Problems with Mylar Replacement


by Tim van Beveren, Aviation Editor, Miami

The MD-11 modification program of Swiss national Airline Swissair got stuck already at its start. The reason: Boeing cannot provide sufficient substitute material for the mylar thermal acoustic insulation blanket replacement plan. In the aftermath of the tragedy of Swissair flight 111, which crashed on September 2, 1998 during an in-flight fire emergency killing all 229 people on board the FAA had issued already in June 2000 an airworthiness directive ordering to replace insulation blankets containing mylar from aircraft in service. This became necessary after it was learned that mylar insulation blankets might ignite and actually "fuel" a fire inside the aircraft cabin. A potential high risk appears whenever blankets and electrical wiring are in close vicinity to each other. An electrical phenomena known as "arcing" can deteriorate the wire insulation. An open flame, creating heat energy of some 1000 degree Celsius can thereby easily affect the mylar in the vicinity and lead to a catastrophic fire behind closed panels, as was the case on board SR 111.

Zurich based SR-Technics, who provides maintenance for the Swissair fleet, had planned to already have modified a total of three aircraft by today. However, due to a significant delay of an actual nine month waiting period for replacement kits at Boeing, only two aircraft where able to be modified so far. This delay will require that those aircraft scheduled for heavy maintenance due by autumn of this year will have to be grounded for a second time in order to finish the modification. The Swiss flag carrier currently operates a fleet of 19 MD-11 passenger aircraft.

The airline that was directly impacted by a catastrophic fire event on board of one of its modern fleet aircraft is not the only one with problems to get enough replacement sets from Boeing. A survey conducted last week revealed that there are four other operators who admit that meeting the timeline for the modification program of their MD11 is at risk. One operator even calculated that this additional grounding period would cause him an additional cost and revenue loss of 500,000 US $, - for each aircraft of his fleet.

The Federal Aviation Administration  (FAA) issued back in June 2000, as a reaction to the findings of the Swissair 111 crash investigation, an Airworthiness Directive (AD-Note) ordering MD aircraft operators to replace insulation blankets coated with metalized mylar. Various substitute materials with a better flame retardness than "Mylar" were already available in 1994, but were more costly and installation was not required by the aviation authorities at the time.

Boeing spokesperson Vicki Ray of the Seattle based aircraft manufacturer said that Boeing "is trying to increase capacity" to meet the growing customer demands.

However this problem got a new dimension with the February 6, 2000 recommendation of the National Transportation Safety Board (NTSB). The NTSB pointed to new findings relating to a fire emergency on board a Delta Airlines MD-88, which gave another example of mylar blankets imposing a fire risk in McDonnell-Douglas produced aircraft. During the flight on September 17, 1999 from Covington, Kentucky to New York, the flight crew reported a sulfurous smell and then, shortly after that, fumes and smoke entered the forward cabin. The flight crew declared an emergency and performed a landing at Covington Airport in Kentucky. During the descent, a flight attendant discharged at least one Halon fire extinguisher into a floor grill, through which a "glow" was reportedly seen. The Board investigating this accident urged the FAA to proceed faster than the projected five-year compliance deadline for exchanging mylar insulation blankets. The Board requested that the FAA issue an airworthiness directive, requiring the replacement with approved substitute materials "at the earliest maintenance opportunity".

The NTSB, already back in December 1999, while investigating a fire incident in the forward cargo control unit of a parked Delta Airlines MD-11 had pointed out to the FAA of the

 potential hazardous risks associated with mylar insulation blankets. Several pins inside an electrical control unit vaporized when excessive electrical current hit the unit. The vaporization created hot gases that escaped through the units' back cover and ignited the adjacent mylar covered insulation blanket.

FAA spokesperson Les Dorr confirmed last week that the FAA, together with Boeing, the Canadian Transportation Safety Board and representatives of the MD-11 operators, have just started "phase four" of a special MD-11 modification program which should lead to significant safety improvements in the worldwide MD-11 fleet. The newly published nine additional Notices of Proposed Rulemaking (NPRM) for wire modification and improvements are also now part of this program. The deadline for comments is April 6. These new AD's effectiveness is expected shortly.

The last produced MD-11 was delivered to the German Lufthansa Cargo this past Wednesday. This aircraft is the 200th MD-11 wide body jet aircraft built in the former McDonnell-Douglas plant in Long Beach, California. A total of 646 wide body aircraft were built there during the last  three decades. In 1997, the Boeing Company merged with its financially struggling competitor.  

SR Grounds its Fleet
Swissair Financially Dead
SR Grounding Unnecessary