Graham Warwick/WASHINGTON DC

The US Federal Aviation Administration has launched a review of McDonnell Douglas DC-8 cargo conversions to determine whether safety concerns exist similar to those it believes affect some Boeing 727 freighter modifications. Reviews of freighter conversions ranging from the Boeing 737 to the Lockheed L-188 Electra are expected to follow.

Because of the controversy generated by its handling of the 727 freighter issue - airworthiness directives (ADs) severely reducing the payload of some aircraft remain in abeyance while consultations continue with affected operators - the FAA has adopted a different approach with the DC-8. The agency has formed a working group with modifiers and operators to determine the existence and extent of any problems.

"There will be problems, as there are with the 727," says Charles Perry, president of cargo conversion developer Aeronautical Engineers (AEI). The problems he refers to are the difficulties faced by modifiers in validating the loads assumed - in the absence of data from the aircraft manufacturer - when designing the freighter modification. Alerted by structural problems experienced with GATX Airlog's Boeing 747 freighter conversion, the FAA turned its attention to the 727 and now the DC-8.

Some 70-80 cargo DC-8s are covered by the review, which does not include freighters manufactured or modified by McDonnell Douglas or its licensee, Aeronavali. More than 210 DC-8 freighters are still in service. As with the 727, concerns exist with only those cargo conversions developed by a third party and awarded a supplemental type certificate (STC) by the FAA.

Miami-based AEI is one of four holders of STCs for 727 freighter modifications. It is also one of four companies to hold an STC for a DC-8 cargo conversion. Perry says that some 100 727s and 20 DC-8s have been modified using AEI's designs. Other 727 STC holders are FedEx, Pemco World Air Services and Mexico-based ATAZ.

Although Pemco says that it has also converted eight DC-8s, the other STC holders involved in the FAA working group are ATAZ, Fine Air and Rosenbaum, Perry says. The review is expected to result in ADs requiring strengthening of the floor, and other changes.

The FAA planned to issue ADs restricting affected 727s to 1,360kg per pallet position - down from 3,630kg - in October 1997. Operators, led by FedEx, have resisted strongly and consultations continue. FedEx is planning a test to demonstrate that there are no safety concerns with its conversion.

Tom McSweeny, director of the FAA's aircraft certification service, plans to make his recommendation on the 727 issue to FAA Administrator Jane Garvey in May, regardless of whether the FedEx test is complete. "We feel strongly that, without some change to the floor, there is a safety issue," he says.

Source: Flight International