The US Federal Aviation Administration has finalised airworthiness directives (AD) which impose severe payload limits on Boeing 727s that were converted into freighters by third party maintenance organisations.

The restrictions remain in effect until floor structures on 270 US-registered 727Fs are modified at an estimated cost of $192 million, says the US aviation agency. An additional 100 of the affected freighters are flying with foreign operators. At an estimated cost of $711,000 per aircraft, their voluntary compliance would total $71 million.

The ADs require operators to reduce payloads from 3,632kg (8,000lb) per shipping container to 1,360kg or adhere to operational limitations that allow higher payloads per container up to 2,180kg . Operators have 90 days from the effective date to comply.

The problem concerns aircraft which were not converted by Boeing, where there are concerns about the engineering of conversions without Boeing's load-path data for stress analysis. Inspections have revealed that certain aircraft contain design features which do not meet FAA certification criteria and are under-strength.

The ADs affect FedEx, Pemco World Air Services, Miami-based Aeronautical Engineers and Mexico's ATAZ, which were awarded four supplemental type certificates (STCs) in the mid-1980s. The ADs affect 32 airlines, but FedEx, with 117, is the hardest hit. The express parcels carrier says that the ADs will have a "minimal" impact since it expects to meet the criteria for the 2,180kg exemption, and expects the AD to be modified when studies on the strength of the current floor structure have been completed.

The FAA says the much-awaited final ADs consider industry concerns. The FAA increased the proposed compliance time from 48h to 90 days.

Source: Flight International