Pretoria - Seven of the air force's nine C130 Hercules transport aircraft have been grounded.

Sources and the SAAF said on Thursday the grounding related to a wing life-span problem.

Air force spokesperson Captain Ronald Maseko said: "Information gathered at the Hercules Operators Conference during October 2004 and follow-up information... indicated a possible impact on the predicted life-span of the wings of the Hercules C130 fleet of the SAAF."

He said the information was issued by Lockheed Martin, the original equipment manufacturer, during December 2004.

"The SAAF, as a professional military operator acting in the exigencies of aviation safety, issued a stop-flying instruction for the fleet with effect from February 15... Therefore the fleet was not grounded."

A former pilot said the terms amounted to the same thing.

Three independent sources have said the grounding relates to apparently incorrect modifications or maintenance procedures being carried out on the main wingspar - a rod connecting the two wings.

The SAAF acquired seven of the aircraft in the late 1960s, but the United States shortly afterwards cut off military aid.

This included assistance on the safe operation of the C130s.

Aid was restored only in 1990s after the settlement of a lawsuit related to illegal activities in the US by arms agency Armscor.

The US donated a further five airframes a few years ago, of which two were restored to flying status.

All nine were sent in turn to arms company Denel for a comprehensive upgrade in co-operation with Marshall's, a British aircraft re-manufacturer.

There has been persistent talk in aviation circles that the upgrade programme has not been as successful as expected.

Maseko said two of the nine SAAF C130s were fitted with different wing sections from the seven grounded and the safety instruction did not apply to them.

"These two aircraft are serviceable and being operated by the SAAF."

The latest issue of the African Armed Forces Journal reported that Lockheed Martin appeared keen to establish a continental maintenance depot in South Africa in co-operation with Denel.

With acknowledgements to Iaine Harper, Sapa and News24.