US regulators are advising carriers to conduct an in-depth review of cargo-loading documentation and weight-balance manuals in the wake of the crash of a Boeing 747-400 freighter in Afghanistan.
The latest US FAA recommendation follows a safety bulletin issued three weeks after the 29 April accident in which the departing 747 lost height moments after take-off from Bagram.
It states that air carriers should review their documents to ensure compliance with loading techniques, particularly for special cargo loads.
"The review is to verify that over-simplified procedure substitutions are not used by the air carrier for securing special cargo load," it says.
Manuals must give procedures to determine reaction load for tie-down points in order to make certain that sufficient restraint is applied.
Afghan investigators reportedly indicated in June that heavy armoured vehicles broke loose inside the National Airlines 747 before its departure to Dubai World Central.
The airline has pointed out, however, that the Afghan inquiry "remains open" and that no conclusions have been reached on the cause.
But the FAA update stresses the importance of using approved tie-down points and says that certain methods - notably using simple division of payload weight to calculate the number of straps needed - are ill-advised.
"This method does not reflect the strength, of lack of, the actual vehicle or [aircraft] attach point," it says, and points out: "Straps are only effective for the direction of force for which that strap is restraining the cargo."
It also steers operators away from the practice of simply passing a strap through a vehicle tie-down point and fixing both ends to the aircraft. This looping reduces the overall restraint to the weaker of the two aircraft attachment points. Each strap, says the FAA, should be separately anchored to the cargo load.