Technology update

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Aerospace companies look at security concerns

Alaska Airlines has purchased the Raisbeck Engineering-designed hardened cockpit security system for its fleet of Boeing 737 aircraft.

Regulators, analysts, and aerospace corporations have all begun taking security measures in response to September's terrorist attacks. Various regulating bodies and airframers have begun putting together proposals and teams to enhance security on board aircraft.

Airbus Industries recently initiated several meetings in the U.S. and Europe to review improvements being made to aircraft security. The meetings involved representatives from airline associations, airworthiness authorities, and other manufacturers.

Among the topics discussed at the meetings was secured cockpit doors. Airbus has already had a proposal for reinforced doors on its single-aisle aircraft reviewed and approved by the DGAC and the European Joint Aviation Authorities. The proposal has since been reviewed by other authorities and is awaiting approval. The company has issued detailed design plans for cockpit door modification, and the necessary data and information have been made available to its customers.

Besides the reinforcement of cockpit doors, other security enhancements were discussed with the airlines. These included improved means of communication between the cockpit and cabin and between the aircraft and ground.

The Boeing Co. has also taken action regarding aircraft security by establishing a Security and Safety Services organization under its Commercial Airplanes business. This organization will be charged with helping Boeing customers implement the recommendations of the U.S. Department of Transportation Rapid Response Team on Aircraft Security (known as the Mineta task force). The company has been working with the industry to develop technologies that prevent cockpit intrusion as well as those that enable pilots to monitor the passenger cabin from the cockpit.

As a result of these security recommendations from the Mineta task force, CBL Systems Corp. has developed a Cabin Incident Monitoring and Aircraft Transponder Security system. The system platform is based on an integrated arrangement of "smart" remote sensors, fiber optics, and a network of flight-qualified, FAA-certified digital flight data-acquisition units, which are already in use on the U.S. airline fleet.

"The advantages of using a fiber-optic system in the aircraft environment are tremendous," said Brian Morrison, President and CEO of CBL Systems Corp. "Fiber uses an all-digital format that offers enhanced signal fidelity because fiber is immune to interference either from intentional efforts to disable the system or from the harsh conditions that inherently exist in the aircraft environment. Furthermore, the readily scalable system can significantly increase the capacity of today's aircraft to automate, connect, and support new security capabilities without adding the significant weight that traditional copper wiring and shielding would require."

According to CBL, signals transported by its digital fiber-optic units are immune to high-intensity radiated fields (HIRF), lighting, electromagnetic interference, tampering, and transmission failures. The system is configured to operate in a redundant ring, whereas most wire-based analog systems are connected to a central single point-of-failure. The system's ring architecture connects smart sensors and controls via CBL's bi-directional fiber networks, ensuring a continuous information path with extensive built-in security and diagnostics. As a result, critical data will always be known and communicated despite a localized failure or tampering with any link.

One airline that has already taken some action is Alaska Airlines, which purchased the Raisbeck Engineering-designed hardened cockpit security system for its fleet of Boeing 737 aircraft. The system, which has been in development over the last 12 months, meets all current FAA requirements as well as those envisioned to be implemented by April 2003, according to Raisbeck Engineering.

Additional FAA requirements will be incorporated in the next 18 months. These include a bulletproof cockpit environment that meets NIJ-III (National Institute of Justice) standards as well as increased cabin awareness for the flight-deck crew. Cabin awareness will initially be satisfied by the incorporation of two 1.25-in. thick bulletproof glass windows in the hardened cockpit door. This can later be augmented with an available video system.

The new cockpit door system's locking/unlocking mechanism will be remotely accessible by the flight crew from the cockpit's center pedestal.

Raisbeck Engineering is producing 737 kits at the rate of 100 per month. The company expects to be able to meet other airline demands for the system after completion of the Alaska Airlines order.

- Frank Bokulich

A new look at jet fuel additives

Mike Farmery, Technical and Quality Manager with Shell Aviation in the UK, believes that fuel additives may be the solution to keep fuel from freezing during trans-polar flights.

There is seldom anything simple about aerospace. Whether it is design, engineering, manufacture, or operations, solutions to manifold challenges invariably have technological "side effects," which, in turn, bring new challenges. "Straightforward" is not a word that is often used by aerospace engineers.

So it was when consideration was given to the opening up of new commercial polar routes to provide more, efficient, and economical links between the continents of Europe, North America, and Asia. There would be potential for reduced flight times and increased payloads. But when specialists across the industry considered the potential technology challenges, one of the most important was the likely problem of jet fuel flow in ultra-cold ambient conditions at the typical cruising altitude and speed of aircraft such as the Boeing 777 and Airbus A340.

When it gets extremely cold, jet fuel can become waxy, just like diesel fuel, restricting flow to the engine. If this happens, options are limited to either descending to a lower, warmer altitude or increasing airspeed to enhance aerodynamic warming. Both options would increase fuel burn and reduce the benefits of polar routing.

The temperature at which jet fuel starts to form wax is defined in the specification as the freeze point. This temperature is different for the two main grades of civil jet fuel used in the western world. Jet A (used in the U.S.) has a freeze point of -40°C and Jet A-1 (used virtually everywhere else outside of the former Soviet Union) freezes at -47°C, explained Mike Farmery, Technical and Quality Manager with Shell Aviation in the UK. "Rules for most aircraft state that action must be taken to warm the fuel if its temperature drops to within 3°C of the freeze point. Aircraft departing the U.S. are the most affected, but even Jet A-1 is not enough to guarantee immunity, particularly on very long-haul flights. The challenge is to change the properties of jet fuel to meet the demands of the new routes while minimizing operational costs."

"An additive can be designed to modify specific fuel properties and can be delivered to an individual aircraft traveling along a particular route (trans-polar)," said Farmery.

Technically, reducing the freeze point of jet fuel is relatively straightforward; economically, it is complex, said Farmery. Jet fuel competes for light hydrocarbons with gasoline and diesel fuel. Reducing the freeze point costs money. Also, the vast majority of domestic flights in the U.S. and many intercontinental flights do not need a lower freeze point, which is just as well, as segregating a separate grade at airports for intercontinental polar flights is neither simple nor necessarily cost-effective.

However, there is a way to achieve the standards essential for new trans-polar routes, said Shell, via fuel additives. For safety reasons, aviation authorities have approved relatively few additives for commercial aircraft, but Farmery believes the new Polar routes may change this trend: "An additive can be designed to modify specific fuel properties and can be delivered to an individual aircraft traveling along a particular route. The cocktail of additives to be used can be selected at the aircraft instead of the refinery, rather like a doctor treating a patient."

But the safety issue is crucial. "The huge effort to gain all the necessary approvals has acted as a real block to the widespread application of additive technology in aviation fuel. However, this may be changing," said Farmery. He explained that the U.S. Air Force changed the game in the late 1990s with its initiative to find an additive to improve the thermal stability of jet fuels for its next generation of fighters. The successful result is the so-called "+100 additive," developed by BetzDearborn in the U.S. and marketed elsewhere by Shell Aviation as Air Performance Additive (APA) 101.

Standard jet fuel will start to break down and form coke, gum, and varnish deposits on metal surfaces when thermally stressed to temperatures above 150°C, according to Farmery. Deposits may accumulate in fuel nozzles, fuel manifolds, pumps, valves, filters, and heat exchangers. In addition to generally damaging engine components, these accumulations may lead to combustion instability, cold start problems, augment anomalies, and flameouts.

Additives can be introduced to jet fuel at the refueling stage trather than at the refinery.

APA 101 increases the thermal stability of jet fuel by 56°C, retarding the degradation process and allowing the engine to run at higher temperatures without clogging with ash deposits. The additive is a blend of antioxidants, detergents, dispersants, metal deactivators, and a solvent. Detergents reduce coke deposition by solubilizing polar compounds and preventing their reaction from forming deposits. These compounds are kept in solution by the dispersants. Together, they effectively scrub deposits from systems and components. Antioxidants inhibit the oxidation of fuel and the formation of peroxides and insoluble particles. Metal deactivators chelate trace metals, such as copper, and inhibit the rate of formation of degradation products. A heavy aromatic naphtha is used as a solvent to prevent cold temperature crystallization and increase the solubility of the jet fuel additive.

Shell Aviation, working with BetzDearborn, is already considering civil applications for additives and the measured, electronic delivery of fuel. A flight trial with KLM is under way (previously reported by Aerospace Engineering), and Farmery said that there is good evidence that, in addition to thermal stability benefits, APA 101 may also reduce engine emissions. The full results are expected by early 2002.

"It has changed conventional thinking about the use of additives in jet fuel," said Farmery. "If we can improve thermal stability with an additive, why not the freeze point? There is a long history of cold flow improvers for diesel fuel. In principle, there is no reason why similar benefits could not be achieved in jet fuel. Already, the USAF has a major program in play to find suitable candidates. Its problem is similar to civil aviation—namely long-duration, high-altitude flights. However, the military will be the main beneficiary.

"There is the potential for an aircraft taking standard Jet A at, say, Chicago, injecting an additive, and producing a fuel suitable for long-haul, polar flight, at a fraction of the cost of reformulating the base fuel. The knock-on effects are prolonged high-altitude flight and subsequent fuel economies."

Shell Aviation fuel bowsers are restocked at London Gatwick's tank farm. The bowsers and other tankers are used for jet refueling outside hydrant distribution systems.

The problem, though, is finding a generally suitable and acceptable cold-flow fuel additive. Such additives for Jet A and Jet A-1 are about five years away from certification at present, believes Farmery. But the need for urgency in completing their development is not just to meet the polar route requirements. "Thinking further ahead, additives could be used to improve performance or reduce emissions," he said. "Depending on aircraft type or operation, the fuelling vehicle could inject a cocktail of additives designed to optimize performance for that particular aircraft and that particular flight.

"The real barrier to this is not so much developing the additive technology, but rather the process of additive approval," he said. "Much of the success of our current aviation business can be attributed to its excellent safety record. That achievement is the result of careful attention to the management of change in all areas of activity, fuel composition included."

At present, the high capital costs of engines and airframes make additive testing very expensive, and the differing requirements of manufacturers can create duplication. Approval for a new additive could take 5-10 years, said Farmery. He believes that a quicker, but no less thorough process is needed if the benefits of performance-improving additives are to be realized for aviation fuel. Work is already under way to develop more transparent and efficient processes with engine manufacturers, fuel suppliers, and specification groups. But the fuel industry cannot afford to jeopardize its first-class safety record.

Farmery said that in the short term, preventing fuel waxing in aircraft 35,000 ft above the North Pole will produce real economic benefits. Over the longer term, additive technology has the potential to bear much greater fruit. "In the automotive industry, engine and fuel developments have gone hand in hand, each one facilitating and stimulating the other," he said. "Additives have enabled engine designers to push their technology to create clean and efficient engines beyond anything that could have been envisaged 25 years ago.

"The same benefits are promised to the aviation industry. Manufacturers are already looking at exploiting Shell's APA 101 thermal stability additive to allow them to design engines that run hotter and are therefore more efficient. If the industry is successful in developing the right technologies and if aviation authorities give their approval, many different types of additives could be making significant contributions to commercial aviation by the end of the first decade of the 21st century."

- Stuart Birch

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