Air Transport World

Prodigious project. (engine pylon modification program for Boeing 747 aircraft)

LONDON--As the vanguard of Boeing 747s fitted with strengthened engine pylons rolls out of engineering hangars around the world, the industry is hitting its stride in one of the most extensive modification programs in its history.

Designed to prevent in-flight engine separations of the type that caused an El Al freighter to crash into an Amsterdam apartment complex, the modifications are fleet-wide and apply to all 747s up to the 1,046th ship off Boeing's Everett assembly line. The modifications were incorporated into the production line, starting last October.

Since the first 747 flew in 1969, 25 have become write-offs, 20 were dismantled, 25 are "no status" and 46 are parked. This left a fleet of 930 to be modified at the start of 1995. Depending on the age of the airplanes, the work must be completed within a timetable of 2 1/2-6 1/2 years. Boeing said that by early May, 26 airplanes had been completed and work was in progress on 12 others.

The cost of the program is difficult to pin down. Boeing is not prepared to talk about it, commenting: "Total cost is secondary to the issue of flight safety." One informed estimate is that taking learning curve into account, at least 9 million man-hours will be involved industrywide. The tab for this work will come to at least $372 million, plus the cost of kits, development, tooling and trials. One senior engineer involved in the mods told ATW: "It's likely to turn out to be a bigger job than Section 41."

The industry's 21 maintenance providers with the facilities and skills to do the job are rubbing their hands at the scope of the work involved and the prospect of a guaranteed longterm flow of work in their overcrowded marketplace.

Engineering marketeers are pitching hard and prices are extremely competitive. Attracting the first airplane into the shop is vital, for Boeing will not send one of its 20-strong teams of specialists for a facility's initial job demonstration until an airline had been signed up.

The modification program was ordered by the U.S. FAA and Boeing after two almost identical fatal accidents involving 747 freighters, in which an engine separated in flight and hit the companion engine, knocking it off, as well.

After completing a review of the design of the nacelle strut, Boeing concluded that strengthening its structure and the corresponding wing structure was required for the entire 747 fleet. One of the main considerations of the mod was that the new fixture should have greater resistance to lateral loads.

Put simply, the modification involves installation of two additional mountings made from corrosion-resistant steel. These mountings are redundant, their fail-safe task being to back up the existing mounting structure, providing an extra line of protection against in-flight separation if any of the attachments fail. …

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