No Fire in the Hole

For existing airplanes, FAR No. 88 requires manufacturers to conduct a one-time design review of the fuel tank system for each transport airplane model in the current fleet to ensure that failures could not create ignition sources within the fuel tank. Also, manufacturers must then design specific programs for the maintenance and inspection of the tanks to ensure the continued safety of tank systems. There are also operational changes for existing airplanes, like not running the fuel boost pumps on the B-737 when a tank is empty. As expected, additional ADs resulted from feedback from the new information received from the design review of existing aircraft.

Technological changes in aviation
As we follow the regulatory and technological change and progress, we see it is slow and deliberate. Aviation is a world unto its own. An example is from the venture capital world of finance. A venture capital investor looks for a new technology or idea and expects to put in money and that the idea will mature in no more than five years. They expect to at least triple their investment return and get out in order to reinvest with another new start-up. Aviation innovation may take more than a decade before it gets on a large number of aircraft. Safety, security, reliability, and affordability must be the end result of the regulatory and technological changes over time. Keep ‘em Flying.

Fred Workley is president of Workley Aircraft and Maintenance Inc., which is headquartered in Alexandria, VA. Workley wrote Eye on Washington and Maintenance Matters for AMT from 1996 to 2005.

More Than A Decade of Regulatory and Technological Change

July 1996: Trans World Airlines (TWA) 800 accident.

December 1997: National Transportation Safety Board hearings TWA-Flight 800.

March 19, 2001: FAA required all transport aircraft to have smoke detector systems in Class ‘C’ and ‘D’ cargo compartments.

1998: Aviation Rulemaking Advisory Committee (ARAC) Fuel Tank Harmonization Working Group (FTHWG), Final Report, Recommendations for inerting of fuel tanks received significant attention.

2000: “Proof of Concept” tests at FAA facility in Atlantic City.

April 18, 2001: Advisory Circular (AC) “Fuel Tank Ignition Source Prevention Guidelines,” AC 25.981-1C, revised 9/19/08. Provides guidance for demonstrating compliance with the certification requirements for prevention of ignition sources within fuel tanks of transport airplanes.

April 18, 2001: AC “Fuel Tank Flammability Minimization,” AC 25.981-2A, revised 9/19/08. Pertains to minimizing the formation or mitigation of hazards from flammable fuel air mixtures within fuel tanks. AC has a section on fuel tank inerting using inert gas, like nitrogen, to keep the oxygen level in the tank ullage below a combustible level to prevent fuel tank flammability.

May 7, 2001, effective date June 6, 2001: Special Federal Aviation Regulation No. 88.

July 2001: Fuel tank inerting recommendations available from the FAA.

December 2002: Probe Patents issued.

May 2003: Small Business Innovation Research (SBIR) grants to develop fuel-resistant coating and time delay technique.

October 2003: Inerting System Patent issued.

June 2004: SBIR grants to improve fuel resistant coating and phase delay technique.

2004: Environmental tests to RTCA/DO-160C successful, ground and flight tests of fiber optic oxygen sensing with RTD temperature and remote pressure transducer.

July 21, 2008: Final rule U.S. DOT/Reduction of Fuel Tank Flammability in Transport Category Aircraft.

2008: Breakthrough with fiber optic oxygen sensing and fiber optic temperature sensing in one fuel tank probe with advances in phase shift technique.

April 2008: Report of ongoing research on “Composite and Aluminum Wing Tank Flammability Comparison Testing” of next generation aircraft.

July 2009: Successful environmental tests to RTCA/DO-160E for probes, fiber optic cables including burn and acoustics with operating electronics.

2009: Fiber optic oxygen, fiber optic temperature, and fiber optic pressure under development in one probe with significant progress in frequency domain fluorescence using time gated “phase-lock” detection and new testing profiles simulating different stages of flight. Test plans include absorption of ambient temperature and air conditioning system heat on the ground into fuselage and wing structure thus affecting climb and increased oxygen during descent and holding at 10,000 feet using calibrated nitrogen gases and different fuel loads.