certification.

“But that’s not all. The glass ‘peephole’ and its cover were also rigorously tested. Then there was the question of decompression. If the cockpit area starts to decompress rapidly, there must be a way to stop the huge weight of air in the cabin from bursting through. A special automatic relief valve was designed and fitted near the base of the door which will allow pressure equalisation from cabin to cockpit, but not the other way around.

“The door was tested in a special pressure chamber to near the aircraft’s maximum pressure differential and when the valve operated it had the sound of a loud bang. The equalisation was almost instantaneous. The doors are also fitted with mechanical combination locks – no two have the same code. “We have made doors designed for airlines such as Comair (B737s), an airline in Thailand, a B747 in Nigeria and AirQuarius, in South
Africa, among others. Depending on the aircraft type they weigh in the region of 40 to 50 kg each and cost anywhere from 30 000 to 40 000 US dollars,” he explained.

But that is by no means all that goes on in these premises. The company designs, certifies and manufactures aircraft structures; manufactures and repairs aircraft composite structures; offers thermo/vacuum forming;
has three-axis CNC routing and also pattern and mould-making – among other specialities.
For example, during our visit in one corner we found dozens of airline-style cabin trolleys. These are not used for serving refreshments or food to passengers. They are to contain duty-free items on sale on international flights and, because they will contain valuable items, need to be totally tamper-proof.

Heavy ballast equal to the maximum weight the cargo pod will be licensed to carry, is loaded aboard one of the pods in preparation for certification testing.

Stainless steel is used to reinforce the corners, special material adorns the sides, top and bottom, back and, of course, the door which is fitted with a special lock. All have had to be specially designed, tested and then certified by the Civil Aviation Authority before they can be used on an aircraft. In another part of the workshop is a special stretcher designed to fit into a corporate-style jet aircraft used for mercy flights. Strong, yet
light (25 kg), firm but comfortable for the patient, its underside contains special stanchions which clip into the aircraft’s seat rails.

One of the purpose-made medical stretchers designed to fit into a specific jet aircraft used for mercy services. (Photos Courtesy : Aero Services).

A screw device enables the top third of the stretcher to raise or lower for more patient comfort. The restraining harnesses are placed in such a way as to cause the minimum of discomfort, but give all the body support
necessary taking into account the degree of severity of the patient’s injuries. All this – every part of the stretcher – has had to be meticulously designed, tested and then submitted to the SACAA for certification, a task which took six months to complete.

CARGO CONVERSION

But the biggest job among the many currently being undertaken in Aero Service’s Boksburg North factory is the second ship-set of freighter conversion modules for SA Airlink’s Jetstream 41 aircraft.
The airline approached Aero Services in May 2010 to prepare a proposal for the conversion of its fleet of BAE J41 Jetstream turboprop airliners into dedicated freighters. Various technical concepts were developed and the following month the modular pod concept was selected as being the most suitable.

Subsequently, a contract to design, manufacturer and certify the modification under SACAA Supplementary Type Certification (STC) was awarded and installation of that first ship-set took place early last year with STC approval having been granted shortly afterwards in June 2011. The second set was in the final stages of production at the time of writing. It all sounds as simple as A-B-C. Far from it. Hundreds, if not thousands, of man-hours went into the design. To start with, Airlink did not want any modifications made to the airframe itself so allowing the aircraft to be easily returned to passenger configuration if required. The main cargo bay is situated between Stations 180 and 477 (aft of the main entry door and just forward of the right-hand emergency exit door). All existing carpeting, sidewall panels, PSU panels and ceiling panels had to be removed along with the seats, galley and lavatory.

Part of the factory showing the distinctive duty-free cabin trolleys (left) mentioned in the article.

Then the six Aero Services-designed and manufactured cargo pods were installed to create the main cargo bay. Each pod is selfcontained and attaches only to the seat tracks with eight standard stanchion fittings. The aft 9-G barrier consists of a frame and an integral net and is situated at Station 503.
The barrier is attached solely to existing hard points on the airframe and replaces the original retaining wall of the main baggage bay formed previously by the lavatory and galley. Smoke detection is accomplished by detectors located in the roof of each cargo pod and the existing detectors in the aft cargo and ventral baggage bays. Each cargo pod is designed to carry 380 kg of freight. Before an STC could be issued for the pods, every component had to be designed and manufactured and then the whole pod had to be tested. Just the paperwork fills several lever-arch files packed to the brim with drawings, specifications etc.

TESTING

The restraining nets are certified to stop a force of 9-G or the equivalent of 3 420 kg. The pods were tested to withstand a force 9-G forwards, 6-G downwards and 3-G upwards and 3,5-G to each side.
Even the walls of the pods had to be tested for strength and fire resistance and their ability to retard flames.

Delving deeper, each component of each pod had to be manufactured by moulding or machining – there are no off-the-shelf parts. For the moulding, special dies had to be manufactured and then machined or hand sanded to minute tolerances – no process can be accused of being “slap happy”. In some cases, even the tools to make the parts had themselves to be manufactured on site. So, the next time you sit in a seat aboard an aircraft, take a look around and see what is actually involved. Your seat belt itself had to be designed by someone whose work then had to withstand the rigors of certification testing. Even the seat pocket in front of you was once designed by someone and then tested along with the rest of the seat. Every nut and bolt, every fastener, every piece of material, every panel – you name it and someone, somewhere has been responsible – like Chris Scott and his team at companies like Aero Services around the world – for its design and certification.
Who said it’s a piece of cake?