Wednesday, February 1, 2006
Scope of Insulation Replacement Narrowed
Clarification regarding thermal acoustic blanket change-out is contained in a final rule published by the Federal Aviation Administration (FAA) on December 30, 2005 (FR Doc 05-24654, Docket No. FAA-2005-23462). The ruling does not appear to affect insulation blankets but does effect insulation wrapped around air piping, ducts, and such.
As the FAA says, "Ducts are intended to convey a fluid medium from one point to others and, therefore, provide a potential fire propagation path by the nature. Because air ducts are the most significant and common, we are limiting the replacement provision in this amendment to insulation air ducts only. Therefore, other types of piping, or fluid lines, are no longer covered by the replacement provision."
Air ducts must be covered in insulation that meet the new standard, which is to say the radiant heat and direct flame test. Exempt from this requirement is "insulation that is integral to the duct and cannot be replaced without replacing the duct." These assemblies "will no longer be covered by the regulations for replacement." Also, other piping or ductwork, used less extensively in the aircraft and which often features specialized insulation, need not be replaced. As the FAA explains, "Insulation blankets are defined as an encapsulated assembly consisting of a core insulating material and a moisture barrier film or cover surrounding the core. They represent the largest usage of thermal/acoustic insulation in the airplane and are, therefore, the most significant from a fire safety standpoint. Insulation blankets are most often used against the airplane fuselage structure but are also used around ducts and under floor panels."
The FAA says its original rulemaking inadvertently included other types of less extensively used insulation, which is sometimes replaced on a piecemeal basis and which "has very little, if any safety benefit."
Moreover, the FAA says "compliant replacements are not readily available." Basically, the FAA confesses that it was not aware of these issues when it issued the original rule and is limiting the scope to that insulation which is used extensively and which harbors the greatest fire hazard.
The FAA did not provide a cost-benefit calculation, but it did offer this assessment:
"The original requirement was sufficiently broad that operators could have been out of compliance, even without realizing it. Those operators would have been subject to fines and they would have experienced maintenance schedule disruptions. By narrowing the scope of the requirement, operators can comply with reasonable effort, and the safety intent of the original rule is preserved.
"Although we cannot provide a quantitative estimate of the losses resulting from the fines and maintenance schedule disruptions, we believe these would have been significant."
The rule applies to aircraft manufactured before September 2, 2005, which is to say all transport category aircraft involving a retrofit requirement. Newly-manufactured airplanes should be using insulating materials throughout that pass the new standard for flammability resistance.
Comments on the 13-page rule are due February 28. The rule itself goes into effect January 30. The rule appears to be an appropriate response to industry's concerns. The preponderance of fire-propagating material will still be gone, with only 2% to 5% by weight remaining. Much of that will be shrouded or encased, such as within the casing of microwave ovens, where it cannot do any harm in the context of concern. The FAA stuck to its requirement that the rule apply to Part 91, 135 and 121 aircraft, and not just to Part 121 aircraft.
Scope of Insulation Replacement Not Defined
Based on the comments received, the FAA reopened on November 23 the comment period on a notice of proposed rulemaking (NPRM) regarding Mylar film covering thermal acoustic insulation blankets (FR Doc 05-23153, Docket No. FAA-2005-20836). The film is known as polyethylene teraphthalate (PET), and more generally as simply AN-26, and the FAA wants it removed from approximately 800 Boeing B727s, B737s, B747s, B757s and B767s in U.S. registry (there are about 1,600 affected airplanes in the worldwide fleet). Readers may recall that earlier the FAA ordered the replacement of flammable metalized polyethylene teraphthalate (metalized Mylar, or MPET) from about 800 Douglas built jets; this action was taken in the aftermath of the Swissair Flight 111 disaster, in which an MD-11 was lost due to a runaway fire in the so-called "attic" space over the cockpit and cabin.
Now it's the turn of Boeing jets, which aren't outfitted with the flammable metalized Mylar version, but through December 1988 Boeing jets were manufactured with insulation blankets covered in plain Mylar that is still deemed flammable, according to the FAA. As the FAA says, it is "in the process of upgrading the flammability standards for thermal/acoustic insulation for [all] transport category airplanes." However, the FAA received numerous comments from industry on its original proposal to replace AN-26 blankets with ones meeting the latest standards, and the FAA now seeks additional input in order to sort out what needs to be done.
The responses received so far indicate a number of potential problems:
As Lufthansa remarked, "In the NPRM there is no AMOC defined or approved. Before final release there should be AMOCs for ... spray on fire retardant or covering of existing insulation material with fire retardant materials approved."
Boeing agreed, saying in its request for an extension to the comment period, "Within this additional time, Boeing will have completed full scale testing of a proposed in-situ full scale spray-on fire retardant solution. This has a direct impact on the industry recommendations for viable solution(s)."
"The 72 month mandated compliance period for the affected airplanes will result in increased ground time and/or special maintenance visits for many of these airplanes, which will be an economic hardship. UPS is requesting that the compliance time be extended to 96 months and believes this will not compromise safety of the fleet. The insulation blankets on the affected airplanes can be replaced with a minimal impact of additional out of service time at that interval."
US Airways noted that the rule will impose a "significant adjustment of current maintenance plans" and that the problem is not simply one of removal and replacement:
"As currently proposed, this rulemaking would significantly extend the scheduled maintenance time required, due to fabrication of compliant insulation material and subsequent replacement of suspected insulation material, necessitated by the inability to currently identify AN-26 material."
The Air Transport Association (ATA) concurred, arguing for more time based on the fact that AN-26 poses less of a fire hazard than metalized Mylar:
"A video recording of the tests of insulation blankets encapsulated with MPET film culminated with a blaze that engulfed the test fuselage crown. In contrast, a video of corresponding tests of AN-26 insulation shows that the material will propagate small flames that wax and wane as they move in lines or fronts."
"The wording...would require that anytime a blanket is removed to gain access during unscheduled line maintenance, the mechanic has to make a determination if the blanket is constructed of AN-26 and if so, replace it immediately. This is an enormous undertaking...In addition, the most likely event requiring unscheduled removal of insulation blankets would be ground damage to the aircraft. In this case, the mechanic would refer to the structural repair manual (SRM) instead of the maintenance manual. The SRM is a Boeing controlled manual on an annual revision cycle, so there would be little chance of getting this manual revised within the 6 month time frame specified...The requirement...could generate significant out of service time if a blanket has to be removed while the aircraft is away from base since a replacement blanket would not be readily available. The number of blankets removed for access during such events is usually small (one or two). Therefore, we believe that any perceived increase in safety from replacement of this small number of blankets is outweighed by the potential for significant unscheduled out of service time and the difficulty of trying to ensure compliance."
Boeing concurs, citing the experience with blanket replacement in the Douglas fleet:
"We are asking the FAA to include criteria in the AD for areas of the airplane that may be exempt due to accessibility or because replacement action increases the risk to the airplane for other safety reasons, primarily system disruption. This was not done up front with [the Douglas-built aircraft] and was required later, resulting in flight deck and EE [electronics and equipment] bay exemption areas."
The Air Transport Association (ATA), representing most U.S. scheduled carriers, said the cost of replacing the metalized Mylar blankets in Douglas aircraft is instructive:
"If actual labor and parts costs for replacing AN-26 insulation surpass estimates of the proposal in amounts comparable to the MPET effort, the U.S. fleet cost of compliance will increase from the $334,113,225 estimated ... to $508,358,545."
Based on the extension, additional comments on the AN-26 replacement are due February 21.
To Prevent An Uncontained Engine Failure
Comments are sought on a December 30 NPRM concerning Pratt & Whitney JT8D-1 and JT8D-200 series turbine engines (FR Doc E5-8099, Docket No. 2001-NE-30-AD). The FAA proposes to supersede an existing AD by requiring replacement or replating the front hubs and discs of the high pressure compressor to counter cracking before they reach their life limit. Earlier, the FAA had mandated only repetitive visual and fluorescent magnetic particle inspections (FMPI) for cracking, but a P&W investigation indicates more must be done.
This is a big deal, as the FAA's proposed action affects nearly 3,000 engines installed on aircraft of U.S. registry. Of these, 175 would require disassembly and reassembly, at an average cost of about $16,600 per engine.
Comments due February 28.