Thu, Dec 2, 2010 — David Evans
Among the recent regulatory actions: (1) continued problems with B737 cockpit warnings, (2) more SFAR 88-related work on electrical systems, (3) a special condition for B787 fuel tank safety, (4) an AD affecting more than 4,000 Robinson helicopters, and (5) an emergency AD concerning Bell helicopters.
14 September 2010 Federal Aviation Administration (FAA)
FR Doc 2010-22847 Docket No. FAA-2010-0853
Notice of Proposed Rulemaking (NPRM), airworthiness directive (AD), Boeing 737-600, -700, -800, -900 airplanes
The notice purports to solve a warning problem, to wit, to insure that the warning horn sounds if the stabilizer is not correctly set before takeoff. The FAA describes the problem thusly:
“We received reports that the warning horn did not sound during the takeoff warning system test of the S132 ‘nose up stab takeoff warning switch.’ Certain airplanes were found to have switch failures, which resulted in lack of aural warning when the stabilizer was positioned outside of the green band limits. Also, operators found that both internal contacts would not actuate during switch rotation.
“A takeoff warning switch failure … could result in auto-rotation, resulting in tail strike, stall, high-speed runway overrun, rejected takeoff, or failure to clear terrain or obstacles after takeoff, which could reduce the ability of the flightcrew to maintain the safe flight and landing of the airplane.”
Without the warning horn, diagnosing the configuration problem could well take more time than the few seconds the crew has to diagnose the problem and input the correct flight control commands. Roaring off the end of the runway or flying to low after rotation to clear obstacles could easily end in a fiery death for all aboard.
The FAA wants almost 1,000 “Next Generation” B737s inspected within 6 months. The 6 month clock begins ticking after a final rule is published.
Still unaddressed by the FAA is the problem of similar warnings for takeoff mal-configuration and for cabin depressurization in flight. The same warning for two separate conditions may have contributed to crew confusion in the depressurization of a Helios B737 on a 2005 flight from Cyprus to Greece. All 121 aboard lost consciousness, and the airplane continued on autopilot until fuel was exhausted near Athens. The lawyer for families of the dead, Constantinos Droungas, said, “Boeing put the same alarm in place for two different types of dysfunction. One was a minor fault, but the other – the loss of oxygen in the cockpit – is extremely important.”
1 October 2010 FAA
FR Doc 2010-24711 Docket No. FAA-2010-0952
NPRM, AD, Airbus A330 and A340 airplanes
This action results from design review of fuel and wiring systems mandated by Special Federal Aviation Regulation, SFAR 88. This regulation took effect in December 2002 and covered all transport category airplanes weighing 7,500 pounds or more. Dozens of ADs resulted, correcting wiring problems that could precipitate a fuel-vapor explosion in the tank. SFAR 88 was published in response to the explosion that downed TWA 800 in 1996, which was attributed to electrical arcing in the center wing tank of a Boeing 747-100.
The publication of this proposed AD nine years after SFAR 88 was published reflects, frankly, a lack of urgency concerning the elimination of ignition sources inside fuel tanks.
The FAA says:
“Failure of the auxiliary power unit (APU) bleed leak detection system could result in overheat of the fuel tank located in the horizontal stabilizer and the ignition of fuel vapors in that tank, which could result in a fuel tank explosion and consequent loss of the airplane.”
Inspections/corrections must be done within 6 months after the final rule is published. Given that the final rule will be published anywhere from 6-12 months hence, it will take at least a decade to redress a hazard that should have been designed out when these airplanes were still on the drawing boards.
Comments are due 15 November.
23 November 2010 FAA
FR Doc 2010-29409 Docket No. NM415
Special Condition No. 25-414-SC
Final Special Condition, Boeing 787-8 Airplane; Lightning Protection of Fuel Tank Structure to Prevent Fuel Vapor Ignition
The B787 is Boeing’s new airplane that features an all-composite structure. Traditional aluminum structure airplanes have a built-in protection against lightning, in that the metal skin essentially prevents a lightning strike from penetrating to the interior of the airplane.
A composite structure offers no such protection. Lightning will penetrate into the inner reaches of the airplane. This means that lightning could provide an ignition source for fuel-air vapors in the fuel tanks. Boeing plans to outfit the B787 with a nitrogen generation system (NGS). This system will flood the fuel tanks with an inert gas, greatly reducing the prospect of a lightning-triggered fuel tank explosion.
According to the FAA, the NGS is necessary because it is not possible to design a multiple-fault-tolerant structure on the all-composite B787. Such a structure is:
“(U)niguely challenging and impractical for certain aspects of the electrical bonding of structural elements. Such bonding is needed to prevent occurrence of fuel tank ignition sources from lightning strikes. The effectiveness and fault tolerance of electrical bonding features for structural joints and fasteners is partially dependent on design features that cannot be effectively inspected or tested after assembly without damaging the structure, joint, or fastener.
“Examples of such features include … metal foil or mesh embedded in composite material such as in a wing skin joint or a mounting bracket installation. In addition … it is not practical to inspect for failures … Examples of such failures include separation or loosening of cap seals over fastener ends and actual structural failures of internal fasteners. This inability to practically detect manufacturing errors and failures of structural design features critical to lightning protection results in degraded conditions …”
In other words, over time, the vulnerability of the fuel tank to lightning penetration and explosion increases over time. The NGS will compensate for structural flaws by filling fuel tanks with nitrogen gas. However, the NGS need not operate 100% of the time; there are not two NGS systems on the airplane for assured safety and redundancy.
As the fine print admits, the NGS will provide “some relief” from ignition prevention requirements.
The National Air Traffic Controllers Association (NATCA) proposed that the special condition be modified in two ways:
(1) Eliminate the allowance for single failures that can result in an ignition source, unless [emphasis added] the fuel tank is shown to have a flammability reduction means that prevents the tanks from becoming flammable [all the time] or,
(2) Do not allow dispatch of any airplane with the inerting system that is not functioning if the design does not have two independent features that will prevent an ignition source.
The FAA disagreed, saying Boeing must only show that “fault tolerance” is “impractical” and that “determining appropriate dispatch relief, if any, is the function of the Flight Operations Evaluation Board and not the function of special conditions.”
To cut though the technical jargon and the bureaucratic niceties of airplane dispatch, it is highly likely passengers will be exposed to a greater probability of fuel tank explosion on the all-composite B787 than if the plane were built of aluminum.
The special condition is effective 23 December 2010.
For the existing fleet of aluminum airplanes, the FAA mandated inerting or equivalent means (e.g., foam blocks) in July 2008 to prevent another fuel tank explosion of the type that downed TWA flight 800 in 1996. That final rule also decreases the safety standard, and readers are invited to read our discussion of that rule for parallels to this Special Condition for the B787. (See Air Safety Journal, August 2008, “Significant Regulatory & Related Activity”)
24 November 2010 FAA
FR Doc 2010-29203 Docket No. FAA-2010-0711
Final Rule, AD, Robinson Helicopter Co., Model R22 and R44 Helicopters
AD requires action to prevent the tail rotor (T/R) control pedal bearing block support from breaking. A broken support can bind the T/R control pedals, resulting in loss of control.
All helicopters must be inspected for cracks within 100 hours of service. Cracked supports must be replaced. And if the support is not 0.50 inches thick, it must be replaced.
The FAA says this action is prompted by two reports of broken supports in flight, which resulted in the T/R control pedals becoming jammed.
This AD affects 4,500 helicopters in U.S. registry.
Effective 29 December 2010.
24 November 2010 FAA
Emergency Airworthiness Directive
Before further flight, certain fittings must be replaced to prevent failure of the main rotor system. The failure of the main rotor has led to fatal accidents.
The FAA says:
“Bell states in ASB [Alert Service Bulletin] 212-10-142 that they have determined that fittings may not have been manufactured in accordance with the engineering design requirements and may fracture as a result of a non-conformance. They also state that a possibility exists that undetected cracks during the quenching operation could have occurred at manufacture.
“We are issuing this EAD because we evaluated all the available information and determined the unsafe condition is likely to exist or develop in other products of this same type design.”
A magnetic particle inspection is required to detect cracking.
It appears that Bell has a quality assurance problem on the production line.