Each failed African airline has a slightly different scenario behind it's failure but for what its worth, I think that one of the largest causes is the size of the figures involved in an airline. When you're talking millions of dollars for a plane, millions and millions of dollars in operating fees (legit or otherwise), hundreds of staff in a number of locations, offices and departments, fees paid to dozens of offices in each region/country operated over or into, it becomes all too easy to 'lose' just how many staff are actually required, how much money is actually being spent well or spent badly, how much is creamed off the top, how much is 'paid' to facilitators, what the real cost of operations are, and how many fees are really necessary or even paid. Airlines have operations in several different countries, so it becomes even easier to disguise how much is being re-directed out of the country of origin, and under different rules and laws.
When you start talking airline anywhere in the third world, it conjures up glamour, money and prestige. And as soon as politicians or governments smell the size of money required, they become involved in some form or other. And suddenly one's overheads become 'heavier' than planned, and staff selection becomes biased towards family members, contractors have family connections requiring additional salaries and corruption starting at the top, starts to filter all the way down the chain. Add to this a government minister demanding a plane for a private trip and to hell with the schedules, costs and paying passengers, and the trouble starts to accelerate. Factor in that an airline almost always has more than the minimum staff required to attract trade union or labour laws about hiring/firing, and now you can't get rid of dead wood staff without massive issue. Bring in politics - your benefactor is now out of favour and needs his money back in a hurry for a court case, or the facilitator who promised that whatever issue would be sorted out, suddenly is under impeachment and things get very difficult.
Lastly, air travel is still the privilege of the rich/middle class person, and beyond most people in Africa, even if its budget orientated. Because of the legitimate overheads, prices are still more than most people can afford, and because of the illegitimate overheads, costs are kept down by cutting maintenance costs (the plane still flies, why do we need this), training (just get someone local to train the next guy), and standards (we've always done it this way, it works, why change it). For a while, egos and money will keep things afloat, but eventually the bubble will pop, and another airline struggles to keep above water.
