Gaborone - The managing director of Skynet Worldwide Express, a Johannesburg based courier company, was among the five people missing after their Cessna 414 disappeared over Botswana on Wednesday, the company said on Sunday.
Spokesman Mark van Niekerk said Carl du Plessis, 39, was on his way to Maun, in the Deception Pan area in the north east of the central Kalahari Game Reserve, to launch a new branch of Skynet when the plane disappeared.
The search for survivors or wreckage from the crash entered its fourth day on Sunday, the civil aviation department in Botswana said on Sunday.
"After an evaluation last night (Saturday), we decided to give it another day and extend the search area to the north," an aviation spokesman said on Sunday.
Botswana Defence Force helicopters and fixed wing aircraft, aided by civil fliers, were searching for the South African registered twin engine, Cessna 414, which was flying from Gaborone to Maun in Botswana.
It was more than halfway to Maun when the pilot radioed Gaborone flight control and said there were oil pressure problems with one engine.
A second plane from the same charter company flying the same route landed at Maun.
Civil Aviation authorities said unusually thick vegetation that sprung up rapidly after the recent heavy rains was hampering the search.
Aviation sources are increasingly pessimistic of any passengers being alive.
A Botswana-based aircraft accident expert, Bill Scott, feared there was either an explosion or fire on board the plane.
"That nothing more was heard from the pilot points to him losing the plane in the air... the engine catching fire," Scott said.
"Without complications, he should have been able to shut down one engine and continue, or at least land and walk away."
Reports monitored by Scott indicate the plane was no more than 160km outside Maun when the pilot radioed Gaborone.