Which Aircraft Have AN-26 Insulation, and What's the Problem? - NewsChannel5.com | Nashville News, Weather & Sports

Which Aircraft Have AN-26 Insulation, and What's the Problem?

FAA test of PET insulation FAA test of PET insulation

AN-26 is the brand name for a flammable, polyethyleneteraphthalate (PET) film that covers insulation blankets used in hundreds of Boeing aircraft.

Manufactured by Orcon Corp., it's also known as non-metallized Mylar.

The Federal Aviation Administration says AN-26 insulation was installed on about 1,600 Boeing aircraft between July 1981 and December 1988.  Of those, 831 are registered in the U.S.  The FAA says the series of aircraft with AN-26 are:

  • 727-200 and 727-200F
  • 737-200, 737-200C, 737-300 and 737-400
  • 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747SR and 747SP
  • 757-200 and 757-200PF
  • 767-200 and 767-300

(Some of those same aircraft are lined with Kapton, a type of wiring known for its explosive discharges.)

Insulation blankets wrap the hull of an airliner to protect passengers from the noise and extreme temperatures of flight.  They're also supposed to provide some protection to hold off a fuel fire outside of a plane long enough for passengers to evacuate.

The flammability of such insulation blankets became an issue after a 1993 incident in which an MD-87 experienced an in-flight fire while on final approach to Copenhagen, according to a 2000 FAA report.

The aircraft sustained "considerable damage" after an electrical arc had ignited an insulation blanket covered with a metallized version of the PET film (metallized Mylar).

The report details other incidents involving the same material.

Those blankets had passed the FAA's flammability test - known as the vertical Bunsen burner test - for insulation materials.

Then, in September 1998, an electrical arc is believed to have ignited metallized Mylar blankets on an MD-11, according to the Transportation Safety Board of Canada

The aircraft, known as SwissAir Flight 111, crashed into the Atlantic Ocean just off Nova Scotia, killing all 229 people on board.

A month after the Swissair tragedy -- five years after the MD-87 incident -- the FAA announced it would come up with a new flammability standard for insulation blankets within six months and would "require that existing materials be replaced with insulation that can pass the new test." 

The FAA missed that deadline. 

Then, in August 1999, the FAA announced that it was proposing the removal of metallized Mylar insulation blankets from DC-10, MD-11, MD-80, MD-88 and MD-90 aircraft - and that it should be accomplished within four years.  The rule became final in May 2000, but the FAA ended up giving the airlines five years to comply.

It wasn't until September 2000 that the FAA came up with the new flammability standard that it had promised. 

The rule did not become final for another three years -- a full decade after the MD-87 incident.

Meanwhile, in June 2002, Delta Airlines told the FAA's fire safety experts that it had experienced an on-board electrical fire when a shorting wire ignited an AN-26 insulation blanket during maintenance.

According to minutes from the meeting, "Delta will replace the AN-26 insulation blankets in approximately 150 of its aircraft during each aircraft's next regular heavy maintenance (HMV) - an aircraft goes through an HMV every 6 years."

It was another three years later, on April 1, 2005, before the FAA announced that it was proposing to require operators of those aircraft to "replace or modify" those insulation within six years. 

The FAA said the rule was necessary because it had "received reports of inflight and ground fires" on aircraft with AN-26.

According to a summary prepared by the FAA's Technical Center, tests "demonstrated that an arc from a typical aircraft electrical wire could easily ignite the AN-26 and that the fire could propagate on the AN-26,"  "The flames from the AN26 were capable of igniting other aircraft materials and in a cascading fashion cause a catastrophic fire."

So far, nothing has happened.

A spokesman for the airline industry's Air Transport Association (ATA) says in a statement to NewsChannel 5:

"Final disposition of the proposal has taken longer than normal.  When the rule was proposed, there were no service instructions for replacing the thousands of insulation blankets in each of the affected airplane models.  Boeing attempted to develop an innovative method for addressing the matter -- a spray-on product -- in order to expedite resolution and minimize impact.  ATA member airlines actively participated in full-scale prototyping of the product, but to date, there has been no FAA technical approval.  Boeing then developed the first-ever, detailed service instructions for replacing blankets, as recommended by the carriers."

There has been no formal action in the rulemaking process since June 2007.

The FAA says it's getting close.

"As shown by the number of ADs [airworthiness directives] issued to eliminate ignition sources, other rules issued to require enhancements to wiring design and maintenance practices, as well as the thermal/acoustic insulation blanket final rules, it is clear the FAA takes smoke and fire issues very seriously.  Due to the scope and estimated cost of the AN-26 proposed rule, we received a significant number of comments.  We are required to evaluate every comment received on the proposed rule.  At this time, we have completed the evaluations and are in the process of finalizing the proposed rule."

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