BERLIN - Global demand for air freight rose slightly in September, a slight improvement on the previous month, a leading industry association said on Wednesday. Air freight volumes rose 1 percent in September, but load factor - a measure of how full planes are - fell to just 43.2 percent, the lowest level since 2009 as carriers added more capacity, IATA said in its monthly air freight figures. “Although slightly improved from August, the global trend is fragile, and the improvement is narrowly based,” IATA director general Tony Tyler said in a statement.