The fact that Gerry Bench is busy is testament to the high safety standards of an already safe airline industry. Bench is president and chief executive of TDG Aerospace, an 18-person privately owned engineering firm that develops fixes that airlines must install on their Boeing aircraft when the US Federal Aviation Administration mandates special safety rules and airworthiness directives.
Front and centre on TDG's plate of late has been development of equipment and supplemental type certificates to satisfy fuel pump, relay and ground-fault protection aspects of Special Federal Aviation Regulation (SFAR) 88. SFAR 88 was issued in 2001 in the wake of the fuel tank explosion that brought down a TWA Boeing 747-100 in 1996 after departure from New York Kennedy airport, killing all 230 on board.
Broad in nature, SFAR 88 required manufacturers to perform wholesale analyses of fuel systems in order to determine what changes might be needed to eliminate ignition factors, including short-circuit paths. Results are being codified into issue service bulletins and are generally followed up by FAA ADs to make the upgrades mandatory. So far, service bulletins and mandates have been issued for the Boeing 757 and 767.
MD-80 FIX
Bench was watching the SFAR 88 developments with interest in 2001, having started the firm in 1990 to develop a solution to help Boeing MD-80 operators meet an AD that required them to de-ice their aircraft when cold-soaked fuel in the wing tanks led to frost forming on the upper surfaces of the aerofoil. Problems would occur on the following take-off, when the ice would break off on rotation and get sucked into the rear-mounted turbofans.
TDG's "NOFOD" solution comprised a "new skin that goes over the old skin" that would use resistive heaters every time the aircraft landed to prevent frost. "There were 1,100 MD-80s at the time," says Bench. "We sold almost 800 systems for the model."
Bench says: "When SFAR 88 came out, I [told] my engineers, 'We know we can build a ground-fault interrupter, but let's build a smart one'."
The result was the universal fault interrupter, a component that not only prevents a short-circuit current surge, extended dry pump operation and uncommanded pump operation, but tells maintainers what type of fault occurred, in which cable, how many power cycles occurred before the fault and how much current flowed when the ground fault took place.
The system was so comprehensive, Bench says airlines argued to the FAA that it negated the need for fuel tank inerting. The FAA ultimately did mandate that manufacturers begin installing fuel tank inerting systems in addition to the other preventative measures in July 2008.
To date, TDG has sold nearly 700 of its fuel tank safety STCs that are based on the universal fault interrupter technology, a fix the FAA considers a means of compliance to the AD. For operators, the TDG solution means a lower-cost way of implementing the mandate compared with the Boeing bulletin, says Bench, adding that a TDG STC for the 757 costs between $14,000 and $20,000 per aircraft, not installed. Bench says TDG has an 85% market share for the domestic 757 fleet and nearly 50% for the European fleet. Airlines must complete the work by mid-2011.
A similar STC that meets a Boeing 767 tank safety mandate will be completed by year's end, says Bench.
737 IN THE WORKS
The FAA had proposed to mandate a fix for the 737NG, but rescinded the notice of proposed rulemaking owing to problems with the Boeing bulletin defining the fix, which Boeing continues to work on. In the meantime, Bench says American Airlines and Delta Air Lines have already been purchasing universal fault interrupters for their 737NG fleets regardless, due to an earlier rule requiring them to provide electrical protection or carry 455kg (1,000lb) extra fuel in centre tanks to prevent pumps overheating.
Bench says there is a potential for about 1,500 kits between the forthcoming 767 work and the remainder of the 737NG fleet, once the proposed AD is reissued.
For the 737 Classic, for which Bench developed the intellectual property for the fix, there is no mandate in sight, despite the fact that most centre fuel tank explosions to date have occurred on that model, he says.
Source: Flight International
